JPS61161966A - Switching transistor drive circuit - Google Patents

Abstract

PURPOSE:To eliminate the turning ON state of a switching transistor due to noise by providing a protecting winding in a rive transformer, and connecting a diode between the protecting winding and one end of control power source outputs. CONSTITUTION:A power source circuit has a power source 10, a power converter 20 and a switching transistor drive unit 30. The unit 30 has a controller 31, a resistor 32, diodes 33, 36, a transistor 34, and a drive transformer 35. A series circuit of the resistor 32, the drive winding (a) of the transformer 35 and the transistor 34 and a series circuit of the protecting wining (d) of the transformer 35 and the diode 36 are connected with the output terminal of a control power source 13. The diode 33 is connected in parallel with a series connecting circuit of the winding (a) and the transistor 34. A noise from a switch 11 or the exterior can be reduced to the forward bias or lower of a switching transistor 23 by suitably selecting the winding ratio of the first winding (b) of the transformer 35 to the winding (d).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a driving circuit for switching transistors. In particular, it relates to a drive circuit that switches a switching transistor via a current feedback drive transformer.

〔overview〕

The present invention provides a switching transistor drive circuit in which the output voltage of a current feedback drive transformer connected to a drive switch that is opened and closed by a drive control signal generated in a control circuit is applied between the base and emitter of a switching transistor. , by providing a protective winding in the current feedback drive transformer and suppressing the output voltage of this transformer by the voltage induced by this protective winding, this switching transistor is suppressed by the noise caused by the transient voltage applied to the switching transistor. This is to prevent the appearance of a turn-on state.

[Conventional technology]

In power conversion devices such as switching regulators, current feedback switching transistor drive circuits are used to reduce power consumption in the drive circuits.

FIG. 3 is a circuit diagram showing the configuration of a conventional example of this type of drive circuit. AC power supplied from input power supply terminals 51 and 52 is rectified and smoothed by rectification and smoothing circuit 12 . The output voltage El of the rectifying and smoothing circuit 12 is applied to a series connection circuit of the primary winding of the transformer 21, the switching transistor 23, and the second winding C of the drive transformer 35. The primary winding current of the transformer 21 is interrupted by the on/off operation of the switching transistor 23, and a transformed voltage is generated on the secondary side, which is rectified and smoothed by the rectifying and smoothing circuit 22 and sent to the power output terminal 6.
1 and 62.

Transformer 21. The power converter 20 is configured by the switching transistor 23 and the rectifier and smoothing circuit 22. The output voltage of the power converter 20 is fed back to the control circuit 31, and the control circuit 31 turns on and off the transistor 23. A drive signal is generated. On the other hand, the control power supply 13 supplies a voltage Ez to each of the resistor 32, the drive winding a of the drive transformer 35, the series connection circuit of the collector and emitter of the drive switch transistor 34, and the control circuit 31. The transistor 34 is turned on and off by a drive signal output from the control circuit 31. A diode 33 is connected in parallel to a series connection circuit of the drive winding a and the transistor 34. The polarity of the diode 33 is opposite to the voltage E2. Further, the first winding of the drive transformer 35 is connected to both ends of a resistor 24 connected between the base and emitter of the switching transistor 23. The polarity of each winding of the drive transformer 35 is indicated by a * in the figure. The drive transformer 35, the diode 33, and the transistor 34 constitute a switching transistor drive circuit, and the switching transistor 23 is turned on and off by this drive circuit in response to a drive control signal given from the tui circuit 31.

Next, the operation of this drive circuit in a steady state will be explained. When the transistor 34 continues to be on, a constant current is maintained in the path from the power supply 13 - the resistor 32 - the drive winding a -> the transistor 34 . Therefore, since no voltage is developed across the first winding of drive transformer 35, switching transistor 23 is in an off state. Next, when the transistor 34 is turned off, the above-mentioned current is cut off, so a current ib is induced in the -th volume lab, the switching transistor 23 starts to turn on, and the collector current of the switching transistor 23 starts to flow. This current passes through the knee tt & Ic, so the second volume! Positive feedback is provided from IIc to the first winding, and the switching transistor 23 is rapidly turned on.

Next, when the transistor 34 is turned on, the drive winding a of the drive transformer 35 is short-circuited by the transistor 34 and the diode 33, and the first winding is also short-circuited by the transformer action, and the switching transistor 23 is turned off. become a state. After the switching transistor 23 is turned off, the first winding of the drive transformer 35 is in an open state, so the drive transformer 35 connects the drive winding a through the resistor 32.
Next, when the transistor 34 is turned off, the switching transistor 23 is turned on, as described above. is driven.

