Please give clear values:the output it not the expected voltage.
Thanks for the reply.Hi,
Please give clear values:
* what voltage do you expect
* what voltage do you measure? At wich load current?
Klaus
The transformer's datasheet mentions TNY266. Atleast I do not see a major difference in parameters between TNY266 and TNY276 which could lead to such a behaviour.Hi,
Why/how did you choose the transformer to this application. (Not saying it's right or wrong)
I just see that the switcher model is not listed in the transformer's datasheet.
Did you follow PCB layout considerations very closely? In doubt show your PCB layout.
Klaus
Since R3 is 1K Ohms and parallel to the LED of PC817, then my understanding is that majority of the curent should pass through the internal led and not via R3. I am also little confusedHi,
I doubt this is your problem at all from what you describe.
What happens if you make R3 e.g. 330R?
I'm not sure if I'm getting something embarrassingly wrong here, I probably am knowing myself..., but if I (firstly, choose to ignore the parallel value of the feedback voltage divider itself [in parallel with any load resistor - that you don't have at present, you say] in parallel with the 1.034k into the TL431) calculate:
5V - (Vf LED + Vf TL431) e.g. 5V - (1.7V + 2.495V) = 5V - 4.195V = 0.805V
Then 0.805V/1.034kOhms = 778uA iK...
TL431 never works for me with less than at least >1mA iK.
--- Updated ---
...So, at the other extreme: (5V - (Vf LED + Vf TL431))/34 Ohms = ~23mA. That must return to ground through the TL431, then. Is that right? Does that mean that the TL431 either has <1mA or >23mA iK?
Hi,
Why/how did you choose the transformer to this application. (Not saying it's right or wrong)
I just see that the switcher model is not listed in the transformer's datasheet.
Did you follow PCB layout considerations very closely? In doubt show your PCB layout.
Klaus
Thanks for the reply.If you are actually using a 30V rated schottky diode for the 24V output, the observed behavior is most likely caused by diode reverse breakdown and respective overcurrent shutdown of the switcher. Please calculate the maximum reverse voltage of D6 with 230 V AC input, you get about 100 V.
I measured the voltage at BP/M and it is 5.9V exactly as per the datasheet. So, probably this pin isn't the problem. EN/UV is also dependent on the feedback (but not sure yet, as to what's wrong is going on here)Hi again,
I was having a quick browse of the datasheet for the TinySwitch-II Family out of curiosity, and couldn't help but notice the BP/M connection in your schematic is different to figure 14 on page 8, described as: "The circuit shown in Figure 14 is a low cost, high efficiency, flyback power supply designed for 12 V, 1 A output from universal input using the TNY278." but the 'typical application' on page 1 is not the same as yours either. I also read that EN/UV has a current range window of 75 to 115uA and then it shuts off, but your resistor is 3.9M and in the schematic there it's 3.6M, so that can't be the problem. Page 2, figure 2 - is it possible that the cap to ground or something about the EN connection makes the device stop switching? I'd guess it was either the En pin or the BP/M pin that causes the issue - guess being the operstive word.
Forward pulse voltage = 325V/4.4 + 24V.Also how did you exactly calculate the reverse voltage to 100V?
Thanks but what is 4.4 here?Forward pulse voltage = 325V/4.4 + 24V.
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