JP6921138B2 - Dimmable lighting system - Google Patents

Description

The present invention relates to dimmer triggering circuits for low load applications, such as LED-based light sources. The present invention further relates to a dimmer system that includes such a dimmer trigger circuit.

In general, phase-controlled dimmers also have a triode for alternating current called a triode. A triac is a bidirectional switch that can carry current in either direction when triggered, that is, when it turns on. It can be triggered by applying a positive or negative voltage to the gate electrode, i.e., if a small current is applied to that gate. This current only needs to be supplied for a short period of time, that is, for microseconds. In other words, the triac needs to be triggered or "fired". Once triggered, the device continues to conduct until the current through it drops below a certain threshold, such as at the end of a half cycle of an alternating current (AC) mains (also known as zero crossover). .. As a result, the triac then "turns off."

These dimmers work well for dimming incandescent light bulbs that carry relatively high currents. Various problems are encountered when these dimmers are used with smaller loads, such as light sources based on light emitting diodes (LEDs). This is especially problematic when replacing standard incandescent bulbs with LED retrofit bulbs in situations where traditional triac dimmers are installed for use with bulbs.

The LED light source may not carry enough current to allow the triac in the dimmer to turn on as needed, resulting in inability to dimm the light or instability of the dimmer. Make it work. A small resistive load on the dimmer may result in inaccurate dimming behavior, causing voltage vibrations at the dimmer output caused by multiple firings of the triac. At low dimmer settings, the LED drive circuit may cause a short flash of light from the LED light source to toggle on and off. Moreover, the human eye perceives luminosity according to a logarithmic curve as a whole, whereas the LED has an almost linear response, and the intensity of the emitted light is approximately proportional to the current flowing through the LED. .. When operating with a conventional dimmer, the LED light source will not appear to dim smoothly. Also, the perceived change in luminosity is not directly related to the knob position of the dimmer. Small changes in the supply voltage may result in visible flickering of the light emitted by the LED light source.

The present invention attempts to solve these problems in various ways according to various embodiments. According to certain aspects, the present invention relates to a lighting system for working with a dimmer circuit having a triac connected to a load. The load has a drive circuit that supplies current to a light source having one or more LEDs. The current is at least partially determined by the adjusted setpoint value. The system further comprises a setpoint filter circuit that obtains a dimmer setpoint value that is at least partially determined by the dimmer circuit settings and produces an adjusted setpoint value. The sensitivity of the adjusted setpoint value to changes in the dimmer setpoint value is low at low dimmer setpoint values.

The setpoint filter circuit may be configured to increase the adjusted setpoint by a low percentage of low dimmer setpoint values and a high percentage of high dimmer setpoint values. The adjusted change in the setpoint value in response to the change in the dimmer setpoint value preferably approximates an exponential response. The setpoint filter circuit preferably produces a full range of adjusted setpoint values that are less than the full range of dimmer setpoint values, and preferably a tuned setpoint value that has a minimum value greater than 0. Generate.

The setpoint filter circuit has a first substantially constant value in the first part of the dimmer setpoint value range and is low in the second part of the dimmer setpoint value range. Increased at a rate, increased at a high rate during the third part of the dimmer setpoint value range, and a second substantially constant value during the fourth part of the dimmer setpoint value range. May be configured to generate a tuned setpoint with.

The setpoint filter circuit may further include a second or higher lowpass filter for filtering the received dimmer setpoint value. The setpoint filter circuit may include a differential amplifier that produces an intermediate setpoint value. It controls the transistor to produce a tuned setpoint value.

The drive circuit may be designed with a voltage control circuit and a current control circuit. The voltage control circuit controls the voltage at the output of the drive circuit according to the voltage setpoint. The current control circuit modifies the voltage setpoint according to the current setpoint. The current control circuit may be designed to operate within a predetermined range. The voltage setpoint is maintained at the boundary value when the current control circuit is at the boundary of its operating range.

The setpoint filter circuit may obtain the dimmer setpoint value from the voltage at the output terminal of the dimmer circuit. Alternatively, the setpoint filter circuit may derive the dimmer setpoint value from the starting angle of the dimmer triac. The dimmer setpoint value may be derived from the time delay between the first trigger of the triac and the zero intersection of the supply voltage after the zero intersection.

The lighting system may further include a dimmer trigger circuit for triggering the dimmer triac. The dimmer setpoint value is at least partly due to the time of occurrence of one or more rising and / or falling edges of the current through the dimmer trigger circuit, or the voltage associated with the rising and falling edges. May be determined. Therefore, the dimmer setpoint value is at least partially due to the time delay between the rising and falling edges of the current flowing through the dimmer trigger circuit, or the voltage associated with the rising and falling edges. It may be decided. The lighting system of the present invention may be designed to operate when the dimmer triac is on and the current from the dimmer circuit is less than the holding current of the dimmer triac.

The lighting system may further include a dimmer trigger circuit for triggering the dimmer triac. The dimmer trigger circuit is a voltage level detector for detecting whether the input voltage of the dimmer trigger circuit is below the threshold, and a current when the voltage detected by the voltage level detector is below the threshold. It may include a bipolar current source circuit that supplies and is otherwise deactivated. The lighting system may be designed so that the maximum current from the dimmer trigger circuit is less than the holding current of the dimmer triac. When the dimmer triac is on or the dimmer triac is off, the current from the dimmer trigger circuit is less than the triac holding current. The dimmer trigger circuit is designed to consume an average power of less than 100 mW in operation.

In another aspect, the invention is used in a lighting system having a triac dimmer circuit, a light source having one or more LEDs, and a drive circuit for supplying current to the one or more LEDs. Regarding the setpoint filter circuit. The current is at least partially determined by the adjusted setpoint value. The setpoint filter circuit has an input circuit for obtaining a dimmer setpoint value whose at least a part is determined by the setting of the dimmer circuit, and an adjustment circuit for generating an adjusted setpoint value. .. The sensitivity of the adjusted setpoint value to changes in the dimmer setpoint value is low at low dimmer setpoint values.

The setpoint filter circuit may be designed so that the adjusted setpoints increase at a low rate of low dimmer setpoint values and a high rate of high dimmer setpoint values. Also, the adjusted change in the setpoint value in response to the change in the dimmer setpoint value may approach an exponential response. The tuning circuit may be configured to generate a full range of adjusted setpoint values that is less than the full range of dimmer setpoint values, or a tuned setpoint value that has a minimum value greater than 0. It may be configured to generate. The input circuit may have a second or higher low pass filter for filtering the received dimmer setpoint value. The tuning circuit may have a differential amplifier that produces an intermediate setpoint value. It controls the transistor to produce a tuned setpoint value.

