JP3036120B2 - 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. 2, when a base current is supplied via a resistor 13 to a transistor 12 serving as a current-driven switching element provided with a load 11 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, so that the potential of the emitter of the transistor 12 becomes equal to the power supply voltage Vee of the DC power supply E. Is almost equal to At this time, the ON voltage Von, which is the base potential for maintaining the ON state of the transistor 12, is equal to the power supply voltage Ve.
e must be equal to or higher than the sum of the base-emitter voltage of the transistor 12 and the on-voltage Vo
A boost power supply circuit 14 is used to generate n.

As shown in FIG. 2, 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. This boost power supply circuit 1
4 turns on / off the transistor 15 under duty control to charge the capacitor C via the diode D with the electric energy induced in the induction coil L when the transistor 15 is turned on. Of the charging voltage of the DC power source E
The pressure is increased as described above. The boosted charging voltage of the capacitor C is used as a power supply voltage for the base current of the transistor 12.

Then, 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.

[0006] 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.

[0007]

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, the booster power supply circuit 14 causes the transistor 1
2 is detected by the boost control circuit 16 so that the base current Ib always becomes equal to a predetermined current (target current) Ip for turning on the transistor 12. Can be controlled.

That is, the 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 boost 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, it is possible to eliminate power loss and heat generation due to the resistor 13. 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.

As described above, when power is supplied to the load 11, the capacitor C is supplied with a boosted voltage Vin (= on voltage Von) boosted by the boosting power supply circuit 14 so that the transistor 12 is turned on. 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 cutoff, the ON voltage V
When the capacitor C is charged in the on state, the transistor 15 is turned off, so that the capacitor C is applied with the stop voltage Vt, which is a voltage obtained by subtracting the voltage drop due to the check diode D from the power supply voltage Vee, and is charged. Is done. When the time during which the power supply to the load 11 is cut off becomes longer, a leak current flows from the capacitor C via the check diode D and the transistor 12, and the capacitor C naturally discharges. An amount of electric energy corresponding to the difference voltage of the stop voltage Vt is lost. That is, 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 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 the supply to the 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.

The present invention was made to solve the above problems, when the purpose of that cut off the power supply to the load is broken the capacitor while suppressing the increase of the boosted voltage < br /> corrupted can be prevented, and even if the time is switched to cut off from the supply power supplied to the load has passed, quickly leading edge of the drive switching element when the power supply to the load again It is an object of the present invention to provide a switching element drive circuit that can perform the switching.

[0016]

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 current-driven switching element is boosted by the above-described step-up power supply circuit, which is boosted and used as a power supply voltage for the drive current of the current-driven switching element, and the conduction / non-conduction of the third switching element based on the drive signal. A drive control circuit for controlling the supplied drive current; and a drive control circuit for supplying the same
A current detector that detects a drive current for driving the switching element and outputs a voltage proportional thereto, a voltage detection circuit that detects and outputs a boosted voltage of the boost power supply circuit, and an output of the current detector, or A boost control circuit that compares an output of a voltage detection circuit with a predetermined reference voltage to control a switching operation of the second switching element; and an output of the current detector and the voltage detection circuit based on the drive signal. And a selection circuit for selecting any one of the outputs and inputting the selected output to the boost control circuit.

[0017]

When the power is being supplied to the load, the selection circuit selects the detection voltage from the current detector and outputs it to the boost control circuit. The boost control circuit controls the second switching element of the boost power supply circuit based on the detected voltage and the reference voltage so that the drive current of the current drive type switching element becomes constant. Further, when the power supply to the load is shut off, the selection circuit selects the detection voltage from the voltage detection circuit and outputs it to the boost control circuit. The boost control circuit controls the second switching element of the boost power circuit based on the detected voltage and the reference voltage so that the boost voltage of the boost power circuit becomes constant. As a result, even when the power supply to the load is cut off and the time elapses, the rise of the drive of the current drive type switching element can be accelerated when the power supply to the load is performed again. Further, it is possible to prevent the boosted voltage of the boosted power supply circuit from exceeding the withstand voltage of the capacitor and being destroyed when the power supply to the load is cut off.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. In this embodiment, the configuration of the boosting power supply circuit 14 is the same as that of the conventional switching element driving circuit shown in FIG.

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 20 includes a transistor 18 as a third switching element, a resistor R3, and an inverter 19, and turns on / off the transistor 18 based on a high or low level drive signal input via the inverter 19. It is turned off to control the base current Ib supplied to the transistor 12 at the next stage. That is, when the drive signal is at the low level, the transistor 18 is turned off, the transistor 12 at the next stage is turned off, and the power supply to the load 11 is cut off. When the drive signal is at a high level, the transistor 18 is turned on and the transistor 12 at the next stage is turned on to supply power to the load 11.

Analog switch 2 constituting a selection circuit
As shown in FIG. 1, a drive signal is input to one of the analog switches 21 and a drive signal is input to the other analog switch 22 via the inverter 19. That is, when a high-level drive signal is input, the analog switch 21 is turned on and the analog switch 22 is turned off. When a low-level drive signal is input, the analog switch 22 is turned on and the analog switch 21 is turned off.

The boosting control circuit 16 inputs the divided voltage Vs from a voltage dividing circuit as a voltage detecting circuit composed of the resistors R1 and R2 via the analog switch 22, and converts the detected voltage Va of the current detector 17 into an analog switch. 21 and a predetermined reference voltage Vr. The reference voltage Vr is equal to the base current Ib of the transistor 12.
Is set in advance to make the target current Ip, and also a voltage set in advance to make the boosted voltage Vin the on-state voltage Von.

