Are my TL494's faulty?

Thread Starter

michael bore

Joined Jan 17, 2018
6
So, I just got a pack of 10 TL494 straight from the One Hung Low market on aliexpress and when I build the test circuit in the datasheet, or even apply power to them they start pulling around 200-300mA and my supplies current limit kicks in. The chips themselves get a little hot, has anyone else had an issue with this? Did I just get faulty parts or am I an idiot?
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I replaced the 160 ohm resistors with 1k ones since I dont have a power resistor rated that high so the current draw should be even lower. When I even just set pin 13 to ground or to vcc and hook up pin 12 to power and pin 7 to ground the chip still draws too much current and my power supply kicks in to limit the current. Before trying this out I hooked up the circuit for just power, the oscillator and grounded pin 13 with another tl494 and I probed the oscilator and it was giving me a much higher frequency in the 500-600mV range which was something strange as well. Has anyone else had a similar issue?
 

dl324

Joined Mar 30, 2015
16,846
Did I just get faulty parts or am I an idiot?
Only buy semiconductors from reputable sources; or sources that can and are willing to verify the authenticity of what they sell.

Even reputable sources will certify that their parts are genuine. When I order from Newark, the letter of authenticity comes from the CEO.

I don't order anything from AliExpress unless I'm willing to accept counterfeit/knock off product.
 

Thread Starter

michael bore

Joined Jan 17, 2018
6
I've been mainly using it to build up some basic electronic components such as opamps, 555's, power mosfets ect... But I've never had an issue like this where the IC just doesnt work.
 

dl324

Joined Mar 30, 2015
16,846
But I've never had an issue like this where the IC just doesnt work.
It might be that you just don't know if you've been impacted by counterfeit parts. Not working at all is better than not quite working correctly. If the devices were partially functional, you could waste a lot of time trying to discover that.

People who sell counterfeit parts will sometimes throw in some fully functional parts to trick people who think they can QA a sample. With the smart counterfeiters, you need to do 100% incoming QA.

Don't buy parts from places like AliExpress, eBay, or Amazon and expect to get genuine parts. Save yourself some time and grief; buy authentic parts from reputable distributors.
 

ebp

Joined Feb 8, 2018
2,332
I would try it with all pins open circuit except for Vcc, ground and the oscillator. It shouldn't take more than a few mA. I assume you are confident you power supply is not behaving badly. Be sure to decouple the power supply close to the chip - there may be some sort of odd sensitivity, but it seems unlikely. Switcher control chips don't generally get nice clean noise-free power supplies.

I'm kind of surprised it's still in production. The part dates from over thirty years ago and there have been a great many new and better introductions since then. I'm amused at the suggested applications, and have a hard time believing anyone would design it into any of those things. It might be useful for some sort of PWM application, but I would certainly never use it for a switcher.

I once purchased a bunch of DACs, if I recall, directly from Analog Devices via a sales rep, back in the days when AD didn't sell through distributors. Most of the parts were DOA.
 
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