Hi all!
My fist time opening a thread.

Here comes my problem:

I am doing a simple step down converter with a LM2576-ADJ.
Its input is 12V and it has a output of 3.3V.
I am using a 100uF input cap, a 220uH/3A toroidal coil, a 1000uF output capacitor and a SR105 diode.
The schema used is the same it says the datasheet, using a resitor divider in order to get the 3.3V ant the output.


The problem is that I mounted it on a breadboard and it worked perfectly.

Now i have soldered on a prototype board and it doesn't work.
All the components are well soldered (there is continuity between all of them)
When I measure the output voltage on the LM2576-ADJ it says 0V, and it also has 0V on Vref, and it is supposed to be 1.23V.



What do you think is wrong? What may be burnt?


Thank you for the help.

 

I'd do the following:

1. Check there are no shorts
2. Check the polarity of the diode
3. Check the polarity of the capacitors
4. Check continuity across the inductor
   
5. Check pin 5 (ON/OFF) is LOW (some of these chips use HIGH for on - caught me out once!)
6. See how much the input voltage drops when you connect, or if the chip gets hot

If it gets hot, and/or there's a lot of voltage drop, then it suggests something bad going on (normally a short though!)

Out of interest, why aren't you using the -3.3 version if you're generating 3.3V?

 

I'd do the following:

1. Check there are no shorts
2. Check the polarity of the diode
3. Check the polarity of the capacitors
4. Check continuity across the inductor
   
5. Check pin 5 (ON/OFF) is LOW (some of these chips use HIGH for on - caught me out once!)
6. See how much the input voltage drops when you connect, or if the chip gets hot

If it gets hot, and/or there's a lot of voltage drop, then it suggests something bad going on (normally a short though!)

Out of interest, why aren't you using the -3.3 version if you're generating 3.3V?

I already checked points 1 to 5 and it was ok. Although, I will test it again, just in case...
About the point 6 I will check as soon as I change my tester battery (yes, all the handicaps come at once...)

About your question, it's a very small prototype, and the ADJ model was the only one the electronic shop had. If later on we can purchase it somewhere on the internet, we probably get the 3.3V version.

Thank you for the help

 

Hi,

Are these exactly the same components you used on your breadboard?

What load are you expecting to drive (in terms of current)? I've been looking through the datasheet for the recommended component selection procedure, and a few bits need to know the load you're driving.

I've used these (and LM2575, LM2676) before, and haven't had many problems (even if I ignored the component selection criteria). About the only one I had was buzzing from the inductor - but that was due to an insufficient output capacitance. And the time when the on/off was inverted compared to the others (that was the LM2676).

 

Hi guys,

Mea Culpa right here...

Bad soldering on the diode... of course it didn't work...

Thank you very much!