Next, the operation of the switching element drive circuit configured as described above will be described. When the drive signal is at a high level, the analog switch 22 becomes non-conductive and the divided voltage Vs is not input to the boost control circuit 16, the analog switch 21 becomes conductive and the boost control circuit 16 supplies the detection voltage Va of the current detector 17. Is entered. In addition, inverter 1
The output of the transistor 9 becomes low level, the transistor 18 is turned on, the base current Ib flows through the transistor 12 in the next stage, and the transistor 12 is turned on to supply power to the load 11.

That is, the boost control circuit 16 detects the detection voltage V
a is smaller than the reference voltage Vr, the transistor 12
Of the base current Ib is smaller than the target current Ip, the duty ratio of the duty control of the transistor 15 is increased, the boosted voltage Vin is increased, and the base current Ib approaches the target current Ip. Conversely, when the detected voltage Va is higher than the reference voltage Vr, the boost control circuit 16 determines that the base current Ib of the transistor 12 is larger than the target current Ip, lowers the duty ratio of the duty control of the transistor 15 and lowers the boosted voltage Vin to reduce the base current. Ib approaches the target current Ip.

Therefore, when the drive signal is at a high level, that is, when power is being 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 always becomes equal to the target current Ip. Is controlled. When the drive signal is at a low level, the analog switch 21 is turned off and the detection voltage V of the current detector 17 is turned off.
a is not input to the boost control circuit 16, the analog switch 22 is turned on, and the divided voltage Vs is input to the boost control circuit 16. Further, the output of the inverter 19 becomes high level, the transistor 18 is turned off, and the base current Ib does not flow through the transistor 12 at the next stage.

That is, the boosting control circuit 16 outputs the divided voltage V
When s is smaller than the reference voltage Vr, the boosted voltage Vin is lower than the on-voltage Von, and the duty ratio of the duty control of the transistor 15 is increased to bring the boosted voltage Vin closer to the on-voltage Von. Conversely, the boost control circuit 16
When the divided voltage Vs is higher than the reference voltage Vr, the boosted voltage Vin is higher than the on-voltage Von, and the duty ratio of the duty control of the transistor 15 is reduced to bring the boosted voltage Vin closer to the on-voltage Von.

Therefore, when the drive signal is at a low level, that is, when the power supply to the load 11 is cut off, the boosting power supply circuit 14 uses the boosting control circuit 16 so that the boosted voltage Vin is always equal to the ON voltage Von. Controlled. As described above, in the present embodiment, the boosting power supply circuit 14 is controlled by the boosting control circuit 16 so that the base current Ib of the transistor 12 becomes constant (= the target current Ip) when power is supplied to the load 11. When the power supply to the load 11 is interrupted, the boosted voltage Vin is controlled to be constant (= on voltage Von), so that the power supply to the load 11 is interrupted from the supply. When the power supply to the load 11 is performed again, the rise of the drive of the transistor 12 can be accelerated even if the time has elapsed after the switching to Further, it is possible to prevent the boosted voltage Vin from exceeding the breakdown voltage of the capacitor C and breaking the power supply when the power supply to the load 11 is cut off.

The present invention is not limited to the above embodiment. For example, the transistor 12 is not limited to a bipolar transistor but may be a SIT (static induction transistor).
Any current-driven switching element such as the above may be used. Further, in the above-described embodiment, the reference voltage Vr is shared. However, the reference voltage Vr may be provided based on the drive signal in the boost control circuit 16 by providing the corresponding reference voltage.

[0028]

According to the present invention as described in detail above, according to the present invention, even if the time to switch the power supply to the load cut off from the supply has elapsed, switch when the power supply to again load
The rising of the driving of the chucking element can be accelerated. Further, there is an excellent effect that it is possible to prevent the boosted voltage of the boosted power supply circuit from being broken beyond the withstand voltage of the capacitor when the power supply to the load is cut off.

[Brief description of the drawings]

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

FIG. 2 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 Transistor as an element, 20... Drive control circuit, 21
22 ... Analog switch forming a selection circuit, L ... Induction coil, D ... Reverse diode, C ... Capacitor, E ...
DC power supply, Vr: reference voltage, R1, R2: resistors forming a voltage dividing circuit as a voltage detecting circuit

Claims (1)

(57) [Claims] 1. A switching element driving circuit for supplying a current to a current driving type switching element having a load on the ground side to drive the current driving type switching element, wherein a voltage of a DC power supply which is a power supply of the current driving type 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. A boosted power supply circuit that is boosted to a power supply voltage for driving current of the current-driven switching element by boosting the power supply voltage to a voltage equal to or higher than a power supply voltage of the current-driven switching element; A drive control circuit for controlling a drive current supplied to a switching element; It is supplied to the dynamic switching element the switch
A current detector for detecting a drive current for driving the switching element and outputting a detection voltage proportional thereto, a voltage detection circuit for detecting and outputting a boosted voltage of the boosted power supply circuit, and a detection detected by the current detector. A step-up control circuit for comparing a voltage or a detection voltage of a voltage detection circuit with a predetermined reference voltage to control a switching operation of the second switching element; and detecting the current detector based on the drive signal. A switching element drive circuit, comprising: a selection circuit that selects one of a voltage and a detection voltage of the voltage detection circuit and inputs the selected voltage to the boost control circuit.