[Problem that the invention seeks to solve]

However, this drive circuit has a drawback as explained below during periods when the power supply voltage is not determined, such as when the power is turned on and off.When the switch 11 is closed at time T0 and the power is turned on, the output voltage E of the rectifier and smoothing circuit 12 , and the output voltage Et of the control power supply 13 have waveforms as shown in FIG. That is,
At time T, the voltage E8 becomes a positive value ■1 that determines the on state of the transistor 34, and at time Tt, the voltage E8 becomes the positive value ■1, which determines the ON state of the transistor 34.
1 becomes a voltage value v2 that allows normal operation, and then reaches a voltage value v2 which is a normal operating voltage. Time T! Thereafter, the transistor 34 performs on/off control according to the normal operation of the control circuit 31, and the switching transistor 23 is turned on/off in accordance with the control signal. However, from time T0 to T,
In this case, transistor 34 is in an off state. In this state, the transistor 23 may be turned on due to noise generated from the switch 11 or external noise.

Since transistor 34 is off, the positive feedback action of drive transformer 35 turns on switching transistor 23, similar to when switching transistor 23 is turned on during normal operation. Since the voltage E1 already has a fairly high voltage value and the transistor 34 cannot be turned on until time T, the switching transistor 23 cannot be turned off, so the transformer 21 is saturated and There is a drawback that a large current passes through the switching transistor 23 and the switching transistor 23 is destroyed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching transistor drive circuit that solves these drawbacks and prevents malfunctions caused by noise when power is turned on and off, thereby preventing damage to the switching transistor.

[Means for solving problems]

The present invention provides an electric current comprising a first winding connected to each of the base and emitter of a switching transistor, a second winding connected in series to a switch circuit of the switching transistor, and a drive winding. a feedback drive transformer, and further includes a power supply terminal that inputs a control power supply, a control circuit that generates a drive control signal for the switching transistor, and a path that connects the power supply terminal and one end of the drive winding. As a means for solving the above-mentioned problem, the current feedback drive transformer is equipped with a protective winding;
Further, the present invention is characterized in that it includes circuit means for supplying current to the protective winding so as to suppress the voltage of the first winding to a low level during a period of current rise.

[Effect]

If the switching transistor is turned on due to noise during the transient period until the applied voltage of the drive switch reaches the operating voltage of the drive switch, the switching transistor should be kept open until the applied voltage of the control circuit reaches the operating voltage. Since the voltage applied to the switch circuit of this switching transistor has already reached a value close to a steady value during this period, a large current passes through the switching transistor, causing destruction of this switching transistor.

In this invention, by appropriately selecting the winding ratio between the first winding and the protection winding, the voltage generated in the first winding is suppressed to a value below the forward bias of the transistor, thereby preventing switching caused by noise. The appearance of a turned-on state of the transistor is prevented.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS A circuit according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit connection diagram showing the configuration of this embodiment circuit. FIG. 2 is a waveform diagram showing the voltage transient state of each part of this embodiment circuit.

First, the configuration of this embodiment circuit will be explained based on FIG. This embodiment circuit includes a power supply section 10 and a power conversion section 20.
and a switching transistor drive section 30 according to the present invention. Here, the switching transistor drive section 30 includes a control circuit 31, a resistor 32, and a diode 3.
3 and 36, a transistor 34, and a drive transformer 35. A series circuit of a resistor 32, a drive winding a of a drive transformer 35, a transistor 34, a protection winding wAd of the drive transformer 35, and a diode 3 are connected to the output of the control power supply 13.
6 series circuits are connected. A diode 33 is connected in parallel to the series connection circuit of the drive winding a and the transistor 34. Here, the polarities of the diode 36 and the diode 33 are opposite to the output voltage E2 of the control power source 13. Both ends of the first winding c of the drive transformer 35 are connected to the base and emitter of the switching transistor 23, and the second winding c is connected in series to the collector circuit of the switching transistor 23. Here, the polarity of each winding is shown in the figure.
It is indicated by a mark. The connection between the collector terminal A of the switching transistor 23 and the terminal B of the second winding C is turned on and off according to a drive control signal applied to the base of the transistor 34. Terminals A and B are connected in series to the primary winding of transformer 21 and to the output of rectifying and smoothing circuit 12, and control terminal 71 is connected to the input of control circuit 31. The output of the transformer 21 is rectified and smoothed by a rectification and smoothing circuit 22, and the converted output is connected to power supply output terminals 61 and 62. Power output terminal 61 is connected to control terminal 71 .

