JP4591392B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply apparatus that performs power conversion by switching operation of two or more switching elements such as a half bridge type and a full bridge type.

  FIG. 3 shows a circuit diagram of an inverter circuit having a half bridge configuration as a typical example of a conventional switching power supply device. One end of a series circuit of main switching elements 2, 3 made of, for example, a MOSFET is connected to the positive electrode of the DC power supply 1. The negative electrode of the DC power supply 1 is grounded. The main switching elements 2 and 3 are respectively formed with body diodes that conduct from the source to the drain. A series circuit of capacitors 4 and 5 is connected in parallel to both ends of the series circuit of the main switching elements 2 and 3, and one end of the capacitor 4 is connected to the drain of the main switching element 2 connected to the positive electrode of the DC power supply 1. One end of the capacitor 5 is connected to the source of the main switching element 3. A primary winding 6 a of the transformer 6 is connected between a connection point between the source of the main switching element 2 and the drain of the main switching element 3 and a connection point between the other end of the capacitor 4 and the other end of the capacitor 5. ing. At this time, the dot side terminal of the primary winding 6a is connected to the connection point of the main switching elements 2 and 3, and the non-dot side terminal of the primary winding 6a is connected to the connection point of the capacitors 4 and 5.

  The anode of the diode 7 is connected to the dot side terminal of the secondary winding 6b of the transformer 6, and the anode of the diode 8 is connected to the non-dot side terminal of the secondary winding 6b. Is connected to one end of the choke coil 9. The other end of the choke coil 9 and the center tap terminal of the secondary winding 6b are connected to a pair of output terminals 11 and 12, respectively, and a smoothing capacitor 10 is connected between the output terminals 11 and 12. During operation of the switching power supply, output power is supplied from the output terminals 11 and 12 to a load (not shown).

  The main switching elements 2 and 3 are alternately driven by different drive circuits. That is, the main switching element 2 is driven by the high side drive circuit 20a, and the main switching element 3 is driven by the low side drive circuit 20b. Since these drive circuits have the same configuration, only the configuration of the high side drive circuit 20a will be described below. Regarding the configuration of the other low-side drive circuit 20b, the subscript “a” of the number given to each circuit element of the high-side drive circuit 20a may be read as “b”.

  Explaining from the input side of the high-side drive circuit 20a, a series circuit of a primary winding 23a of the drive transformer 22a and a switching element 24a made of, for example, a MOSFET is connected between both ends of the DC power supply 15. The switching element 24a includes a body diode that conducts from the source to the drain. The positive electrode of the DC power supply 15 is connected to the dot-side terminal of the primary winding 23a and at the same time to the non-dot-side terminal of the primary winding 25a. The dot-side terminal of the primary winding 25a and the switching element 24a The diode 26a is connected in parallel with each other in such a direction that the cathode is on the primary winding 25a side and the anode is on the switching element 24a side. The negative electrode of the DC power supply 15 is grounded together with the source of the switching element 24a and the like. The gate of the switching element 24a is connected to an output terminal of a PWM control IC 16 that outputs a pulse drive signal to drive the switching element 24a. The PWM control IC 16 performs well-known pulse width control on the pulse driving signal so that the output voltage is stabilized based on an output feedback signal from a feedback circuit (not shown). Note that the PWM control IC 16 obtains an operating power supply from the DC power supply 15.

  A series circuit of a resistor 28a and a diode 29a is connected between both ends of the secondary winding 27a of the drive transformer 22a. The diode 29a is connected in such a direction that the resistor 28a side is a cathode and the non-dot side terminal of the secondary winding 27a is an anode. In addition, a resistor 30a is connected between both ends of the secondary winding 27a. The anode of the diode 31a is connected to the dot-side terminal of the secondary winding 27a, and a series circuit of resistors 36a and 37a is connected between the cathode of the diode 31a and the collector of a transistor 32a such as a pnp transistor. The connection point of the resistors 36a and 37a is connected to the gate of the main switching element 2. The gate of the main switching element 2 is connected to the emitter of the transistor 32a through the resistor 35a. A parallel circuit of a resistor 33a and a speed-up capacitor 34a is connected between the anode of the diode 31a and the base of the transistor 32a.

