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Part Number: TPS92310
Please find the attached Isolated 7Watts CC circuit. I have a problem at output voltage which is having 3Volts of ripple out put. Tried increasing the Cout(to 470Uf + 220Uf) but still ripple(50Hz , 3Vpp) been seen.
In reply to Chandrashekhar V9:
Attached the xls with calculation for our design, one more observation is from xls we get,
ZCD pin resistor R10(In our case R65) 643 kΩ(In EVM and our case 66.5K)
ZCD pin resistor R12(In our case R58) 13 kΩ(In EVM and our case 11K)
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In one of the board we changed the value of R65 to 499 and R58 to 30K and added RCD snubber(R=SMF3W150KJ, C=1812B102K202CT, D=1N0007), now we are able to see constant voltage and no hiccup of OVP , also we see expected current output for 7 series LEDs.
But now big problem started, We see U15(TPS92310DGS), R55(3 ohm resistor), Q1(STD3NK80ZT4) getting damaged in some of the boards even with the some of working boards also. We are sure rework is good.
PS: we observer this type of behavior(U15, R55, Q1 getting damaged) even without snubber circuit when we removed R50(Current limiter) and added 0.5 Amps fuse in that place. We removed R50 and tried with fuse because this resistor was frequently getting damaged.
In reply to Irwin Nederbragt:
Hi Irwin, Sorry it is 499K Ohm typo error.
what are your resistor values in series with the LEDs, I saw 50 ohms and someone stated they were changed to 1 ohm? --> I already mentioned that 50 Ohm is replaced with Short.
Also, We expect the Vout of 23V to 24V becuase 7*3.2V(LED VF) = 22.4 V Rgds Chandra
Looks like we nailed down to the issue we had it.
1. Wrong calculation of two resistor of Vzcd, Proper values are between 63K~73K and 11K. Attached the sheet for our circuit.
2. Missing snubber circuit also related to this high current and voltage spikes in primary side. Which is said optional in EVM.
3. Mosfet miss leaded because chosen FET is not good compared to the one in EVM for SOA. Mosfet SOA and Miller region we need to validate with our circuit and layout. Also found mosfet we are using is not same as been used in EVM, Coss is almost 10 times more in our mosfet, Below is the SOA, for our mosfet not sure about the Id at SOA region for our mosfet because we are at 75Khz switching frequency.
4. Layout improvements required to increase thickness of traces in certain area.
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