How to reduce VIPER17 start-up voltage (from the default ≈100 Vdc to 50 Vdc)

[emontllo]

Hello,

I would like to operate a flyback converter at a wide rectified voltage range (from 50 Vdc to 380 Vdc). My design is currently based on the ST VIPER17L.

Is there any way to reduce the start-up voltage of a VIPER? Although the Brown out protection can be deactivated and the flyback can effectively work at 50 Vdc rectified voltage, it is not possible to start the driver at low voltage.

I have already tested the flyback with a start-up voltage of 100 Vdc and then reduced the bus voltage to 50 Vdc it and it does work perfectly.

Any recommendation, external power-up circuit, or suggestion would be greatly appreciated.

 

[emontllo]

Re: How to reduce VIPER17 start-up voltage (from the default ≈100 Vdc to 50 Vdc)

I just designed this small circuit (reusing some components already in the flyback circuit). This charges the Vdd capacitor with 2 mA until it reaches 10 V.
If the auxiliary winding is providing power to Vdd it should reach 14 V --> precharge circuit off. I chosed a PNP transistor that should withstand the peak power during initial charge.

Any comments?

 

[emontllo]

Re: How to reduce VIPER17 start-up voltage (from the default ≈100 Vdc to 50 Vdc)

I have already tested this precharge circuit to power the IC externally and it still does not work. Definitively, the VIPER requires a drain voltage between 80V and 100V to start operation. I will need to switch to a different flyback control / drive IC.