JP3010791B2 - Switching element drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching element drive circuit.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 3, when a base current is supplied via a resistor 13 to a transistor 12 as a current-driven switching element having a load 11 provided on the ground side, a switching element driving circuit is used. A boost power supply circuit 14 is used.

That is, when the transistor 12 is turned on, the emitter-collector voltage of the transistor 12 is negligibly smaller than the power supply voltage Vee of the DC power supply E.
Of the power supply voltage Vee. At this time, the ON voltage Von which is a base voltage for maintaining the ON state of the transistor 12 needs to be equal to or higher than the voltage obtained by adding the base-emitter voltage of the transistor 12 to the power supply voltage Vee. The boost power supply circuit 14 is used to generate the ON voltage Von.

As shown in FIG. 3, the boosting power supply circuit 14 includes an induction coil L, a capacitor C, a check diode D, a second
, A booster control circuit 16 and the like.

The boost power supply circuit 14 includes a transistor 15
Is turned on / off by duty control to charge the capacitor C via the diode D when the electric energy induced in the induction coil L is turned on. The charging voltage of the capacitor C is reduced by repeating this operation. The voltage is increased to the power supply voltage Vee of the DC power supply E or higher.
The boosted charging voltage of the capacitor C is used as a power supply voltage for the base current of the transistor 12.

The boosted power supply voltage (hereinafter, referred to as
The duty ratio of the transistor 15 is controlled by the boosting control circuit 16 so that the boosted voltage Vin is always a constant voltage. That is, the boost control circuit 16 inputs the divided voltage Vs from the voltage dividing circuit including the resistors R1 and R2 and the predetermined reference voltage Vk in order to detect the boosted voltage Vin at that time. The reference voltage Vk is a target voltage Vp (a target voltage for turning on the transistor 12). The on-voltage Von necessary for turning on the transistor 12 and a voltage drop due to the resistor 13 connected to the base terminal are used as the reference voltage Vk. Is a voltage set in advance to obtain a voltage obtained by adding

That is, when the divided voltage Vs is smaller than the reference voltage Vk, the boost control circuit 16 increases the boosted voltage Vin.
Is lower than the target voltage Vp, the duty ratio of the duty control of the transistor 15 is increased to bring the boosted voltage Vin closer to the target voltage Vp. Conversely, the boost control circuit 16
When the divided voltage Vs is higher than the reference voltage Vk, it is determined that the boosted voltage Vin is higher than the target voltage Vp.
5, the duty ratio of the duty control is lowered to increase the boosted voltage V
in is brought close to the target voltage Vp. Therefore, the boosting power supply circuit 14 controls the boosting control circuit 16 so that the boosted voltage Vin is always equal to the target voltage Vp.

Then, the boost power supply circuit 14 generates a boosted voltage Vi.
A base current Ib determined by the difference between n and the power supply voltage Vee (= Vin−Vee) and the resistor 13 flows to the base of the transistor 12 to drive the transistor 12.

[0009]

However, since the base current Ib is determined by the resistance value of the resistor 13 as described above, power loss and heat generation have been problems.

Therefore, a base current Ib supplied to transistor 12 by boosting power supply circuit 14 is detected, and base current Ib is always equal to a predetermined current (target current) Ip for turning on transistor 12. Next, it is conceivable that the boosting power supply circuit 14 is controlled by the boosting control circuit 16.

That is, a base current Ib of the transistor 12 is detected, and a voltage (detection voltage) Va proportional to the base current Ib is output to the boosting control circuit 16. The boost control circuit 16 receives the detection voltage Va and a predetermined reference voltage. The reference voltage is a voltage set in advance to set the base current Ib of the transistor 12 to the target current Ip.

The boost control circuit 16 detects the detection voltage V
When a is smaller than the reference voltage, it is assumed that the base current Ib of the transistor 12 is smaller than the target current Ip, the duty ratio of the duty control of the transistor 15 is increased, and the boosted voltage Vin is increased to bring the base current Ib closer to the target current Ip. Conversely, when the detection voltage Va is higher than the reference voltage, the boost control circuit 16 determines that the base current Ib of the transistor 12 is higher than the target current Ip,
5, the duty ratio of the duty control is reduced, and the boosted voltage Vi is reduced.
By decreasing n, the base current Ib approaches the target current Ip.
Accordingly, the boosting power supply circuit 14 always controls the base current Ib of the transistor 12 to the target current Ip
Is controlled to be equal to In other words, the base current Ib of the transistor 12 is fixed (= the target current Ib
p), the boost power supply circuit 14
6 to be controlled.

