Switched mode laboratory powersupply

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Hi Everyboby!


I have a "cute" 750VA toroidal transformer, this is a 50Hz type. very very heavy :)

So, I was thinking about, what if I build a laboratory PSU with this trafo, and the electronics is a simple DC/DC converter. A step-down regulator.
The trafo hax 4x23V secundaries, and I plan to use 2-2 series connected, to get about 65V DC.
The specifications would be:
Output voltage: 0-50V, or 0-55V
Output current: 7-8Ampers.
And here comes the "trick". Becouse, I plan to use a step-down converter, I can achieve more current, when the output voltage is lower than 65V DC. For example, when the output voltage is 12V, then the output current can be 20A, or even more, 30A.


Has anyone made a switched mode lab. powersupply?
How can I reach that the output waveform is totally flat? no spikes, no high frequency components....
I could put a simple emitter-follower after the dc/dc regulator, and on the emitter-follower is dropping only a few volts, jut enough, to attenuate the noise.

Any thoughts? :)
 
One common solution is to have a linear regulator with a switching preregulator. That way you can keep the voltage drop over the pass transistor(s) in the linear regulator low and independent of the output voltage. However, with the currents you talk about, you will still have to burn away quite many Watts in the linear regulator.
 
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