Protection circuit
US4599578A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jun 19, 1984 |
| Grant date | Jul 8, 1986 |
| Priority date | — |
| Expiry date | Jun 19, 2004 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03F1/52
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
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 t…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.