JPH0648977Y2 - Bias power supply circuit for static induction transistor - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a SIT bias power supply circuit for a linear amplification circuit using an electrostatic induction transistor (hereinafter abbreviated as SIT).

[Conventional technology]

In-vehicle amplifiers that do not receive commercial power from the power source, or amplifiers that use a gasoline engine generator as the power source, are used as unstable power sources. Conventionally used SIT
As shown in the example of the block diagram of FIG. 3, the amplifier using the + B power source 5 which is the output of the rectifying and smoothing circuit 11 is not sufficiently stabilized, and the fixed bias circuit 12 as the bias of the amplifier is an AC power source. 1 is rectified. SIT4 drain-source voltage V used in these amplifiers
The relationship between _DS and the current is + B power supply 5 for drain between the gate and the source as shown in the characteristic curve diagram of FIG.
Separately from the above, the source gate voltage V _SG is applied as a bias. The operating point of the amplifier changes to class A, class B, or class AB depending on the value of the voltage V _SG applied, and the drain voltage is blocked with respect to the voltage V _DS , that is, the amplifier is different. As is clear from this figure, when the voltage V _SG is -5 volts and -1
In the case of 5 volts, the amplifier will be different.

In the circuit for obtaining the bias voltage from the AC power supply 1 as shown in FIG. 3, when the AC voltage 1 rises, the + B power supply 5 also rises, and when the bias voltage also rises, the voltage amplification factor μ
Is It is represented by. In order to reduce this change, a transistor 6 and a constant voltage diode 7 are conventionally included as shown in FIG.
A bias circuit in which the voltage changes according to the change in the DC voltage output from the rectifier 3 is also used.

[Problems to be solved by the invention]

However, in the conventional bias circuit shown in FIG. 5, when the AC power supply 1 becomes lower than the rated voltage, that is, when it is reduced to 90 V or less, the bias voltage is reduced together with the + B voltage 5, and the voltage amplifier operates in a small size. To do.
Because, as shown in FIG. 4, the voltage amplification factor μ of SIT
Will be amplified in a small place. For example, V _SG is -30V
From μ to −25 V, μ changes from 13.3 to 12.0,
The B voltage 5 cannot be blocked. Therefore, the drain voltage cannot be blocked, the drain current from the + B power source 5 becomes large, and finally the SIT 4 is damaged, so that the AC power source 1 decreases, which is also dangerous.

[Means for solving problems]

The present invention eliminates the above-mentioned drawbacks of the prior art, and outputs a + B power source (5) for drain required for the electrostatic induction transistor (4) by using a DC voltage (V _DC ) rectified and smoothed from the AC power source (1). A power supply circuit having B power supply circuit means (1) and bias power supply circuit means for outputting a bias voltage (V _G ) for a gate, wherein the bias power supply circuit means changes the voltage in accordance with the change in the DC voltage. A variable voltage circuit for bias (8), a constant voltage circuit for bias (9) for converting the DC voltage into a constant voltage capable of voltage adjustment, and outputting the constant voltage.
The outputs of the two voltage circuits are connected to the backflow prevention diodes (71, 7
2) and a means for connecting, and the connecting point (Q)
Is a bias power supply circuit for an electrostatic induction transistor in which an output passing through is the bias voltage.

[Action]

In order to prevent the amplification factor from greatly changing in accordance with the change in the bias voltage of the base, another bias constant voltage circuit is provided to keep the bias voltage constant, and the amplifier is designed so that the bias voltage does not drop below a certain fixed value. Operate stably.

〔Example〕

An embodiment of the SIT bias power supply circuit of the present invention is shown in the circuit diagram of FIG.

As shown in the drawing, the input from the AC power supply 1 becomes a DC voltage V _DC of a specified voltage in a rectifying / smoothing circuit 11 including a transformer 2 and a rectifier 3. This DC voltage V _DC is applied to the bias voltage changing circuit 8. This bias voltage changing circuit 8
Is the same as in the conventional case of FIG.
And a constant voltage diode 7, and the voltage changes according to the change of the DC voltage. Further, a bias constant voltage circuit 9 in which a voltage is supplied to the gate of SIT4 is obtained by branching the DC voltage V _DC and including a transistor 6'and a constant voltage diode 7 '. The variable voltage circuit for bias 8 and the constant voltage circuit for bias 9 are connected to each other with the diode 71 and the diode coupling point Q interposed therebetween to prevent the flow of current between the circuits. The bias voltage can be changed by the variable resistor 10 in the bias constant voltage circuit 9. + B
The power supply 5 is obtained by taking a part of the output of the rectifying / smoothing circuit 11 or by taking the same AC power supply from another rectifying / smoothing circuit (11) as shown in FIG. 3 of the conventional example.

By using the circuit according to the present invention, as shown in FIG. 2, for example, the AC voltage V _AC is 9 V depending on the relationship between the AC voltage V _AC of the _AC power source 1 and the gate bias voltage V _G.
The gate bias voltage V _G is almost constant even at 0 V or less. The thick solid line shown in (8) here indicates the output of the bias variable voltage circuit 8, and the thick broken line shown in (9) shows the output of the bias constant voltage circuit 9. Therefore, there is no danger of an excessive current flowing due to a change in the bias voltage V _G , and the operating point of the amplifier is from class AB to class C, but the AC voltage V _AC is 7
It can handle voltage fluctuations of 0 V or less.

[Effect of device]

As described above, according to the present invention, by providing the bias constant voltage circuit 9 in parallel with the bias variable voltage circuit 8 and further providing the diodes 71 and 72 for preventing backflow, the + B power source 5 is stabilized. Even when the voltage is not applied, the amplifier operates safely, and a large power amplifier such as SIT can be made low cost and light weight.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a bias power supply circuit for SIT according to the present invention, FIG. 2 is a characteristic curve diagram showing a relation between a bias voltage of a gate and a change of AC voltage by the circuit of FIG. 1, FIG. Is a block diagram of an example of a conventional bias circuit, FIG. 4 is a characteristic curve diagram showing a change of current with respect to a change of drain-source voltage of SIT with a bias voltage as a parameter, and FIG. 5 is an example of a conventional bias circuit. It is a circuit diagram which shows a part. In addition, 1: AC power supply, 2: Transformer, 3: Rectifier, 4: SIT, 5: + B
Power supply, 6,6 ': Transistor, 7,7': Voltage regulator diode, 7
1, 72: diode, 8: variable voltage circuit for bias, 9: constant voltage circuit for bias, 10: variable resistor, 11: rectifying / smoothing circuit, 12: fixed bias circuit.

Claims (1)

[Scope of utility model registration request] 1. A B power supply circuit means for outputting a drain + B power supply necessary for an electrostatic induction transistor by using a DC voltage obtained by rectifying and smoothing an AC power supply, and a bias power supply circuit means for outputting a bias voltage for a gate. In the power supply circuit, the bias power supply circuit means converts the DC voltage into a variable voltage circuit for bias (8) in which the voltage changes in accordance with the change in the DC voltage, and outputs the DC voltage converted into a constant voltage that can be adjusted. A bias constant voltage circuit (9) and means for coupling the outputs of the two voltage circuits via the respective backflow blocking diodes (71, 72) are provided, and the output passing through the coupling point (Q) is Bias power supply circuit for static induction transistor with bias voltage.