The setpoint filter circuit may derive the dimmer setpoint value from the voltage at the output terminal of the dimmer circuit. The dimmer set point value may be derived from the starting angle of the dimmer triac. This may also be achieved by deriving the dimmer setpoint value from the time delay between the first trigger of the triac and the zero intersection of the supply voltage after the zero intersection.

In yet another aspect, the invention relates to a lighting system for working with a dimmer circuit having a triac. The system has a light source with one or more LEDs and a load with a dimmer trigger circuit for triggering the dimmer triac and a drive circuit for supplying current to the one or more LEDs. Have. The current supplied by the drive circuit is at least partially determined by the dimmer setpoint value. The dimmer set point value is at least partially derived from the starting angle of the dimmer triac.

The drive circuit preferably derives the dimmer setpoint value from the time delay between the first trigger of the triac and the zero intersection of the supply voltage after the zero intersection. The dimmer setpoint value is at least partly due to the time of occurrence of one or more rising and / or falling edges of the current through the dimmer trigger circuit, or the voltage associated with the rising and falling edges. May be determined. The dimmer setpoint value is at least partially determined by the time delay between the rising and falling edges of the current flowing through the dimmer trigger circuit, or the voltage associated with the rising and falling edges. You may.

The drive circuit may include a voltage control circuit and a current control circuit. The voltage control circuit controls the voltage at the output of the drive circuit by the voltage setpoint. The current control circuit modifies the voltage setpoint by the current setpoint. The current control circuit preferably operates within a predetermined range. The voltage setpoint is maintained at the boundary value when the current control circuit is at the boundary of its operating range. The lighting system may be configured such that the current from the dimmer circuit when the dimmer triac is on is less than the holding current of the dimmer triac. The maximum current due to the dimmer trigger circuit may be less than the holding current of the dimmer triac. The lighting system may be configured such that the current from the dimmer trigger circuit is less than the triac holding current when the dimmer triac is on and when the dimmer triac is off. The lighting system may have a setpoint filter circuit for generating an adjusted setpoint value from the dimmer setpoint value. The sensitivity of the adjusted setpoint value to changes in the dimmer setpoint value is low at low dimmer setpoint values.

A further aspect of the invention relates to a lighting system for working with a dimmer circuit having a triac. The system has a light source with one or more LEDs and a load with a dimmer trigger circuit for triggering the dimmer triac and a drive circuit for supplying current to the one or more LEDs. Have. The drive circuit has a power factor correction circuit. The current supplied by the drive circuit is at least partially determined by the dimmer setpoint value. The dimmer set point value is at least partially derived from the starting angle of the dimmer triac.

FIG. 1 schematically shows a conventional dimmer connected to an incandescent light bulb. FIG. 2A is a diagram of a waveform example of the AC applied voltage via the dimmer circuit. FIG. 2B is a diagram of an example voltage waveform across a dimmer load with different dimmer settings. FIG. 2C is a diagram of an example voltage waveform across a dimmer load with different dimmer settings. FIG. 3 is a schematic diagram of a lighting system according to an embodiment of the present invention, which includes a dimmer trigger circuit connected to an LED light source. FIG. 4 is a schematic diagram showing additional details of a dimmer trigger circuit used in a lighting system according to an embodiment of the present invention. FIG. 5 is a schematic view of another embodiment of the dimmer trigger circuit. FIG. 6 is a simplified circuit diagram of an embodiment of a dimmer trigger circuit. FIG. 7A is a diagram of voltage-current operation between the terminals of the dimmer trigger circuit of FIG. FIG. 7B is a diagram of voltage-current operation between terminals of an embodiment of a dimmer trigger circuit including a microprocessor. FIG. 8 is a simplified circuit diagram of an embodiment of a setpoint filter circuit. FIG. 9A is a diagram showing an example of an adjusted setpoint change with two tilts. FIG. 9B is a diagram showing an example of adjusted setpoint changes that approximate an exponential response. FIG. 10 is a simplified circuit diagram of the secondary side of the embodiment of the LED drive circuit. FIG. 11A is a diagram of an example of the dimmer output voltage when the dimmer triac current is on the holding current of the triac. FIG. 11B is a diagram of an example of a dimmer output voltage when the dimmer triac current is discontinuous or equal to or less than the triac holding current. It is a simplified circuit diagram of the 2nd stage side of another embodiment of an LED drive circuit.

The following is a description of certain embodiments of the invention given for illustration purposes only. FIG. 1 schematically shows a conventional dimmer 1 connected to a load 3, which is typically an incandescent light bulb. The dimmer 1 has a variable resistor R1 connected in series and a triac TR1 connected in parallel with a capacitor C1. In this description, the combination of resistor R1 and capacitor C1 will be referred to as an RC circuit or timer circuit. In addition, the dimmer has a trigger component (ie, a component suitable for triggering the Triac TR1). Generally, alternating current diodes (diacs) are used for this purpose. A diac is a bidirectional trigger diode that guides a current after exceeding a diac threshold voltage called a diac trigger voltage. Diac continues to conduct. On the other hand, the current flowing through it is maintained above the threshold current. When the current decreases below the threshold current, the diac changes to a high resistance state. These characteristics are well adapted as trigger switches for triacs.

The dimmer 1 of FIG. 1 has a diac D1. The diac D1 is connected between the variable resistor R1 and the capacitor C1 at the first end, and is connected to the gate of the triac TR1 at the second end. The dimmer 1 has two terminals (ie, terminals T1 and T2). The dimmer 1 and its load 3 are continuously connected in series through an AC power source.

As described above, when the current passing through the triac TR1 drops below the threshold value, the triac TR1 turns off. Once the AC power zero crossover has passed, the RC circuit will "see" the actual AC power voltage and charge the C1. Note that this charging current further flows through the incandescent bulb 3. Once the voltage through C1 reaches the trigger voltage of the Dyac D1, the Dyac D1 begins to guide and supply current to the gate of the TR1. On the other hand, the capacitor C1 is discharged. As a result, the Triac TR1 triggers and turns on. The current begins to flow through the Triac TR1. The capacitor C2 is discharged.

By adjusting the resistance of R1 (eg, by operating a dimmer knob or potentiometer), the time required to reach the diac trigger voltage through C1 can be set. Higher values of resistor R1 will result in longer time required to reach the diac trigger voltage on C1. Therefore, the conduction interval of the Triac TR1 will be shorter. It will be understood by adjusting the time the current is flowing through the Triac TR1. The electric power supplied to the light bulb 3, that is, its illuminance can be adjusted.

The component may be added to the basic dimmer circuit described above for the filter of electromagnetic interference (EMI) generated by the switching of the Triac TR1. For example, the capacitor C2 may be included via the triac TR1 and the inductor L1 connected in series with the triac TR1. These additional components are useful in reducing the EMI so that the capacitor C2 via the triac flows through the dimmer 1 (and load 3), charges the capacitor C1 and triggers the triac. Will increase the current ordered. This is because this current must charge both capacitors C1 and C2.

