JP2011072107A - Power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfy the standard of a noise terminal voltage by moving a resonance frequency of an oscillation transformer to a low-frequency side by a simple constitution. <P>SOLUTION: A capacitor C5 is connected between secondary-side terminals of the oscillation transformer T1 in an insulation type step-down switching power supply having the oscillation transformer T1 and a switching element IC1. The capacitor C5 has a small capacity at a level of, for example, 100 to 1,000 [pF] which does not affect oscillation. Meanwhile, a capacitive element having a surge absorption capability is connected in place of the capacitor C5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an isolated step-down switching power supply device having an oscillation transformer and a switching element.

  FIG. 3 shows a circuit diagram of a conventional power supply device. T1 is an oscillation transformer, and IC1 is a switching element. High frequency noise generated from the switching element IC1 and the oscillation transformer T1 is fed back to the power supply. A filter is inserted in the input unit as a means for suppressing it, thereby keeping the noise terminal voltage within the standard. The noise terminal voltage countermeasure components are L1: common mode filter, C1, C2: X capacitor (across the line capacitance), and C3, C4: Y capacitor (line bypass capacitance). The X capacitor acts on normal mode noise and is a noise countermeasure component between lines. The Y capacitor acts on common mode noise and is a noise countermeasure component between line and ground.

  For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-114339) and Patent Document 2 (Patent Document 2) describe a technique for suppressing high-frequency noise of a switching circuit from returning to an AC power supply by using a common mode filter or a normal mode filter. JP-A-2006-294561). However, these documents do not suggest moving the frequency band of high-frequency noise.

JP 2006-114339 A JP 2006-294561 A

  Since the oscillation transformer T1 has a specific resonance frequency, and the impedance is low in the vicinity of the specific resonance frequency, the noise suppressing effect in the vicinity of the resonance frequency is reduced. As a result, the noise terminal voltage becomes high near the resonance frequency of the oscillation transformer T1. In the conventional example, in order to lower the increased noise terminal voltage, the above-described input filter inductance value is increased or the capacitance of the X capacitor is increased.

  However, there is a limit to satisfying the standard by reducing the peak value of the noise terminal voltage using noise terminal voltage countermeasure components, and mounting problems such as increasing the filter inductance value and the capacitor capacity increase the component size. There was also. In addition, when the winding method of the oscillation transformer T1 is changed or when the mounting block is filled with resin, the resonance frequency is changed by changing the line capacitance of the oscillation transformer T1, and the peak of the noise terminal voltage is the standard. In some cases, it moved to the high frequency side and could not meet the standard.

  An object of the present invention is to solve such a problem, and it is an object to satisfy the noise terminal voltage standard by moving the resonance frequency of the oscillation transformer to the low frequency side with a simple configuration.

  As shown in FIG. 1, the power supply device according to claim 1 is characterized in that a capacitor C5 is connected between the secondary terminals of the oscillation transformer T1 in the insulated step-down switching power supply having the oscillation transformer T1 and the switching element IC1. Is.

  As shown in FIG. 1, the power supply device according to claim 2 has a surge absorbing capability in place of the capacitor C5 between the secondary terminals of the oscillation transformer T1 in the isolated step-down switching power supply having the oscillation transformer T1 and the switching element IC1. A capacitive element is connected.

  According to the first aspect of the present invention, the capacitor is connected between the secondary side terminals of the oscillation transformer in the isolated step-down switching power supply having the oscillation transformer and the switching element, whereby the resonance frequency of the oscillation transformer is regulated by the noise terminal voltage. It is possible to move to a low frequency side, so that the noise terminal voltage standard can be satisfied over the entire frequency range where noise is restricted. Further, since only a small-capacitance capacitor needs to be connected, the noise terminal voltage standard can be satisfied easily and inexpensively without increasing the size and number of input filters.

  According to the second aspect of the invention, the same effect as that of the first aspect of the invention can be obtained, and a capacitive element having surge absorption capability can be connected as means for moving the resonance frequency of the oscillation transformer to the low frequency side. Thus, circuit protection against surge voltage can be realized at the same time, and the component cost of the entire power supply device can be reduced.

It is a circuit diagram of Embodiment 1 of the present invention. It is a frequency characteristic figure of the noise terminal voltage of Embodiment 1 of the present invention. It is a circuit diagram of a conventional example. It is a frequency characteristic figure of the noise terminal voltage of a prior art example.

