Uc3845 test circuit

[Gaber Mohamed Boraey]

Hello
I've built this circuit

I hope it's clear enough for you
I've biased with 12-15 v, the Vcc pin, and here is the signal shape I've got on oscilloscope on the pwm pin, the IC output pin, and Vref by the way is 5v

And here are the readings

As you see, no pulses at all,
Is it something wrong with the circuit?, or my scope settings or what!, although I've got the scope calibrated before measure

How can I add led to the circuit to check if light with pulses and use as reference to know that the IC is good or bad beside the scope signal?

 

[Easy peasy]

Really the pwm output should be filtered and sent back to the feedback pin via a pot - this allows you to vary the pwm and check the feedback loop is working.

--- Updated Aug 26, 2024 ---

also - try 470nF + 10uF on the Vcc to gnd . . . .

 

[Gaber Mohamed Boraey]

Hello friends
Anymore help?

--- Updated Aug 26, 2024 ---

Really the pwm output should be filtered and sent back to the feedback pin via a pot - this allows you to vary the pwm and check the feedback loop is working.

--- Updated Aug 26, 2024 ---

also - try 470nF + 10uF on the Vcc to gnd . . . .

Okay, I will try this modification and see, thanks for your care to help
How you think of this signal I got?, something wrong with my scope or with the. Circuit itself.?

 

[Easy peasy]

Since we can't see your real circuit - there is no way of knowing how many errors are built into it.

--- Updated Aug 27, 2024 ---

The high frequency suggests the timing cap is open circuit.