Modifing a TL494 SMPS current limiting.

Other Hardware General Electronics
1

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.

2

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..

3

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

4

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..

5

how is the pot connected ?

6

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

Thanks.. Tom.. :slight_smile:

7

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

Thanks.. Tom.. :slight_smile:

It's not mine it was taken from the datasheet of the IC

8

MikeLemon:
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?

9

tinman13kup:
In other words, it may/may NOT even be the same circuit you wish to modify?

Yes ofcourse that is just for reference.

10

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... :slight_smile:

11

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... :slight_smile:

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

12

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.

13

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.

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.

14

MikeLemon:
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... :slight_smile:

15

I have a feeling he's too busy for that, too.

16

Hi guys,

I'm trying to use this power supply as a battery charge too.
Did you find the solution?

I want to use a microcontroller to control the power supply, and create the voltage/current pattern for properly charge the battery.

About this power supply on the photo (S-400-12), I found the schematic in this web site:
http://imajeenyus.com/electronics/20151028_smps_variable_voltage/index.shtml

And already got some results replacing the resistors around the pin2 of the TL494 with a 10k potentiometer. Doing this I became able to control the output voltage between 1VDC and 21VDC.

17

Cut/desolder some of the current shunt wires to the left of the big smoothing inductor. Simple.

// Per.

18

Can't suggest that.

19

Zapro:
Cut/desolder some of the current shunt wires to the left of the big smoothing inductor. Simple.

// Per.

Hello Zapro,
can you better explain your idea?

  1. Cutting ALL this current shunt resistor will make the system simple stop to working.
  2. Cutting just some of them, will make the current limiter of the TL494 to active with less current.

Doesn't looks like that you are interesting in this project anymore. "/

Sorry to disturb.

20

Cutting some of the shunts will make the TL494 go into current regulation earlier, what you asked for.

If you look at pictures of the different versions of these power supples, they have different number of shunts soldered in according to the model.

If you cut 50% of the shunts, then it would only be able to supply half the current.

// Per.