lm2576 buck converter circuit

Sep 03, 2014 3 Replies
S

I put together a 5V regulator circuit using an LM2576, pretty much accordin g to the reference schematic in the datasheet. The one deviation is that I don't have any schottky diodes on hand. Not a single one. I do have lots of UF switching diodes in the junk box though.



So... I put in a UF4007 in place of the 1N5822 in the schematic. Tried it o ut. It worked. I understand the forward voltage drop of the UF4007 is much higher than the 1N5822. Can someone give me a quick idea of what affect thi s will have on the circuit?



I'm hoping to get about 1.5A - 2A out of this regulator. If the UF diode is good enough (for some reasonable definition of "good enough"), then I'll h old off my schottky order until I need some other stuff to economize on the shipping. If it's not good enough, then I'll order the schottky diodes soo ner rather than later.


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R

The UF4007 has a forward voltage of 1.7V instead of 0.5V for the 1N5822. At

2A this is 1.7V*2A = 3.4W. That is above the max of 2W specified in the datasheet. Depending on the input voltage the diode will only conduct for appr. (1-5V/Uin) of the time. So the average might be below the limit. The higher the input voltage the worse it will get.
Reinhardt
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ing to the reference schematic in the datasheet. The one deviation is that I don't have any schottky diodes on hand. Not a single one. I do have lots of UF switching diodes in the junk box though.

** Then you can use two or three in parallel.

UF series diodes are good for 1 amp and Vf drops as the chip heats up @ -2m V for each degree C.

BTW: Types UF4001 through UF4004 have much lower Vfs - almost half.

... Phil

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K

And the absolute maximum rating for the LM2576 output is GND - 1V so the chip may burn out. In my experience, the Simple Switchers do indeed burn out or severely malfunction when the reverse current diode isn't good enough.

I'd use one of the many synchronous regulators that are available for

0-6V outputs. Their efficiencies can be amazing and there's no need for a big diode.
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