Isolated Offline flyback with no auxiliary coil
Isolated Offline flyback with no auxiliary coil
(OP)
Hello,
My offline flyback auxiliary coil voltage wanders too much with changes in load. So i am going to try and power the PWM controller from isolated "off-the-shelf" DCDC converters connected to the 24V isolated secondary of the flyback.
I've never seen this circuit in a book or anywhere....and wonder if there is some subtlty i have overlooked, very grateful if readers could cast an eye and give any comments......
[IMG]http://i3.tinypic.com/4t9gfmo.jpg[/IMG]
My offline flyback auxiliary coil voltage wanders too much with changes in load. So i am going to try and power the PWM controller from isolated "off-the-shelf" DCDC converters connected to the 24V isolated secondary of the flyback.
I've never seen this circuit in a book or anywhere....and wonder if there is some subtlty i have overlooked, very grateful if readers could cast an eye and give any comments......
[IMG]http://i3.tinypic.com/4t9gfmo.jpg[/IMG]





RE: Isolated Offline flyback with no auxiliary coil
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Isolated Offline flyback with no auxiliary coil
RE: Isolated Offline flyback with no auxiliary coil
You need some voltage feedback to help with the regulation.
Why don't you have a third coil on the transformer to power the drive circuit once it begins running? Sometimes, this coil can be used to power the driver circuit and provide the feedback for voltage regulation. And, the circuits never use relays to switch from the "bootstrap resistor" to the running power supply.
Try doing some more research for reference designs. A proper design usually involves a circuit with an opto-isolator in the feedback path and are much simpler than what you are proposing. Look for Topswitches as one possibility to do what you want.