  A low-side drive circuit 20b having the same configuration as that described above is connected to the gate of the main switching element 3.

  Next, the operation of the conventional switching power supply device having the above configuration will be described. In the half-bridge configuration inverter circuit of FIG. 1, as in Patent Document 1, in order to prevent erroneous firing of the main switching element, the transistor is turned on while an on-pulse is input to the gate of one of the main switching elements. The gate voltage of the other main switching element that is turned off is discharged.

  The PWM control IC 16 outputs a pulse drive signal to the gates of the switching elements 24a and 24b, and performs switching operations so that the switching elements 24a and 24b are alternately turned on by providing a predetermined dead time (time not simultaneously turned on). On / off operation). The main switching elements 2 and 3 are alternately switched in synchronization with the switching elements 24a and 24b, thereby generating an alternating current in the primary winding 6a of the transformer 6 and inducing an induced voltage in the secondary winding 6b. , 8, choke coil 9 and smoothing capacitor 10 rectify and smooth the output power from output terminals 11 and 12 to the load.

  When the switching element 24a of the high side drive circuit 20a is turned on, a current flows from the DC power source 15 to the primary winding 23a of the drive transformer 22a, and an induced voltage is induced in the secondary winding 27a. Since the induced voltage is positively generated from the non-dot side to the dot side of the secondary winding 27a, the base voltage of the transistor 32a becomes positive and turns off, and the diode from the dot side of the secondary winding 27a is turned on. A current flows through the resistors 36a and 37a through 31a, and a gate current flows into the gate of the main switching element 2, whereby the gate charge capacity is charged, and the gate voltage of the main switching element 2 corresponding to the voltage across the resistor 37a is positive. The main switching element 2 is turned on.

  When the switching element 24a is turned off, excitation energy of the drive transformer 22a is released, and a regenerative current flows to the DC power source 15 through the diode 26a due to a voltage generated between both ends of the primary winding 25a, and between the ends of the secondary winding 27a. A reverse voltage having a negative polarity is generated from the non-dot side to the dot side. The reverse voltage causes the diode 29a to turn on and energize, while a base current flows through the transistor 32a and the transistor 32a turns on. By this turn-on, the gate charge capacity of the main switching element 2 is rapidly discharged through the resistor 35a, and the main switching element 2 is turned off.

  On the other hand, when the switching element 24b of the low-side drive circuit 20b is turned on, an induced voltage is induced in the secondary winding 27b in the same manner as the high-side drive circuit 20a, and the base voltage of the transistor 32b becomes positive and is turned off. The switching element 3 is turned on.

When the switching element 24b is turned off, excitation energy of the drive transformer 22b is released, and a regenerative current flows to the DC power source 15 through the diode 26b due to a voltage generated between both ends of the primary winding 25b, and between the ends of the secondary winding 27b. A reverse voltage having a negative polarity is generated from the non-dot side to the dot side. The reverse voltage causes the diode 29b to turn on and energize, while a base current flows through the transistor 32b and the transistor 32b is turned on. By this turn-on, the gate charge capacity of the main switching element 3 is rapidly discharged through the resistor 35b, and the main switching element 3 is turned off.
JP 2000-197343 A

  However, in the above-described half-bridge configuration inverter circuit, one transistor is in a switching state while one transistor is off. In particular, when the ON width is short, the reverse voltage of the drive transformer becomes small, and there is a possibility that the discharging transistor remains in the OFF state. Therefore, in the main switching elements 2 and 3, there is a concern about abnormal gate voltage operation due to disturbance noise. That is, along with the high-speed switching operation of the main switching elements 2 and 3, due to the capacitance component of the semiconductor itself, the gate current flows in the transistor in the off state and turns on, leading to a malfunction.

