JP7614557B2 - Power supply and lighting equipment - Google Patents

Description

Embodiments of the present invention relate to a power supply device having a switching element and a lighting device equipped with this power supply device.

Conventionally, for example, in lighting devices, power supplies equipped with power conversion circuits that use switching elements to convert input power into a specified DC power are used to light the light source. In this power supply device, a noise filter is provided on the input wiring connected to the input section of the power conversion circuit to reduce noise generated by the switching elements, etc.

Since installing a noise filter on the input wiring is time-consuming, it is desirable to be able to reduce noise without installing a noise filter on the input wiring.

JP 2016-162596 A

The problem that this invention aims to solve is to provide a power supply device and lighting device that can reduce noise.

The power supply device of the embodiment includes a power conversion circuit having a switching element and converting input power into a predetermined DC power, a composite line filter with sections that is connected to an input of the power conversion circuit and reduces noise in a high frequency range of 30 MHz or more , and a normal mode choke that is connected to the input of the power conversion circuit and reduces noise in a high frequency range of less than 30 MHz . The line filter is connected between the power conversion circuit and the normal mode choke.

The power supply device of the embodiment is expected to reduce noise.

1 is a circuit diagram of a lighting device including a power supply device according to an embodiment. 4 is a graph showing the relationship between frequency and impedance of the line filter of the power supply device. 3 is a graph showing an enlarged portion of FIG. 2. FIG. 4 is a table showing characteristics of the line filter.

An embodiment will be described below with reference to the drawings.

As shown in FIG. 1, the lighting device 10 includes a light source 11 and a power supply device 12 that receives power from an external AC power source E to turn on the light source 11.

The light source 11 is, for example, a light emitting diode (LED), which is a semiconductor light emitting element. Note that other semiconductor light emitting elements such as organic electroluminescence (EL) may be used in addition to light emitting diodes. The light source 11 may be, for example, configured as an integrated unit with the power supply device 12, or may be configured as a light source unit that is detachable from the fixture body and electrically connected to the power supply device 12 when the light source unit is attached to the fixture body.

The power supply device 12 also includes a noise prevention circuit 15, a rectifier circuit 16, and a power conversion circuit 19 including a power factor correction circuit 17 and a constant current circuit 18.

The noise prevention circuit 15 has a capacitor C1 connected to both ends of an AC power source E such as a commercial AC power source, a pair of normal mode chokes L1 connected to both ends of the capacitor C1, and a composite line filter 21 with a pair of input terminals connected to the pair of normal mode chokes L1.

The normal mode choke L1 is a choke coil that primarily reduces noise from normal mode components, and has the characteristic of reducing noise in the low frequency range, for example, below 30 MHz.

The composite line filter 21 is a so-called composite type with sections (or hybrid type) that is capable of reducing noise over a wide range from high to low frequencies, and is a common mode/normal mode composite choke coil that has both the inductance value of the common mode component and the inductance value of the normal mode component.

As shown by the solid lines in the graphs of Figures 2 and 3, the composite line filter 21 has impedance peaks at frequencies below 30 MHz, but the impedance value at 30 MHz is 1 kΩ or more and the line capacitance is 7 pF or less, so it has the characteristic of effectively reducing noise in the high frequency range above 30 MHz.

The rectifier circuit 16 is a full-wave rectifier circuit that full-wave rectifies the AC voltage from the AC power source E, and has a pair of input terminals connected to a pair of output terminals of a composite line filter 21, which is connected to the AC power source E via the noise prevention circuit 15. A capacitor C2 is connected to a pair of output terminals of the rectifier circuit 16. The rectifier circuit 16 and the capacitor C2 form a full-wave rectifier circuit that rectifies the AC voltage input from the AC power source E via the noise prevention circuit 15, smoothes the high-frequency voltage generated by the power factor improvement circuit 17 in the subsequent stage, and converts it into a full-wave rectified waveform.

The power factor correction circuit 17 is composed of a boost chopper circuit that boosts the rectified and smoothed DC voltage to improve the power factor. The power factor correction circuit 17 includes a series circuit of an inductor L2 and a switching element Q1 connected across the capacitor C2, and a series circuit of a diode D1 and a capacitor C3 connected in parallel across the switching element Q1.

Switching element Q1 is a MOS-FET field effect transistor, with its drain connected to the high potential side of capacitor C2 via inductor L2, its source connected to the low potential side of capacitor C2, and its gate connected to a control circuit that controls switching element Q1.

The constant current circuit 18 is composed of a step-down chopper circuit that steps down the DC voltage boosted by the power factor correction circuit 17 to a predetermined voltage required to light the light source 11 and makes it a constant current. The constant current circuit 18 includes a series circuit of a switching element Q2 and a diode D2 connected to both ends of a capacitor C3, and a series circuit of an inductor L3 and a capacitor C4 connected to both ends of the diode D2. The light source 11 is connected to both ends of the capacitor C4.

Switching element Q2 is, for example, a field effect transistor such as a MOS-FET, with its drain connected to the connection point between the cathode of diode D1 and capacitor C3, its source connected to the connection point between the cathode of diode D2 and inductor L3, and its gate connected to a control circuit that controls switching element Q2.

Figure 4 also shows the board 30 of the power supply device 12. The power input section of the board 30 has a noise prevention circuit mounting area A adjacent to the input connector CN1, where the noise prevention circuit 15 is mounted. A capacitor C1, a pair of normal mode chokes L1, and a composite line filter 21 are mounted in this noise prevention circuit mounting area A.

Next, the operation of the power supply device 12 will be explained.

