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Help me with setting up a transistor switch

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I am using simple transistor switch(to turn on Relay) on 2n2222 that turn On when +5V on Base and turn Off when 0...-5V on Base

How can I make it so that when +5V on Base it turns Relay On and then it stays always on even when voltage on Base drop 0...-5V

Of coarse I can use additional Relay but is it possible to make it without additional relay?
 

Re: transistor switch

One option is that you could use a double pole relay and use the other switch to permanently turn on the relay by bypassing the transistor.
Another option is to use a SCR, by connecting the gate to transistor emitter(assuming you are using a npn transistor) and grounding the cathode and connecting the anode to the relay terminal which was previously connected to the collector. Also use a pull down resistor to the emitter.

Hope this helped.
 

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    sz

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Re: transistor switch

Thanks. What SCR would you recommend for Relay 5V 70mA
 

Re: transistor switch

Ypu can use for example a C106D1, a very well known SCR.
Another option is to use the SCR used on the Christmas Lights ( usually are 4 each ) but now I don't know the type.

Mandi
 

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