JPH0722863A - Current limiting circuit - Google Patents

Abstract

PURPOSE:To prevent the distortion like a spike generated by the condition of a load connected to an amifier by cascoding voltage level shift elements and limiting VBE of an output transistor TR to a certain value. CONSTITUTION:Collector currents of TRs TR7 and TR8 are outputted by currents of resistors R1 and R2 between emitters and bases of TRs TR5 and TR6 constituting the amplifier where TRs TR5 and TR7 and TRs TR6 and TR8 are cascoded from both ends of resistors R1 and R2. Currents of resistor R1 and R2 are detected by TRs TR3 to TR6 and are current-converted by TRs TR7 and TR8 to turn on TRs TR9 and TR10 through resistors R5 and R6, and VBEs of output TRs TR1 and TR2 are limited by diodes D1 and D2 and TRs TR9 and TR10 to limit the emitter currents of output TRs TR1 and TR2 to a certain value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier current limiting circuit.

[0002]

2. Description of the Related Art As shown in FIG. 3, the current limit of the final-stage element of an amplifier in a conventional power amplifier or the like is normally detected by detecting the voltage across the emitter resistors R1 and R2 of the final-stage element and detecting the transistor TR3. , TR4 is turned on and output transistor TR
The bases of 1 and TR2 and the output terminals are short-circuited via the diodes D1 and D2, respectively, to limit the output currents of the transistors TR1 and TR2 of the final stage element.

[0003]

The current flowing through the emitter resistors R1 and R2 greatly changes when the output transistors TR1 and TR2 are turned on and off when the final stage element of the power amplifier is in the class B amplification operation. The counter electromotive force is generated by the inductance of the resistor and the inductance of the printed circuit board, etc., and a spike-like voltage is generated across the resistors R1 and R2. This distortion is the same as the switching distortion and crossover distortion of the output transistors TR1 and TR2, and is hidden as a factor of deterioration of the amplifier distortion.

[0004]

Therefore, according to the present invention, a circuit for limiting a current of a power amplification element of a power amplifier has a voltage level shift element connected in series with the power amplification element,
The voltage level shift element is cascode-connected, the current flowing through the voltage level shift circuit element is detected, and the base current of the output transistor is limited to limit VBE or VGS of the power amplification element to a constant value. It is a current limiting circuit that limits the current.

[0005]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. The emitters of the output transistors TR1 and TR2 having different polarities are connected to the load RL.

Circuits of level shift elements connected in series are connected to the collectors of the output transistors TR1 and TR2, respectively, and the signal inputs to the bases of the output transistors TR1 and TR2 are a capacitor C1 and bias constant current sources A1 and A2.
Are respectively connected to the power sources + Vcc1 and -Vcc1.

In the circuit of the level shift element, the collectors of the output transistors TR1 and TR2 are connected to the emitters of the transistors TR3 and TR4 via resistors R1 and R2, respectively.
The bases of the transistors TR3 and TR4 are connected to the power supplies + Vcc3 and -Vcc3 via the biasing constant current sources A3 and A4, respectively, and the collectors are connected to the power supplies + Vcc2 and -Vcc2,
The transistors TR3 and TR4 are biased in the ON state.

Transistors TR7 and TR2 are connected between the emitters and bases of TR5 and TR6, which form a cascode-connected amplifier of transistors TR5 and TR7 and TR6 and TR8, from both ends of the resistors R1 and R2. , TR8 collector current is output.

The emitters of the transistors TR7 and TR8 are connected to the power supplies + Vcc2 and -Vcc2, respectively, and the collectors of the transistors TR5 and TR6 are connected to the transistor TR, respectively.
The bases of 7 and TR8 are connected and also connected to the power sources + Vcc2 and -Vcc2 via resistors R3 and R4, respectively.

The emitters of the transistors TR7 and TR8 are connected to the power sources + Vcc2 and -Vcc2, respectively, and the collectors are connected to the transistors TR9 and TR1 via the resistors R5 and R6, respectively.
Connected to the base of 0, the collectors of the transistors TR9 and TR10 are respectively connected to the bases of the output transistors TR1 and TR2 via the diodes D1 and D2. The emitters of the transistors TR9 and TR10 are both connected to the emitters of the output transistors TR1 and TR2.

Therefore, the currents flowing through the resistors R1 and R2 incorporated as level shift elements are detected by the transistor detection transistors TR5 and TR6, and the transistors TR7 and T7 are detected.
After converting the current by R8, the transistors TR9 and TR10 are turned on via the resistors R5 and R6, respectively, and the VBE of the output transistors TR1 and TR2 is limited by the diodes D1 and D2 and the transistors TR9 and TR10.
1, Limit the emitter current of TR2 to a constant value.

FIG. 2 is a circuit diagram showing another embodiment of the present invention. A part of the cascode connection is different from that of FIG.

Since the emitter of the output transistor and the load are directly coupled without using the emitter resistance used in the conventional circuit shown in FIG. 3, the internal resistance of the amplifier is low both statically and dynamically. Yes, you can get feedback (not shown,
A stable output signal can be obtained regardless of (without).

Therefore, it is possible to provide a high-performance amplifier with low distortion, without generation of spike-like distortion due to back electromotive force caused by wiring conditions of the output line of the amplifier.

[0015]

According to the present invention, since the voltage level shift element is cascode-connected and the VBE of the output transistor is limited to be constant, spike-like distortion caused by the load condition connected to the amplifier can be prevented. It is possible to obtain a current limiting circuit whose operation is stable.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a diagram showing a conventional circuit.

[Explanation of symbols]

 TR1 ~ 10 Transistor D1,2 Diode R1 ~ R6 Resistance

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[Procedure amendment]

[Submission date] July 28, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

Circuits of level shift elements connected in series are connected to the collectors of the output transistors TR1 and TR2, respectively, and a signal input to the bases of the output transistors TR1 and TR2 includes a base bias power source BT1 and bias constant current sources A1 and A2. Power supply + Vcc1, -via each
Connected to Vcc1.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Therefore, the current flowing through the resistors R1 and R2, which are incorporated as level shift elements, is level-shifted from the output end.
Power supply BT3, BT2 through transistors TR3, TR
4 and detection transistors TR5 and TR6 detect and control
And your, transistor TR7, TR8 via respective resistors R5, R6 after current conversion at the transistor TR9,
Turn on TR10 to output transistors TR1, TR2
VBE of diode D1, D2 and transistor TR
9 and TR10 limit output transistor TR1, TR
Limit the emitter current of 2 to a constant value.

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 3]

Claims (1)

[Claims] 1. A circuit for limiting a current of a power amplification element of a power amplifier, comprising a voltage level shift element cascade-connected to the power amplification element, said voltage level shift element being cascode-connected, said voltage level A current flowing through the shift circuit element is detected, and the base current of the output transistor is limited to limit VBE or VGS of the power amplification element to a constant value, thereby limiting the current of the power amplification element. Current limiting circuit.