(Embodiment 1)
FIG. 1 shows a circuit diagram of Embodiment 1 of the present invention. 1 is a filter unit, 2 is a rectifier circuit unit, 3 is a snubber circuit unit, 4 is an oscillation circuit unit, 5 is a feedback circuit unit, 6 is a control power circuit unit, and 7 is a Y capacitor. In the isolated step-down switching power supply having the above configuration, the capacitor C5 is connected between the secondary side pins of the oscillation transformer T1 of the oscillation circuit section 4.

  The capacitor C5 needs to have a small capacity that does not adversely affect the oscillation. For example, it is about 100 [pF] to 1000 [pF]. Since the resonance frequency of the oscillation transformer T1 is changed by connecting the capacitor C5, the frequency band at which the noise terminal voltage peaks changes. Specifically, the noise terminal voltage standard can be satisfied as a whole by moving the resonance frequency of the oscillating transformer T1 from the high frequency side where the noise regulation is severe to the low frequency side where the noise regulation is loose.

  FIG. 2 shows the peak of the noise terminal voltage when the capacitor C5 is present in FIG. The horizontal axis represents frequency (0.15 to 30.0 [MHz]), and the vertical axis represents noise terminal voltage [dB (μV)].

  Hereinafter, the circuit configuration of FIG. 1 will be described in detail. The input side of the filter unit 1 is connected to a connector E connected to a commercial AC power supply via a fuse Fs and a surge protection element ZNR. The filter unit 1 includes capacitors C1 and C2 and a filter coil L1.

  An AC input terminal of the diode bridge DB1 of the rectifier circuit unit 2 is connected to the output side of the filter unit 1. A capacitor C6 is connected to the DC output terminal of the diode bridge DB1. The capacitor C6 is designed to realize a minimum smoothing function using a relatively small capacitor from the viewpoint of suppressing inrush current at power-on and improving the input power factor.

  One end of the primary winding of the insulating oscillation transformer T1 of the oscillation circuit unit 4 is connected to the positive electrode of the capacitor C6. The other end of the primary winding of the oscillation transformer T1 is connected to the negative electrode of the capacitor C6 via the switching element IC1.

  The switching element IC1 is an integrated circuit in which a high-frequency oscillator capable of feedback-controlling the pulse width and a switching element driven on and off by a PWM signal output from the high-frequency oscillator are built in an 8-pin DIP package. A light receiving element PC2 of a photocoupler is connected to the feedback input terminal of the switching element IC1, and the pulse width of the PWM signal is controlled according to the signal fed back from the secondary side of the oscillation transformer T1.

  A surge voltage absorbing snubber circuit section 3 is connected to the primary winding of the oscillation transformer T1. The snubber circuit unit 3 includes resistors R1 and R2, a capacitor C7, and a diode D1. When the switching element IC1 is turned off, a surge voltage due to counter electromotive force is generated in the primary winding of the oscillation transformer T1. The surge voltage causes the diode D1 to conduct, and the resistors R1, R2 and the capacitor C7 absorb the surge voltage.

  A smoothing capacitor C8 is connected to the secondary winding of the oscillation transformer T1 through a diode D2 for half-wave rectification. Further, a capacitor C5 for moving the resonance point to the low frequency side is connected in parallel. The secondary winding output of the oscillation transformer T1 is rectified by the diode D2, charged in the capacitor C8, and becomes a low DC voltage. The winding direction of the primary winding and the secondary winding of the oscillation transformer T1 is opposite in the forward type and the flyback type, but here, an example of the flyback type is shown.

  When the switching element IC1 is on, a current flows from the capacitor C6 through the primary winding of the oscillation transformer T1. At this time, since the diode D2 is in a reverse blocking state and no current flows through the secondary winding, electromagnetic energy is accumulated in the oscillation transformer T1. When the switching element IC1 is turned off, a back electromotive force due to electromagnetic energy is generated in the forward direction of the diode D2, and the diode D2 is turned on to charge the capacitor C8.

  The voltage of the capacitor C8 is input to the control power supply circuit unit 6 and becomes the output voltage V1. Further, the parallel circuit of the capacitors C9 and C10 is charged via the diode D3, and becomes the output voltage V2. Further, the voltage is stabilized by the three-terminal regulator IC2, and the parallel circuit of the capacitors C11 and C12 is charged to become the output voltage V3. Capacitors C10 and C11 are small-capacitance capacitors for high-frequency bypass, and capacitors C9 and C12 are smoothing capacitors for voltage stabilization.