Next, the operation of the circuit of this embodiment will be explained based on FIGS. 1 and 2. When the switch 11 is closed, the control power supply 12
The output voltage E2 rises and reaches the voltage value vI at time T+, and the on state of the transistor 34 is established, and at time T! Then, the voltage value becomes V2 and the operation of the control circuit 31 is guaranteed, and then the voltage value becomes the normal voltage value V3 and normal driving operation is performed. Since the transistor 34 is guaranteed to be on after time T1, the drive section wAa of the drive transformer 35 is short-circuited by the transistor 34 and the diode 33, and the first winding is also short-circuited by the transformer action, so that the switching transistor 23 is not turned on due to noise or the like, and normal operation is guaranteed after time Tt.

Between times T0 and T+, if the switching transistor 23 is turned on due to noise or the like, the forward bias of the switching transistor 23 is caused by the first winding of the drive transformer 35. A voltage corresponding to is generated,
A voltage corresponding to the winding ratio between the first winding and the first winding is also generated in the protective winding, %ld.

Since the protective winding d is connected to the control power supply 13 via the diode 36, the voltage generated in the protective winding d is regulated according to the voltage EI. Therefore, by appropriately selecting the turns ratio between the first winding and the protective winding d, the voltage Et generated in the first winding can be generated in the time (T o ~ TI) until the voltage Et reaches the voltage value V. Voltage switching transistor 23
The forward bias can be lower than VSW. This prevents the switching transistor 23 from being erroneously turned on due to noise generated from the switch 11 or external noise.

Next, in steady operation, when the transistor 34 is on, a current flows through the path of the power supply 13 - the resistor 32 - the winding a - the transistor 34, and the circuit operates in the same way as the conventional circuit. Further, when the transistor 34 is turned off, the above current is cut off, so that a current i is induced in the first winding, and the switching transistor 23 is injected in the same way as in the conventional circuit.
is turned on. The voltage generated across the first winding at this time becomes the base-emitter voltage of the switching transistor 23. On the other hand, a voltage corresponding to the turns ratio of the first winding S is generated in the protective winding d of the drive transformer 35, but since the voltage EI has already reached the voltage value ■, the protective winding By appropriately selecting this winding ratio so that the voltage generated at d is smaller than the voltage E1, no current flows through the protective winding d, and the circuit operates exactly the same as the conventional circuit.

〔Effect of the invention〕

As explained above, the present invention provides a protective winding in the drive transformer and connects a second diode between the protective winding and one end of the control power supply output, so that the output voltage of the control power supply is low. This has the effect of preventing destruction of the switching transistor due to malfunction caused by noise or the like in the switching transistor.

[Brief explanation of the drawing]

FIG. 1 is a circuit connection diagram showing the configuration of a circuit according to an embodiment of the present invention. FIG. 2 is a waveform diagram showing the input power to the power converter and the output power of the control power source when the power is turned on. FIG. 3 is a circuit connection diagram showing the configuration of a conventional circuit. 10...Power supply part, 11...Switch, engineering 2.22...
- Rectification and smoothing circuit, 13... Control power supply, 20... Power converter, 21... Transformer, 23... Switching transistor, 24.32... Resistor, 30... Switching transistor drive Part, 31... Control circuit, 3
3.36...diode, 34...transistor,
35... Drive transformer, 51.52.61.62.71
...Terminal, a... Drive @ line of drive transformer 35, b.
...first winding of drive transformer 35, C...drive transformer 3
5 second winding, d... protection winding of drive transformer 35;

Claims (1)

[Claims] (1) A current feedback comprising a first winding connected to each of the base and emitter of the switching transistor, a second winding connected in series to the switch circuit of the switching transistor, and a drive winding. a type drive transformer, and further includes a power terminal for inputting control power, a control circuit for generating a drive control signal for the switching transistor, and a path connecting the power terminal and one end of the drive winding. In the switching transistor drive circuit, the current feedback drive transformer includes a protection winding, and during a period of current rise, the switching transistor drive circuit includes a drive switch that is inserted and opened and closed by the drive control signal. A switching transistor drive circuit comprising circuit means for applying a current to the protective winding so as to suppress the voltage of the switching transistor to a low level.