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Help with TL494 PWM


Jul 29, 2011
Jul 29, 2011
Hi there people. I'm currently doing a project to make a levitating system with the use of an electromagnet and a control circuit to vary the current in the electromagnet, thus getting the object to levitate. The sensor I'm using is UGN3503 hall effect sensor, and this measures the change in magnetic flux and gives and output voltage proportional to the change. This is fed into the TL494 chip, which then gives a PWM signal based on the error amplifier. This signal then goes to a power mosfet, which turns the electromagnet on and off.

Here's what I've done:

Pin 1 - Hall effect output
Pin 2 - Reference voltage
Pin 3 - Left it open
Pin 4 - Left it open
Pin 5 - 220 nF Capacitor
Pin 6 - 2.7k Resistor
Pin 7 - Ground
Pin 8 - 12V supply
Pin 9 - Gate pin of a power mosfet
Pin 10 - Shorted to 9
Pin 11 - 12V supply
Pin 12 - 12V supply
Pin 13 - Ground
Pin 14 - Into pin 2
Pin 15 - Left it open
Pin 16 - Left it open

I am failing to get any PWM signals at all, what have I done wrong?

Here is the data sheet
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