  In recent years, as the switching speed increases due to higher frequency, the switching speed performance of the semiconductor has been dramatically improved, and the drain-source voltage movement of the main switching element is fast, which causes noise malfunction.

  In view of the above problems, an object of the present invention is to provide a switching power supply device that does not cause an abnormal increase in drive terminal voltage due to a high-speed voltage change of a main switching element and can obtain a stable switching operation in the entire load region.

In claim 1 of the present invention, a drive circuit is connected to each of the drive terminals of the plurality of main switching elements, and power is intermittently supplied from the power source to the inductance element by alternately switching the main switching elements. A switching power supply device that extracts and outputs electric power from the inductance element, wherein the drive circuit includes a transformer having a primary winding and a secondary winding, and an electric current that is intermittently passed through the primary winding. Switching means for applying an induced voltage of the secondary winding to the drive terminal of the main switching element to perform a switching operation, and conducting by the reverse voltage generated in the secondary winding during an off period of the main switching element to make the main switching A main switch discharge element for discharging the drive terminal voltage of the element, Using the induced voltage of the secondary winding which constitutes the serial transformer by supplying exciting energy to the other of the transformer increases the reverse voltage, thereby reverse voltage superposing unit Ru turns on the main switching discharge element It has.

  In this way, even if the ON width of the switching means is shortened due to high frequency and sufficient excitation energy is not accumulated in the other transformer, the induced voltage of the secondary winding of one transformer is utilized to utilize the other transformer. Can be supplied with excitation energy. As a result, the reverse voltage generated in the secondary winding of the other transformer can be increased, and the main switch discharge element can be reliably conducted, and the drive terminal voltage of the main switching element can be reliably discharged during the OFF period, resulting in malfunction. Can be prevented.

  According to claim 1 of the present invention, it is possible to provide a switching power supply device that does not cause an abnormal increase in the drive terminal voltage due to a high-speed voltage change of the main switching element and can obtain a stable switching operation in the entire load region.

  Hereinafter, preferred embodiments of a switching power supply device according to the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same location as a prior art example, and since description of a common part overlaps, it abbreviate | omits as much as possible.

  FIG. 1 is a circuit diagram in which minus bias circuits 50a and 50b as reverse voltage superimposing means are provided in the half-bridge configuration inverter circuit shown in FIG. 3 as an embodiment of the switching power supply apparatus according to the present invention. That is, also in the switching power supply device according to the present invention, the high-side drive circuit 20a is connected to the gate as the drive terminal of the main switching element 2, the low-side drive circuit 20b is connected to the gate of the main switching element 3, and the main switching element 2 , 3 are alternately switched to supply current intermittently from the DC power source 1 to the primary winding 6a of the transformer 6 corresponding to the inductance element, and the power is taken out from the secondary winding 6b to output terminals 12, 13 To the load.

  The minus bias circuit 50a is configured by providing a secondary winding 40a serving as a fourth winding in the drive transformer 22a of the high side drive circuit 20a. The dot side terminal of the secondary winding 40a is connected to the non-dot side terminal (GND side) of the secondary winding 27b of the drive transformer 22b constituting the low side drive circuit 20b, and a diode 41a is connected in series to the non-dot side terminal. Is connected to one end of a parallel circuit of a resistor 42a and a capacitor 43a, and the other end of the parallel circuit is connected to the dot side of the secondary winding 27b of the drive transformer 22b constituting the low-side drive circuit 20b. Connected to the terminal. Similarly, the minus bias circuit 50b is configured by providing a secondary winding 40b serving as a fourth winding in the drive transformer 22b of the low-side drive circuit 20b. The dot side terminal of the secondary winding 40b is connected to the non-dot side terminal (GND side) of the secondary winding 27a of the drive transformer 22a constituting the high side drive circuit 20a, and a diode is connected in series to the non-dot side terminal. The cathode of 41b is connected, and the anode is connected to one end of the parallel circuit of the resistor 42b and the capacitor 43b, and the other end of the parallel circuit is connected to the secondary winding 27a of the drive transformer 22a constituting the high-side drive circuit 20a. Connected to the dot side terminal.