As a result, since the base current Ib of the transistor 12 is not determined by the resistor 13, power loss and heat generation by the resistor 13 can be eliminated. However, a third switching element is provided between the boost power supply circuit 14 and the base terminal of the transistor 12, and the switching element is turned on / off by a drive signal to arbitrarily supply and cut off the base current Ib of the transistor 12. There is a switching element drive circuit of a type that performs control to drive and control the load 11.

In this case, when the third switching element is turned off, that is, when the power supply to the load 11 is cut off, the base current Ib of the transistor 12 does not flow and the detection voltage Va becomes zero. The boost control circuit increases the boost voltage Vin to make the base current Ib the target current Ip. As a result, there is a possibility that the boosted voltage Vin exceeds the withstand voltage of the capacitor C.

Further, as described above, when power is supplied to the load 11, the capacitor C is boosted by the boosted power supply circuit 14 so that the transistor 12 is turned on (the boosted voltage Vin (= on voltage Von)). Will be charged.
That is, the voltage between the terminals of the capacitor C at that time is equal to the ON voltage Von.

Therefore, when the power supply to the load 11 is switched from supply to cut-off, when the capacitor C is charged with the ON voltage Von, the transistor 15 is turned off, so that the capacitor C is switched from the power supply voltage Vee to the power supply voltage Vee. A stop voltage Vt, which is a voltage obtained by subtracting a voltage drop due to the check diode D, is applied and charged. And the load 11
If the time during which the power supply to the power supply is interrupted becomes longer, the capacitor C and the non-return diode C and the transistor 12
The leak current flows through and causes a spontaneous discharge,
The capacitor C loses an amount of electric energy corresponding to a difference voltage between the ON voltage Von and the stop voltage Vt. That is, if the time during which the power supply to the load 11 is cut off becomes longer,
The voltage between the terminals of the capacitor C falls from the ON voltage Von to the stop voltage Vt.

When all of the electric energy charged in the capacitor C at that time when the power supply to the load 11 is switched from supply to cutoff flows as the base current Ib of the transistor 12, the voltage between the terminals of the capacitor C The voltage will be zero. When the transistor 15 is turned off, the stop voltage Vt is applied to the capacitor C and the capacitor C is charged. In other words, when the time during which the power supply to the load 11 is cut off becomes longer, the voltage between the terminals of the capacitor C becomes equal to the stop voltage Vt.

That is, when the power supply to the load 11 is cut off and the time elapses, the boosted voltage Vin of the boosted power supply circuit 14
Approaches the stop voltage Vt. Then, when power is supplied to the load 11 again, the transistor 12 is driven until the boosted voltage Vin reduced to a value equal to the stop voltage Vt is boosted and the base current Ib of the transistor 12 is increased to the target current Ip. Will not be. That is, when the power supply to the load 11 is switched from the supply to the cutoff and the time elapses, when the power supply to the load 11 is performed again, the driving of the transistor 12 starts up with a delay.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to prevent a capacitor from being destroyed by suppressing a rise in boosted voltage when power supply to a load is cut off. It is an object of the present invention to provide a switching element drive circuit having a simple circuit configuration, which can speed up the rise of a current drive type switching element when power is supplied to a load again.

[0020]

According to the present invention, there is provided a switching element driving circuit for supplying a current to a current driving type switching element provided with a load on the ground side to drive the current driving type switching element. The voltage of the DC power source, which is the power source of the switching element, is applied to the induction coil, and the second
The switching operation of the switching element causes the capacitor to charge the capacitor via the non-return diode when the electric energy induced in the induction coil is turned off when the capacitor is turned off, thereby reducing the charging voltage of the capacitor to the power supply voltage of the DC power supply. The boosted power supply circuit boosted as described above and used as a power supply voltage for the drive current of the current-driven switching element, and supplied to the current-driven switching element by conduction / non-conduction of the third switching element based on the drive signal A drive control circuit for controlling a drive current to be applied, a current detector for detecting an output current of the boost power supply circuit and outputting an output voltage proportional thereto, and comparing the output voltage detected by the current detector with a reference voltage. A boost control circuit for controlling the switching operation of the second switching element, It said third switching element when the non-conductive, and its gist that it is constituted by a commutation circuit for commutating the output currents of the booster power supply circuit based on.