FIG. 2A is a diagram showing a waveform of an AC applied voltage via the dimmer 1 via terminals T1-T3. 2B and 2C show voltage waveforms generated through the load (terminals T2-T3) at different dimmer settings for the variable resistor R1 assuming a resistor load 3. The AC applied voltage becomes 0 at the zero intersection t0 in a half cycle. At this point, the triac stops conducting and the voltage through the load 3 is close to zero. Since a certain current (for example, the current for charging the capacitors C1 and C2) continues to flow through the dimmer 1 and the load 3 connected in series, the voltage through the load 3 is not exactly zero.

As shown in FIG. 2B, at time t1, the capacitor C1 is fully charged, triggering the Diac D1 which sequentially triggers the Triac TR1. The voltage through the load 3 rises substantially to the power supply voltage, and the current through the load 3 increases significantly. If the load is high enough, the triac will continue to remain until the next zero intersection t0. Therefore, during period A of each half cycle, the triac is off and the capacitor C1 is charging. The charge rate of C1 and the length of time of period A depend on the dimmer setting, i.e. the resistance of the variable resistor R1 as set by the dimmer knob. During period B, the triac is on, the load 3 is connected via the supply voltage, and the normal operating current is flowing through the dimmer and the load. As can be seen from the waveform in FIG. 2B, the average voltage during each half cycle shrinks slightly, resulting in a small decrease in the current flowing through the resistive load. It is visible as a slight dimming when the load is an optical bulb.

In FIG. 2C, the dimmer setting is modified to increase the resistance of the variable resistor R1 which further dims the light. At time t2, the capacitor C1 is fully charged, triggering the Diac D1 and the Triac TR1. The triac continues to remain until the next zero intersection t0. Therefore, the triac is turned off for a long period C and turned on for a short period D. Therefore, during each half cycle, the waveform of FIG. 2C has an average voltage. It can be seen as a large amount of dimming when the load is an optical bulb, resulting in a large reduction in the current flowing through the load, which is greatly reduced. It can be seen that after the zero crossing after the triac turns on, which is called the triac starting angle, the dimmer controls the phase by adjusting the delay.

In FIG. 1, when the triacs are turned off and they are used to dimm a load such as an incandescent light bulb that exhibits a sufficiently high load and produces sufficient current when properly charging the capacitor C1. A dimmer such as the dimmer 1 of the above functions properly. That is, the current flowing through the load after zero crossover of the supply voltage needs to be high enough to allow charging of the capacitor C1 in the RC circuit (and C2). If a sufficiently high current does not flow through the load 3, the Triac TR1 will not be triggered at all, or will not be triggered only if the dimmer knob is set so that the resistance of R1 is low enough. .. The typical result is that the dimming function of the dimmer 1 does not work, that is, the light may not be dimmed.

A load, such as an incandescent light bulb of sufficient power, provides a current path for charging the RC circuit, as a condition for the dimmer 1 to function properly. However, recently there are low load and discontinuous applications (eg, built-in rectifiers and capacitors) that do not produce enough current to enable proper functioning of the dimmer 1. That is, after zero crossover of the supply voltage, there is insufficient current through the load for proper charging of the RC circuit.

A well-known example of low-load applications is an LED light source that includes an electronic coupling circuit that drives one or more light emitting diodes (LEDs) that require DC current. The LED circuit 13 generally includes one or more LEDs, a rectifier and one or more smoothing capacitors, and thus may be a discontinuous load. In this description, embodiments of the present invention will be further described in combination with LED circuits. However, embodiments of the present invention allow other low load or discontinuous load applications (ie, dimmers such as dimmer 1 schematically shown in FIG. 1) to function properly. Therefore, it must be understood that it may be used in combination with an application) that cannot supply the required charging current to the RC timer circuit of the dimmer. A load that keeps the rectifier front-end with a smoothing capacitor can be considered a discontinuous load application.

FIG. 3 schematically shows a dimmer system 10 according to an embodiment of the present invention connected to the LED circuit 13. The dimmer system includes a dimmer 1 and a dimmer trigger circuit (DTC) 12 connected in series via an AC applied voltage. The LED circuit 13 is connected in series with the dimmer 1 and is connected in parallel with the DTC 12. The combination of loads such as the DTC 12 and the LED circuit 13 may be referred to as a dimmable device.

4 and 5 show DTC 12 in more detail and generally. The DTC 12 includes a voltage level detector 15 and a bipolar current source circuit 18 including a current source circuit 17 and a rectifier 19. The voltage level detector 15 is connected to the current source circuit 17. Both the voltage level detector 15 and the current source circuit 17 are connected to the DC terminals of the rectifier 19.

The voltage level detector 15 is arranged so as to detect whether or not the absolute value of the voltage difference between the terminals T2 and T3 (that is, the output of the rectifier 19) is less than the threshold value. The bipolar current source circuit 18 is arranged to be activated if the voltage detected by the voltage level detector 15 is maintained below the threshold and otherwise deactivated. Therefore, the bipolar current source circuit 18 in the DTC 12 is a voltage-dependent current source. Further, the DTC 12 as a whole can be considered to act as a current source depending on the bipolar voltage. As described in more detail below, such a DTC 12 can be designed to consume an average power of less than 100 mW. In a good embodiment, the DTC 12 may consume an average power of 10-50 mW. Desirably, the consumption of DTC12 is about 30 mW. Many conventional dimmers with such consumption can operate as intended.

The voltage level detector 15 may have a microprocessor. The microprocessor is arranged to detect whether or not the absolute value of the input voltage of the dimmer trigger circuit 12 is less than the threshold value. If the input voltage of the dimmer trigger circuit 12 is less than the threshold, the microprocessor may provide a signal instructing the bipolar current source circuit 18 to supply current. In some embodiments, the microprocessor may instruct the bipolar current source circuit 18 to supply current after zero crossover of the input voltage, as described in more detail in FIG. 5B.

The voltage level detector 15 may include a comparator to detect whether the rectified input voltage is below the threshold value. The comparator includes two inputs and one output, as schematically shown in FIG. The first input is connected to a reference potential, i.e., a potential equal to the threshold (30 V in this example). The second input is arranged to receive the input voltage of the dimmer trigger circuit 12. If the input voltage of the dimmer trigger circuit 12 of the second input of the comparator is less than the threshold of the first input of the comparator, the output of the comparator will be the current as discussed above by the bipolar current source circuit 18. May be supplied. Operational amplifiers or voltage comparators may be used to implement the comparators, as will be appreciated by those skilled in the art.

