Author Topic: TL494 PWM will not operatate in push-pull despite pins 13 and 14 being shorted  (Read 614 times)

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Offline Verliebt_in_München17Topic starter

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[SOLVED] My trigger was set to alternate.
So the circuit works comepletly fine, it's just that the IC won't seem to work in a push-pull configuration, which i want it to be, i have triple checked every connection possible, and i have concluded that my circuit design could be wrong so i need somebody to help me find any other triggers that could lead the IC to stay hard-locked in single-ended mode.
I will be providing addition information and pictures upon request.

Schematic


Underside


Comparision of the sawtooth wave on pin 5 and one of the outputs


  :-BROKE
My bad if the images are too large, no idea how to make them smaller

« Last Edit: May 18, 2024, 03:49:07 pm by Verliebt_in_München17 »
 

Offline Benta

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The whole upper half of your circuit is dysfunctional.
You have three inputs connected together, but none of them are driven by an output or a voltage source. On top of that, there's a questionable "capacitor divider" with no apparent purpose.
 

Offline DavidAlfa

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The TL494 outputs are made by NPN BJTs, so depending on how you connect them, they can push or pull, but not both.

You can combine both outputs for a full push-pull stage, IIRC you can do so with this:
- C1 to VDD.
- E1 and C2 connected together, this is the output.
- E2 to GND.



Your circuit doesnt make much sense. How do you expect it to work without any feedback?
If you want to test the PWM output with a potentiometer, try the test circuit included in the datasheet.
« Last Edit: May 17, 2024, 11:35:29 pm by DavidAlfa »
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Online xavier60

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The DSO shows the output being half the oscillator frequency. That indicates push-pull mode.
The output signals are expected to be antiphase to each other.
EDIt: It's odd that the output transitions don't align with the step in the oscillator sawtooth.
Maybe the DSO is set to Alternate Trigger mode?
Maybe this explains the original problem. The 2 outputs will appear to be in phase.
« Last Edit: May 18, 2024, 03:18:07 am by xavier60 »
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Offline Verliebt_in_München17Topic starter

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Yes, the scope's trigger is set to alternate beacuse i was getting an unstable reading, i'll try to see if the problem was with my scope all along

edit: yes it was, thanks for correcting my newbie mistake
 

Online xavier60

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The DSO will have settings to improve triggering stability that can be experimented with.
Starting with selecting a fast transition to trigger from. For example, the negative step of the oscillator waveform rather than the positive going ramp.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 


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