JPS6215032B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter for powering a capacitive load such as an EL lamp (electroluminescent lamp).

EL lamps have a type of capacitor structure in which a light emitter containing a special fluorescent material dispersed in a dielectric material is sandwiched between two electrodes in a sandwich style.
When an alternating current voltage is applied between the two electrodes, an alternating electric field is applied to the fluorescent material of the luminescent material, causing it to emit light. Also this EL
Lamps include materials whose brightness increases in proportion to the magnitude and frequency of the applied voltage, so rather than applying commercial AC power voltage, lamps use dry batteries, storage batteries, or DC voltage obtained by rectifying commercial AC voltage via an inverter. In many cases, it is converted into high-frequency, high-voltage AC voltage for lighting. This type of inverter basically has a circuit as shown in FIG. 1 in the past.

That is, in FIG. 1, 1 is a DC power supply, 2 is a filter circuit, 3 is an inverter, and 4 is an EL lamp as an example of a capacitive load. Inverter 3
is a transformer 5 connected to the EL lamp 4, a transistor 6 whose emitter and collector are connected to the transformer 5 and the filter circuit 2, a bias capacitor 7 connected between the base of the transistor 6 and the transformer 5, and the base of the transistor 6. and a resistor 8 connected between the collector and the collector, and performs the following oscillation operation. First, when the switch 9 of the DC power supply 1 is turned on, the capacitor 7 is charged via the filter circuit 2 and the resistor 8. When the capacitor 7 is charged to a certain constant voltage value, a forward voltage is applied between the base and emitter of the transistor 6. The bias voltage causes transistor 6 to conduct (ON), and current flows between the collector and emitter and through transformer 5. When the transformer 5 is saturated by the product of this current and the number of turns of the winding of the transformer 5 (ampere turns), the transistor 6 becomes non-conductive (OFF) again, and the above operation is repeated thereafter. This transistor 6 is ON-
An alternating current voltage is applied to the EL lamp 4 at the timing of repeating OFF.

By the way, since the EL lamp 4 is a capacitive load,
The inverter 3 will not oscillate properly unless a special transistor 6 is used that takes into account the phase shift caused by the equivalent resistance and equivalent capacitance of the load. Further, even if the inverter 3 is somehow caused to oscillate, it actually only oscillates as shown in the waveform of FIG. To explain each waveform A to H in this Fig. 2, A shows the DC input current Iin entering the filter circuit 2, B shows the input voltage Vin applied to the inverter 3, and C shows the input current Iin of the inverter 3. ', D indicates the output voltage Vout of the transformer 5, that is, the voltage applied to the EL lamp 4, and E indicates the output current of the transformer 5, that is, the input current of the EL lamp 4. The reason why the waveforms C, D, and E become asymmetrical and unstable in both the vertical and horizontal directions is due to the phase shift in the circuit caused by the capacitive load, and the ON-
This is due to the difference in OFF timing, etc. What I would like to focus on here is the waveform of the output voltage Vout of the transformer 5. This AC voltage has a higher and lower waveform with respect to the zero volt line, with the maximum positive value V2 being larger than the maximum negative value V1. is asymmetrical. On the other hand, the EL lamp 4 lights up due to the application of this output voltage Vout, and this EL
The brightness of the lamp 4 increases in proportion to the voltage and frequency of the output voltage Vout. However, the output voltage
Since the positive voltage of Vout is low, the luminous efficiency during this half cycle is poor, and the brightness of the EL lamp 4 has to be reduced.

The cause of this is that the transformer 5 is magnetically saturated due to the superimposed current of the current passing through the transistor 6 in the transformer 5 and the output current Iout of the transformer 5. As the charge is rapidly discharged through the transformer 5, the falling slope of the output voltage Vout of the transformer 5 becomes steep, and the input current Iin' of the inverter 3 and the output current Iout of the transformer 5 have steep peak values. .