When the AC power supply E is turned on, the AC voltage is input to the rectifier circuit 16 through the noise prevention circuit 15, the AC voltage is rectified by the rectifier circuit 16 and smoothed by the capacitor C2, and the full-wave rectified voltage after this rectification and smoothing is supplied to the power factor correction circuit 17.

In the power factor correction circuit 17, the control circuit turns on and off the switching element Q1 at a predetermined switching frequency, and the rectified and smoothed DC voltage is boosted to a predetermined voltage. The boosted DC voltage is smoothed by the capacitor C3 and supplied to the constant current circuit 18.

In the constant current circuit 18, the control circuit turns on and off the switching element Q2 at a predetermined switching frequency, and the DC voltage output from the power factor correction circuit 17 is stepped down to a predetermined voltage and made constant current. This constant current DC voltage is supplied to the light source 11, which lights up.

In addition, the noise prevention circuit 15's capacitor C1, normal mode choke L1, and composite line filter 21 reduce noise generated mainly by the switching element Q1 of the power conversion circuit 19.

As shown by the solid lines in the graphs of Figures 2 and 3, the composite line filter 21 has impedance peaks at frequencies below 30 MHz, but the impedance value at 30 MHz is 1 kΩ or more and the line capacitance is 7 pF or less, so it has the characteristic of effectively reducing noise in the high frequency range above 30 MHz.

The dashed lines in the graphs of Figures 2 and 3 show the characteristics of a comparative example composite line filter (hereinafter referred to as the comparative example line filter).

The composite line filter 21 and the comparative line filter differ in coil size, number of turns, L value, and line capacitance. The line capacitance occurs because the coil windings are covered with an insulator, and the insulator is placed between the windings, creating a structure similar to that of a capacitor. When the coil is large and the number of turns is large, the line capacitance becomes large. The effect of line capacitance is small in the low frequency range, but in the high frequency range, the larger the line capacitance, the greater the leakage current, which has the effect of reducing impedance.

Compared to the comparative line filter, the composite line filter 21 has a smaller coil size, fewer turns, and a smaller L value and line capacitance.

Therefore, compared to the line filter of the comparative example, the composite line filter 21 has a characteristic that there is an impedance peak at a high frequency, the impedance is high in the high frequency range from the impedance peak (including 30 Hz or higher), and the impedance is low in the low frequency range from the impedance peak. Therefore, the composite line filter 21 has an impedance value of 1 kΩ or more at 30 MHz and a line capacitance of 7 pF or less, and therefore has excellent characteristics in reducing noise in the high frequency range of 30 MHz or higher compared to the line filter of the comparative example.

The table in FIG. 5 shows the parallel resonance frequency f 0 , inductance L, and line capacitance Cp, which are the impedance peaks, for the line filter of the comparative example, the composite line filter ₂₁ , and a second comparative example, a line filter for use in the high frequency range whose impedance peak is at a frequency of 30 Hz or higher.

The parallel resonant frequency _f0 is generated by the line capacitance Cp and is generated by the resonance of the inductor and the capacitor. The parallel resonant frequency _f0 is expressed by the following formula.

The line capacitance Cp can be calculated from the parallel resonance frequency _f0 and is expressed by the following formula.

In addition, because the composite line filter 21 has excellent characteristics for reducing noise in the high frequency range above 30 MHz, it is less effective at reducing noise in the low frequency range. However, the normal mode choke L1 used in combination can reduce noise in the low frequency range, complementing the noise reduction effect.

The Electrical Appliance and Material Safety Law also prescribes noise limits for terminal noise voltage at 5 kHz to 30 MHz, radiated electric field strength at 30 MHz to 30 MHz, and radiated magnetic field strength at 9 kHz to 30 MHz. By using the normal mode choke L1 in combination with the composite line filter 21, it is possible to suppress noise levels below each limit over a wide frequency range.

In this way, in the power supply device 12 of this embodiment, the input section of the power conversion circuit 19 has an impedance peak at frequencies below 30 MHz, but the impedance value at 30 MHz is 1 kΩ or more, and the line capacitance is 7 pF or less, so a composite line filter 21 that has the characteristic of effectively reducing noise in the high frequency range above 30 MHz is used in combination with a normal mode choke L1 that reduces noise in the low frequency range, making it possible to reduce noise over a wide range.

Moreover, the composite line filter 21 used here is smaller in size than the line filter of the comparative example, so that it is possible to provide space for mounting the normal mode choke L1 within the limited space of the noise prevention circuit mounting area A of the board 30, thereby achieving wide-band noise reduction without increasing the size of the board 30.

Although the power supply unit 12 can reduce noise when used in the lighting device 10, it can also be used in other electrical devices.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

REFERENCE SIGNS LIST 10 Lighting device 12 Power supply device 19 Power conversion circuit 21 Line filter L1 Normal mode choke Q1 Switching element

Claims (4)

A power conversion circuit having a switching element and converting input power into a predetermined DC power;
a composite line filter with sections for reducing noise in a high frequency range of 30 MHz or more , connected to an input section of the power conversion circuit;
A normal mode choke connected to an input of the power conversion circuit for reducing noise in a high frequency range below 30 MHz ;
Equipped with
The line filter is connected between the power conversion circuit and the normal mode choke.
A power supply device comprising: 2. The power supply device according to claim 1, wherein the line filter has an impedance peak at a frequency less than 30 MHz and an impedance value at 30 MHz of 1 kΩ or more. 3. The power supply device according to claim 1, wherein the line filter has an impedance peak at a frequency less than 30 MHz and a line capacitance of 7 pF or less. A lighting device comprising the power supply device according to any one of claims 1 to 3.

Images