[0021]

The output current of the booster power supply circuit is detected by a current detector, and the booster power supply circuit is controlled by the booster control circuit so that the current is constant regardless of whether power is supplied to or interrupted from the load. When power is supplied to the load, the output current of the boost power supply circuit is used as the drive current of the current drive type switching element. When the power supply to the load is cut off, the output current of the boost power supply circuit is returned to the DC power supply through the commutation circuit. As a result, even when the power supply to the load is cut off and the time elapses, the rising of the drive of the current drive type switching element does not delay when the power supply to the load is performed again. Further, when the power supply to the load is cut off, the boosted voltage of the boosted power supply circuit does not exceed the withstand voltage of the capacitor.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An embodiment of the present invention will be described below with reference to FIG.

In this embodiment, the boost power supply circuit 14
Is the same as that of the prior art switching element drive circuit shown in FIG. 3, and therefore, the same reference numerals are used and the detailed description is omitted.

The current detector 17 detects the base current Ib of the transistor 12 and outputs a detection voltage Va which is a voltage proportional thereto. The drive control circuit 19 includes a transistor 18 as a third switching element and a resistor R3. The drive control circuit 19 turns the transistor 18 on and off based on a high or low level drive signal, and is supplied to the next-stage transistor 12. Base current Ib.
That is, when the drive signal is at a high level, the transistor 1
8 turns off, the transistor 12 at the next stage turns off, and the load 11
The power supply to the is cut off. When the drive signal is at a low level, the transistor 18 is turned on, and the transistor 12 in the next stage is turned on to supply power to the load 11.

The boost control circuit 16 receives the detection voltage Va of the current detector 17 and receives a predetermined reference voltage V
Enter r. The reference voltage Vr is a voltage set in advance to set the base current Ib of the transistor 12 to a target current Ip which is a predetermined current for turning on the transistor 12.

A series circuit of a plurality (two in this embodiment) of diodes 20 constituting a commutation circuit has its anode connected to the emitter of the transistor 18 of the drive control circuit 19 and its cathode connected to the power supply E. Connect to The number of the diodes 20 to be connected in series is larger when the forward current flows through the diode 20 than the potential difference between the emitter of the transistor 12 and the emitter of the transistor 18 when the transistor 12 is turned on and the base current Ib flows. Is set in advance so that the potential difference between the emitter of the transistor 18 and the power supply voltage Vee (= the voltage between the anode and the cathode of the diode 20) becomes higher.

Next, the operation of the switching element drive circuit configured as described above will be described. When the drive signal is at a low level, the transistor 18 of the drive control circuit 19 is turned on, the base current Ib flows through the transistor 12 in the next stage, and the transistor is turned on to supply power to the load 11. At this time, since the potential difference between the emitter of the transistor 12 and the emitter of the transistor 18 is lower than the voltage between the anode and the cathode of the diode 20, no current flows through the diode 20 and the current flowing through the current detector 17, ie, the boost All output currents Io of the power supply circuit 14 become base currents Ib of the transistor 12. As a result, the current detector 17 detects the base current Ib (= output current Io) of the transistor 12 and outputs the detection voltage Va to the boost control circuit 16.

When the detected voltage Va is smaller than the reference voltage Vr, the booster control circuit 16 determines that the base current Ib of the transistor 12 is smaller than the target current Ip,
5, the duty ratio of the duty control is increased to increase the boosted voltage Vi.
By increasing n, the base current Ib is brought closer to the target current Ip.
Conversely, the boost control circuit 16 determines that the detection voltage Va is equal to the reference voltage V
r, the base current I of the transistor 12
Assuming that b is larger than the target current Ip, the duty ratio of the duty control of the transistor 15 is reduced, and the boosted voltage Vin is reduced to bring the base current Ib closer to the target current Ip.

