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LM2576 Adj 'switcher'
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Davy:
Wonder  if anyone knows the regulation % of a LM2576- adj 'switcher regulator'. I get  1.1v drop on the output between no load and full load.

On a DC supply I can set the voltage to 11.6 and it draws around 2.14 Amps, on a switcher it drops to 10.5V, the circuit anf board layout is as shouwn on the datasheet.

This is for a uV LED light panel I've built, is this voltage drop normal, the data sheet seems vague to me, may be I need to 'up' the on-load voltage, rather than set it off-load. Thanks,

Dave.

MagicSmoker:
Not enough info - post the input voltage and specific inductor you are using.
T3sl4co1l:
1.1V drop sure, which is how many percent of nominal output?

How much of that is taken up in the first few percent of rated current -- does it need a "bleeder" load to meet spec?

As I recall, the internal error amp has unimpressive gain (about 80x), so the regulation is poor as regulators go, but more than adequate, and 1.1V would have to be out of a total 40V+ nominal output to be due to regulator operation.  So I suspect there may be a leakage current, or minimum duty cycle limitation, that's causing your output voltage to rise when very lightly loaded.

Or if it's because voltage is falling below nominal, at high currents, you might not have enough supply voltage (maximum duty cycle and dropout limitations), or you're using inferior components (inductor, diode, capacitors) that are costing voltage in a somewhat roundabout way.

Tim
Davy:
Using a 200uH inductor wound with 55 turns of 24SWG, measured on a Peak LCR meter, SR560 diode with two 1000uf 25V capacitors Panasonic FR series, low ESR, the input voltage is 15V.

Now then let me explain.
I repaired many a Nikko Baby 10 TVs', these are small portable TVs in the CRT days, they used a custom block regulator that ran very hot and was often failing, they replaced it with one of these regulators that ran from a 12 to 15V supply the output being 10.7V if I can remember correctly..... thats where I got the inductor size and used the same  yellow core  with a white edge, that had 55 turns on only used a single 1000uF, can't recall the current consumption but was well over an amp, thats how I came to build this circuit since it would run cooler than a linear regulator,  from memory it used a 1K to ground and something like 7.8K to o/p side.

I might be able to get my hands on a spare Nikko Babay 10 'switcher' then I'll do a comparison.

The PCB tracking is as per regulator data sheet. Don't get me wrong it does work and very well and cool indeed just that the 1.1V drop set me wondering, once set the voltage stay's 'put'.

Dave

MagicSmoker:

--- Quote from: Davy on July 21, 2019, 05:59:08 pm ---Using a 200uH inductor wound with 55 turns of 24SWG, measured on a Peak LCR meter, SR560 diode with two 1000uf 25V capacitors Panasonic FR series, low ESR, the input voltage is 15V.
--- End quote ---

Erf... #24SWG is way too small a wire for that amount of current, and 200uH is way too much inductance for this current and switching frequency (~52kHz). You need to triple up on the #26 and also cut the number of turns in half (resulting in approximately 1/4 the inductance). Also, the yellow/white core is almost certain powdered metal so expect high losses in it, too.

Finally, the guaranteed minimum peak current rating is only 3.5A for this device, so expecting 3A nominal output current from it might be a bit optimistic. I'm surprised you say it is running cool, since the "typical" voltage drop across the internal switch is 1.4V so that would result in ~4W of dissipation right there.

EDIT- strikeout applied to where I mixed up #24SWG with #26SWG

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