JPH11225470A - Power circuit for driving switching element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify gate power circuit formation, by connecting diodes, resistors, and capacitors in series to the junction point between an N-channel field-effect transistor and a free wheel diode from (+) side power line, and taking the voltage charged into the capacitors as the input of a constant voltage circuit. SOLUTION: When voltage Vin is applied to input + power line 1, charging current runs through a diode D2, a resistor R1, a capacitor C2, a choke coil 7, and a capacitor C1, and constant voltage Vd is applied to a capacitor C3. When the voltage Vd is applied to the gate of a field-effect transistor 5 (FET1) through the first photo coupler 11, the FET1 is conducted so that the voltage of a reference voltage line 4 becomes Vin, and a capacitor 8 is charged through the choke coil 7 to feed current to a load. When Off voltage of 0 volt is applied, the current runs through a free wheel diode 6 to charge the capacitor 8 and supply the current to the load from output + power line 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control power supply circuit, a bridge circuit, and an inverter circuit for a battery forklift, and more particularly to a constant-voltage gate drive power supply based on the source terminal of an N-channel field effect transistor.

[0002]

2. Description of the Related Art Conventionally, as a gate drive circuit,
Some are found in -266681. According to this method, first, a constant voltage circuit must be configured. There is also a limitation on using a P-channel field effect transistor to obtain a constant voltage.

If the input voltage is higher than the withstand voltage of the above element, it cannot be used. On the other hand, some N-channel field-effect transistors have a high withstand voltage. In order to make the N-channel field effect transistor conductive, it is desired that the gate voltage is higher than the source voltage by more than ten volts.

[0004] This is because an N-channel field effect transistor connected to the (+) side power supply line and a switching element or a free wheel diode are connected in series (-).
In a switching circuit connected to a power supply line to form an arm, another constant voltage circuit is required.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power supply circuit for driving a switching element in which a constant voltage power supply for driving a gate of a field effect transistor is simplified.

[0006]

According to the present invention, a diode, a resistor, and a capacitor are connected in series from a (+) side power supply line, and the N-channel field effect transistor and the switching element are connected.
Alternatively, the capacitor is connected to a connection point of a freewheel diode, and the voltage charged in the capacitor is used as an input to the constant voltage circuit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to FIG. Input (+) power supply line 1 to field effect transistor 5
The FET 1 and the freewheel diode (D1) 6 are connected in series to the (-) power supply line 2 (hereinafter also referred to as FET).

A connection point between the field effect transistor 5 (FET1) and the freewheel diode (D1) 6 is called a reference voltage line 4. Choke coil (L1) from reference voltage line 4
7, the capacitor (C1) 8 is connected to the output (+) power line 3 and the (-) power line 2.

These circuit components constitute the main circuit of the step-down power supply circuit. A diode D2, a resistor R1, and a capacitor C2 are connected in series from an input (+) power supply line 1 and connected to a reference voltage line 4. An output of a first constant voltage circuit 9 including a transistor T1, a resistor R2, a Zener diode Z1, and a capacitor C3 is connected to a constant voltage line 10.

From the output terminal of the first photocoupler 11, a resistor R
4 is connected to the bases of the totem poles of the transistors T4 and T5. The emitters of the totem poles of the transistors T4 and T5 connected to the constant voltage line 10 and the reference voltage line 4 are connected to the gate of the field effect transistor 5 via the resistor R4.

The output side of the first photocoupler 11 is the emitter of transistors T2 and T3 forming a totem pole. When the photodiode (PD1) 12 is energized, the output voltage goes high.

The output of the second constant voltage circuit 13 comprising a transistor T6, resistors R5, R6 and a zener diode Z2 is connected to a capacitor C4 via a diode D3.

A reference voltage 16 is connected to a reference voltage terminal of an error amplifier (EA) 15 incorporated in the switching regulator element 14, and a voltage Vout of the output (+) power supply line 3 is supplied to a control terminal of the error amplifier (EA) 15. Resistance R7, R8
Is applied separately.

The output of the control system is connected to the photodiode (PD1) of the first photocoupler 11 via the resistor R9 from the emitters of the transistors T7 and T8 forming a totem pole.
12 is connected.

Next, the operation of the circuit will be described. Input (+)
A voltage Vin is applied to the power supply line 1.

A diode D2, a resistor R1, and a capacitor C
2, a charging current flows through the choke coil L1 and the capacitor C1. The capacity of the capacitor C2 is 1 of the capacitor C1.
/ 100, the voltage of the capacitor C2 is almost Vin
Becomes Further, since a load is connected in parallel with the capacitor C1, the charging current flows to the load. A constant voltage Vd is applied to the capacitor C3.

A voltage is applied to the switching regulator element 14 from the second constant voltage circuit 13, and an on / off signal is output from the output.

The driving circuit for the transistors T4 and T5 is connected to the field effect transistors 5 and F through the first photocoupler 11.
The Vd voltage or a voltage close to 0 volt is applied to the gate of ET1 as the on / off voltage.

When the ON voltage is applied, the FET 1 conducts, and the voltage of the reference voltage line 4 becomes Vin. The capacitor C2 is no longer charged. The voltage of the capacitor C3 does not change suddenly and is Vd. When the FET 1 conducts, when the capacitor (C1) 8 is charged through the choke coil (L1) 7, a current flows to the load.