Therefore, when the drive signal is at a low level, that is, when power is supplied to the load 11, the boosting power supply circuit 14 uses the boosting control circuit 16 so that the base current Ib of the transistor 12 is always equal to the target current Ip. Is controlled.

When the drive signal is at the high level, the transistor 18 is turned off, and the base current Ib does not flow through the transistor 12 at the next stage. Then, the output current I of the boost power supply circuit 14
All o flows through the diode 20 and returns to the induction coil L. As a result, the current detector 17 detects the output current Io of the boosting power supply circuit 14 flowing through the diode 20 and outputs a detection voltage Va to the boosting control circuit 16.

When the detected voltage Va is smaller than the reference voltage Vr, the boost control circuit 16 outputs the output current Io to the target current Ip.
Assuming that the output current I is smaller, the duty ratio of the duty control of the transistor 15 is increased, the boosted voltage Vin is increased, and the output current I
o is brought close to the target current Ip. Conversely, the boost control circuit 1
6, when the detection voltage Va is higher than the reference voltage Vr, the output current Io is made larger than the target current Ip, the duty ratio of the duty control of the transistor 15 is reduced, the boosted voltage Vin is lowered, and the output current Io approaches the target current Ip.

Therefore, when the drive signal is at a high level, that is, when the power supply to the load 11 is cut off, the boosting power supply circuit 14
Is controlled such that the output current Io is always equal to the target current Ip.

As described above, in the present embodiment, the boosting power supply circuit 14 uses the boosting control circuit 16 so that the output current Io of the boosting power supply circuit 14 is always constant (= the target current) regardless of whether the power supply to the load 11 is turned on or off. Ip), the power supply to the load 11 is interrupted, and even if a certain period of time has elapsed, the drive of the transistor 12 starts up more quickly when the power is supplied to the load 11 again. can do. Further, when the power supply to the load 11 is shut off, the boosted voltage Vin can be prevented from exceeding the withstand voltage of the capacitor C and destroyed.

In addition, since the circuit can be composed of two diodes 20, the circuit scale can be simplified and reduced in size. Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG.

The configuration of the second embodiment differs from that of the first embodiment shown in FIG. 1 in that the boosting control circuit 16 when the power is supplied to the load 11. Since only the method of determining the reference voltage Vr to be input to FIG. 1 is used, for the sake of convenience of explanation, portions having the same configuration as in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and only different configurations will be described.

The current detector 21 is connected between the load 11 and the ground, detects an emitter current of the transistor 12 which is a power supply current supplied to the load 11, and outputs a voltage (hereinafter, detection voltage) Vb proportional thereto. Output to the boost control circuit 16.

The boost control circuit 16 receives the detection voltage Va of the current detector 17 and the detection voltage Vb of the current detector 21. Then, the duty of the transistor 15 is controlled so that the ratio between the detection voltage Va and the detection voltage Vb becomes constant. That is, the boost control circuit 16 controls the duty of the transistor 15 so that the ratio between the base current Ib and the emitter current Ie of the transistor 12 becomes constant. That is, when the ratio between the base current Ib and the emitter current Ie of the transistor 12 is smaller than a predetermined value, the duty ratio of the duty control of the transistor 15 is increased to increase the ratio between the base current Ib and the emitter current Ie to a predetermined value. Approach. Conversely, transistor 12
When the ratio between the base current Ib and the emitter current Ie is larger than a preset value, the duty ratio of the duty control of the transistor 15 is reduced to bring the ratio between the base current Ib and the emitter current Ie closer to the preset value.

Next, the operation of the switching element drive circuit configured as described above will be described. When the drive signal is at a low level, that is, when power is supplied to the load 11,
When the emitter current Ie of the transistor 12 fluctuates to a value higher than the rated value due to the fluctuation of the load 11, the transistor 1
2, the base current Ib also needs to be increased accordingly. Therefore, the boost power supply circuit 14 is controlled by the boost control circuit 16
The duty ratio of the transistor 15 is increased to increase the base current Ib so that the ratio between the emitter current Ie and the base current Ib of the transistor 12 that has changed to a value larger than the rated value becomes equal to a preset value.

