Amplifiers – With semiconductor amplifying device – Including protection means
Patent
1984-06-19
1986-07-08
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including protection means
330288, 361 79, H03F 304, H02H 720
Patent
active
045995788
ABSTRACT:
To protect a transistor its emitter current is converted by a resistor into a voltage which by means of a voltage-current converter is converted into a current which is proportional to the emitter current. The collector-emitter voltage is converted by means of a voltage-current converter into a current which is proportional to the difference between a knee voltage which is applied to the converter, and the collector-emitter voltage, the converter not producing an output current for collector-emitter voltages exceeding the knee voltage. The difference between the output currents of the converters is compared with the current carried by a current source. The protection circuit becomes operative when this difference current exceeds the current carried by the current source. A control amplifier then drives the transistor in such manner that the difference current becomes equal to the current. Above the knee voltage a residual current which has a value proportional to the current carried by the current source continues to flow through the transistor T.sub.1. As a result thereof the value of the residual current depends to a lesser extent on variations, which reduces the risk of damage to the transistor due to overloading at high collector-emitter voltages.
REFERENCES:
patent: 4355341 (1982-10-01), Kaplan
Phillips Data-Handbook: Integrated Circuits, "20 W Hi-Fi Audio Power Amplifier", Jan. 1983.
Mullins James B.
Rich Marianne R.
Streeter William J.
U.S. Philips Corporation
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