Best topology for Isolated 5 W power supply WITHOUT optocoupler feedback

Best topology for Isolated 5 W DC/DC power supply WITHOUT optocoupler feedback

Hello,

I need to design an isolated DC/DC converter with the following specs:
- Input voltage: 14 VDC to 36 VDC
- Multiple output voltages: 12 V 12 V 5 V
- Total power: <= 5 W
- Optocouplers should be avoided (high reliability circuit operating in tough conditions)
- Low input current ripple desired for low conducted emissions
- Robustest (1), simplicity (2) and stability (3) are more important than efficiency and output ripple specs.

I have been studying it with a Flyback, however input current ripple is high and difficult to filter appropriately. Push-pull is an option to but I am worried about core saturation problems.

My questions are:
- Which topology would you suggest for the application
- Specific control IC meeting the specs
- Would a 2 stage converter (e.g. fixed duty isolated push-pull + buck converter) be a good choice?

Thank you!

Re: Best topology for Isolated 5 W DC/DC power supply WITHOUT optocoupler feedback

hi,
it may help you.


Matthai.

Maybe use a PWM feedback signal at high frequency
that's inductively coupled (explicit xfmr or at high
enough frequency, even a PCB trace pair at safe
separation).

Most commercial DC/DC modules are using flyback for multiple output modules. It's the only way to get off without secondary regulation or other multi stage designs. Input ripple can be LC-filtered. Inter-windings capacitance and respective injected interference current are a more serious problem in isolated DC/DC, I think.

Thank you for your comments.
A properly filtered flyback seems to be a good option, I will try to filter it properly with Pi or multiple stage LC. Regarding feedback, I am thinking on using an auxiliary winding for indirect voltage feedback, is this a good alternative? provably load regulation will not be very good but I was thinking on LDOs (Reliability and simplicity is more important than efficiency in this design!) for fine regulation of the outputs.

if you don't want to use optocoupler then I suggest to add another output of around 12V and take feedback from it without opto i.e. this output should have ground common to input ground path. topology is flyback.