  The voltage of the capacitor C8 is divided by the resistors R6 and R7 and applied to the reference input terminal of the variable shunt regulator IC3. Thereby, the variable shunt regulator IC3 operates as a Zener diode corresponding to the voltage dividing ratio of the resistors R6 and R7. The cathode terminal of the variable shunt regulator IC3 is connected to the positive electrode of the capacitor C8 through a series circuit of resistors R4 and R5, and the anode terminal of the variable shunt regulator IC3 is connected to the negative electrode of the capacitor C8. Therefore, the cathode terminal of the variable shunt regulator IC3 becomes a constant voltage with respect to the secondary side ground potential.

  In the feedback circuit unit 5, a light-emitting element PC1 of a photocoupler is connected between the positive electrode of the capacitor C8 and the cathode terminal of the variable shunt regulator IC3 via a resistor R3. A voltage obtained by subtracting a predetermined voltage (= the cathode-anode voltage of the variable shunt regulator IC3 + the forward voltage of the light-emitting element PC1 of the photocoupler) from the voltage of the capacitor C8 is applied across the resistor R3. Since the current flowing through the resistor R3 also flows through the light-emitting element PC1 of the photocoupler, the optical signal intensity of the photocoupler light-emitting element PC1 is proportional to the difference between the voltage of the capacitor C8 and the predetermined voltage. When the voltage of the capacitor C8 becomes larger than the predetermined voltage, the optical signal intensity of the light emitting element PC1 of the photocoupler increases in proportion to the difference, and the resistance value of the light receiving element PC2 of the photocoupler decreases accordingly. By variably controlling the pulse width of the PWM signal of the switching element IC1 according to the resistance value of the light receiving element PC2 of the photocoupler, feedback control can be performed so as to make the voltage of the capacitor C8 constant.

  A connection point between the secondary winding of the oscillation transformer T1 and the negative electrode of the capacitor C8 is grounded as a ground level of the secondary circuit. This grounding point may be connected to a stable potential such as a chassis.

  On the other hand, the negative electrode of the DC output terminal of the diode bridge DB1 of the rectifier circuit unit 2 is connected to the ground level of the secondary circuit via a series circuit of capacitors C3 and C4. Capacitors C3 and C4 are small-capacitance capacitors and are used as Y capacitors 7. Accordingly, when viewed from a high frequency, the negative electrode of the DC output terminal of the diode bridge DB1 of the rectifier circuit unit 2 is connected to a stable potential such as a chassis of the power supply device, and common mode noise can be reduced. Note that when viewed in terms of direct current and low frequency alternating current, the primary side and the secondary side of the oscillation transformer T1 are insulated.

  In the conventional example of FIG. 3, the resonance point of the oscillation transformer T1 is about 0.7 to 0.8 [MHz] as shown in FIG. 4, but in this embodiment, as shown in FIG. By connecting a capacitor C5 of several hundred [pF] between the secondary side pins of the transformer T1, the resonance point of the oscillation transformer T1 is lowered to about 0.4 to 0.5 [MHz] as shown in FIG. To do. As described above, the resonance point of the oscillation transformer T1 moves from the high frequency side where noise regulation is severe to the low frequency side where noise regulation is loose, so that the standard of the noise terminal voltage can be satisfied as a whole.

(Embodiment 2)
In the present embodiment, instead of the capacitor C5 of the first embodiment, by connecting a capacitive element having a surge absorption capability, the same effect as that of the first embodiment is obtained, and protection against a surge voltage is simultaneously performed. Here, as the capacitive element having the surge absorbing ability, a ceramic surge absorber mainly composed of zinc oxide, such as a zipper manufactured by Fuji Electric Co., Ltd., is suitable. Since this element is excellent in responsiveness and has a large surge absorption capability, it can absorb and protect a steep and large surge voltage caused by lightning or the like, and can be used as a circuit protection element.

  In addition, the power supply device of Embodiment 1 or 2 can be used as a power supply device for an LED lighting device, and can also be used as a power supply device for other electronic devices.

T1 Oscillation transformer IC1 Switching element C5 Capacitor

Claims (2)

A power supply device comprising a capacitor connected between secondary terminals of an oscillation transformer in an insulated step-down switching power supply having an oscillation transformer and a switching element. A power supply device comprising a capacitive element having surge absorption capability connected between secondary terminals of an oscillation transformer in an insulated step-down switching power supply having an oscillation transformer and a switching element.

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