Post Go back to editing

LT3751 - High Voltage Regulation Issue - Low Switching frequency and no amplitude modulation

Category: Hardware
Product Number: LT3751

Greetings,

i am facing issues with the LT3751. I am using the LT3751 as a high voltage regulator to get 1200V Output at 300W, powered by a 48V supply. The simulation in LTSpice is working fine, the regulation systems works and i can get Output voltages of 1200V with an output power of 300W or even more. Nevertheless while testing the designed board, i face different issues:

1) The LT3751 is operating at a frequency of 16kHz, when it enters charging mode or maximum output delivery mode. If I read the datasheet correctly, it should at least be in the range of 26kHz?

2) Independent of the load, the LT3751 never gets to regulate the amplitude of the input current, but is constantly varying the duty cycle. I tried to fix this issue with stabilizing the feedback and the power supply, as well as changing the Imax with different Rsense, but nothing changed this behavior. The feedback is isolated with an optocoupler.

Consequently the LT3751 Output Power is limited to around 200W, instead of the 300W from the simulation.

Any hint, what might be the problem is appreciated :)