  Next, the operation of the above circuit configuration will be described with reference to FIG. Here, only the operation of the minus bias circuit 50a will be described, but the effect of the minus bias circuit 50b on the low side drive circuit 20b is the same as that of the minus bias circuit 50a on the high side drive circuit 20a described below.

  The basic operation as a switching power supply device is not changed from the conventional one. Accordingly, the switching elements 24a and 24b and the main switching elements 2 and 3 are alternately switched by the PWM control IC 16, thereby generating an alternating current in the primary winding 6a of the transformer 6 and inducing an induced voltage in the secondary winding 6b. The output power is supplied from the output terminals 11 and 12 to the load after rectification and smoothing by the diodes 7 and 8 and the choke coil 9 and the smoothing capacitor 10. However, since FIG. 2 is a waveform diagram of the switching power supply device having a higher frequency, the switching element 24a as the main switch discharge element and the ON period Ton (ON width) of the main switching element 2 are very short in FIG. It has become.

  When the switching element 24a of the high side drive circuit 20a is turned on, a current flows from the DC power source 15 to the primary winding 23a of the drive transformer 22a, and an induced voltage V1 is induced in the secondary winding 27a. Since the induced voltage V1 is positively generated from the non-dot side terminal to the dot side terminal of the secondary winding 27a, the base voltage of the transistor 32a becomes positive and turns off, and the dot of the secondary winding 27a is turned off. A current flows from the side terminal to the resistors 36a and 37a through the diode 31a, and the gate current Ig flows into the gate of the main switching element 2 to charge the gate charge capacity, so that the gate voltage Vg of the main switching element 2 becomes positive. The main switching element 2 is turned on. In the on period Ton, the drain voltage Vd of the main switching element 2 is approximately 0V.

  In the off period Toff in which the switching element 24a is turned off, the excitation energy of the drive transformer 22a is released, and a regenerative current flows to the DC power source 15 through the diode 26a due to the voltage generated between both ends of the primary winding 25a, and the secondary winding 27a A negative voltage V1 (V1 <0) having a negative polarity is generated between the non-dot side terminal and the dot side terminal. However, since the ON width of the switching element 24a is very short, the excitation energy accumulated in the drive transformer 22a is small and the reverse voltage V1 is small. Therefore, the base current cannot be sufficiently supplied to the transistor 32a, and the transistor 32a does not turn on quickly and its conduction amount gradually increases. Therefore, the gate charge capacity of the main switching element 2 is also gradually discharged through the resistor 35a, and the main switching element 2 is gradually turned off without being quickly turned off. Accordingly, the drain voltage Vd of the main switching element 2 gradually increases.

  On the other hand, when the switching element 24b of the low-side drive circuit 20b is turned on, an induced voltage is induced in the secondary winding 27b in the same manner as the high-side drive circuit 20a, and the base voltage of the transistor 32b becomes positive and is turned off. The switching element 3 is turned on. At the same time, due to the induced voltage of the secondary winding 27b, a current flows from the non-dot side terminal to the dot side terminal through the parallel circuit of the resistor 42a and the capacitor 43a and the secondary winding 40a on the high side drive circuit 20a side through the diode 41a. Excitation energy is supplied to the drive transformer 22a. With this excitation energy, the reverse voltage V1 is superimposed on the other secondary winding 27a of the drive transformer 22a and generated. Due to the superimposed reverse voltage V1, the base current flowing through the transistor 32a increases rapidly, and the transistor 32a is completely turned on. By this turn-on, the gate charge capacity of the main switching element 2 is rapidly discharged through the resistor 35a, and the main switching element 2 is quickly turned off.

