How to limit current in SMPS

Thread Starter

arman74

Joined Jul 1, 2017
41
Hey guys.
Im designing a SMPS for charging 10 series li ion battries. I want to have a 42v 2A unit.
My question is that with the ICs having no current sense resistors in primary or secondary will the current be limited only by calculating the transformer winding turns or should i implement a current limit on the secondary or i should use a switching IC with external or internal sensing resistor?
 

Dodgydave

Joined Jun 22, 2012
9,075
I would use a TL494 chip, it has two built in op amp comparators, one to use as voltage control, and the other for current limit.

There are other 8 pin devices that have current sense on the Primary winding, usually in series with the Mosfet driver, which is how the majority of switchmode psus work. Yes the current output is limited to the size of transformer windings and the rectifier diodes.
 

Thread Starter

arman74

Joined Jul 1, 2017
41
I would use a TL494 chip, it has two built in op amp comparators, one to use as voltage control, and the other for current limit.

There are other 8 pin devices that have current sense on the Primary winding, usually in series with the Mosfet driver, which is how the majority of switchmode psus work. Yes the current output is limited to the size of transformer windings and the rectifier diodes.
Thanks.
If I dont limit the current via ics or any thing else, is transformer or other devices harm?
 

ronsimpson

Joined Oct 7, 2019
607
If I dont limit the current via ics or any thing else, is transformer or other devices harm?
It is hard to find a commercial power supply with out current limit. It is common to have a current limit that protects the power transistors and transformer. In switching supply this is very fast responding.
In a battery charger there is a second current limit that watches the battery charge current. This loop is slow and keeps the average current down to what the batteries can handle.

Are you building a (power line to 24V 2A) power supply?
 
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