How to test TL494 / KA7500 PWM Controller IC

[@MrMental-m1u]

Thank you for the simple explanation of how these work. ...yeah! ;D

[@g4z-kb7ct]

I just built this. It worked but adjusting the pot didn't do anything and the LEDs flashed anyway. It turned out this circuit isn't 100% reliable as a chip tester. The whole point of this is to test chips that are likely to be faulty. I tested a known bad chip (bad in an unknown way) and the LEDs flash. I discovered the issue is the feedback pin on my chip is stuck at 0.065v so the LEDs will flash regardless of the pot position. So while the bad chip works in the test circuit the feedback is not active so it won't work on a real smps... that's a false-positive. If I had not discovered this I might put the chip back into the power supply then wonder why it doesn't work. This needs a revision 2 so it actually uses the feedback pin. It really needs something that changes the feedback from about 1.5v to 2.0v so it moves +- 0.5v after a few seconds up and down continually to exercise the feedback function. Pin 3 can be measured with a multimeter to ensure it's actually moving to verify the feedback is good. I also went back to look at another power supply where I changed the TL494 and it turned out that new chip also has faulty feedback. Wish I had discovered that before pulling and testing all the other parts, not finding anything else faulty and pulling my hair out in frustration hehe!

[@armandine2]

given pins 1, 2, 15 and 16 (the error amp inputs) are all at ground why wouldn't pin 3 be too and not variable ?- I wonder if the pot is actually at Vref and therefore is an input, not an output.

[@josechandia8437]

Muchas Gracias mi hno por esta enseñanza. Saludos desde Argentina.....!!!

[@johnprescott6614]

Short but not easy, need some time to digest everything. Thank you Richard, have a good weekend.

[@LearnElectronicsRepair]

Hi John. I'm always happy to help anyone who is willing to learn electronics repair - We all learn at different speeds and in different ways - anything that is not clear enough, or I skipped over (sometimes it is hard to put yourself in the position of of someone learning what you already know) just tell me and I'll try to explain it again in more detail

[@johnprescott6614]

​@@LearnElectronicsRepair You're helping a lot already. If you could do a video on how to approach failures in electronics (motherboards/laptops/gpus) with a basic checklist, that would be realy nice.

[@LearnElectronicsRepair]

@@johnprescott6614 OK I'll work on that idea John. Thanks

[@g4z-kb7ct]

@@johnprescott6614 So you can't build this simple circuit but you want to know how to fix highly advanced pc motherboards and gpus? Eh? You need to learn how to crawl and walk before you can run. Watch youtube repair vids for a couple of years and you will have a good understanding of what is required and the basics of how to fix stuff.

[@theinnovati0nlab782]

Very nice tutorial! Thanks for the video. I am equally working on a high power DC-DC boost converter design. Basically my goal is to design a synchronously controlled interleaved boost converter system - capable of delivering high output currents even at low input voltages. If this works, then I will see about modifying the circuit to operate with synchronous rectification - for better efficiency. Texas instruments did a wonderful job with the TL494 datasheet by explaining all the design considerations and calculations....Switching frequency, power inductor selection, dead-time control, filter capacitor selection.....etc. These will be covered in my next video. Thanks again! The Innovati0n Lab

[@ACoTam2]

Thank you so much! i was nearly sure i will need to buy another TL494, but actually it's just a broken potentiometer that makes everything not working!

[@kasmanikasrim59]

Thanks for this video!!

[@fursino]

Thanks, I did also what you proposed and it is very useful since I could detect indeed a broken TL494.

[@robjordan63]

Very interesting. I'm trying to fix an SMPS currently and I'm pretty inexperienced. It's based on a simpler PWM chip, KA7552, and I'm going to build a similar test rig to see if I can make it oscillate.

[@longthienuy]

I want to make a LED strip dimming driver from KA7500 inverter circuit, boosting 24VDC to 220VDC. How can we adjust the voltage output ?

[@armandine2]

I have a 5V reference but only 87mV at the feedback pin? I think I may have blown my pin compatible NEC uPC494 chip in haste.

[@warrenwhite3618]

Great video. Can you explain how this chip is used in an audio amplifier? Trying to fix a constant thumping coming from speaker, no sound. I've changed capacitors that 'usually' cause this problem. Now I've traced it to this chip, that outputs a pulse 'C2' direclty to a large capacitor. I can actually hear a noise in the circuit, sounds like a mechanical relay.

[@uksuperrascal]

Had same prob turned out to be an OC via - the thump was the psu when running ok and amp on ok - but it was not getting the ok Im running sig back to the started now stop the start up seq sig. hence the thump on the speaker.as the psu tried to start over and over again. and what made it harder to find was the via was under the IC. So soldered strand of wire in the via to fix the via. thump stopped -PS the amp was called a Thump Amp LOL

[@turbobobster]

Looking for help on this one, I have built and tested this circuit. I bought 5 Tl494 and found each of them to be missing the 5v on pin 3 so after hours of checking everything I ordered the ka7500, to my surprise it worked so I now have dead on arrival Tl494s. There is however an operational difference with the ka7500 compared to the video, it does not switch off when I pull pin 3 to ground like the video. Has anyone experienced the same thing?

[@techeng3940]

That was very useful thank you very much

[@LearnElectronicsRepair]

You're welcome!

