JPH0350902A - Field effect transistor amplifier - Google Patents

Abstract

PURPOSE:To reduce the number of components and to miniaturize an amplifier including an alarm circuit by inserting a common voltage application point and a fixed power supply voltage terminal and detecting a voltage at the common voltage application point to a power voltage current setting circuit being one terminal of the resistor. CONSTITUTION:A drain common voltage source terminal 5 of an automatic bias circuit 3 being a transistor(TR) common voltage current setting circuit and a bias circuit and a voltage terminal 7 of a stabilized power supply 6 are interconnected by a resistor 8, and a resistor 10 and two diodes 11, 12 branched into two ways are connected between the terminal 5 and a voltage comparator 9 to monitor the voltage at the terminal 5. Moreover, as the mechanism of alarm detection, a voltage drop of a stabilized voltage at the terminal 5 is changed by a change in the current sum of drain currents of each stage flowing to the resistor 8 in two fault modes of short-circuit and opening between electrodes of one FET or over. Thus, a fault is detected by utilizing a change in a voltage VR of the resistor.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an alarm device for an amplifier configured by connecting field effect transistors in multiple stages, and in particular to an alarm device for detecting amplifier failure due to breakdown between electrodes of field effect transistors. Regarding circuit configuration.

[Prior Art] As shown in FIGS. 2(a) and 2(b), a conventional alarm circuit of this type includes a resistor 10 and its terminal connected to the drain terminal 13 of each field effect transistor 1 connected in multiple stages. Two diodes 11 and 12 having directions in both directions are connected, and furthermore, all branch lines by these diodes are grouped together for each diode direction and then led to the voltage comparator 9.

As a result, when the field effect transistor 1 is destroyed, the output state of the voltage comparator 9 changes and drives the drive circuit 14 of the alarm indicator 15 to display an alarm on the alarm indicator 15, or By driving the system switching device 16, switching from the working amplification system to the standby system was performed.

Generally, the failure mode of a field effect transistor is considered to be a short circuit or an open circuit between the electrodes of the field effect transistor, and an alarm can be output by using the accompanying voltage fluctuation at the drain terminal 13 on the field effect transistor side.

The correspondence between each failure mode and drain voltage VDS is as follows:
Regardless of the selection of two types of field effect transistor power supply voltage/current setting circuits, the conventional auto bias circuit 3 shown in FIG. 2(a) and the conventional bias circuit 4 shown in FIG. 2(b), both Both trends are as follows.

According to the conventional example shown in FIGS. 2(a) and 2(b), a VDS window is set by giving two voltage comparison values to the voltage comparator 9, one on the high voltage side and one on the high voltage side. An alarm is output if the VDS of one or more field effect transistors deviates from this window due to the causes mentioned above.

For example, when VDS changes above the high-voltage threshold due to the above-mentioned failure mode, the diode 11 turns on, and the voltage at the input terminal 17 of the voltage comparator 9 connected to it rises, causing the given voltage to rise. As a result of the comparison with the comparison value obtained, the output of the output terminal 19 is inverted,
The drive circuit 14 is driven.

Conversely, when VDS changes below the low voltage threshold, the diode 12 turns on.
Similarly, an alarm is output after a comparison is made based on the voltage drop at the input terminal 18 of the voltage comparator 9 connected thereto.

[Problems to be Solved by the Invention] In the conventional field effect transistor amplifier described above, when considering a field effect transistor amplifier with multistage connection,
In proportion to the number of field-effect transistor stages, the number of alarm voltage lead-out wiring from the drain terminal of the field-effect transistor, the number of resistors, and the number of diodes are required, which increases the number of parts and requires amplification, power supply, and alarm circuits. When constructed on a microstrip substrate, there is a problem in that a complex state of circuitry occurs in combination with the field effect transistor power supply voltage/current setting circuit, and the wiring becomes complicated.

[Means for Solving the Problems] The present invention has been made in view of the above problems, and aims to significantly reduce the number of parts, simplify circuit wiring, and downsize the amplifier itself including the alarm circuit. In order to achieve this purpose, in a field effect transistor amplifier in which field effect transistors as amplifying elements are connected in multiple stages, a common power supply voltage and current setting circuit is provided for all field effect transistors. After inserting a resistor between the common voltage application point for creating the drain-side power supply voltage and current that is applied to the drain side and the stabilized fixed power supply voltage terminal, connect it to one end of the resistor, which is the power supply voltage and current setting circuit. The device is configured to detect a failure of one or more field effect transistors by detecting a voltage at a common voltage application point.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIGS. 1(a) and 1(b) are block diagrams showing one embodiment of a field effect transistor amplifier according to the present invention.

