POWER SUPPLY DESIGN

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what program do you use for simulation? Will the resistors in ladyphoebe's circuit be okay with the power capacity she assigned?
 
I forgot about how to design a differential input. I remember that the "long tail" (my R2) should have a high resistance or be a very high resistance current source. So I increased the value of R2 and the resulting opamp has very good voltage regulation.
 

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Now it's beginning to look like a power supply,although there's still much to do.For a start could someone remove the dead short between T1 emitter and R3?
 
I wanna ask if its possible if i can add a LED in series after with resistor 1k ohm . About the how much power each resistors can sustain, Is it fine that 0.33 ohm and o.22 should have 3W, the 1k ohm have 2W and the others are 0.5 W?
 
The simple formula for power dissipation is the current squared times the resistor value so for an output of 3A then each 0.33 ohms resistor has 0.75A in it and the power dissipated is 0.186W. A 1/4W resistor will be fine.

The 0.22W resistor with 3A in it dissipates 1.98W so use a resistor size larger than 2W because a 2W resistor dissipating 1.98W is extremely hot.

If you add an LED in series with 1k at the output then it will not light when the output is less than 2V for a red LED or 3V for a blue LED. Also when the output voltage is low then the LED will be very dim.

One problem, all opamps have a frequency compensation capacitor to prevent them from oscillating at a high frequency when negative feedback is used because phase shifts in the amplifier change the negative feedback to positive feedback at high frequencies. Try a 100pF capacitor between the base and collector of your Q3.
 
in that case, where can i put a LED?
 
Audioguru,a 0.33 ohms 1/4W resistor mounted on a PCB and inside a warm case will almost act like a fuse if the power supply is subjected to a sustained short.Normally you see-even in the cheap Chinese power supplies-wirewound resistors of 3-5Watts.
 
Rolf Zetterberg said:
Audioguru,a 0.33 ohms 1/4W resistor mounted on a PCB and inside a warm case will almost act like a fuse if the power supply is subjected to a sustained short.Normally you see-even in the cheap Chinese power supplies-wirewound resistors of 3-5Watts.
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Q4 in the latest schematic limits the output current to 0.68V/0.22 ohms= 3.1A so each 0.33 ohm resistor has a maximum current of 0.77A and a power dissipation of 195mw. If it is too warm (it won't be hot) then use 0.22 0hm resistors for only 130mW each.
 
Yes,I know that and your calculations are correct,but how do you explain all the home-built and professional and less professional power supplies that I've seen through life almost all use oversized resistors here?In fact,I can't recall a single one using 1/4W resistors in this position.
Imagine a power supply shoved in under a shelf together with other instruments in a summerwarm room and running for hours at full power-it gets very warm inside.This puts strain on all components.A resistor should never be used at it's full rating(or even close to that) in this environment!Also,if one the resistors in question burns off,then all the load is placed upon the remaining three that could result in even more unnecessary problems.
 
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