Part Number: UCC28C43
Tool/software: WEBENCH® Design Tools
We are students and we try to design isolated dc-dc converter for our PLC project. We use UCC28C43D driver. Our project was designed by WeBench Power Designer (link to design webench.ti.com/.../6). When we tried to start up DC-DC feedback didn't work. We analysed device behaviour and found one problem. Resistor R12 had very small value and internal power supply was overload. We changed R12 to 1 kOhm resistor and voltage feedback was ok. But DC-DC behaviour wasn't ok. DC-DC had discontinuous operation. What could be the reason?
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In reply to Umayal Ramanathan:
This is actual link to the last design.
In reply to Anton Kocherov:
Can you share the Vds and Vout waveforms if possible?
In reply to Sahil Gupta:
drain to source wave forms. Load 100 Ohm.
Can you see if this behavior is observed when you increase the load to 50 ohms/10ohms/5ohms/1.65 ohms?
We are checking on the compensation, meanwhile you can try to see if you are able to find the cause.
I answer instead of Anton. As the output current increases, the pulse on the mosfet becomes more stable, and the output voltage decreases. What is the reason? Oscillogram for a slice.
on 5 Omhs
on 1.6 Omhs
In reply to Mikhail Kolobov:
Hi Anton, Mikhail,
Can you confirm these things:
a. Shunt regulator used in the board(it should be low voltage 1.24 Volts, LMV431). 2.5 Vref shunt regulator should not work for this low Vout?b. Current sense resistor valuec. Voltage on COMP pin and voltage across R12 resistor(at Vinmin of 10 volts)d. Duty cycle value at Vinmin(10 volts) and Vinmax(28 volts) e. if you can share few details on transformer used for the design,that might help as well
Hi, Sahil. Result of measure on Comp pin and R12 in archive. R sense value 0.1 Omh, i tryed to use 0.3 omh, but changing the Rsense value does not change output waveform. About transformer: We use planar transformer based on N49 ferrite ELP 14/3.5/5. Number of coil on primary vinding 30, Calculating inductanse 533uH.Measure.rar
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