The rectifier 19 is the AC side (ie, the terminals connected to terminals T2 and T3, respectively) and the DC side (ie, other in the DTC 12 such as the voltage level detector 15 and the current source circuit 17 in the bipolar current source circuit 18). It has a component and a terminal connected to a reference potential). The voltage level detector 15 and the current source circuit 17 form a unipolar circuit. The rectifier 19 is arranged so that the current generated by the current source circuit 17 can be supplied to the dimmer as a bipolar current.

The DTC 12 allows the dimmer 1 to work as if it were loaded by a normal incandescent light bulb. When the AC applied voltage is low enough, i.e. less than the threshold mentioned above, the DTC 12 is activated, allowing sufficient current to flow into the RC circuit of the dimmer 1. If the AC applied voltage is high enough, i.e. above the threshold, the DTC 12 will be deactivated and will not carry any sufficient amount of current, thereby minimizing wasted power. Note that only the absolute threshold is needed so that the voltage level detector 15 is located on the DC side of the rectifier 19. This means that when the threshold is 30V, DTC12 is activated in the range of 30V to + 30V.

In some embodiments of the DTC 12, the threshold is located between 3V and 50V when used with respect to a 230V main power system at 50Hz. In other embodiments of DTC12, the minimum threshold is 10V. If the DTC 12 is connected to a 120V mains system at 60Hz, as used in the United States, for example, the threshold may be located between 3V and 25V.

For example, as schematically shown in FIG. 1 for a triac TR1 triggered by a diac D1, the current provided by the DTC 12 is a voltage through the load until the triac in the dimmer is triggered. Efficiently keep it at zero. As soon as the triac switches on, the voltage at terminal T2 increases significantly. As a result, the current source circuit 17 in the DTC 12 is deactivated.

Therefore, if the voltage of T2 exceeds the threshold and otherwise the DTC acts like an open circuit, the DTC ideally only conducts current. However, in practice, some current will flow through the DTC while being deactivated. Desirably, the current provided by the current source circuit 17 in the DTC 12 with deactivation is negligible. If the current is on the order of at least two magnitudes less than the maximum current that the current source circuit 17 of the DTC 12 can provide, the current may be considered negligible. For example, if the maximum current provided by the current source circuit 17 in the DTC 12 is 15 mA and its value remains less than 100 μA, the current is considered negligible.

If, after the zero crossing, there is simply a discontinuous load (ie, a load that carries a discontinuous current such that the current is zero for some part of the voltage cycle), the DTC 12 will be in the dimmer. It acts as a supplement to the state of the triac. That is, when DTC is on, the triac in the dimmer is off, and vice versa. A bridge rectifier with a capacitor at the output is one example of a discontinuous load.

On the other hand, after the zero intersection has passed, in addition to the discontinuous load, in the presence of yet another load, if the input voltage of the DTC 12 exceeds the previously described threshold, adjust until the DTC 12 stops. Both the DTC 12 and the triac in the light device 1 may be turned on at the same time. In such cases, the DTC12 and triac in the dimmer 1 do not act completely complementaryly. For one millisecond, power is consumed when both DTC and Triac are on. However, this consumed power will be negligible. For example, for a threshold of 30 V and a current source circuit 17 arranged to supply a current of 20 mA, the peak power will typically not exceed 0.6 W (this peak power is very small). Although it occurs only for the interval). Also, the average power will not exceed 30 mW.

Generally, when passing through a zero crossing, the triac turns off (if it was on) and the DTC 12 stays. If the triac turns on, the DTC 12 turns off. Therefore, the DTC 12 is arranged to supply current when the absolute voltage of T2 is below the threshold. This current only needs to be sufficient to allow charging of the capacitors in the RC circuit of the dimmer, holding the triac or hypostatic current or of the dimmer in question. It has nothing to do with the minimum load. If the DTC is activated (when the triac is off) and when the DTC is deactivated (when the triac is on), the current of the DTC 12 may be less than the holding current of the dimmer triac. This provides the advantage that the DTC 12 can be used in combination with a triac that has a holding current greater than the maximum current provided by the DTC 12. Thus, even though the DTC 12 can supply a maximum current of, for example, 20 mA, a dimmer containing a triac with a holding current of, for example, 100 mA, greater than 120 mA, will allow dimming for low load applications. Can be used for.

To enable proper functioning of the DTC 12 in the lighting system, for example, when connected to an LED circuit 13 as shown in FIG. 2, the capacitance on the AC side of the rectifier 19 will be as will be appreciated by those skilled in the art. , Desirably minimized. Desirably, no additional capacitance exists between terminals T2 and T3.

Therefore, the DTC 12 may be used to provide a method of triggering a dimmer in an AC circuit. Such a method would include detecting whether the absolute value of the DTC's input voltage is below a threshold. Subsequently, if the detected voltage is below the threshold, the current is provided by the current source circuit. The current flows through the DTC and dimmer. If the detected voltage is not less than the threshold, only a negligible current will flow through the DTC and dimmer. Prior to detecting the value of the DTC input voltage, the input voltage may be generated by adjusting the AC voltage of the AC circuit. Subsequently or instead, the input voltage may be converted to a voltage suitable for detection. Finally, the current provided by the current source circuit may be limited.

FIG. 6 shows a simplified circuit diagram of a DTC embodiment such as the DTC 12 shown in FIGS. 3 and 4. It must be understood that this embodiment is an example of one possible implementation of the invention. Many implementations are possible, as will be appreciated by those skilled in the art. For example, instead of the bipolar NPN transistor, another switch such as a bipolar PNP transistor, an IGBT (Integrated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) may be used. In this embodiment, the bipolar current source circuit 18 further includes a current source circuit 17 and a rectifier 19. The rectifier 19 includes a full-wave diode bridge rectifier. The current source circuit 17 includes two resistors R2 and R3 and two NPN transistors Q1 and Q2. The voltage level detector 15 includes an NPN transistor Q3 and two resistors R4 and R5.

In this embodiment, the DC power supply V1 is connected to the collector of transistor Q3 of the voltage level detector 15. The resistor R6 is chosen such that a desired base current may be applied to Q1 when Q3 is off. The DC power supply V1 may be an external power supply. It must be understood that an additional current source may be used to obtain the desired base current instead of the DC power supply V1 and resistor R6. The resistors R4 and R5 are designed to form a voltage divider when the voltage at T4 is below the threshold, as when the voltage at T7 is off at Q3.