Here, FIG. 1(a) uses an auto-bias circuit 3 characterized in that VGS changes so as to maintain the set values of VDS and IDS as a field-effect transistor voltage/current setting circuit. Figure 1 and (b) are
Similarly, as auto bias circuit 3, VGS setting
This is an example in which a bias circuit 4 fixed to VGS is used to control DS and IDS.

According to FIG. 1, the drain-side common voltage source terminal 5 and the stabilized power source 6 are connected to the auto-bias circuit 3 and the bias circuit 4, both of which are field-effect transistor voltage and current setting circuits. A resistor 8 is connected to the voltage terminal 7, and a resistor 10 and two diodes 11 and 12 branched in both directions are connected between the voltage and current setting circuit side terminal 5 of the resistor 8 and the voltage comparator 9. The voltage at terminal 5 is monitored by connecting .

The alarm detection mechanism in this embodiment is as follows:
For two failure modes: short-circuit or open circuit between the electrodes of the field-effect transistor, the regulated voltage at terminal 5 changes by changing the total current I total of the drain current IDS of each stage flowing through resistor 8. V reg
The voltage drop against the voltage also varies.

Therefore, a failure can be detected by using fluctuations in the resistor end voltage VR (terminal voltage at terminal 5), and the total current r of each failure mode and drain current IDS at that time
The correspondence between total and resistor end voltage VR tends to be as shown below in both FIGS. 1(a) and 1(b).

In this embodiment, as in the conventional example, the change in voltage VR due to the above-mentioned failure is detected by a combination of a resistor 10, bidirectional diodes 11 and 12, and a voltage comparator 9. A voltage V consisting of two voltage comparison values on the high voltage side and low voltage side for the device 9
By setting a window of R, an alarm will be output if the voltage VR is outside this window.

When compared with conventional methods, the basic fault detection method for both methods is to detect voltage fluctuations at any point on the drain side power supply circuit caused by drain side current changes due to field effect transistor failure modes. but,
In the present invention, the voltage fluctuation detection point is collectively provided on the common voltage source side of each field effect transistor voltage/current setting circuit by adding the resistor 8 shown in FIG. Compared to the detection method in which voltage monitor lines are drawn out from each voltage terminal, when multistage connection of field effect transistors is assumed, the number of components related to resistors and diodes can be significantly reduced, the circuit wiring can be simplified, and the alarm circuit can be included. The amplifier itself can be made smaller.

[Effects of the Invention] As explained above, the present invention provides a field effect transistor amplifier in which field effect transistors serving as amplifying elements are connected in cascade in multiple stages, in which all individual power supply voltage and current settings provided for the field effect transistors are adjusted. After inserting a resistor between the common voltage application point for creating the drain side power supply voltage and current that is commonly applied to the circuit and the stabilized fixed power supply voltage end, the power supply voltage and current at one end of the resistance are inserted. By detecting the voltage at the common voltage application point to the setting circuit, 1
Since the present invention is configured to detect a failure of one or more field effect transistors, it is possible to significantly reduce the number of parts, simplify circuit wiring, and downsize the amplifier itself including the alarm circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a field effect transistor amplifier according to the present invention, and FIG. 2 is a block diagram showing a conventional field effect transistor amplifier. Field effect transistor DC cut capacitor Auto bias circuit Bias circuit terminal Stabilized power supply voltage terminal Resistor 10 1 2 3 4 5 6 7 8 9 Voltage comparator Resistor Diode Diode Drain terminal Drive circuit Alarm indicator Working/standby system switch input terminal Input terminal output terminal

Claims (1)

[Claims] In a field effect transistor amplifier in which field effect transistors as amplifying elements are connected in multi-stage cascade, a drain side power supply voltage current is created which is commonly applied to all individual power supply voltage and current setting circuits provided for the field effect transistors. A resistor is inserted between the common voltage application point for the power supply and the stabilized fixed power supply voltage terminal, and the voltage at one end of the resistor, which is the common voltage application point to the power supply voltage and current setting circuit, is detected. A field effect transistor amplifier characterized in that a failure of one or more field effect transistors is detected by: