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Topic: Modifing a TL494 SMPS current limiting. (Read 267 times) previous topic - next topic

MikeLemon

Hi there.

I'd like to modify this 12V 30A  which uses the TL494 PWM controller IC for battery charging purposes:



There is a voltage adjust pot available which is fine but now I want to be able the current with a variable pot here is the reference schematic from it's datasheet:



I've been suggested to replace R1 with an equivalent pot but I doubt it, any suggestions? I'd be useful to get an equation along with the solution for calculating the current limit.

Thanks for your time.

Wawa

Pin15 of the chip has a 1volt reference, made with a voltage divider (R1, R2).
If voltage across R13 reaches that 1volt set point, current limiting kicks in.
Not hard to work out that 10A must flow through the 0.1ohm resistor for that.

So yes, if you replace the 1k resistor with a pot you should be able to adjust that set point and have adjustable current limiting.
Wise to add a (100k) bleed resistor from wiper/pin15 to ground, in case the wiper looses contact.
Leo..

MikeLemon

Well thanks but this pot still doesn't manage to do alot..

Wawa

#3
Aug 05, 2017, 03:58 am Last Edit: Aug 05, 2017, 04:00 am by Wawa
You talk about a 30Amp supply, and post a 10Amp supply diagram.
Are you sure the current sense parts are the same.
Did you measure voltages with a DMM on pin15 of the chip without and with your pot added.
I assume you use all three pins of the pot, not as a 2-pin variable resistor.
Leo..

racpi

richard

TomGeorge

Hi,
Can you please post a copy of your circuit, even an edited version of the circuit you have already posted.

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

MikeLemon

Hi,
Can you please post a copy of your circuit, even an edited version of the circuit you have already posted.

Thanks.. Tom.. :)
It's not mine it was taken from the datasheet of the IC

tinman13kup

It's not mine it was taken from the datasheet of the IC
In other words, it may/may NOT even be the same circuit you wish to modify?
Tom
It's not a hobby if you're not having fun doing it. Step back and breathe

MikeLemon

In other words, it may/may NOT even be the same circuit you wish to modify?
Yes ofcourse that is just for reference.

TomGeorge

Hi,
Well now is the time to get pencil and paper out and reverse engineer a schematic around the part of the circuit of the TL494 and the output terminals.


Tom... :)

Everything runs on smoke, let the smoke out, it stops running....

MikeLemon

Hi,
Well now is the time to get pencil and paper out and reverse engineer a schematic around the part of the circuit of the TL494 and the output terminals.


Tom... :)


Nah no thank you not worth the time and effort...

polymorph

So... worth it for us to try and sort it out from what you didn't bother to tell us isn't the schematic. But not worth it for you to look at the circuit and determine what parts and values it actually uses.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - tinyurl.com/q7uqnvn
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

MikeLemon

So... worth it for us to try and sort it out from what you didn't bother to tell us isn't the schematic. But not worth it for you to look at the circuit and determine what parts and values it actually uses.
Sorry for late answer was quite busy the last time and anyway's I was just expecting a quick answer the solution already came in.

Thanks anyways.

TomGeorge

Sorry for late answer was quite busy the last time and anyway's I was just expecting a quick answer the solution already came in.

Thanks anyways.
Did you get a solution?
What was it?
Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

polymorph

I have a feeling he's too busy for that, too.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - tinyurl.com/q7uqnvn
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

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