The collector of Q1 in this embodiment of the current source circuit 17 is connected to the terminal of the rectifying diode bridge, labeled T4. The base of Q1 is connected to the collector of Q2 and further to the collector of Q3 in the voltage level detector 15. When the voltage of T4 is less than the above-mentioned threshold value, Q3 is off. Also, R6 will now supply current to the base of Q1. As a result, the voltage of T6 is increased so that Q1 turns on. As a result, Q1 conducts an electric current. Also, the voltage of T4 decreases even more depending on the impedance of the source. It results in a lower voltage at T7. Therefore, the switch-off time of Q3 is limited. When the current passing through Q1 exceeds a certain value, the base voltage of Q2 exceeds the switch-on voltage. Also, Q2 conducts and thereby stabilizes the potential at T6. Therefore, the collector current passing through Q1 is controlled. Resistors R2 and R3 design a current source with appropriate characteristics. That is, when the emitter current through transistor Q1 exceeds a certain value (eg, nominal current in the range of 10 to 20 mA), transistor Q2 begins to conduct. Therefore, the combination of transistor Q2 and resistors R2 and R3 provides a feedback circuit that effectively limits the collector current of transistor Q1. R3 sets the current to approximately 0.6 / R3. When the triac is started, R2 functions to protect Q2. The combination of transistors Q1, Q2 and resistors R2, R3 forms a stable current source circuit 17 for a voltage T4 higher than about 1 V with respect to the negative terminal of the rectifier 19. If the voltage above T4 falls below approximately 1V, the collector current will decrease. A 220Ω resistor may be added in series with the Q1 collector, satisfying EMI conditions and limiting the current slope at low voltage levels.

The current source circuit 17 is activated when the voltage level detector 15 detects that the voltage of T4 is lower than the predetermined threshold, and is deactivated when the voltage of T4 is higher than the predetermined threshold again. Will be done.

To obtain a DTC12 designed to supply a current of 15 mA when the voltage of T2 is between -30V and 30V, the standard values of the components shown in FIG. 6 are: R2: = 4.7 kΩ; R3 = 27 Ω; R4 = 6.6 MΩ (generally constructed by locating two resistors with values of 3.3 MΩ in series); R5 = 100 kΩ; R6 = 47 kΩ; Q1 = FMMT458; Q2 = BC817; Q3 = BC817; V1 = 10V. The current provided by DTC12 and with the components with the above values during activation, shown in FIG. 6, will be approximately 20 mA. On the other hand, during inactivation, the ideal current would be only about 49 μA. Adding a leak current through transistor Q1 may add a few μA.

FIG. 7A shows a graph of the calculation of the behavior of _{the current I DTC} (ie, the current through the DTC) as a function of _{the voltage V DTC (ie, the voltage through the DTC).} In this calculation, the DTC of FIG. 6 is used such that the above standard values are used for each component. Therefore, when the voltage via the DTC falls below the threshold of 30V, the DTC is arranged to provide an absolute value of 20mA for the maximum current. The rectifier may supply current to the dimmer in the opposite direction.

It can be noted that when the V _DTC is close to 0, the I _DTC is equal to 0 and rises rapidly to the design current at some value of the _{V DTC , in which case the I DTC does not exceed 20 mA.} The low current near 0 of the V _DTC is only supplied by the current source circuit 17 as needed, that is, the dimmer 1 has its timer (directly on the grid while the current is higher). Due to the fact that it only limits the current that charges the circuit. The curved shape shown in FIG. 7A, which is related to the current source circuit 17 schematically depicted in FIG. 5, is the result of transistor Q1 which is saturated at low voltage.

FIG. 7B shows a graph of voltage-current operation between the terminals of the dimmer trigger circuit embodiment of FIG. 4, which typically comprises a microprocessor or a direction-sensitive component. As shown in FIG. 7B, just before the passage of the zero crossing, the triac in the dimmer 11 may be turned on at the same time, while the DTC 12 may be switched on. As a result, power is consumed for a short period of time, that is, the time required for the voltage via the DTC 12 to go from the threshold to zero. In embodiments that include the microprocessor as the voltage level detector 15, the microprocessor may be programmed so that after passing through the zero intersection, it simply allows the bipolar current source circuit 18 to be activated. As a result, the voltage-current operation between the terminals of the DTC 12 is schematically shown in FIG. 7B.

In Figure 7B, the I _DTC experiences a kind of hysteresis can be easily understood. That is, the value of _{I DTC} at a _{V DTC is} determined by the previous value of _{V DTC.} Part of the graph where I _{DTC is determined by past values of V DTC} is schematically illustrated by the gray line. Part of the graph where I _{DTC is determined by past values of V DTC} is schematically illustrated by the black line. The arrow indicates the direction of change of _{V DTC.}

[Setpoint filter circuit]
In a lighting system as depicted in FIG. 3, the LED drive circuit in the load 13 includes a current controller that supplies DC current to the LED and a DC current, so the light intensity of the LED becomes the power supply voltage. It is typically arranged so that it does not depend on it. The current controller controls the LED current within the range of the system. As a result, no change in power supply voltage will produce a change in LED current. The LED current is controlled by the setpoint. Different current levels are due to different setpoint values. In some embodiments of the invention, the average rectified voltage measured by the voltage level detector 15 of the DTC 12 may be used in the drive circuit as a setpoint. Setpoint filter circuits may be used to further optimize load dimming. This optimization may result in dimming the load in a range different from the dimmer setting. As a result, the entire range of adjusted setpoints is generated over the entire range of dimmer settings (ie, dimmer setpoint values). For example, the circuit may change the drive circuit setpoint by generating 0-100% or more adjusted setpoints corresponding to a series of 30-80% dimmer knob settings.

The optimization is more sensitive to darkening in the low luminosity region (ie, 1-10% within the set luminosity range) and darkening in the high luminosity region (eg, 10-100% within the set luminosity range). It may take a form that is a little perceptible. Where the lighting system contains an LED light source, the setpoint filter circuit uses this to create a selected luminosity (ie selected by the dimmer knob setting) with a perceived intensity that approaches closer. can do. A typical incandescent light bulb typically converts about 10% of the electrical energy consumed to visible light and uses electric power to heat the tungsten filament so that it emits light. Incandescent light bulbs exhibit a progressive response curve. The light generation from the light bulb is approximately proportional to the effective voltage to the third power (cubic response). It should be noted that for phase controlled voltage waveforms, the RMS voltage has a non-linear relationship with the effective voltage.

The human eye generally perceives the intensity of light by a logarithmic curve. Therefore, when the load current is changed linearly by adjusting the dimmer, the cubic response of incandescent light is fairly well matched with the logarithmic response of the human eye. Also, the dimming of light is perceived as relatively linear and smooth. However, LEDs show an almost linear response rather than a three-dimensional response. Here, the intensity of the emitted light is approximately proportional to the current flowing through the LED. Therefore, when the load current is changed linearly, the perceived change in light intensity has no intuitive relationship with the knob position of the dimmer.

The setpoint filter circuit is used by the drive circuit to generate a setpoint with a progressive response that approximates an exponential change when the dimmer settings are changed. Can be used to adjust the setpoints that are made. FIG. 8 shows a schematic of an embodiment of a setpoint filter circuit for the generation of an approximation of exponential changes in the case of setpoints. The circuit includes a low pass filter (LPF) containing a resistor R10-R13 and a capacitor C10. The input 20 to the LPF may be obtained, for example, from the output of the rectifier of the DTC 12 shown in FIG. 6 or from another point that provides the voltage rectified via the load in a timely manner.

