# 5V - 12V circuit design

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#### mblair86

Joined Oct 30, 2009
1
Hello guys,

I'm an ME trying to do an Electrical Engineer's job for this project. A portion of our project involves using solenoid as a component to our projectile system. However, our control circuit has a pin output of 5V. The solenoid requires 12V (and I assume a large load of current), I believe this is a simple circuit design, but I am somewhat lost in the configuration of the circuit. I believe our design requires a BJT and NPN. Please let me know if you can help.

Signed,
Mechanical Guy

#### MikeML

Joined Oct 2, 2009
5,444
Or a "Logic-Level NFet". +5V signal to the gate will sink amps of current though a load connected between drain and +12V. If the load is inductive (solenoid) place diode (cathode to +12V, anode to drain across the coil. In4004-7 for the diode. Buz11 for the Fet.

Connect a 10K 1/4W resistor from FET gate to source to guarantee that it turns off if it loses the gate signal. NFet source connects to ground.

#### beenthere

Joined Apr 20, 2004
15,808
Can you give the spec's on the solenoid - especially the current it needs? And how often does it operate on and off?

#### SgtWookie

Joined Jul 17, 2007
22,201
Here's an easy way to do it using a logic-level power MOSFET:

The connector on the left is your logic level input.
R1 serves two functions; limit the maximum current that your uC has to source/sink from the gate of the MOSFET, and keep the gate from "ringing"; oscillating at high frequency due to inductance in the connecting wiring.
It should be connected as close to the MOSFET gate as possible.
R2 keeps the gate from "floating" to arbitrary voltage levels if the I/O port fails or is accidentally set to input by mistake - or if R1 fails.
D1 takes care of the reverse-EMF pulse that occurs when current through the relay coil gets turned off.

Digikey and Mouser both stock the MOSFET IRLD014. Mouser's cheaper, but Digikey will ship USPS 1st class for very small orders; that can save you money.

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#### bountyhunter

Joined Sep 7, 2009
2,498
Hello guys,

I'm an ME trying to do an Electrical Engineer's job for this project. A portion of our project involves using solenoid as a component to our projectile system. However, our control circuit has a pin output of 5V. The solenoid requires 12V (and I assume a large load of current), I believe this is a simple circuit design, but I am somewhat lost in the configuration of the circuit. I believe our design requires a BJT and NPN. Please let me know if you can help.

Signed,
Mechanical Guy
My 33 years of EE power design would tell me the best solution is to replace the 12V solenoid with a 5V solenoid. Since a solenoid is just a coil on a steel rod, you can make it work with any voltage. Might be a drop in replacement available.

#### SgtWookie

Joined Jul 17, 2007
22,201
After re-reading the problem statement, I realized that the IRLD014 will probably not be adequate for the task. An IRLZ44 can sink over 40A, and it's a logic level MOSFET.

Bountyhunter,
I'm thinking our OP wants the solenoid to give something a healthy whack to send it on it's way. If the 12v solenoid were exchanged for a 5v solenoid, I would expect that the wire gauge and number of turns would have to increase considerably to get the same physical force output? Or am I barking up the wrong tree here? Solenoids are not one of my specialties.