JP6546955B2 - Switching power supply circuit - Google Patents

Description

  The present invention relates to a switching power supply circuit having a pulse transformer for driving a switching element.

  As a circuit used for a power supply of an LED or the like, one that alternately turns on / off two switching elements connected in series is known. Circuits of this type are described, for example, in Patent Documents 1 to 3.

  As two switching elements connected in series, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor) is used. In this type of power supply circuit, two switching elements are disposed on the high side and the low side to configure the upper and lower arms, and when the high side switching element (hereinafter referred to as high side) is on, the low side switching element (hereinafter referred to as the low side) Is controlled to be in the off state and the high side in the off state, so that the low side is in the on state, and when either one is on, the other is in the off state.

  This type of switching power supply circuit controls the output by changing the frequency while fixing the switching duty. Usually, a power control IC (hereinafter referred to as an IC) of one chip is used as the switching circuit, and rectangular wave pulses are alternately output from first and second output terminals provided in the IC. , The two switching elements are turned on and off.

  In high voltage power supply circuits, it is difficult to control the high side directly by the IC. For example, in a power supply circuit having a voltage higher than that of the prior art such as 700 volts or more, the voltage applied to the IC is high, so the high side can not be turned off directly by the output voltage of the IC. For this reason, as shown in Patent Document 2, it is known to connect a pulse transformer between the output terminal of the IC and the high side in a high voltage power supply circuit.

  FIG. 2 shows an example of a switching power supply circuit using a pulse transformer. In FIG. 2, the high side Q1 and the low side Q2 are connected in series. The gate of the high side Q1 is connected to one end of the second winding N2 of the transformer T2, the source of the high side Q1 is connected to the drain of the low side Q2, and a high voltage is applied to the drain of the high side Q1. The gate of the low side Q2 is connected to a first output terminal OUT1 provided in the IC1, the source of the low side Q2 is grounded, and the drain of the low side Q2 is connected to the source of the high side Q1. The second output terminal OUT2 provided in the IC1 is connected to the first winding N1 of the transformer T2 via the transformer drive circuit TD1. A load (not shown) is connected to the output side of the high side Q1 and the low side Q2 via a transformer T1. A capacitor Cr for resonance is connected between the low side Q2 and the primary winding of the transformer T1.

  As shown in FIG. 3A, in this circuit, based on a pulse from the second output terminal OUT2 of IC1, the transformer drive circuit TD1 is turned on / off with respect to the first winding N1 of the transformer T2. By supplying the voltage, a pulsed voltage is induced in the second winding N2 of the transformer T2. Since this voltage is applied to the gate of the high side Q1, as a result, the high side Q1 turns on according to the output of the pulse from the second output terminal OUT2 of IC1. On the other hand, when the pulse from the first output terminal OUT1 of the IC1 is applied to the gate of the low side Q2, the low side Q2 is turned on. Since the first output terminal OUT1 and the second output terminal OUT2 output pulses at alternate timings, the high side Q1 and the low side Q2 alternately turn on and off.

Patent No. 5254386 Unexamined-Japanese-Patent No. 2010-35388 Japanese Patent Application No. 2015-888888

  By the way, in this type of high voltage switching power supply circuit, the dv / dt at the time of switching becomes high, so the high side Q1 tends to have a self turn-on phenomenon. That is, when the gate voltage is lowered due to the inversion of the second winding N2 of the transformer T2 and the Q1 is switched from on to off, the dv / dt rises rapidly and the Ciss is charged through the Crss of the high side Q1. The gate voltage may rise again, and the high side Q1 may be switched on. From such a phenomenon, when the high side Q1 which is originally turned off is turned on, both the high side Q1 and the low side Q2 are turned on, and a short circuit in the high voltage circuit causes a malfunction such as a large current flowing in the power supply circuit. .

  The waveform diagram of the high side Q1 of FIG. 3 (a) illustrates the self turn-on phenomenon as described above. Even after the pulse from the second output terminal OUT2 is turned off, the gate of the high side Q1 is A voltage is applied. As a result, a phenomenon occurs in which the high side Q1 and the low side Q2 are simultaneously turned on.

  An object of the present invention is to provide a switching power supply circuit capable of preventing a malfunction by preventing a self turn-on phenomenon from occurring in the high side Q1 at the time of switching.

The high voltage switching power supply circuit of the present invention is characterized by having the following configuration.
(1) High side switching element Q1 and low side switching element Q2 connected in series.
(2) The first and second output terminals output pulses alternately, the first output terminal controls the on / off of the low side switching element Q2, and the second output terminal is the high side. A power control IC 1 that controls on / off of the switching element Q1.
(3) A transformer drive circuit TD1 connected to the second output terminal of the power control IC 1 .
(4) A pulse transformer T2 in which the first winding N1 is connected to the output side of the transformer drive circuit TD1 and the second winding N2 is connected to the high side switching element Q1.
(5) A third winding N3 having a reverse polarity to the second winding N2 provided on the second winding N2 side of the pulse transformer T2 .
(6) provided between the third winding N3 and the high-side switching element Q1 of the opposite polarity, the gate of the high side switching element Q1 when off the high-side switching element Q1 - switching to short-circuiting between the source Element Q3.
(7) A transformer T1 in which a winding on the input side is connected between the source of the high side switching element Q1 and the source of the low side switching element Q2.

A switching power supply circuit having the following configuration is also an aspect of the present invention.
(1) The switching element Q3 is turned off when the switching element Q1 is turned on, and the third winding N3 of the reverse polarity is connected to the gate of the switching element Q3, and the high side The drain of the switching element Q3 is connected to the gate of the switching element Q1.

