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0-30 Vdc Stabilized Power Supply


Sallala
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Hi Phaethom,
1) The voltage of C1 is low because a 24VAC transformer is 25VAC without a load and its peak is 35.4V. the rectifiers drop it to about only 34VDC.
2) Pin 4 of U2 has a 5.6V zener diode. Maybe you used one that is made for a high current, so its voltage is low in this circuit.
3) Pin 6 of U1 should be 11.2V but maybe you used a zener diode made for a high current so its voltage is low in this circuit.

Even with your low voltages, the output amplifier has a gain of 3.07 so your max output voltage should be near +30.7V, not just +19.98V. R11 and R12 determine the gain of the output amplifier. Check their values.

What is the part number of the 5.6V zener diodes that you used?

Without a load and with the voltage pot and the current pot turned to max, is the current-regulating LED turned on? What is the output voltage? What is the voltage at pin 6 of U2?

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1.if I use an ammeter for it ...it will show the ampere that the load use or the ampere that was set ?


The stupid thing will only show the current flowing trough it, but this hasn't always to be the current flowing trough the load :D
In plain: You can connect a switch across the output terminals of the project and produce a shortcut by pushing it. Then you can adjust the current limit, flick the switch back and use the project the normal way with the ammeter showing the current flowing trough the load.
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An ammeter in series with the load causes a voltage drop that ruins the excellent voltage regulation of the project.

Instead, connect the ammeter in series with the output transistors then its voltage drop is made-up by the circuit since it is inside the negative feedback loop. But maybe the voltage drop is high enough to reduce the max voltage output of the project at high current.

You can use a voltmerter to measure the voltage across R7 which is the current-sensing resistor, then calibrate it for amps.

You can also use a voltmeter to measure the voltage produced by the current-setting pot then calibrate it for the amps setting.

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The stupid thing will only show the current flowing trough it, but this hasn't always to be the current flowing trough the load :D
In plain: You can connect a switch across the output terminals of the project and produce a shortcut by pushing it. Then you can adjust the current limit, flick the switch back and use the project the normal way with the ammeter showing the current flowing trough the load.


beacause of my bad english...Icant understand your answer. i am also an amature in electronic.so please explain it more clear



Instead, connect the ammeter in series with the output transistors then its voltage drop is made-up by the circuit since it is inside the negative feedback loop. But maybe the voltage drop is high enough to reduce the max voltage output of the project at high current.


can you draw a diagram (or mybe a shematic) for me (about out put transistors)??????? :-*
i cant understand it.

You can use a voltmerter to measure the voltage across R7 which is the current-sensing resistor, then calibrate it for amps.

You can also use a voltmeter to measure the voltage produced by the current-setting pot then calibrate it for the amps setting.

and what is the range of each voltmeter????which of them show the current flowing trough the load.and which of them show the amps that was set with p2.
note : its not NOT NECESSARY for me to set current at special place.but it IS important for me to show the current flowing trough the load...

so help me please with diagram not with written message. :-*

I hope you apologize me for my gossips :-[ :'(




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Hi Arman,
An Amp-meter shows the current in the load.

Here is the schematic modified with an amp-meter in series with the output transistors so its voltage drop is made-up bu the circuit.

Or you can use Ohm's Law to calculate the voltage across R7. R7 is 0.47 ohms. 3A through 0.47 ohms produces a voltage across it of 3A x 0.47 ohms= 1.41V. Calibrate a voltmeter to show 0.3V when a voltage divider has 1.41V across it then the meter will show the load's current.

P2 is the current-setting pot. It is in series with R17 and R18 and they are fed from pin 6 of U1 which is 11.2V. When P2 is set for 3A it has 0.17V across it which can be amplified and fed to a voltmeter to indicate the current setting of P2.

post-1706-14279143262181_thumb.png

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The original project might work with a 24V/1A transformer but its ordinary opamps will be operating with a supply voltage higher than their absolute max rating.

If the opamps survive then the low output voltage indicates that maybe a transistor or diode is connected backwards.

i check all of the diodes and transistors and ... but it steel doesnt work
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