As a solution to this problem with inverter 3, the two transistors are turned on and off alternately.
Operate it and improve the output voltage so that it is vertically symmetrical.
Push-pull type inverters have been proposed and put into practical use to apply voltage to EL lamps. Although the use of two transistors in this way certainly improves the brightness of the EL lamp, it also complicates the inverter circuit and increases the number of parts, making it expensive.

The present invention was made in view of the problems of such inverters, and includes a transistor bias circuit.
The ON-OFF operation of the transistor prevents magnetic saturation of the transformer, which consists of a capacitor connected to the collector and base of the transistor, and a resistor connected between the connection point of the resistor and bias capacitor and the base of the transistor. The present invention provides an inverter that solves the problem caused by the phase shift of a capacitive load by adding a new timing adjustment means. For example, FIG. 3 shows an embodiment in which the present invention is applied to the inverter of the EL lamp lighting circuit shown in FIG. is an inverter according to the present invention.

The difference between the above inverter 10 and the conventional inverter 10 is that it consists of a CR circuit in which a capacitor 11 is connected between the base and collector of the transistor 6, and a resistor 12 is connected between the midpoint of the resistor 8 and the capacitor 7 and the base of the transistor 6. Add adjustment circuit 13. This timing adjustment circuit 13 finely adjusts the ON-OFF timing of the transistor 6 by changing the charging time constant or the discharging time constant of the capacitor 7. In fact, this timing adjustment circuit 13
In order for this to work effectively, it is necessary to limit the numerical values within a certain range, for example, the DC power supply 1 is 5V, the dimensions of the EL lamp 4 are 3.8cm x 9cm (equivalent capacitance and equivalent resistance are 22000PF, 59KΩ), and the resistance When the capacitor 8 is 3.9KΩ and the capacitor 7 is 6.8μF, the capacitor 11 of the timing adjustment circuit 13 is set to 0.03 to 0.06μF, and the resistor 12 is set within the range of 100 to 200Ω. When the timing adjustment circuit 13 is set in this way, the inverter 10 oscillates with various waveforms as shown in waveforms H to N in FIG.

In other words, the DC input current Iin to the filter circuit 2 and the input voltage Vin applied to the inverter 10 in the circuit shown in FIG. 3 are different from those in the circuit shown in FIG. Almost the same, but
The input current Iin' to the inverter 10 becomes two substantially symmetrical chevron waveforms on the left and right by adjusting the ON-OFF timing of the transistor 6 by the timing adjustment circuit 13, as shown by waveform C in FIG. Vout and the output current Iout have sinusoidal waveforms that are substantially symmetrical vertically and horizontally, as shown by waveforms R and N in FIG. That is, in the circuit shown in FIG. 3, when switch 9 is turned on at time t1 in FIG. Base current is supplied.
At this time, in addition to the conventional circuit that goes through the resistor 8 - capacitor 7 - feedback winding and primary winding of the transformer 5, the capacitor 11 - resistor 12 - capacitor 7 -
As a result of the capacitor 7 being charged through the circuit passing through the feedback winding and the primary winding of the transformer 5, the terminal voltage rises at an early phase, and the phase of the collector current of the transistor 6 also advances accordingly. That is, in the circuit of FIG. 3, the timing adjustment circuit 13
is provided, the phase of the base current becomes earlier than in the conventional circuit shown in FIG. 1, and accordingly, the phase of the input current Iin' of the inverter 10 advances. As the collector current of the transistor 6 flows into the primary winding of the transformer 5, the output voltage of the transformer 5 increases.
Vout also rises, and an output current Iout with a phase lead of 90° flows through the capacitive load 4.

When most of the input voltage Vin is applied to the primary winding of the transformer 5, the reverse charging current of the capacitor 7 based on the induced voltage in the feedback winding, that is, the base current of the transistor 6, decreases, so that the input
Iin' begins to decrease, and finally, at time t2 in Fig. 4,
When the output voltage Vout of the transformer 5 reaches the maximum positive value, the output current Iout becomes 0 because the load 4 is capacitive.
become.

