Switch current limiter 2 - a more efficient solution

198

01:39:39

This circuit uses a little bit of digital circuitry to turn off the switching MOSFET as soon as the inductor current hits 3A. For more details on this type of circuit, take a look at the description of the previous version http://everycircuit.com/circuit/5816291173335040 
I will be using this circuit (and this improved feedback circuit with a latch) to improve my boost and buck converter circuits.

published 6 years ago

kiani

6 years ago

The pulse width is allowed ti go byond 50%, on time. is that not a problem for the FET.! The current limit idea is good in that it reduces the pulse, limiting the total power.. Some systems make the fet totaly turn off and then if restart (into over load) min pukse eidth snd again. Until over current has been corrected.

PrathikP

6 years ago

Is a pulse width beyond 50% a problem for the FET?

kiani

6 years ago

I am not sure in your psu, and for fet...for switch mode psu.. The pluse width is limited to 50%, tovsyop transfirmer saturation and protrction of the switching transistor. Also perhaps efficiency, etc... It is never more than 50%, both in forward convertor and flyback.

kiani

6 years ago

So the on time is not more than off period. Most of the time it is limited even below 50%,, like 45 48% max.

PrathikP

6 years ago

That's when a transformer is involved. It isn't really beneficial (in a wall adaptor for example) to go beyond 50-60% duty cycle. The switch current limiting in cheap wall adaptors uses the exact same circuit as the previous version of this circuit.

PrathikP

6 years ago

And if there is switch current limiting, there is no reason to limit the initial duty cycle to 50% worrying about inductor) transformer saturation because the current limit takes care of that

PrathikP

6 years ago

And the other reason i can think of for limiting the duty cycle in a flyback is because it's snubber network needs a bit of time to dissipate the residual energy.

kiani

6 years ago

Right.. Flyback convertors have a little gap added in the cores, so perhaps you are right about that. So maybe you could go a little beyond 50 %..

PrathikP

6 years ago

The TNY series of ICs like the TNY267 allow upto 68% duty cycle. The LM2596 (a buck converter IC) can go upto the full 100%>

PrathikP

6 years ago

The full 100% duty cycle is a little wierd.

kiani

6 years ago

Perhsps it meant for functionalities,, otherwise 100% duty cycle = saturation of all inductors and chokes,..

PrathikP

6 years ago

And a bit of the magic smoke

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