[@randydicotti3975]

Nice tutorial. Actually great. Tell me, would this same circuit work on a TL594 which is essentially the same chip with higher input tolerance

[@LearnElectronicsRepair]

It should

[@Youtube_free_always]

I have many of this tl 594,and fews tl494

[@Youtube_free_always]

I have many of this tl 594,and fews tl494

[@gloubiboulgazeblob]

By looking at the TL594 datasheet, you can see the same configuration on page 7/figure 12. So the answer is YES.

[@daz41262010]

great tutorial :)

[@lodaalex]

Thanks so much ser

[@iblesbosuok]

Fujitsu has MB3759 which quiet tough.

[@abdallahelectronic19]

thank you ,i have a problem with this ic tea 1716 in led tv power supply NO POWER, her problem is that it was exposed to high voltage, and I found the main capacitors swollen, I replaced them, but the IC heats up greatly, but it is fine because I removed it and tried it in another card and it worked fine. Where is the problem? Is it in the components surrounding the ic tea 1716?

[@LearnElectronicsRepair]

Hi Abdullah Generally, if an IC is getting hot then it is either: 1. faulty (which you proved it is not) 2. Something wrong with the power supply voltage to the IC (here is the link to the datasheet so you can check the supply voltages) pdf1.alldatasheet.com/datasheet-pdf/view/751523/PHILIPS/TEA1716T.html 3. It has excessive load on the output(s). This chip drives the MOSFET gates - one for the PFC and two for the SMPS transformer. MOSFETs are supposed to have practically an infinitely high gate-source and gate-drain resistance. I would have a look at the gate drive circuit - can you measure the resistance from pins 7 (GATEPFC), 10 (GATELS) & 13 (GATEHS) of TEA1716 to ground. Do you see any low resistances? If you can compare resistances with the other card, even better. Also remove the three FETS and test them. If the two cards have the same FETs, try swap them from one board to the other

[@abdallahelectronic19]

@@LearnElectronicsRepair Thank you, sir, for your interest in my question. I tried several times to measure the surface elements around the IC, but for example the resistors I found them to be good, but the capacitors I did not measure, but I will follow the steps as you told me in the evidence 10 7 13 To ground

[@techeng3940]

Can you please explain how is the voltage 3.3v regulated in the atx power supply using tl431 and pnp transistor?

[@LearnElectronicsRepair]

Circuits vary so I can't answer that definitively without either the PSU or a schematic. The TL431 is a voltage reference, I made a video here. TL431 video kzbin.info/www/bejne/gqeqlpuvjLGGbpI This comments section is intended for the TL494 video... ;-) But anyway, the TL431 is usually closely connected to the LED in the opto-isolator - the idea is is that two close tolerance resistors are used to set the turn on voltage of the TL431. These resistors connect between ground and the voltage supply you want to regulate. When the TL431 turns on it conducts, and the current flows via the LED in the opto-isolator, therefore also illuminating the LED and turning on the photo-transistor that controls the PWM feedback. By choosing the value of the resistors you can make the LED illuminate at whatever voltage you like. Simples.... but... The minimum possible turn on voltage of TL431 is 2.5V (no matter what resistor values you select) and the LED is in series with TL431. As the LED also has a forward voltage drop (let's say 1.25V) the lowest voltage rail you could control using this circuit is 2.5V+1.25V = 3.75V (approximately) To get around this you can use the TL431 to switch on a PNP transistor instead, and the transistor then turns on the LED in the opto-isolator. In this case the minimum voltage rail you could regulate would be 2.5V + 0.6V (base -emitter voltage of the transistor) = 3.1V (approximately) To work on even lower voltages you need a version of TL431 that has a lower internal voltage reference, for example 1.2V like the one I found in my video. This short and easy to understand Texas Instruments article explains this better than I can, and also shows the typical circuit both standalone TL431 and TL431 + PNP transistor e2e.ti.com/blogs_/b/powerhouse/posts/powerlab-notes-how-to-regulate-a-low-voltage-isolated-supply I hope that helps Richard

[@techeng3940]

@@LearnElectronicsRepair Thank you very much for the answer, I mean the 3.3v regulation separate from optocoupler. I have an ATX power supply that has a strange voltage regulation system for 3.3v that takes the 5v AC from a separate Schottky diode and regulates it through two coils and the tl431 and asmall pnp Th base of transistor is not controlled by the tl431 but through the 5 AC! I couldn't understand it well honestly

[@techeng3940]

@@LearnElectronicsRepair The circuit works on tl494 and lm339 as a control and I couldn't find a schematic for it

[@LearnElectronicsRepair]

@@techeng3940 Ok... as I think I suggested earlier, register on badcaps.net forum (it is free to join) then post in the Power Supply Repairs section with some pics of your PSU and description of the fault and what you already tried. I am 100% sure you will get help there from others as well as myself. www.badcaps.net/forum/ They really are a helpful and friendly bunch there.

[@techeng3940]

@@LearnElectronicsRepair I fixed the psu, there is no problem with it now But I found the way to regulate the voltage 3.3 is strange! so I searched for it Thank you very much Mr. Richard

[@abdoelectro2449]

THANKS

[@ucupbintangtoedjoe4489]

Verry Verry much 😕 YESS I like it😮

[@thomasndonye9865]

Hi, am looking for a PWM driver circuit that can drive mosfet and control speed of my big 48v 5kw DC motor. Please share to me if you can.

[@uksuperrascal]

Blink Blink - Who needs an Arduino?

[@psanmuk]

Thank you

[@ankur0077nca]

Do this for Dr b 2002 , Dr b 2005 Dr b 2003

[@jonathanrose456]

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