# transistor switch

Discussion in 'General Electronics Chat' started by hssucgang, Jul 19, 2007.

1. ### hssucgang Thread Starter New Member

Jul 19, 2007
1
0
is there any transistor switch or relay switch that works on 2 volts?

2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Two volts should work pretty much with all standard bipolar junction transistors (BJTs). This is not sufficient voltage to operate a field effect transistor. A darlington BJT transistor would probably not be a good choice.

hgmjr

3. ### GonzoEngineer New Member

Jul 8, 2007
46
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Try an Optoisolator

4. ### lightingman Senior Member

Apr 19, 2007
374
22
If you are trying to switch 2 volts with a transistor, remember that the forward voltage drop accross the device is about 0.7 volts.....2 volts will switch a transistor on without a problem, through a resistor (about 2K2) into the base........ Daniel.

5. ### ashok_ece2006-2010 New Member

Jul 19, 2007
1
0
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6. ### nomurphy AAC Fanatic!

Aug 8, 2005
567
12
Is 2V your source voltage (Vcc), or your drive voltage? In either case, the general answer is, yes.

As noted above, a general bipolar transistor (2N3904 / 2N3906) only requires ~0.7V on the base-emitter. Some FET's can be used with a lower drive voltage, for example the NTD3055 FET requires a gate voltage of only 2V.

7. ### nanovate Distinguished Member

May 7, 2007
665
1
If you are going to drive a relay with a bjt you should not forget that you need to have enough current available to go into the base.

Roughly I_C = I_B * beta
I usually use beta = 50 for relay drive ckts (for margin) and look at the coil resistance and voltage of the relay to get my I_C. Then calculate the I_B. From this I can size the base resistor accordingly.

R = (2V-0.7)/I_B

Using R = 2K2 you can easily drive 30mA of coil current.

John