This LPF circuit achieves a virtually ripple-free setpoint for the LED current controller during unstable dimmer performance due to an incorrect triac start that may occur at a start angle between 0 and 90 degrees. It serves a dual purpose, acting as a low-pass filter to eliminate fluctuations in the light source and as a barrier between the low-voltage circuit and the high-voltage input of the LED drive circuit. A primary filter, or a tertiary or high-level filter may be used, but a secondary LPF is preferably used to measure the rectified power supply voltage and determine its average voltage. This filter is in fault (hiccup) mode (when the DC capacitor charges when the drive circuit starts at a low input voltage (beyond the low input voltage) and switches off again due to lack of supply current. It may be provided at some point to maintain a filtered terminal voltage below the hysteresis threshold) while switching on again, etc., until sufficient supply is available).

If the dimmer is to darken the load, the triac should be turned off, for example, during period C in FIG. 2C, until after the appropriate phase delay according to the dimmer settings.
If the triac is started between 90-170 degrees during a half cycle, the triac start is generally stable and predictable. However, when the triac is started, it will charge the DC link capacitor (the capacitor on the DC side of the rectifier of the drive circuit) in a very short time after no more current will flow. The triac will then turn off as the current drops below the triac's holding current (usually only a few hundred microseconds after the trigger). In the absence of current flow, the voltage through the drive circuit will follow the supply voltage (eg, the voltage at T2 will follow the voltage at T1).

At a triac start angle between 0-90 degrees, double (or multiple) start of the triac may occur. Alternatively, some starts may be skipped. Double start may occur if the dimmer is connected to a resistive load that is too small to maintain the load current on the hold current of the triac so that the triac turns off again after the start. However, it is too large to generate enough current through the dimmer circuit to charge the capacitor C1 and cause the triac to re-trigger. If the DC link voltage is lower than the current value of the power supply voltage, a skipped start may occur because the triac simply switches on. If the trigger pulse comes early (approaching zero crossing), the triac will be triggered. However, the input rectifier will not start because it does not allow negative current. Suitable values for the components of the LPF in this embodiment are: 10 MΩ for R10 and R11, 3.9 MΩ for R12 and R13, 22 μF for C10. The LPF is designed as a secondary filter that filters out erroneous switching of the dimmer triac.

The output from the LPF is supplied to the integrated operational amplifier U10. Further, the output 22 from the U10 is an intermediate setpoint value representing a coarse dimmer knob setting. It has a threshold voltage of about 2V and is used to drive the gate of transistor Q10, which manages the progressive function. The source terminal of Q10 is connected to a voltage divider that includes resistors R18, R19 and R20. Further, the drain terminal is connected to the reference voltage Vref drawn from the standard integrated voltage reference U11. The resulting signal 24 at the source terminal of Q10 may then be used as an input to the current controller of the LED drive circuit.

The lower average voltage through the load results in a reduced reference voltage Vref so that the dimmer setting is changed to darken the load. When the output of U10 is low, the transistor Q10 is turned off and the value of the adjusted setting signal 24 is determined by the output of U10 and the voltage dividers R18 / R19 / R20. If the output of the U10 rises sufficiently to turn off the transistor Q10, the tuned set signal 24 is determined by the output of the U10 and the resistors R19 and R20. In this example, the faster section is activated from 40-305mA (between approximately 130V and 175V) and then a slow change range between 10-40mA (average input between approximately 70V and 130V), or The gate-source threshold voltage of Q10 is utilized to achieve the other required maximums. Suitable values for the embodiment of the circuit of FIG. 8 are: R14 = 278 kΩ; R15 = 680 kΩ; R16 = 470 kΩ; R17 = 39 kΩ; R18 = 270 kΩ; R19 = 33 kΩ; R20 = 1.72 kΩ; C11. = 100nF; C12 = 100nF; C13 = 10nF; C14 = 100nF. For the U10, a LM358ADR dual operational amplifier from Texas Instruments may be used. For Q10, a 2N7002 N channel enhancement mode field effect transistor from Fairchild Semiconductor may be used. Also, for U11, an adjustable precision shunt adjuster from Zetex Semiconductor or Texas Instruments may be used.

The output 24 of the setpoint filter is used as a reference so that the LED current controller darkens approximately smoothly for the user. Since the human eye has a logarithmic sense of brightness, "low gear" and "high gear" setpoint shapers are performed. As shown in the example in FIG. 9A, the setpoint filter circuit produces a tuned setpoint change with two slopes. In the example shown in FIG. 9A, the actual dimmer setting SP1 is plotted on the horizontal axis. Further, the adjusted setpoint SP2 output by the setpoint filter is plotted on the vertical axis. As shown in the figure, the adjusted setpoint remains at a very low value of 34 up to the break point for the first part of the dimmer setting range (0-20% in this example), and the range For the second part (20-50% in this example), it rises at a low rate of 31 and for the third part of the range (50-80% in this example) it rises at a high rate of 32, for the fourth part of the range. For the portion (80-100% in this example), the high value 35 (100% non-dimming value in this example) remains. Therefore, the setpoint filter produces a tuned dimmer setpoint with a progressive response of "two gears". It approaches an exponential response. This progressive behavior of the tuned setpoint results in a smooth perceived change in brightness due to the logarithmic response of the human eye, so that the dimmer setting is linearly increased by the LED light source. Produces a progressive response corresponding to the intensity of light from.

This progressive response significantly reduces sensitivity to changes in the dimmer start angle (ie, changes in the triac's turn-on delay after zero crossing) at low light settings. Changes in the dimmer start angle occur, for example, as a result of changes in the AC applied voltage. These changes cause visible flickering of darkened light sources, especially at low light dimmer settings. The tuned setpoints generated by the setpoint filter circuit shown in FIG. 9A reduce the sensitivity of the lighting system to these changes, reduce or eliminate flicker, low dimmer setting flats 34 and shallow tilt. Has 31.

The double-slope adjusted setpoint curve shown in FIG. 9A is an approximation of the ideal exponential response as shown in FIG. 9B. Adjusted setpoint curves with three, four or more slopes may be implemented using techniques known to those of skill in the art to come closer to the exponential curve. A microprocessor may also be used to generate a tuned setpoint that follows an ideal exponential response.

