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TL 494 feedback loop doubt

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Achu:
Hi

Im tying to make a boost converter circuit.All the designs based on tl494 are shown to have positive feedback.
In my knowledge in if the o/p voltage increases feedback increases and pwm duty cycle will also increase and this will
cause a domino effect.
Maxim website shows a negative feedback loop.

Im confused please correct me guys.

dietert1:
From Fig. 9 of the TI TL494 datasheet you can understand that the input + and - denomination is unusual.
The schematic you have appears to be correct. They exchanged the two comparators for current and voltage but that shouldn't matter.

Regards, Dieter

T3sl4co1l:
Right, the output is inverting (see the pair of NOR gates).  Or inverting again depending on if you use the C or E pins as output, and with an inverting driver (as shown here) or not.

Tim

Cliff Matthews:
It would seem RV1 in that voltage-sense divider could seriously do harm to the TL494..

xavier60:
The way that the OR-ing diodes are wired means that whichever op-amp's output is the highest will take control of the PWM, reducing it. The op-amps need to be configured as non-inverting.
The output phasing has to also be correct. When the TL494's transistors are on, the switching element should also be turned on.

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