Issue in voltage regulation using TL494

[anshuii]

TL;DR

am using given schematic for voltage regulation using TL494. When feedback not given, A and B are not connected, getting a pulse of 35% duty of 0-12V. But when feedback given ( A & B connected), in output I am getting a 12V DC rather than a pulse even though the terminals of error amplifiers have some difference of voltage & sudden large amount of current flow at point C and D. why the pulse is getting vanished with 12V dc & sudden increase in current from 0.5 to 1.5A . any blunder in ckt

 

[Tom.G]

Wiring of the 1K resistor in the lower right of the schematic is wrong.

C1 and E1 (pins 8, 9) are shorting the power supply to ground, which has probably destroyed the IC.

Since Output 1 is not used I suggest leaving C1 and E1 (pins 8, 9) not connected.

V_CC (pin 12) should be connected directly to the power source. (get rid of the 1K in the lower right)

(see data sheet section 9.3.6 Error Amplifiers)
2_IN- (pin 15) should be connected to V_REF (pin 14)
2_IN+ (pin 16) should be connected to GND
(see data sheet section 10.2 Typical Application)

For more details, see Application Report SLVA001E at:
https://www.ti.com/lit/an/slva001e/...com%2Fproduct%2FTL494%3FCMP%3Dconv-poasamples


NOTE:
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This IC is designed to drive bi-polar transistors. You probably need extra circuitry to drive a field effect transistor (FET). The Gate of a FET is a capacitor and generally needs high peak currents to rapidly charge and discharge that capacitance. The present circuit ahs a 1K pull-up resistor driving the FET gate capacitance, comprising a lowpass filter. Check the resulting time constant and compare that to the switching frequency and switching time. The idea is to quickly switch the FET between On-Off-On to avoid operating in the high-dissipation linear region.

Replace the IC with a new one and try again.

Cheers,
Tom