The tuned setpoints generated by the setpoint filter circuit are used as setpoint inputs to the current controller to drive the LEDs. FIG. 10 shows a simplified circuit on the two-stage side of the transformer T10 of the LED drive circuit. As described above, the setpoint filter circuit of FIG. 8 produces a setpoint voltage 24 tuned via R20 in a partially linear manner as a function of the output of the integrator U12. The adjusted set point 24 is input to the operational amplifier U12 via the resistor R21. If the voltage through the second shunt resistor R24 is equal to the voltage through R20, the integrating circuit is unstable. The shunt resistor R24 is connected in series with LEDs 1-4 which are connected in series. The amplifier U12 coupled with R20-24 and C15 forms the current controller circuit 27.

The output of U12 supplies a feedback signal to the shunt regulator U11 and the opt coupler U13 via the resistors R22 and the voltage dividers R25 and R26. The opt coupler U13 supplies a feedback signal to the flyback controller on the primary side of the T10. This portion of the circuit forms the voltage controller circuit 26. The output of U12 can be regarded as a reference value for the voltage controller around U11. If the current through the R24 is too low, the voltage feedback from the U12 will cause a higher voltage control setpoint. This will reduce the current through the opt coupler U13, signal the flyback controller and increase its power flow so that the commanded reference power supply is obtained and the required LED current is achieved. If the current through R24 is too high, the feedback signal will cause a low voltage setpoint. The flyback controller will reduce the power flow in two stages as the LED current is reduced.

The values suitable for the embodiment of the circuit of FIG. 10 are as follows. R20 = 1.72kΩ, R21 = 4.7kΩ, R22 = 8.2kΩ, R23 = 2.7kΩ, R24 = 39Ω, R25 = 12kΩ, R26 = 2.49kΩ, R27 = 2.7kΩ, C15 = 1nF, C16 = 3 μF. For the U12, a LM358ADR dual operational amplifier from Texas Instruments may be used. Further, for U13, a PS2801C-1 photocoupler from NEC may be used. As for the PWM control unit, the UCC28600 from Texas Instruments may be configured to operate in a mode in which a constant output voltage is suppressed.

[Time-based setpoint control]
If the power signal that drives the LED and the information signal that sets the intensity of the LED are both embodied in the same signal and the average voltage is through the load, the lighting system described above can be considered a system. .. This arrangement generally depends on the voltage through the load, depending on the knob setting of the dimmer. If this is not the case, the dimming of the load may not always match the dimmer setting, especially due to the operation of the dimmer with low or discontinuous loads.

As discussed above, the lighting system described herein may operate at loads below the holding current of the dimmer triac. The DTC described above will produce enough current to guarantee the triggering of the triac. Once triggered, the DTC will generate only a negligible current and deactivate it. For light loads and for rectifiers with a DC link capacitor load, the dimmer will fall below the holding current of the dimmer triac. If the load / drive circuit has active power factor correction at the front end, the load acts more like a resistor and, in some cases, charges and starts the dimmer circuit as shown in FIG. 11B. Each may bring.

FIG. 11A shows the case where the dimmer setting is due to the start of the triac at time t1 after the zero intersection t0 in each half cycle, and the triac flashes through the dimmer triac, as described above. It is a graph which shows the waveform of the voltage through the load (for example, the terminal T2-T3 of the circuit of FIG. 3) when the coupling current divided by the DTC is zero with the load immediately after the charge DC link capacitor.

FIG. 11B shows an example of a voltage waveform with the same dimmer settings when the dimmer is connected to a small resistor load that is too small to maintain the load current on the triac's holding current. This type of small resistive load may be present in a drive circuit with a modified active power factor that modifies the front end that drives a DC circuit with low power consumption.

At time t1, the triac is triggered and the voltage rises rapidly. However, the current flowing through the triac is not sufficient to maintain the triac in conduction, the triac turns off again, and the voltage through the load drops due to the resistance characteristics of the load. Since the voltage through the dimmer is increasing, the RC circuit in the dimmer will recharge, even if the DTC is always activated and without triggering the dimmer triac again. right. As a result, the triac is triggered multiple times during each half cycle as shown in FIG. 11B. A triac-based dimmer is connected to a low power resistor load so that the active power factor correction circuit booths a converter with discontinuous switching for DC link drive or direct LED drive. If so, such multiple triggers of the triac may occur.

As can be seen by comparing the average voltage of each half cycle of FIGS. 11A and 11B, this multiple trigger results in a very disturbing voltage and a lower average voltage through the load. If this voltage is used to guide the setpoint that controls the intensity of the LED, it will result in a vibrating setpoint. If the mean (or RMS) voltage is used to set the intensity of the LED light source in this situation, false dimming with unstable light output will occur.

The solution to this problem is to use time information to control the LED light source intensity rather than voltage level information. The time delay from the zero intersection to the first trigger of the triac following the zero intersection may be used to derive a control value for the LED light source intensity, which is also called the starting angle or phase control value. This time delay value varies depending on the charging time of the RC circuit of the dimmer (which depends on the dimmer knob setting) and is unaffected by multiple triac starts that may occur later in half a cycle. ..

The microprocessor may be used to derive the LED intensity setpoint value from the time delay value. One way to implement this is to measure when the rising and falling edges of the current through the DTC occur, or to measure the voltage associated with these rising and falling edges. The rising and falling edges of these currents are shown, for example, in FIG. 7B and correspond to moments. DTC is activated when the triac turns off at zero crossing (rising edge). When the triac is triggered, the DTC is deactivated (falling edge). The time between the two rising edges indicates the cycle time between zero crossings of the supply voltage. The time between the rising and falling edges indicates the time delay between the zero crossing and the start time of the first triac. From these measurements, the triac start angle can simply be calculated. This can be conveniently done in the embodiments shown in FIGS. 3 and 6 by measuring the rising and falling edges of the voltage of T6 at the base of transistor Q1 of the current source circuit 17 of DTC 12. In the embodiment described above, this voltage will be about 0.5V when DTC is activated and Q3 is on, and when DTC is deactivated and Q3 is off. , Will be about 1.5V.

The time between the associated rising / falling edges can be measured using a clock. It starts when an edge is detected and stops when the next related edge is detected. The time between the rising edge of the DTC current and the next falling edge of the DCT current can be determined and divided by the time between the two rising edges to determine the triac-off duty cycle. The triac on-duty cycle is then (1-off-duty cycle). Progressive features can be used to guide the current setpoint for LEDs. This function can also be an exponential function with saturation. Such clocks and progressive features can be implemented using a microprocessor or microcontroller, as understood by one of ordinary skill in the art.

With this solution, the system is designed for applications in dimmable circuits with universal power inputs (eg, AC power voltages from 90V to 240V) for use in countries with different AC voltages. can do. Since the light source intensity control value depends on the time delay value, not the voltage value, the input voltage value and the resulting average load voltage do not change as in the function of the AC applied voltage. This allows a single design to be used throughout the world, thereby reducing manufacturing costs with significant economies of scale.

