Electronics > Beginners
TL431 linear power supply
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not1xor1:
For an output limited to a 2.5-25VDC range there is no need of a voltage boost stage. In the circuit below a LED and a diode allow the LM358 go a couple of volts beyond its worst case maximum output.
BTW the zener should be at least 2W and the load resistor (1kΩ across the output stage and ground) should be at least 5W.
The 2 leds display CV / current limit mode.
I forgot to change Q8 (a BC327 would be OK) and to put a reverse diode on the output.

xavier60:
That's a neat way of driving the overload LED. Is D11 still needed? It would be adding to the regulators dropout voltage.
mike_mike:
I am very very impatient to see a final version of this schematic, in order to build it.
I can built it only starting from the next week.
Kleinstein:
D11 is still very useful to allow a lower minimum output voltage. Due to the LED, the OP can not pull the voltage down so far.
One could get away without if D2 and R14 are also left out. The LED D10 current would than be only limited by the OP internal current limit - should be OK with the LM358, but could be too much with another OP.

If worried about the dropout, one could use a separate rectifier and filter stage for the current source around Q7 and Q8. This could give some 1 V extra, as there can be less drop due to ripple.
Cliff Matthews:
Dumb question since 30v 2-watt zener could be $$... Would jelly bean LM317 and small heat sink be just as stable?
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