As described above, in this embodiment, the high-side drive circuit 20a and the low-side drive circuit 20b are connected to the gates as drive terminals of the plurality of main switching elements 2 and 3, respectively, and the main switching elements 2 and 3 are alternately connected. A switching power supply device that intermittently supplies power from a DC power source 1 to a transformer 6 corresponding to an inductance element by switching operation, and extracts and outputs power from the transformer 6, and includes a high-side drive circuit 20 a and a low-side drive circuit. 20b is a drive transformer 22a, 22b having primary windings 23a, 23b and secondary windings 27a, 27b, and induction of the secondary windings 27a, 27b by intermittently passing a current through the primary windings 23a, 23b. PWM control as a switching means for applying a voltage to the gates of the main switching elements 2 and 3 for switching operation The gate voltage as the drive terminal voltage of the main switching elements 2 and 3 when the control IC 16 and the switching elements 24a and 24b and the main switching elements 2 and 3 are turned off by the reverse voltage generated in the secondary windings 27a and 27b. Transistors 32a and 32b as main switch discharge elements for discharging the other drive transformer using the induced voltage of the secondary winding 27b (27a) constituting one drive transformer 22b (22a). 22a supplies excitation energy to (22b) increases the reverse voltage includes whereby the transistor 32a, the negative bias circuit 50a as the reverse voltage superposing unit 32b Ru turns on, the 50b.

  In this way, even if the on-width of the switching elements 24a and 24b is shortened due to high frequency and sufficient excitation energy is not accumulated in the other drive transformer 22a (22b), the secondary of one drive transformer 22b (22a) Excitation voltage of the winding 27b (27a) can be used to supply excitation energy to the other drive transformer 22a (22b). As a result, the reverse voltage generated in the secondary winding 27a (27b) of the other drive transformer 22a (22b) can be increased, and the transistor 32a (32b) can be reliably turned on. The voltage can be surely discharged in the off period Toff, and malfunction can be prevented. As described above, it is possible to provide a switching power supply apparatus that does not cause an abnormal increase in the drive terminal voltage due to a high-speed voltage change of the main switching elements 2 and 3 and that can obtain a stable switching operation in the entire load region.

  In addition, this invention is not limited to the said Example, It can change in the range which does not deviate from the meaning of this invention. The inverter circuit is not limited to a half-bridge configuration, and may be any type as long as it uses two or more main switching elements such as a full-bridge configuration.

It is a circuit diagram of a switching power supply device in the present invention. 2 is a waveform diagram showing the operation of each part of the circuit of FIG. It is a circuit diagram of the switching power supply device in a prior art example.

1 DC power supply 2, 3 Main switching element 6 Transformer (inductance element)
16 PWM control IC (switching means)
20a High side drive circuit
20b Low side drive circuit
22a, 22b Drive transformer
23a, 23b Primary winding
24a, 24b Switching element (switching means)
27a, 27b Secondary winding
32a, 32b Transistor (Main switch discharge element)
50a, 50b Negative bias circuit (reverse voltage superimposing means)

Claims (1)

A drive circuit is connected to each of the drive terminals of the plurality of main switching elements, and power is intermittently supplied from the power source to the inductance element by alternately switching the main switching elements, and the power is extracted from the inductance element. A switching power supply device for output,
The drive circuit includes a transformer having a primary winding and a secondary winding;
Switching means for applying an induced voltage of the secondary winding to the drive terminal of the main switching element by causing a current to intermittently flow through the primary winding, and switching operation;
A main switch discharge element that conducts by a reverse voltage generated in the secondary winding during an off period of the main switching element and discharges a drive terminal voltage of the main switching element;
Using the induced voltage of the secondary winding which constitutes one of the transformer by supplying exciting energy to the other of the transformer increases the reverse voltage, thereby reverse voltage Ru turns on the main switching discharge element A switching power supply device comprising superimposing means.

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