which NPN trasistors can I use?

[newbie111]

pic transistor

I would like to try this connection in the diagram


my q is can i use any npn transistors?


Thanks

 

[sabu745]

Re: pic transistor

You can use following transistors
BCX40
2N3019
2N3020
2N4239
2N3109
BC211
BC301
BCX45

 

[IanP]

Re: pic transistor

Transistors (working as a switch) are rated for the maximum collector current, for example, the BC141 Icmax-1A (another parameter is the collector-emitter voltage but in low-voltage applications this rating is not very important) ..

In you case, if you want a transistor to drive a relay, first you have to learn what is the relay’s coil op. current (or coil resistance), then select a transistor that can do it (with a safety margin) ..

For example, if the coils’s current is 30mA you can select a transistor with ICmax>300mA (safety margin) ..
So, 2N2222, BC337, BC338, BC639, ZTX-series … and so on .. should do ..

Rgds,
IanP

 

[pranam77]

Re: pic transistor

I would like to try this connection in the diagram
my q is can i use any npn transistors?
Thanks

As i saw the schematic, NPN transistors are used in the circuit to drive the relays. Did you intend to ask "can i use any PNP transistors?" If that was your question, using PNP in place of NPN will compliment the present state of the relay.
Cheers

 

[miredox]

Re: pic transistor

I don't agree: since the pic works on 5V, and the relays on 12V, and both voltages are referring to the same ground, you can not use a PNP transistor:

- If you use a PNP transistor as emitor follower, with the collector connected to the ground, you will not be able to switch the relay off, as the voltage on the relay can only be switched between 12V (input low) and 7V (12V - 5V, input high).

- A PNP transistor in a common emitor setup will even be worser, the transistor will always be switched on. You could solve this by adding a zener diode in series with the 820 ohm resistor, but this is not really recommended. Much more simple with a NPN transistor.

For a NPN transistor: check the resistance of the relay coils. Any transistor that can handle the current required by the relay can be used. Hfe will also never be a problem with a 820 ohm resistor at the base.