From the next moment, since the load 4 is capacitive, the output current Iout reverses and begins to increase in the negative direction.
Therefore, a positive voltage is induced in the primary winding and feedback winding of the transformer 5, the reverse charging current of the capacitor 7 increases again, the base current of the transistor 5 increases, and the input current Iin' increases again. do. At this time, the phase of the input current Iin' is advanced by the timing adjustment circuit 13, and the phase of the input current Iin' and the output current Iout of the transformer 5 is different, and the superimposed current of the two causes the transformer 5 to No magnetic saturation. During this period, the output voltage Vout decreases, and the negative value of the output current Iout increases. When the output current Iout reaches the negative maximum value at time t3 in FIG. 4, the output voltage Vout becomes 0 and the transistor 6
The base current of Iin' also decreases sharply, transistor 6 enters the cut-off state, and the input current Iin' decreases sharply.

From the next instant, the negative value of the output current Iout decreases, and the output voltage Vout increases in the negative direction. At time t4 in FIG. 4, when the output current Iout becomes 0, the output voltage Vout reaches its negative maximum value.

From the next moment, the output current Iout increases in positive value,
The negative value of the output voltage Vout decreases. In addition,
While this output voltage Vout takes a negative value, a reverse bias voltage is applied to the transistor 6, so the transistor 6 maintains the cut-off state. While the transistor 6 is in the cut-off state, the accumulated charge in the capacitor 11 is discharged through the resistor 8 and the resistor 12, returning to the initial state.

Then, at time t5 in FIG. 4, when the output current Iout reaches the maximum positive value, the output voltage Vout becomes 0, and the transistor 6 is released from the reverse bias state and is again in the same state as at the beginning (time t1). become.

Thereafter, the same operations as those at times t1 to t5 are repeated to cause the inverter 10 to operate in oscillation, and a sinusoidal alternating current voltage having a positive and negative symmetrical shape is applied to the load 4. When the inverter 10 generates sinusoidal oscillation in this manner, the EL lamp 4 lights up with the same brightness depending on the positive voltage and the negative voltage of the output voltage Vout, and the brightness is significantly improved. In fact, the oscillation frequency of the inverter 10 in Fig. 3 is 455Hz, and the brightness of the EL lamp 4 is a relative value.
110, whereas under the same conditions, the oscillation frequency of inverter 3 in Fig. 1 is 476Hz, and the relative brightness of EL lamp 4 is 70. Although the oscillation frequency of the present invention is slightly lower, it is sine It was experimentally confirmed that the luminance was improved by about 55% due to wave oscillation.

As explained above, according to the present invention, by adding a timing adjustment circuit, vertical and horizontal symmetrical sinusoidal oscillation can be achieved with just one transistor.
When used as an inverter for EL lamps, the brightness of EL lamps can be significantly improved, and an inexpensive inverter can be provided.

Note that the present invention is not limited to inverters for lighting EL lamps, but can be implemented similarly for capacitive loads.

[Brief explanation of the drawing]

Figure 1 shows a conventional basic inverter.
EL lamp lighting circuit diagram, Fig. 2 is a current/voltage waveform diagram at each point in Fig. 1, Fig. 3 is a circuit diagram of an EL lamp lighting circuit using an inverter according to an embodiment of the present invention, Fig. 4 are current/voltage waveform diagrams at each point in FIG. 3. 4... Capacitive load (EL lamp), 5... Transformer, 6... Transistor, 10... Inverter,
11... Capacitor, 12... Resistor, 13... Timing adjustment means (circuit).

Claims (1)

[Claims] 1. A transistor and a primary winding of a transformer are connected in series, a resistor is connected between the collector and base of the transistor, and a bias capacitor is connected between the base and the feedback winding of the transformer. In an inverter that converts a DC voltage into an AC voltage through the ON-OFF operation of a transistor and applies the voltage to a capacitive load connected to the secondary winding of a transformer, a bias circuit of the transistor is connected to a bias circuit of the transistor. A means for adjusting the timing of the ON-OFF operation of the transistor is added, which consists of a capacitor connected between the collector and the base, and a resistor connected between the connection point of the resistor and bias capacitor and the base of the transistor. Features of capacitive load inverter.