[Hysteresis and minimum current]
A dimmer without an "off" switch acts like a series capacitor when set in the minimum (ie, turns off the light source) position. AC current will flow through this "capacitor" and charge the DC side of the rectifier in the LED drive circuit. This may be sufficient to activate the controller chip in the LED drive circuit after a short period of time. This may discharge the DC link and simply flash the LED. After that, the undervoltage will be detected. The controller will switch off. Also, the cycle will start again. To prevent this unwanted flushing, the current control circuit may provide some positive feedback to generate hysteresis. Thus, the current controller will receive a zero setpoint until the average input voltage exceeds a certain limit. The current setpoint is then switched to a low value (eg, about 30 mA). By moving the dimmer knob back to a lower setting, the LED current may then be reduced (eg, up to about 10mA). Therefore, in this low dimmer setting, the LED may be on or off depending on the previous dimmer setting.

The minimum current through the LED is near no load (ie, low dimmer setting) and is preferred to avoid changes in light intensity due to dimmer circuit interactions. With almost no load, the voltage on the DC side of the rectifier in the LED drive circuit is increased by the LC filter inside the dimmer (for example, the inductor L1 and the capacitor C2 included in the dimmer circuit of FIG. 1). Tend. This increase raises the measured average load voltage, which raises the LED current. This increase in current will reduce the DC voltage. Also, the LED current will decrease again. As a result, the LED current oscillates. This problem can generally be avoided by maintaining the LED current at or above the minimum value of at least 5 mA. If the start angle of the dimmer triac approaches 180 degrees, the circuit will stop driving and a failure mode will occur. However, due to hysteresis, no light will be produced. It's similar to what an incandescent light bulb does.

Hysteresis and minimum current may be implemented in the embodiment shown in FIG. 10 by adding resistors R30 and R31 and a capacitor C17, as shown in FIG. R30 and R23 generate positive feedback around the amplifier U12. When the LED is controlled, the output of U12 is about 2.5V. Also, when the LED is off, the output of the U12 is about 8V. Therefore, a hysteresis of about 10 mV will appear at node 24. The minimum current is determined by a resistor via Q10 (not shown) that raises reference 24 from ground and this hysteresis. If the LED is off and the reference 24 is rising, the U12 will toggle as soon as the input of the U12 rises above the + input. After the toggle, the + input drops to about 10 mV, which increases the setpoint by about 10 mV / R24 = 30 mA. Suitable values are R30 = 1.2MΩ; R31 = 4.7kΩ; C17 = 10nF.

[Over and under voltage protection]
The secondary circuit of the LED drive circuit preferably acts as a current source only between a range (eg, the output voltage between 8.3V and 17.3V) and aims to use voltage control outside this range. ing. If the current setpoint for the LED is 0, then the drive circuit must still be valid. Therefore, to make this possible, the output of the drive circuit is a voltage controlled to avoid undervoltage lockout of the flyback controller chip. For voltages over the current control range, the drive circuit is in voltage control mode to avoid overvoltage in the circuit (especially the power transistor on the primary side of the drive circuit) in the event of LED disconnection or open circuit failure. to go into. The current control range is set by the value of the resistor and a reference power chip can be utilized to achieve a very low tolerance. The built-in overvoltage protection in some flyback controller chips is rather unused due to its too high tolerance.

Accordingly, the present invention has been described by reference to certain embodiments discussed above. The elements and components in one embodiment may be used in other embodiments. The embodiments described above include DTC, which can be omitted. Further, various functions of the drive circuit or setpoint filter circuit described in the context of various embodiments may be omitted from those embodiments or may be included in other embodiments. Would be obvious.

It will be appreciated that the described embodiments will accept various modifications and alternatives well known to those of skill in the art. For example, instead of using a DTC with a full-wave rectifier such as a diode rectifier bridge, two DTCs with a half-wave rectifier may be used. In the latter case, one DTC will be used in one direction of AC current. Also, another DTC will be used in the opposite direction. The circuits described may be designed with bipolar transistors or MOSFETs, or other types of switching devices. The terms "base", "collector" and "emitter", and "gate", "drain" and "source" not only refer to the connection of bipolar transistors or FETs, but are similar to other types of transistors. Note that it should be broadly interpreted as it also refers to connections. Further, embodiments of the present invention have been described with respect to lighting systems. However, the invention may relate to circuits for yet other types of applications.

Claims (11)

A setpoint filter circuit for driving circuit and cooperate to supply the current to one or more LED phase dimmer signals into receive current from the dimmer circuit,
The setpoint filter circuit receives the phase dimming signal from the dimmer circuit, and the dimmer setpoint value whose at least a part is determined by the phase dimming signal received from the dimmer circuit. Generates an adjusted setpoint value based on, and the current is at least partially determined by the adjusted setpoint value.
The sensitivity of the adjusted setpoint value to the change of the dimmer setpoint value is lower at a low value of the dimmer setpoint value than at a high value of the dimmer setpoint value.
The adjusted setpoint value is a setpoint filter circuit that produces an adjusted setpoint value having a minimum value greater than zero. The setpoint filter circuit according to claim 1, wherein when the dimmer setpoint value increases, the adjusted setpoint value increases or is constant. The setpoint filter circuit according to claim 1 or 2, wherein the setpoint filter circuit generates an entire range of the adjusted setpoint values, which is less than the entire range of the dimmer setpoint values. The setpoint filter circuit according to any one of claims 1 to 3, wherein the setpoint filter circuit includes a second or higher low-pass filter for filtering a received dimmer setpoint value. The set according to any one of claims 1 to 4, wherein the setpoint filter circuit comprises a differential amplifier that produces an intermediate setpoint value that controls the transistor to produce the adjusted setpoint value. Point filter circuit. The setpoint filter circuit according to any one of claims 1 to 5, wherein the adjusted setpoint value is substantially constant within a predetermined range of the dimmer setpoint value. The setpoint filter circuit according to claim 6, wherein the predetermined range includes a range of about 90 to 100% with respect to the maximum value of the dimmer setpoint value. The setpoint filter circuit according to any one of claims 1 to 7, wherein the adjusted setpoint value has a minimum value larger than 0 at the lowest value of the dimmer setpoint value. The setpoint filter circuit according to any one of claims 1 to 8, wherein the minimum value of the adjusted setpoint value is about 3% of the maximum value of the adjusted setpoint value. The ratio of the change in the adjusted setpoint value to the change in the dimmer setpoint value is less than 1 at the low value of the dimmer setpoint value and less than 1 at the high value of the dimmer setpoint value. The setpoint filter circuit according to any one of claims 1 to 9, which is larger than 1. A lighting system comprising the setpoint filter circuit according to any one of claims 1 to 10, the one or more LEDs, and the drive circuit.
A lighting system in which a change in the adjusted setpoint value in response to a change in the dimmer setpoint value approximates an exponential response.

Images