How do I work out the transistor needed?

Thread Starter

Jez365

Joined Dec 22, 2016
12
Hi, I need help with determining the transistor needed to power about 17 solenoid valves with a Raspberry Pi which produces 3.3V. I have made this diagram with the circuit:

(There will be 17 connections to GPIO pins on the Raspberry Pi, 17 transistors and 17 solenoids)
I need to know how to work out the transistor needed. Also, will any 12v power supply suffice? And do I need a resistor in this circuit?

Thanks for any help.
 

MrChips

Joined Oct 2, 2009
20,912
You need a transistor that can handle 12V @ 1A.
A logic-level MOSFET such as IRLZ44 would be suitable.

The 12V power supply has to be capable of delivering at least 10A.

You need a 1kΩ resistor in series between the Rpi output pin and the gate of the MOSFET. This is to protect the Rpi output pin in case of a catastrophic failure of the MOSFET.

You will also need a reversed biased diode such as 1N4001 across the solenoid.
 

Thread Starter

Jez365

Joined Dec 22, 2016
12
You need a transistor that can handle 12V @ 1A.
A logic-level MOSFET such as IRLZ44 would be suitable.

The 12V power supply has to be capable of delivering at least 10A.

You need a 1kΩ resistor in series between the Rpi output pin and the gate of the MOSFET. This is to protect the Rpi output pin in case of a catastrophic failure of the MOSFET.

You will also need a reversed biased diode such as 1N4001 across the solenoid.
Thanks so much for the help! Here are the parts I'm going to buy:
Transistor: IRFZ44N IRFZ44
Power supply: 12V 10A 120W
Resistor: A 1kΩ from this pack
Diode: 1N4001
 

MrChips

Joined Oct 2, 2009
20,912
Your circuit diagram is not correct.
The resistor should go where the diode is shown.
The diode goes across the solenoid, cathode lead (band on the diode) connected to +12V supply.
 
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