JP3024259B2 - 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 having a load 11 provided on the ground side, the switching element is driven. The boost power supply circuit 14 is used as a circuit. That is, when the transistor 12 is on, the voltage between the emitter and the collector of the transistor 12 is negligibly smaller than the power supply voltage Vee of the DC power supply E. The voltage is substantially equal to the power supply voltage Vee of the power supply E. At this time, the base voltage Von for maintaining the ON state of the transistor 12 must be equal to or higher than the sum of the power supply voltage Vee and the base-emitter voltage of the transistor 12. Bee
The boosting power supply circuit 14 is used to generate the source voltage Von.

As shown in FIG. 2, the step-up power supply circuit 14 comprises an induction coil L, a capacitor C, a diode D for non-return, a transistor 15, a step-up control circuit 16, and the like. This boost power supply circuit 14 has a transistor 15
The on / off operation of the capacitor C causes the electric energy induced in the induction coil L to be charged to the capacitor C via the diode D when the capacitor is turned off, and the capacitor C is charged by repeating this operation. The voltage is increased to the power supply voltage Vee of the DC power supply E or higher. Then, the boosted charging voltage of the capacitor C is applied to the transistor 1
The power supply voltage is for a base current of 2.

The transistor 15 is duty-controlled by the boosting control circuit 16 so that the boosted power supply voltage (hereinafter, boosted voltage) Vin always becomes a constant voltage. That is, the boost control circuit 16 outputs the boosted voltage V at that time.
In order to detect "in", a divided voltage Vs is input from a voltage dividing circuit including resistors R1 and R2, and a predetermined reference voltage Vk is input. The reference voltage Vk is the boosted voltage Vin
Is a target voltage Vp (a target voltage for turning on the transistor 12, which is obtained by adding a base voltage Von necessary for turning on the transistor 12 and a voltage drop due to the resistor 13 connected to the base terminal. Voltage).

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, and 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.
The base current Ib determined by the difference voltage (= Vin−Vee) between the n and the power supply voltage 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. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a switching element drive circuit that can eliminate power loss and heat generation due to a resistor that determines a base current.

[0008]

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. A boosted power supply circuit that is boosted to a power supply voltage equal to or higher than a power supply voltage for a drive current of the current drive type switching element, and detects a current supplied to the current drive type switching element and outputs an output voltage proportional thereto. The gist of the present invention is that the current detector outputs a current and a boost control circuit that compares the output voltage detected by the current detector with a reference voltage and controls the switching operation of the second switching element.

[0009]

The current supplied from the boosting power supply circuit for driving the current-driven switching element having a load on the ground side is detected by the current detector, and the boosting power supply circuit is controlled by the boosting control circuit so that the current becomes constant. Control. As a result, since the current for driving the current-driven switching element is not determined by the resistor, power loss and heat generation due to the resistor can be eliminated.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. In this embodiment, the only difference from the prior art switching element driving circuit shown in FIG. 2 in the configuration is the method of determining the base current Ib of the transistor 12 in the boosting power supply circuit 14. For convenience, portions having the same configuration as in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. Only different configurations will be described.

The current detector 17 is connected between the plus side of the capacitor C, which is the output side of the boosted voltage Vin, and the base of the transistor 12, and detects the base current Ib of the transistor 12 and is proportional to it. Voltage (hereinafter, detection voltage)
Va is output to the boost control circuit 16. Boost control circuit 16
Inputs a detection voltage Va and a predetermined reference voltage Vr. The reference voltage Vr is a voltage set in advance to make the base current Ib of the transistor 12 a predetermined current (target current) Ip for turning on the transistor 12.

That is, when the detection voltage Va is smaller than the reference voltage Vr, the boost control circuit 16
Assuming that 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 is reduced to the target current Ip.
Approach. Conversely, the boost control circuit 16 detects the detection voltage V
a is greater than the reference voltage Vr, the transistor 12
Assuming that the base current Ib is larger than the target current Ip, the duty ratio of the duty control of the transistor 15 is reduced, and the boost voltage Vin is lowered to bring the base current Ib closer to the target current Ip. Therefore, the boosting power supply circuit 14 is
6 controls the base current Ib of the transistor 12 to be always equal to the target current Ip. In other words, 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 (= target current Ip).

As described above, in this embodiment, the base current Ib of the transistor 12 is used without using the base resistance.
, Power loss and heat generation due to resistance can be eliminated. Accordingly, it is not necessary to provide a means for releasing the heat generated in the resistor, for example, a gap or a radiator for circulating air for cooling the resistor, and the device can be downsized.

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 type transistor).
Any current-driven switching element such as the above may be used.

[0015]

As described above in detail, according to the present invention, there is an excellent effect that power loss and heat generation due to a resistor for determining a base current can be eliminated.

[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]

11: Load, 12: Transistor as current-driven switching element, 14: Boost power supply circuit, 15: Transistor as second switching element, 16: Boost control circuit, 17: Current detector, L: Induction coil, D … Reverse diode, C… Capacitor, E… DC power supply, Vr… Reference voltage

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-92012 (JP, A) JP-A-2-262360 (JP, A) JP-A-3-13008 (JP, A) JP-A-63- 193610 (JP, A) JP-A-4-68814 (JP, A) JP-A-62-105522 (JP, A) JP-A-2-79770 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03K 17/00-17/693 H02M 3/00-3/44

Claims (1)

(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 check diode when the electric energy induced in the induction coil is turned off when the second switching element is turned off, thereby reducing the charging voltage of the capacitor. A boosted power supply circuit that is boosted to a power supply voltage of the DC power supply or more and serves as a power supply voltage for a drive current of the current drive type switching element, and a current supplied to the current drive type switching element is detected and proportional to the detected current. A current detector that outputs an output voltage and an output voltage detected by the current detector are compared with a reference voltage. A boosting control circuit for controlling a switching operation of the second switching element.