HI Guys.
I'm in the process of building a variable bench power supply. 0-50V @5A.
I have wound the transformer secondary for 0-6-12-22-44 taps. By doing this I can geep the dissipation through the output transistors to a minimum.
I would like to build a circuit that can automatically switch the taps in and out as I advance the voltage pot etc.
Obviously only one relay should be on at any given time, otherwise two of the taps may be shorted. BOOM!!
I will have to power whatever circuit and reference voltage from one of these taps as I don't have space for another auxilary power supply to power this circuit too. I was thinking 4 comparators driving npn transistors, switching 4 relays in and out.
Any ideas? Anyone build something similar before?
I'm in the process of building a variable bench power supply. 0-50V @5A.
I have wound the transformer secondary for 0-6-12-22-44 taps. By doing this I can geep the dissipation through the output transistors to a minimum.
I would like to build a circuit that can automatically switch the taps in and out as I advance the voltage pot etc.
Obviously only one relay should be on at any given time, otherwise two of the taps may be shorted. BOOM!!
I will have to power whatever circuit and reference voltage from one of these taps as I don't have space for another auxilary power supply to power this circuit too. I was thinking 4 comparators driving npn transistors, switching 4 relays in and out.
Any ideas? Anyone build something similar before?
You could inspire yourself from automatic voltage stabilizers: they were popular ~30 years ago, but you can still find schematics:
http://4.bp.blogspot.com/-JaW-OdnXs...s1600/TRIAC+CONTROLLED+STABILIZER+CIRCUIT.png
The purpose and voltages are different, but the principle can readily be reused: you just need to adapt the components value.
An advantage of triacs is that your supply won't sound like a castanets band in operation....
http://4.bp.blogspot.com/-JaW-OdnXs...s1600/TRIAC+CONTROLLED+STABILIZER+CIRCUIT.png
The purpose and voltages are different, but the principle can readily be reused: you just need to adapt the components value.
An advantage of triacs is that your supply won't sound like a castanets band in operation....
4 Comparators may not be enough to prevent "boom" . Any fault in comparators, rezistors would easily cause more than one output go high.
So, I think you should add another logic circuit that would drive only one tranzistor "in every case" .
Maybe, a circuit consisted of ex-or gates which will give you a high output only when inputs all are not same and use its "fault" voltage output to let relay drivers work.
And, i dont think a triac would be easy to use since you have AC voltages as low as 6 volts because of its conduction voltages and relatively high hold on currents. So, mechanic relay seems best option in your case.
So, I think you should add another logic circuit that would drive only one tranzistor "in every case" .
Maybe, a circuit consisted of ex-or gates which will give you a high output only when inputs all are not same and use its "fault" voltage output to let relay drivers work.
And, i dont think a triac would be easy to use since you have AC voltages as low as 6 volts because of its conduction voltages and relatively high hold on currents. So, mechanic relay seems best option in your case.
My, now getting quite old, lab supply uses noisy relays to switch the transformer taps as I turn the output voltage adjust knob.
Works well and flawlessly.
There may be a sch for a lab supply somewhere on the net.
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