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Chinese 0-30v 3a psu issues

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m3vuv:
i have 3 of these working from an old gas analyser,would it be an idea to use them in place of the op amps?

Kleinstein:
The OP05 should work, but this OP is relatively slow. This can slow down the response. Especially the current limiting may than take quite some time to respond. In case of a short this can cause quite some current spike. On the positive side the drift is low. So the current limit would be more accurate - still the TC and self heating of the shunt limits the stability.
An 741 type OP would likely give better performance.

Normally the current and voltage settings should not directly interact. This may happen if the regulator is oscillating.

m3vuv:
well ive had a mess about with this,im using a 50a bridge rectifier powered by a transfo from an old 20a psu,smoothed by a 100000uf 50v cap,the original q4 is a 2n3055 in a darlington configuration  driving 4 2n3055 pass transistors with 0.1 ohm emitter resistors,ive 3x 25 watt current sense resistors for different current ranges in place of r7,can anyone think of a way of sensing the current on say on the feed to the bases of the pass transistors,im not sure how to connect a current sense resistor in the pass transistor base feed to u3 without blowing things up,could use it as is but as it is all the output current passes thru the current sense resistor so switching between resistors could be a issue as it will carry the full output current.,also in cc mode u3 output is low,in cv mode its high,could i drive a cv indicator led from it,ie is the op amp capable of outputting enough current ?,also all ic's are mc34071p ic's,regards paul m3vuv.

Kleinstein:
0.1 Ohms emitter resistor are kind of at the low end for 2N3055. It may still work with well matched (e.g. selected or some luck) transistors and good thermal coupling. The 2N3055 are relatively slow, this might effect the compensation. One might consider to use at least for the 1st transistor a faster one (e.g. D44H...).

Current sensing from the base current is not really accurate. It may still be used for an additional fast acting hard current limit. So this would not act on U3, but independently. Changing the current sens resistor to a different position would totally mess up the circuit - essentially start over from scratch.

The OPs are powerful enough to drive a LED. Modern LEDs don't need 20 mA anymore - some 1-5 mA is usually still bright enough.

For high power one usually prefers to have transformer tap switching on some other ways to reduce the power loss.

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