Conversely, if the emitter current Ie of the transistor 12 fluctuates to a value smaller than the rated value due to the fluctuation of the load 11, the base current Ib of the transistor 12 also needs to be correspondingly reduced. Therefore, the boosting power supply circuit 14 uses the boosting control circuit 16 to change the emitter current Ie and the base current Ib of the transistor 12 that have changed to values smaller than the rated value.
Is controlled to reduce the base current Ib by reducing the duty ratio of the transistor 15 so that the ratio becomes equal to a preset value.

As described above, in the second embodiment, the load 1 is reduced by adopting a configuration in which the ratio between the base current Ib and the emitter current Ie of the transistor 12 becomes constant.
A power supply current (= emitter current Ie of the transistor 12) corresponding to the fluctuation of 1 can be supplied.

That is, even if the power supply current fluctuates to a value smaller than the rated value due to the fluctuation of the load 11, the transistor 1 does not receive an excessive base current Ib without flowing into the transistor 12.
2 can be driven to supply power to the load 11. as a result,
The base current I loss in the drive control circuit 19 can be suppressed as compared with the case where an excessive base current Ib is applied to the transistor 12, and the storage time of the transistor 12 (after the base current of the transistor 12 stops, the transistor 12 Time until is turned off)
Can be shortened.

Even if the power supply current fluctuates to a value larger than the rated value due to the fluctuation of the load 11, the transistor 12 can be driven to supply power to the load 11. Of course, when the drive signal is at a high level, that is, when the power supply to the load 11 is cut off, the boost power supply circuit 14
All of the output current Io flows through the diode 20 and returns to the induction coil L.
o is controlled to be always equal to the target current Ip.

The present invention is not limited to the above embodiment. For example, the current detector 21 is
Any configuration may be adopted as long as the power supply current supplied to the load 11 can be detected, such as a connection between the collector of the power supply E and the power supply E.

The transistor 12 is not only a bipolar transistor but also a SIT (static induction type transistor).
Any current-driven switching element such as the above may be used.

[0045]

As described above in detail, according to the present invention, it is possible to speed up the rise of the drive of the transistor when supplying power to the load again with a simple circuit configuration, and to supply power to the load. When the power supply is shut off, the boosted voltage of the boosted power supply circuit can be prevented from exceeding the withstand voltage of the capacitor and being destroyed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a switching element drive circuit embodying the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of a switching element drive circuit embodying the present invention.

FIG. 3 is a circuit diagram showing a conventional switching element drive circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Load, 12 ... Transistor as a current drive type switching element, 14 ... Boost power supply circuit, 15 ... Transistor as a second switching element, 16 ... Boost control circuit, 17 ... Current detector, 18 ... Third switching Transistors as elements, 19 ... drive control circuits, 20 ...
Diode composing a commutation circuit, 21 ... current detector, L
... Induction coil, D ... Reverse diode, C ... Capacitor, E ... DC power supply, Vr ... Reference voltage

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/155 H03K 17/64

Claims (2)

(57) [Claims] 1. A switching element drive circuit for supplying a current to a current-driven switching element provided with a load on the ground side to drive the current-driven switching element, wherein a voltage of a DC power supply which is a power source of the current-driven switching element is applied to an induction coil. The switching operation of the second switching element repeats the operation of charging the capacitor via the non-return diode when the electric energy induced in the induction coil is turned on when the second switching element is turned off, thereby changing the charging voltage of the capacitor to the DC power supply. And a third switching element based on a driving signal, which is turned on and off by a boosting power supply circuit that is boosted to a power supply voltage equal to or higher than a power supply voltage for the driving current of the current driving type switching element. A drive control circuit for controlling a drive current supplied to the element; A current detector that detects an output current of a path and outputs a detection voltage proportional to the output current, and a booster that controls a switching operation of the second switching element by comparing the detection voltage detected by the current detector with a reference voltage. A switching element drive circuit, comprising: a control circuit; and a commutation circuit that commutates an output current of the step-up power supply circuit when the third switching element is non-conductive based on the drive signal. . 2. The switching according to claim 1, wherein a detection voltage of a current detector for detecting a power supply current supplied to the load and outputting a detection voltage proportional thereto is used as a reference voltage of the boosting control circuit. Element drive circuit.