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Modifying a DC-DC boost circuit Answered

I'm building a circuit that would run off roughly 7v and convert it to 12v using the LM2577 (LINK). the datasheet (LINK) provides an example circuit that will output 12v @ 800mA. I need a little more power than that. around 1.25 A. my question is that if the 100mH inductor was replaced with a larger one. say a 150mH one, would that increase the current output? i would also replace the 680uF cap with a bigger one to reduce ripple. FYI the LM2577 is rated to convert 3.5v-40v to 12v.

any information or direction would be appreciated

picture is from the national semiconductor datasheet page 3

2 Replies

lemonie (author)2010-09-05

If you read the pdf, there's a section "application hints", which gives a simple formula for calculating your maximum load current. For 7V in, it gives 1.225A.
Note this is a voltage regulator, current is load-dependent up to the device limitations.


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steveastrouk (author)2010-09-05

Its never as simple as just changing something like component. Everything has knock on effects. Go to National's website for the 2577, and select tools/ webench, and run their design wizard, with the parameters you have - minimum AND maximum input voltage, output voltage and current, and see what the makers recommend - I suspect it isn;t the 2577.

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