LT3022 voltage regulator outputting wrong voltage

Thread Starter

johnny411

Joined Mar 3, 2020
27
here is my circuit. it simulated 100% fine.

6.5v222.PNG

it is fed 8.4v and should output 6.5v. instead its outputting 0.2v. when i first soldered it in, i had the two voltage set resistors flipped. could this have fried it?

any other reasons for this behavior? thanks.
 

AlbertHall

Joined Jun 4, 2014
9,824
The circuit looks OK.
With the resistors swapped I would expect an output of 200mV (no frying).
Check the values of R11 and R12 and make sure that R12 is connected (with it disconnected I would again expect 200mV output).
 

Thread Starter

johnny411

Joined Mar 3, 2020
27
thank you. its working now (the solution was simple - the resistors where right the first time but the power supply was not), 0402 resistors are hard to deal with.

however, the negative voltage (sercond "regulator") is outputting -6.164v. this is the supply for a differential op amp circuit. it simulates at -6.5v, any reason why the actual value is so much lower? i figure for op amps the +- supply should be as close as possible to matching. thanks

-6.5vvv.PNG
 

Thread Starter

johnny411

Joined Mar 3, 2020
27
my bad - the schematic is wrong. the actual value is 237R. so it should be -6.472V. my bad for mislabled schematic, the part number is for 237 so thats whats installed. 0.1% resistors.
 

Thread Starter

johnny411

Joined Mar 3, 2020
27
nothing but whats shown in the above schematic - im soldering on and debugging as i go. i thought that the output filtering would meet the minimum current draw, am i wrong?
 

AlbertHall

Joined Jun 4, 2014
9,824
C15(?) and C35 need to be low ESR and connected by short leads to the chip otherwise it will reduce the regulated voltage. Is this constructed on a PCB?
 

n1ist

Joined Mar 8, 2009
184
On the negative regulator's output, the tantalums (C35, C36) are backwards. Since it is a negative rail, the positive of the caps goes to ground. I'd toss those and put new ones in.
/mike
 
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