how to connect 2n3906 to drive a relay

Other Hardware General Electronics
1

hello every body
im Beginner in electronics :confused:
how to connect a 2n3906(pnp)transistor to drive a relay with nodemcu trig?
base pin >GPIO (does it need resistor between base pin and GPIO?)
collector pin > ?
Emiter pin > ?

2

Have you found an example how to drive a relay with a transistor ?
Because everyone uses a NPN transistor (or a mosfet). A PNP transistor is not going to work.

The transistor is only 40V 200mA, that is a small transistor.
How much current does the relay need ?

Every transistor requires a resistor to the base pin.
This is how to use a transistor: http://www.pighixxx.com/test/portfolio-items/connect-a-relay/
Do you see the diode next to the relay ? That is the fly-back diode. You need that.

3

Hi,
What are you going to power the coil of the relay with, what voltage and from where?

Can you tell us the make and model and if possible a link to its spec/data?

Thanks.. Tom.. :slight_smile:

4

Hi,

siva_007:
how to connect a 2n3906(pnp)transistor to drive a relay with nodemcu trig?

This page covers just about all the options for driving a relay with transistors: relay-switch-circuit.html

NOTE: you can only use a PNP transistor as a high-side switch or emitter-follower if the +V rail is the same as the processor.

You usually use an NPN transistor (or MOSFET) so you can have a separate supply for the relay (if it was a 12V relay for example).

Yours,
TonyWilk

5

TonyWilk:
Hi,This page covers just about all the options for driving a relay with transistors: relay-switch-circuit.html

NOTE: you can only use a PNP transistor as a high-side switch or emitter-follower if the +V rail is the same as the processor.

You usually use an NPN transistor (or MOSFET) so you can have a separate supply for the relay (if it was a 12V relay for example).

Yours,
TonyWilk

tanks tonywilk
i cant use npn transistor because when power on esp , All GPIO suddenly set to High and relay coiled.
your link was useful
i got it
base > GPIO(with resistor)
Collector >GND
Emiter >Relay coil

6

You can drive an NPN with a PNP if your logic pin is active low.