Author Topic: Help me design a DC/DC converter :)  (Read 1098 times)

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Offline syscall

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Help me design a DC/DC converter :)
« on: December 12, 2014, 03:20:18 pm »

I am building a power supply. 0-30V 5A max. Initially i wanted to go for switchmode all around, but then i thought i only need a switchmode dc/dc 'buck' converter and a 150W linear transformer and 10A bridge to feed it. Control and feedback circuitry is going to be based on the atmega8. Do you know any resource with similar designs, so i could check my ideas with someone's project?

I also have a few probably trivial questions:
Suppose the transformer puts 30V 5Amax on the secondary, what maximum range of voltages i can pull from the output with buck topology?
How do I calculate the inductance of the output stage (after the mosfet).
Switching mosfets must switch always, right? i.e you cannot have 100% duty cycle PWM from controller?

Thanks and have mercy on a beginner :)

edit: something like this: (see attachment)
« Last Edit: December 12, 2014, 11:16:42 pm by syscall »

Offline Seekonk

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Re: Help me design a DC/DC converter :)
« Reply #1 on: December 12, 2014, 04:04:33 pm »
A bootstrap supply cap must go to common in order to recharge so it can't be 100%.   However, my solar system is a bootstrap battery instead of a capacitor ( I have rechargeable batteries up the wazoo from local recycling).   I use a UNO for my charge controller and use 12V secondaries from old UPS transformers as the inductor.  At 490hz a little less than ideal but cheap.  With a 255 PWM, that gives you about 200mv steps.  Probably good enough for a bench supply.

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