Author Topic: TL 494 feedback loop doubt  (Read 1309 times)

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Offline AchuTopic starter

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TL 494 feedback loop doubt
« on: May 20, 2019, 03:47:45 pm »
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.
 

Offline dietert1

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Re: TL 494 feedback loop doubt
« Reply #1 on: May 20, 2019, 04:06:46 pm »
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
 

Offline T3sl4co1l

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Re: TL 494 feedback loop doubt
« Reply #2 on: May 20, 2019, 07:16:18 pm »
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
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Offline Cliff Matthews

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Re: TL 494 feedback loop doubt
« Reply #3 on: May 20, 2019, 09:09:15 pm »
It would seem RV1 in that voltage-sense divider could seriously do harm to the TL494..
 

Offline xavier60

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Re: TL 494 feedback loop doubt
« Reply #4 on: May 21, 2019, 01:15:11 am »
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.
« Last Edit: May 21, 2019, 01:24:12 am by xavier60 »
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