Determining current.

[adcurtin]

I made an Lm317 circuit and I'm not sure which to trust measuring the current. With a test load for BR (6 1n4001s and a 10ohm resistor) i measure .850V, which should be 85mA. I measured the current with my multimeter's ammeter mode measured .220 amps with no other load. With the equation for lm317, using 38ohms, it should be giving 32mA. I'm powering this with a 9v and using a 10µF tantalum cap on the output. Which should I trust for the output? (I hooked up a LPC-815 and could tell it was higher than 32mA).

Thanks,
Andy

 

[rog8811]

I measured the current with my multimeter's ammeter mode measured .220 amps with no other load.

If you are saying you put the meter, set on ma, across the driver output it will tell you nothing.

Have you measured the ref voltage to make sure everything is working correctly?


Regards rog8811

 

[adcurtin]

Ok, I did do that. There was a short in the circuit (vin to adj on the lm317). How do I measure the reference voltage? (voltage across Vin and Vout?)

 

[rog8811]

Drawing shows how it is done. If the regulator is working the ref voltage will always be 1.25v.

Regards rog8811