A simple switch circuit using a transistor. When the switch is closed, current flows through the base to the emitter (this junction acts like a diode). This switches the transistor on, so that current can flow from the collector to the emitter. A small base current can control a much larger current from the collector to the emitter.
The transistor wants the collector-emitter current to be 100 times the base current, but it can't, because such a large current through the 300 ohm resistor would bring the collector below ground. So, the transistor is in saturation mode; it brings the collector voltage as low as possible. -- Credits: Mr. Paul Falstad.
|Soundarya said: (Oct 23, 2013)|
|Why we are using the transistor in relay circuits?|
|Ravi Dewangan said: (Apr 28, 2014)|
|In relay circuit transistor act as a switch and amplifier, here the input as base taking low value of signal ranges (milliampere) and in the output as collector to emitter we can connect the input of relay with the Vcc as 5v sufficient for relay operate, when the small signal (from any sensor) are given to the base then the transistor will switched on and it will follow the same current from collector to emitter (NPN) as much is required for operating the relay, relay is electromagnetic conversion device can use for high ranges power switch, so finally using as a switch we are amplifying the whole signal from micro ampere (sensor) to kilo ampere (circuit breaker) very easily. Thank you.|
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