JPH05168246A - Field effect transistor switching drive circuit in high-frequency inverter - Google Patents

Abstract

PURPOSE:To enable a duty ratio to be controlled freely without any limitation while suppressing a gate drive power in a drive circuit of a high-frequency inverter which is constituted by a field effect transistor. CONSTITUTION:A high-frequency source e1 and a DC voltage source ES1 in nearly sinusoidal wave shape are connected between a gate and a source of a field effect transistor Q1 in series and then the field effect transistor Q1 is driven by a signal which is obtained by subtracting a voltage ES of a DC voltage source ES1 from an instantaneous voltage (e) of a high-frequency source e1. The field effect transistor Q1 is switched within a section where a value of the drive signal exceeds a threshold between the gate and the source. Since inclination of the drive signal to an area between the gate and the source is nearly in sinusoidal wave shape, the gate drive power can be suppressed.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field effect transistor switching drive circuit in a high frequency inverter.

2. Description of the Related Art Conventionally, as a circuit for high-frequency switching a field effect transistor, a circuit driven by a rectangular wave is generally used. However, when the frequency is high and several megahertz, the gate-source capacitance (input capacitance Ciss) cannot be ignored, and the invalid drive power that charges the gate-source capacitance increases, making it difficult to operate. The drive circuit comes to be used.
However, if the field-effect transistor is driven by a sine wave, the pulse width is determined by the section exceeding the threshold value of the field-effect transistor and is a sine wave.
The duty ratio is fixed at almost 50%,
The pulse width cannot be changed. Especially in so-called voltage inverters, there is a problem that the down time is required for the signals of the field effect transistors in the upper and lower arms.

SUMMARY OF THE INVENTION The present invention provides a drive circuit for a high-frequency inverter composed of field effect transistors, in which the duty ratio can be freely varied without restriction while suppressing the gate drive power. Is an issue.

In order to solve such a problem, the present invention provides a high-frequency source e1 having a substantially sinusoidal waveform and a shift voltage between a gate and a source of a field effect transistor Q1, as shown in FIG. Connect the supply circuit ES1 in series,
The field effect transistor Q1 is generated by the signal obtained by subtracting the voltage ES of the shift voltage supply circuit ES1 from the instantaneous voltage e of the high-frequency source e1.
To drive.

As shown in FIG. 2, the field-effect transistor Q1 switches in the section in which the value of the gate-source voltage Vgs of the field-effect transistor Q1 exceeds the threshold value. Since the slope of the drive signal between the gate and the source is substantially sinusoidal, the gate drive power can be suppressed. By selecting the value of the voltage ES of the shift voltage supply circuit ES1 circuit,
It is possible to freely change the duty ratio beyond the limit of 50%. The duty ratio can be varied from 50% to 100% by reversing the polarity of the shift voltage Es.

FIG. 3 shows an embodiment of a field effect transistor switching drive circuit in a high frequency inverter according to the present invention. In FIG. 3, four field effect transistors
Q1, Q2, Q3 and Q4 form a bridge inverter circuit, which receives the DC power supply E1 and converts it to a high frequency of 2 MHz and supplies it to the load RL. Between the gate and source of each field effect transistor Q1, Q2, Q3, Q4, a sine wave voltage and a shift DC voltage are connected via resistors R1, R2, R3, R4 and capacitors C1, C2, C3, C4, respectively. Is applied. Regarding the sine wave voltage, from the high frequency sine wave voltage source e1 connected to the primary winding n1 of the transformer T1 to the respective secondary windings n21, n22, n23, n24
Then, high frequency is supplied to each gate circuit.
Regarding the shift DC voltage, each gate circuit is insulated from each other by the shift voltage supply circuit ES1, and DC voltages of approximately equal value are supplied in parallel to the capacitors C1, C2, C3, and C4, respectively. Explaining the configuration of the shift voltage supply circuit ES1, first, the DC power supply E100 is kept at a DC voltage having a variable set value by the variable voltage stabilizing circuit U108. This set value is determined by the selection of the resistor R106 and the variable resistor R107. On the other hand, the pulse generation circuit U104 drives the field effect transistor Q101 via the resistors R102 and R103 to repeat ON / OFF. At this time, the intermittent wave of the voltage corresponding to the output setting voltage of the voltage stabilizing circuit U108 is applied to each primary winding of the transformers T11, T12, T13, T14. And transformers T11, T12, T13, T14 each 2
Rectification diodes D11, D12, D13, D1 connected to the secondary winding
By using 4 and the smoothing capacitors C11, C12, C13, and C14, DC voltages of approximately the same value can be obtained. These DC voltages are isolated from each other and supplied in parallel to capacitors C1, C2, C3, and C4. Next, the operation of this embodiment will be described. The gate-source voltages Vgs (Q1, Q4) of the field effect transistors Q1 and Q4 have waveforms of the same phase as shown in FIG. The line that exceeds the voltage shifted from the broken line in the figure has a zero potential, and the field-effect transistors Q1 and Q4
And turn on. Similarly, for field effect transistors Q2 and Q3, field effect transistors Q2 and Q3 are turned on only during interval t3. Field effect transistors Q1 and Q4
As shown in FIG. 4, there is a section t2 between a section t1 in which and are turned on and a section t3 in which the field effect transistors Q2 and Q3 are turned on, and none of the field effect transistors is turned on in this section. Keep a so-called rest section. Further, a section t4 in which none of the field effect transistors is turned on exists between the section t3 and the section corresponding to the section t1 of the next cycle. The time width of these rest periods t2 and t4 can be freely selected by selecting the value of the shift voltage. The configuration of the shift voltage generating circuit ES1 in FIG. 3 is an example, and other configurations may be used as long as they are insulated from each other and voltages having substantially equal values are obtained. For example, the transformers T11, T12, T13, and T14 can be made into one primary winding and four secondary windings by one iron core. Further, even if the voltage stabilizing circuit U108 is not provided, it is possible to change the shift voltage of each four sets by changing the gate signal pulse width of the field effect transistor Q101.

Since the present invention has the above-mentioned characteristics, the duty ratio can be freely changed without restriction in the drive circuit of the high frequency inverter constituted by the field effect transistor while suppressing the gate drive power. it can.

[Brief description of drawings]

FIG. 1 is a principle diagram of a switching drive circuit of a field effect transistor according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the circuit shown in FIG.

FIG. 3 is an embodiment of a field effect transistor switching drive circuit in a high frequency inverter according to the present invention.

FIG. 4 is a waveform diagram for explaining the operation of the circuit shown in FIG.

[Explanation of symbols]

 E1 ... DC power supply Q1, Q2, Q3, Q4 ... Field-effect transistors R1, R2, R3, R4 ... Resistors C1, C2, C3, C4 ... Capacitor RL ... Load ES1 ... Shift voltage supply circuit e1 ... Sine wave voltage source T1 … Transformer T11, T12, T13, T14… Transformer D11, D12, D13, D14… Diode C11, C12, C13, C14… Capacitor E100… DC power supply Q101… Field effect transistor R102, R103, R106… Resistor U104… Pulse generator circuit C105… Capacitor R107… Variable resistor U108… Variable voltage stabilization circuit

Claims (1)

[Claims] 1. A high frequency source having a substantially sinusoidal waveform and a shift voltage supply circuit are connected in series between a gate and a source of a field effect transistor, and a voltage of the shift voltage supply circuit is changed from an instantaneous voltage of the high frequency source. A field effect transistor switching drive circuit in a high frequency inverter, characterized in that the field effect transistor is driven by the subtracted signal.