• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

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

Status
Not open for further replies.

Flyback

Well-Known Member
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
 

Attachments

alec_t

Well-Known Member
Most Helpful Member
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

Well-Known Member
Most Helpful Member
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

Well-Known Member
Most Helpful Member
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.
 
Status
Not open for further replies.

EE World Online Articles

Loading
Top