problem on TOPSwitch
I read the paper of TOP252-262 TOPSwitch HX family and followed Fig.42 drawing to make a PCB circuit(see attachement).
I made some modification based on the drawing. TOP261YN and TOP261E was chosen insteady of TOP258YN. I want the 24V output and about 10A. So the transformer was redesigned. The data can be seen in attachement. Some resistors are changed, for instanced, R15,R16 and R17. It works. During input power from 60-230V and no-load and light load(1-2A), the output voltage is steady(about 26V). It is OK. But there are a number of problem in it.
1. Noise
If the input power <180V, I can hear a high frequency noise on the board. After input power up to >190V, the noise was gone.
2. IC burnt
I adjusted the input power up to 230V just for 1-2second, I heared a slight ringing sound on the borad. The TOP261 was burnt. I tried twice, it was the same. Two IC were burn-out.
3. Not enough power
When the input power was about 220V, load was 1-3A, the output voltage kept near the same. It was OK.
But if the input power was <210V, a 3A load was added, the voltage would drop about about 3V. the lower input the more drop output voltage.
Even kept the input to 220V, it cannot add to 5A, in that case, the output voltage dropped about 6-7V.
If added more load, it was shutdown. After removed the load it can work again.
What is the problem? How to adjust and make it more powerful(output up to about 10A, 24V) based on the drawing?
Please help.
Thanks
Comments
In fact, the C1 what I used was two capacities with 47uF/400V. Is there any other problem? I don't know whether 68K/2W x 2 is the problem? I used "PI Expert 8" to design it, it shows me 68K too large.
Thank you
Sure 68K too large, app. twice or more.
And one more - what the R19, VR2 circuit must to do? IMHO this is unnecessary, and may implement negative impact.
I did connected a resistor with 18K/2W in parallel with that two 68K/2W resistors, but it was not any improvement.
R19 and VR2 are used to protect TOP261 when output failure(for example, overload or overvoltage).
The transformer design is any problem?
Thanks
Check output rectifier - may be damaged, because the peak inverse voltage across the secondary rectifier diode is given by: PIVs = Vout + (VmaxNs/Np), where Vmax=1.4xVacmax.
It seems like too low Np/Ns. Check yours calculations.
According to your schematic, the bulk capacitor C1 is 22uF which is too small. You are trying to use both flyback voltage and forward voltage for your output but these two voltages are quite different. So please use either flyback or forward. flyback is commonly used with TopSwitch and you can use our PIXLs Designer in PI Expert to help you design.