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Switching supply sees short circuit for very low load resistances

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arve9066

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I am using the Murata OKL-T/1-W12 to produce 1.7V from a 12V battery. This 1.7V has to power a thermoelectric cooler of resistance around 2.5 ohms about 700mA load current. Although I see an open circuit voltage ( even with 1Kohm load as well) of 1.7V, when I connect the thermoelectric cooler I see only 0 V at the output. I think the output short protection gets activated when it sees such a low resistance as load although the device is supposed to provide up to 1A current. Is there anything I could do to get the device working somehow bypassing the output current protection?
 

You might try using the soft-start feature to see if that helps. Have you looked at the output? According to the data sheet these devices current limit using "hiccup" mode, in other words, they don't shut down completely, but 'start' and 'stop'. You should see this on the output, which would indicate that it is, in fact, going into current limit mode. If you just see a flat zero volts, then there might be something else going on.

Stupid question: Can your battery supply the required power?
 

I did test another one of these packages and that one worked just fine. I was curious as to why the other one would not work below a certain load resistance alone. I tried different loads and anything below 75ohms, I get flat 0V at the output.
 

arve9066 said:
I did test another one of these packages and that one worked just fine. I was curious as to why the other one would not work below a certain load resistance alone. I tried different loads and anything below 75ohms, I get flat 0V at the output.
Click to expand...

Wait one worked and one didn't? Did it occur to you that you probably have a defective unit?
 

I just now tested the new unit after I ran out of all troubleshooting options with the new one.. Since the other one worked partially I did not realize it was defective for a long time. The mode of failure is what made me go in rounds a bit..
 

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