Uc3845 test circuit

G

Gaber Mohamed Boraey

Full Member level 4
Joined
Feb 26, 2015
Messages
216
Helped
4
Reputation
10
Reaction score
11
Trophy points
1,298
Activity points
2,757
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?
 

Sort by date Sort by votes
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 ---

also - try 470nF + 10uF on the Vcc to gnd . . . .
 
Upvote 0 Downvote
Hello friends
Anymore help?
--- Updated ---

Easy peasy said:
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 ---

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

Upvote 0 Downvote
Since we can't see your real circuit - there is no way of knowing how many errors are built into it.
--- Updated ---

The high frequency suggests the timing cap is open circuit.
 
Last edited:

Upvote 0 Downvote
You must log in or register to reply here.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…