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| UCC28730: Does not switch as expected, too low output voltage | |
| Part Number: UCC28730 Hello, Im trying to implement UCC28730 into a design. The input voltage should be 270 Vdc - 600 Vdc and output should be 24 Vdc. Im currently using the MOSFET C2M0280120 and the WA8759-al transformer. I have followed the calculation formulas in the UCC28730 datasheet, but still won't get the right output voltage or expected switching characteristics. Below are some photos on the circuity, scope on the gate of the MOSFET Any help on what could solve my problems here would be great. Best regards, David | |
| Considering the layout guidelines on the datasheet, I soldered the parts together like this: and got these results: Gate on mosfet: Source on mosfet: AUX1: VDD on UCC28730: Secondary side: Is this right behaviour? When I loaded the secondary side the MOSFET started switching faster. After this the circuit spontaneously failed and I think it was the UCC28730 that broke. When powered on VDD is now 0 V. | |
| Hello, Most likely you are shutting down due to a fault. One thing I would recommend is moving away from a TVS switch node clamp. I would recommend and RCD clamp on the switch node. Just put a 511K ohm and 1 nF capacitor across the 3 170V diodes. This should help reduce ringing. This design if you are not using the UCC24650 wake up chip will require at least 2 to 3 ma of preloading to keep in regulation under no load condition. You can just use a resistor for this on the output. Double check your transformer polarity to make sure it is correct for a flyback converter. The UCC28730 is trying to startup and it is given 3 gate pulses and it is not starting up due to the following. Input voltage is too low input under voltage Output voltage is to high triggering over voltage protection. Over current protection. The data sheet describes when fault conditions occur. You are correct that using a proto board to wire you power supply is not a good idea. You also appear to be using wire wound resistors. I would avoid doing that as well because they have large inductance. If they are low inductance you should be fine. I do have some recommendations for you. 1. Order the UCC28730 evaluation module so you can evaluate the power supply operation. The following link will get to the User's guide. <secret URL>/lit/ug/sluub75/sluub75.pdf?ts=1588013518855 2. Their is an application for troubleshooting PSR flyback converter at the following link that you may also find helpful. Regards, | |