  According to the present invention, the switching element Q3 is turned on when the switching element Q1 is turned off. In the switching element Q3, since the drain-source voltage is low, that is, dv / dt is low, there is little possibility that a malfunction such as a self turn-on phenomenon will occur. Thereby, the self turn-on phenomenon of the high side Q1 is eliminated, and a switching power supply circuit without malfunction can be provided.

The circuit diagram showing the embodiment of the switching power supply circuit of the present invention. The circuit diagram which shows an example of the conventional switching power supply circuit. FIG. 3 is a waveform diagram comparing the embodiment of FIG. 1 and the prior art pulse waveform of FIG. 2;

Hereinafter, an embodiment of the present invention will be specifically described according to FIG. The same parts as those of the prior art shown in FIG.
[1. First embodiment]
[1-1. Constitution]
In the present embodiment, the third winding N3 is provided in the pulse transformer T2. The third winding N3 is formed to be opposite in polarity to the second winding N2.

  The gate driving switching element (hereinafter referred to as an element) Q3 is connected to the gate of the high side Q1. The lead terminal 4 of the reverse polarity winding is connected to the gate of the element Q3. The source of the element Q3 is connected to the second lead terminal 5 of the third winding N3, and the drain is connected to the gate of the high side Q1. While the element Q1 is turned off, a voltage is applied to the gate of the element Q3 to continue the on state. On the other hand, when the voltage applied to the gate of the element Q3 is lost due to the voltage inversion of the pulse transformer T2, the element Q3 is turned off.

[1-2. Action]
In this embodiment having such a configuration, pulses are output from the first output terminal OUT1 and the second output terminal OUT2 of the IC 1 at alternate timing as shown in FIG. 3 (b). The low side Q2 connected to the first output terminal OUT1 is turned on by inputting a pulse to its gate.

  The pulse from the second output terminal OUT2 is input to the pulse transformer T2 without change in polarity via the transformer drive circuit TD1. As a result, the high side Q1 connected to the pulse transformer T2 is turned on together with the timing at which the low side Q2 is turned off, whereby the high side Q1 and the low side Q2 perform switching operation alternately.

  In the switching operation of the high side Q1, the drain-source voltage of the high side Q1 largely changes in the direction of increasing dv / dt. Then, when the switching operation is turned off from the turn-on, the gate-source capacitance Ciss is charged from the drain-gate capacitance Crss. In the prior art, this causes the gate voltage of the high side Q1 to rise, causing the high side Q1 to malfunction and turn on.

  In this embodiment, as shown in FIG. 3B, the element Q3 is turned off when the high side Q1 is turned on by the second winding N2 of the pulse transformer T2 and the third winding N3 of the reverse polarity. When the high side Q1 is turned off, the element Q3 is turned on.

  As a result, when the element Q1 is turned off, a voltage is immediately applied to the gate of the element Q3, and the element Q3 is turned on to short-circuit the gate-source of the high side Q1, so the drain-gate capacitance Crss of the high side Q1. The gate-source capacitance Ciss is not charged. This can prevent the high side Q1 from malfunctioning and turning on at the time of turning off. On the other hand, since the voltage is low between the drain and the source of the element Q3, the risk of the above malfunction is low.

[1-3. effect]
According to the present embodiment, between the third winding N3 of the reverse polarity of the pulse transformer T2 and the high side Q1, the element Q3 which shorts the gate-source of the high side Q1 when the pulse transformer T2 is off The simple configuration of providing can effectively suppress the self turn-on phenomenon of the high side Q1. As a result, there is no short circuit between the high side Q1 and the low side Q2 at the time of switching operation, and it is possible to provide a switching power supply circuit excellent in reliability.

[2. Other embodiments]
The present invention is not limited to the above embodiment, and at the implementation stage, the components can be modified and embodied without departing from the scope of the invention. In addition, various inventions can be formed by appropriate combinations of a plurality of constituent elements disclosed in the above embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components in different embodiments may be combined as appropriate.

Q1 ... high side switching element Q2 ... low side switching element Q3 ... switching element T1 for shorting between the gate and source of the transistor Q1 ... transformer T2 ... pulse transformer Cr ... capacitor IC1 ... IC
TD1 ... Transformer drive circuit T2-3 ... 1st lead-out terminal T2-4 of second winding N2 ... 1st lead-out terminal T2-5 of reverse polarity third winding N3 ... second winding N2 And the second lead terminal of the third winding N3

Claims (2)

A high side switching element Q1 and a low side switching element Q2 connected in series;
The first output terminal controls ON / OFF of the low side switching element Q2, and the second output terminal outputs the high side switching element Q1. A power control IC 1 for controlling on / off of the
A transformer drive circuit TD1 connected to the second output terminal of the power control IC 1 ;
A pulse transformer T2 having a first winding N1 connected to the output side of the transformer drive circuit TD1 and a second winding N2 connected to the high side switching element Q1;
A third winding N3 having a reverse polarity to the second winding N2 of the pulse transformer T2 ;
Is provided between the third winding N3 and the high-side switching element Q1 of the opposite polarity, the gate of the high side switching element Q1 when off the high-side switching element Q1 - a switching element Q3 for short-circuiting between the source ,
A transformer T1 having an input-side winding connected between the source of the high side switching element Q1 and the source of the low side switching element Q2,
A switching power supply circuit comprising: The switching element Q3 is turned off when the switching element Q1 is turned on, and
The third winding N3 of the reverse polarity is connected to the gate of the switching element Q3,
The switching power supply circuit according to claim 1, wherein the drain of the switching element Q3 is connected to the gate of the high side switching element Q1.

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