Flyback, single stage, 55W, offline, Fully dimmable, No electrolytic capacitors.

[Flyback]

Hello,

We are doing an offline 55W PFC’d Flyback SMPS LED driver. (fully dimmable)
It is a single stage converter, with a constant off time flyback, and uses no electrolytic capacitors.

The schematic and LTspice simulation are as attached. One of the issues which is of concern is that the inverting opamp U11 in the pdf schematic (MCP6001U) , may for a short instant get a voltage on its inverting input that is more negative than minus 300mV. The datasheet doesn’t hint towards problems, but do you believe that this could cause reliability issues?

MCP6001U datasheet:-
https://www.mouser.com/ds/2/268/21733h-26779.pdf

 

[alec_t]

I haven't the strength to analyse the circuit in detail, but could you give the inverting input a weak pull-up to bias it against being driven negative?

 

[crutschow]

If it worries you, put a resistor (say 1-10kΩ) in series with the op amp input with a small Schottky diode to ground (anode).

 

[alec_t]

Playing with your sim, the negative excursion of the inverting input can be drastically reduced by splitting R7 into two 5k resistors in series and moving D47 cathode to the join of the two.