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3.3v regulators broken?

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doctor_prox

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Hi, i am trying to step down 12v to 3.3v. I have two different 3.3v regulators i have tried (1.5a and 3a) and all i ever get out according to my voltmeter is 0.01v. I have tried a 5v reg and it works fine. Whats going on?
The part numbers are LM1085IT-3.3 and LM1086CT-3.3
 
doctor_prox said:
Hi, i am trying to step down 12v to 3.3v. I have two different 3.3v regulators i have tried (1.5a and 3a) and all i ever get out according to my voltmeter is 0.01v. I have tried a 5v reg and it works fine. Whats going on?
The part numbers are LM1085IT-3.3 and LM1086CT-3.3
Click to expand...

Are you wiring them the correct way?, regulators often have different connections. I'm presuming you also have the required capacitors on the input and output?, instability could stop it working.
 
doctor_prox said:
They are the correct way round. The supply is a 12v lead acid battery and i have a 47uF cap between ground and +3.3v
Click to expand...

As I see it there are only two possibilities?, either it's wired incorrectly, or you have faulty components somewhere - possibly both chips are faulty? (which seems highly unlikely). Another possibility is an external component, the 47uF S/C would probably cause this as would anything S/C on the output.

Is the chip mounted on a heatsink?, if so, is it insulated from the heatsink?.

It's a simple enough circuit, there's not many possibilities.
 
Damn you guys are right, its wired wrong :roll: I assumed it would be the same as the 5v ones.
Will i have killed it now?

Edit: Its alive and kicking thanks guys!
 
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