JPH0525812U - Transistor drive circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To enable the use of transistors with low gate-drain breakdown voltage, and to deactivate them when the gate matching circuit is short-circuited. A bias circuit B including voltage dividing resistors 2a and 2b for setting a gate bias voltage of a transistor 5, a gate matching circuit 3 connected between the gate and source of the transistor 5 and the bias circuit B, and the transistor 5 And a capacitor 11 connected between the source and the gate matching circuit 3 and the ground, and a source bias voltage for controlling the operation / non-operation of the transistor 5 is input to the source bias input terminal 10. To do.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a transistor drive circuit that ensures the operation of a transistor such as a field effect transistor.

[0002]

[Prior Art]

 FIG. 2 is a circuit diagram showing a conventional drive circuit for a field effect transistor. In the figure, 1 is a gate bias input terminal, 2a and 2b are gate bias voltage dividing resistors, and these constitute a bias circuit B. To do. 3 is a gate matching circuit for preventing a signal from flowing into the bias circuit, 4 is a signal input, 5 is an electric field transistor (FET) as a transistor, 6 is a drain matching circuit connected to the drain of the field effect transistor 5, Reference numeral 7 is a drain bias input terminal, 8 is a DC cut capacitor, and 9 is a signal output terminal.

Next, the operation will be described. First, a gate bias voltage is applied to the gate bias input terminal 1, and the gate bias voltage is divided by the resistors 2a and 2b and supplied to the gate of the field effect transistor 5 via the gate matching circuit 3. Under such a general bias condition of the field-effect transistor 5, a positive voltage is applied as a drain bias and a negative voltage is applied as a gate bias. The state will be determined by the voltage applied as the gate bias.

Therefore, by applying an appropriate negative voltage to the gate of the field effect transistor 5, the field effect transistor 5 is activated, while by applying a gate bias voltage lower than the pinch-off voltage, the field effect transistor 5 is operated. The transistor 5 becomes non-operating.

[0005]

Since the conventional drive circuit of the field effect transistor is configured as described above, the field effect transistor 5 having a low gate-drain breakdown voltage of the field effect transistor 5 is easily broken. If the gate matching circuit is destroyed for some reason and the gate and source are short-circuited, 0 potential (ground potential) is always applied to the gate, and the field effect transistor is always in the operating state. As a result, there is a problem that the field-effect transistor 5 itself and surrounding circuits are adversely affected.

The present invention has been made in order to solve the above problems, and a transistor having a low breakdown voltage between the gate and the drain can be used, and the transistor does not operate even when the gate matching circuit is short-circuited. The purpose is to obtain a transistor drive circuit that can be brought into a state.

[0007]

[Means for Solving the Problems]

 A transistor drive circuit according to the present invention comprises a bias circuit composed of a voltage dividing resistor for setting a gate bias voltage of the transistor, a gate matching circuit connected between the gate and source of the transistor, and a bias circuit, and a transistor of the transistor. A capacitor connected between the connection point of the source and gate matching circuits and ground is provided, and the source bias voltage for controlling the operation / non-operation of the above transistor is input to the source bias input terminal. Is.

[0008]

[Action]

 The capacitor in this device is inserted between the source of the transistor and the ground, and the source bias to the connection point between the capacitor and the source of the transistor drives the transistor, thereby reducing the withstand voltage of the field effect transistor. It enables use, and when the gate matching circuit is destroyed, it keeps the transistor inactive to prevent the abnormal operation from affecting the peripheral circuits.

[0009]

【Example】

 Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a gate bias input terminal, 2a and 2b are resistors for dividing a gate bias voltage, and these constitute a bias circuit B. 3 is a gate matching circuit for preventing a signal from flowing into the bias circuit B, 4 is a signal input, 5 is an electric field transistor (FET) as a transistor, and 6 is a drain matching connected to the drain of the field effect transistor 5. A circuit, 7 is a drain bias input terminal, 8 is a DC cut capacitor, and 9 is a signal output terminal.

Further, 10 is a source bias input terminal for inputting a source bias voltage, 11 is a gate matching circuit 3, a source of the field effect transistor 5 and a connection point between the source and source bias input terminal 10 and the ground. Is a capacitor connected to.

Next, the operation will be described. First, the voltage applied to the gate bias input terminal 1 is divided by the voltage dividing resistors 2a and 2b, and the divided voltage is supplied to the gate of the field effect transistor 5 at an appropriate level through the gate matching circuit 3. To be done. On the other hand, the voltage applied to the drain bias input terminal 7 is supplied to the drain of the field effect transistor 5 through the drain matching circuit 6.

The operating state and non-operating state of the field effect transistor 5 are determined by the voltage applied from the source bias input terminal 10. That is, when the voltage of the source bias input terminal 10 is 0 volt, the field effect transistor 5 is in the operating state, and when a voltage such that the drain and source potentials of the field effect transistor 5 are equalized is applied, Inactive state. Therefore, in this drive circuit, even if the potential difference between the drain and the gate is always set to a constant value, it is possible to create an operating / non-operating mode by adjusting the potential of the source bias, so that the breakdown voltage between the gate and drain is It becomes possible to use the field effect transistor 5 having a low value.

Further, even if the gate matching circuit 3 is destroyed for some reason and becomes short-circuited, by applying a source bias voltage equal to the potential of the drain to the source insulated from the ground side by the capacitor 11. The field-effect transistor 5 can be made inoperative, and the influence of abnormal operation of the field-effect transistor 5 on the peripheral circuits can be prevented.

Example 2. Although the NPN type field effect transistor 5 is used in the above embodiment, it may be a PNP type field effect transistor, or the field effect transistor may be replaced with a transistor. Therefore, the same effect as that of the above-described embodiment can be obtained.

[0015]

[Effect of the device]

 As described above, according to the present invention, the bias circuit including the voltage dividing resistor for setting the gate bias voltage of the transistor, the gate matching circuit connected between the gate and source of the transistor, and the bias circuit, Provide a capacitor connected between the connection point of the transistor source and gate matching circuit and the ground, and input the source bias voltage that controls the operation / non-operation of the transistor to the source bias input terminal. Since it is configured, it is possible to drive a transistor with low withstand voltage, and even if the gate matching circuit is destroyed, the inactive state of the transistor can be easily obtained, so that the failure ripple to the peripheral circuits can be ensured. There is an effect that can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a drive circuit of a field effect transistor according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional drive circuit for a field effect transistor.

[Explanation of symbols]

 2a, 2b voltage dividing resistor B bias circuit 3 gate matching circuit 5 field effect transistor (transistor) 10 source bias input terminal 11 capacitor

Claims (1)

[Scope of utility model registration request] 1. A bias circuit including a voltage dividing resistor for setting a gate bias voltage of the transistor, and a gate and a source of the transistor so as to prevent a signal input to the gate of the transistor from flowing into the bias circuit. And a gate matching circuit connected between the bias circuits, a capacitor connected between the connection point of the source and gate matching circuits of the transistor and the ground, and a source bias voltage input for controlling the operation / non-operation of the transistor. Drive circuit with a source bias input terminal for.