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Topic: Control a 12v from 5v. (Read 3 times) previous topic - next topic

cjdelphi

This is driving me insane.  - I've tried a TIP31 (lights dimly) and an IRF730

Basically, I have a 12v rail, which goes to the collector (12+) 0 to ground, the circuit is fine, if i feed 12v directly from the rail, both transistors light up the 12v bulb... but, connect the 5v to the transistor, the tip31 glows (a little) and the IRF, does not even light up.


Surely, I can control a 12v source from 5v? without the need of a SSR/Relay ? (I want a 12v car bulb to switch on from 5v without using a relay, this seems futile)

Thanks :) (yes, the IRF has a pull down resistor to stop it from constantly being on, it works if the base gets 12v, if it gets 5v, nada!)

So i'm left wondering... Transistors ? in order to get the power flowing, you need the same voltage in and out? (eg 12v on base, 12v on collector vs 5v base, 12v collector)


Runaway Pancake

5V is a marginal Vgs for the IRF730.  It needs more.
See circuit / attachment.
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cjdelphi

ahhhhh, thank you, i'm so glad it can't be done I honestly thought i was going mad lol

Thanks for the circuit :) - muchos gracias senor.

michael shiloh

For this reason I almost exclusively use logic level MOSFETs, that is, MOSFETs designed to be driven by the relatively low voltage of 5V.

I like the 12N10L from Jameco, part # 1071214 $0.65.

Costs a little more but saves time and extra parts.

johnwasser

Is this how you had it hooked up?

+12 -> bulb -> TIP31 Collector
Arduino digital OUTPUT pin -> 80 (or more) Ohm resistor -> TIP31 Base
TIP31 Emitter -> +12 Ground -> Arduino Ground

Did you remember to set the pin as an OUTPUT?
Did you remember to set the OUTPUT pin to HIGH?

The TIP31 DC Current Gain is about 20 to 25.  You can only draw 40mA from the Arduino pin so you can only switch 800mA (0.8A) with the TIP31.
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