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Bench power supply help

anej

Hi everyone!
So I want to build a 2-channel adjustable (with potentiometer) SWITCH MODE power supply that can deliver 5 A at 12 V. I have 120 VA transformer 2x30V 2x2A. Now I don't know which Package/IC to use to step-down the voltage. I was looking on the internet and i found a package lm2678t but I don't know if that is OK for my project. + How big shoud the rectifier capacitor be ? 1000uF or different ?

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  • 0 in reply to supper_slash

    I am sorry Lupe but the LM138 won't work.  It's max input voltage is 40v.  30vac once rectified and filtered will give over 42vdc.  Also he needs 5A at 12V so the LM138 would have to drop 42-12=30 volts at 5 amps which is 150 watts.  More than the LM138 can handle.  The requirements call for 2 channels at 12 volts, 5 amps.  This is 60 watts which is what each winding can deliver 30 volts at 2 amps = 60 watts.  With a high efficiency switching power supply, you raise the available current as you lower the voltage so that the output power is close to the input power and little is lost in heat.  Only problem is that a switching power supply is not so easy to build from components.  A solution would be to buy a low cost switching power supply module.