Dear Sirs,
I want to design a SMPS for the following Voltages:
Input:
36-75 VDC GND
Outputs:
1. +15V @150mA GND
2. -15V @150mA GND
3. +5V @200mA GND
4. +65V @70mA GND
5. -65V @70mA GND
Please help me how to design this. I hope to hear from you, soon.
Yours sincerely,
M. Ghahari

 

Im sorry but forget about it. Designing a smps requires quite alot of skills, especially in board layout for radio frequency stuff as well as excellent insight in how the smps pwm controllers, gate drives, mosfets and transformers work.

In your case, look for readymade solutions that does what you want.

You will never find one psu that does it all, so your gonna have to look for several and combine them.

 

The best way to do this is a flyback, but you would need some expertise. The 75 VIN rating is a problem as that is far above what most IC's can do, so you can't use a simeple off the shelf simple switcher.

 

As bountyhunter noted a flyback converter with a multiple winding output transformer would work. The transformer would likely need to be a custom design.

The high input voltage can be handled by a high voltage transistor doing the switching at the transformer input.

Do you need each output to be well regulated? If so then you will need the flyback transformer output to generate slightly higher output voltages then needed and use linear regulators on the outputs for precise regulation.

Do the outputs need to be isolated from the input? If so you will need an isolator for the feedback from the output to the input, such as an opto coupler.

 

You do need to define the loading of each output as well as what voltage tolerance is allowed. If they are multiple windings on a transformer, that can be critical to the transformer design. If tight regulation is required, they may need linear regs on them.

We did something similar, the problem with the 36 - 75V input range is you need to step down this voltage to a rail you can use to run a switcher IC from. So you need an "internal rail" to run some control circuits from. I think we used a NPN/zener with a bleed resistor to feed the ICs.

Another option is to use a step-down (buck) with coupled inductor windings for the other outputs. That's still a transformer. You could also use more than one buck with a second inductor winding on each. That gets more complicated.

 

This coupled inductor design handles VIN up to 75V:

http://www.how2power.com/newsletters/1105/articles/H2PToday1105_design_National.pdf


You could add more windings for more outputs, but only the one output is directly regulated.