When the gate voltage of the FET 1 becomes 0 volt, which is the off voltage, the current flowing through the choke coil (L1) 7 passes through the freewheel diode 6 to charge the capacitor (C1) 8 and to output ( +) Power line 3
Supply more current to the load. The voltage of the reference voltage line 4 is 0 V
, And the capacitor C2 is charged.

Next, when the FET 1 is turned on, the capacitor C
2 is supplied to the capacitor C3 via the first constant voltage circuit 9, so that the voltage Vd of the reference voltage line 4 and the constant voltage line 10 becomes substantially constant.

The output (+) power supply line 3 is connected to a capacitor C4 via a diode D4. This means that the output voltage of the second constant voltage circuit 13 is output (+) to the voltage Vout of the power supply line 3.
Keeping it lower, the second constant voltage circuit 13 operates only at the beginning of the operation. Thus, the second constant voltage circuit 13 can be configured to withstand short-time operation. That is, it can be downsized.

FIG. 2 is a diagram in which the power supply circuit of FIG. 1 is applied to a circuit having another function.

The same symbols as those in FIG. 1 have the same functions. In order to reduce the loss of the freewheel diode D1 in FIG. 1, it is replaced with a field effect transistor FET2.

The peripheral circuit 17 includes diodes D3 and D shown in FIG.
4 shows a circuit including a capacitor C4, resistors R7 and R8, and a reference voltage 16. Switching regulator element 14
From the output terminal of the photodiode P of the second photocoupler 18.
D2, and to the (-) power supply line 2 with a resistor R23. Transistors T20, T2 connected to the totem pole from the output terminal of the second photocoupler 18 via a resistor R20.
1 base.

The emitters of the transistors T20 and T21 are connected to the gate of the FET 2 via the resistor R21. A resistor R22 and a diode D20 are connected in series from the gate to the emitters of the transistors T20 and T21. Similarly, a resistor R24 and a diode D2 are connected to the gate of the FET1.
1 is connected.

FIG. 3 is a diagram for explaining the operation of FIG.

(A) shows the output voltage of the switching regulator element.

FIG. 3B shows the emitter voltages of the transistors T4 and T5.

(C) shows the emitter voltages of the transistors T20 and T21.

(D) shows the ON / OFF state of the FET1.

(E) shows the ON / OFF state of the FET2.

(B) and (c) show the first photocoupler 11 and the second
The operation delay characteristics of the photocoupler 18 are shown. Sort out those with the same characteristics. The conduction delay time is T1 and the cutoff delay time is T2
And (D) and (e) show the ON and OFF states affected by the input capacitance, gate resistance, gate voltage, and the like of FET1 and FET2.

The FET1 and the FET2 are of the same type, and the gate voltages are set to the same value. The interruption time T4 is set shorter than the conduction delay time T3. The resistances R4 and R4 are set so that the value of (T1 + T3) becomes larger than (T2 + T4).
24, R21 and R22 are set. FET1, FET2
Can be prevented from being turned on at the same time, and the loss can be reduced by conducting the FET2.

FIG. 4 shows an example in which the present invention is applied to a motor control device.

Field effect transistors FET1, FET
2, a motor 19 is connected to a bridge circuit using FET3 and FET4, and ON / OFF is controlled by a control circuit 20. The same symbols as those in FIG. 1 perform the same operation.

The electric motor 19 is driven by keeping the FET 3 conductive and turning the FET 2 on and off. In this case, the loss can be reduced when the circulating current is flowing by turning on and off the FET1 in the reverse direction of the FET2. The gate drive power supply according to the present invention is also useful when an AC motor is driven by an inverter. The switching element described above can be applied not only to a field effect transistor but also to a transistor and an IGBT.

[0038]

As described above, according to the present invention, the gate power supply circuit of the N-channel field effect transistor connected to the (+) side of the power supply line can have a simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a gate power supply circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an application example to which the invention of FIG. 1 is applied.

FIG. 3 is a characteristic diagram for explaining the operation of FIG. 2;

FIG. 4 is a circuit diagram of a motor control device showing an application example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input (+) power line, 2 ... (-) power line, 3 ... Output (+) power line, 4 ... Reference voltage line, 5 ... Field effect transistor, 6 ... Freewheel diode, 7 ... Choke coil, 8 ... Capacitor, 9 first constant voltage circuit, 10 constant voltage line, 11 first photocoupler, 13 second constant voltage circuit, 14 switching regulator element, 15 error amplifier, 16 reference voltage, 17 peripheral Circuit, 18: second photocoupler, 19: electric motor, 20: control circuit.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hideo Toyoda 2520 Ojitakaba, Hitachinaka-shi, Ibaraki Co., Ltd.Automotive Equipment Division, Hitachi, Ltd. Hitachi, Ltd. Automotive Equipment Division

Claims (2)

[Claims] An N-channel field-effect transistor connected to an input (+) power supply line and a switching element or a freewheel diode are connected in series and connected to a (-) power supply line to form an arm. +) A diode, a resistor, and a capacitor are connected in series from a power supply line, and connected to the connection point of the N-channel field-effect transistor and the switching element or the freewheel diode, and the electric charge charged in the capacitor is passed through a constant voltage circuit. A power supply circuit for driving a switching element, wherein the power supply circuit is a gate drive power supply for the N-channel field effect transistor. 2. The switching element according to claim 1, wherein each of the switching elements constituting the arm is constituted by each of the driving circuits having the same delay characteristic via each of the photocouplers for controlling the output of the totem pole for control by a high level signal and a low level signal. A power supply circuit for driving a switching element, which is applied to a gate of the switching element.