Top250 and Auto-restart
I try to make a 48V 3A with TOP-250YN (Image is attached)
But output voltage is about 4 volts also I have to wait for about 1 minute to output capacitor achieve that voltage!
Bias voltage is too weak and it has 0.5V and it change to 0 and 0.5 by every 1 sec.
this is video of bias voltage reaction:
http://www.4shared.com/video/Hgl8LW7V/MOV03675.html
What is my problem guys?
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First thank you .
It was a light load. 100 ohms resistor but it is not a big diffrent if I remove the 100 ohms resistor.
Anyway I remove TL431 circuit and add zener diode to set a feedback but result is same, The weird things is when I cut the feedback circuit from C-pin !!! Output voltage and reaction is same.
If you found out the problem please let me know , I want to know about amount of startup duty cycle. How can I see it on scop?
Look at output voltage on scope -- if it does not rise signficasntly above 4 volts for a short time you must have error in transformer build or hook-up
This is wave of secondary:
And it comes up realy slowly to 48V about 2 min! I Think the main problem is duty cycle ! it is only 200ns! it is 0.01% of 60Khz! , But I don't know why it happends...
That really sounds like error in tranformer design or hook-up
It Works now!
The problem was hook-up and wiring.
Now I have a small problem and it is output current , it is limited to 0.7A . I try to connect X pin to gnd but it is limited to 1.4 now! what should I do?
See if drain current is reaching datasheet specified max. If it is then I would say there is still issue with transformer
What is DC max limiter in this Ic? I think the problem is max duty cycle
When I put a 1k ohme resistor between optocopler pins (transistor side) output voltage comes up to 34V on 20 ohme load, I saw wave of bias winding voltage on scope and I found out the max duty cycle rise up from 39% (without 1k resistor) to 50% ( with 1k resistor).
Then I saw output voltage of Bias winding.
On light load it was 12.5V but it never rised up from 14.3V (in software it says 12V) and if I tried to gave more amps from output it rise up and instantly IC went to auto-restart mode!
Does supply regulate at no load or light load? Also Tl431 is overstressed as it is a 30V device -- you need to add 20 V dropping zener in series opto anode to Vout path to reduce voltage stress anode to cathode of TL431.