Output Voltage Level Setting Problem
Posted by: koksalocal
on
We designed a power supply with a universal input and multi outputs.
Pleased see attached schematic.
We had a problem in setting the 3.3V output. When we measured the voltage level of this output with no load we saw that the voltage level was at about 3.7V. 2.5 volt of 3.7 volt was across the resitor R10 and remained 1.2 volt was across resitor R9. From a simple voltage diveder stanpoint this result is ver strange. Because the voltage difference on the resistor R9 should be about 0.825V instead of 1.2 volt. We think that some current goes in to the TL431.
What can be the problem?
Files
| Attachment | 大小 |
|---|---|
| schematic.pdf | 165.15 KB |
评论
This sound like insufficient control current from opto coupler. Try reducing R7 to 100 ohms to increase drive current capability of TL431 into opto LED. Also check voltage on C16 which is the bias for the opto output transistor -- there needs to be a minimun of 8V for this bias. If it is lower than this during light load you will need to add more turns and possibly increase C16 value.
