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0-30 Vdc Stabilized Power Supply


Sallala
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Hi audioguru, I tryed it with DC motor and 100n across inputs of voltmeter - when motor is rotating slowly everything is well, but when rotations raise, voltmeter shows absurd numbers (It is a 3V DC motor. Bellow 2V everything is well but then voltmeter starts to show that voltage is about 8V and it is still changing beetween 2 and 8 volts. i measured it with multimeter and it showed 2.7V, so in that multimeter must be some shielding.). This happens only with motor, when i connect another aplience like bulb or radio receiver, everythung is OK. Do you thing that it will help to add one more 100n capacitor accross input of voltmeter? thanks

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Hi again!
I have a problem with supply for my digital meters connected to this PSU. I have made a supply circuit for this meters. There is a diode bridge, capacitors (2x 100n + 100uF) and 78L09 stabilizator. This circuit is connected to output pins on transformer, where is 24V AC. Voltage on output of circuit is exactly 9V, but when i connect it to meters, they show absurd values and the numbers are blinking. But when I connect them to a 9V battery, everything is OK. In the meters manual there is NOT written that supply voltage must be absolutely indepedent on voltage being measured. Is there any way how to modify this circuit to make digital meters work?
Thanks

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a fue more questions:
-can i use 1N5408 diode in the place of D1, D2, D3, D4 where in the circuit was writen to use the 1N5402,3,4 diode 2A - RAX GI837U

-what is the diode that is writen on it 1N 75 2A 227 and can i place it as D7, D8 = 5,6V Zener diode

-can i put 1N4007 diode instead of D11 = 1N4001 diode 1A

- how much Tolerance can i give to the R1 and to R7



Ron

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Before: how much watt i need for the transformator?

I am sorry I missed your question before. In this thread we discuss problems with the original design for this project and fixes for them. The voltage and current of the original spec'd transformer were too small. Increasing the transformer's voltage means that special high voltage opamps must be used. See my recommended parts list.

a fue more questions:
-can i use 1N5408 diode in the place of D1, D2, D3, D4 where in the circuit was writen to use the 1N5402,3,4 diode 2A - RAX GI837U

People who built the original project reported that these little diodes get too hot. A 1000V 1N5408 diode will also get too hot. I recommend using a high-current rectifier bridge module bolted to a metal chassis.

-what is the diode that is writen on it 1N 75 2A 227 and can i place it as D7, D8 = 5,6V Zener diode

A 1N752A zener diode is tested and designed to operate at 20mA. D8 is the project's main voltage reference and R4 in the original project supplies only 1.2mA to it. The 1N752A's datasheet shows that its voltage is low and it barely regulates at such a low current.
I recommend using a BZX79C5V6 zener diode for D8 that is tested and designed to operate at 5mA, and changing R4 for 5.6mA.
D7 can be nearly any 5.6V zener diode.

-can i put 1N4007 diode instead of D11 = 1N4001 diode 1A

A 1N4001 is rated for 50V and a 1N4002 is 100V but cheaper. A 1N4007 is rated at 1000V and is more expensive. The output of this project is only 30V so any of them will work.

- how much Tolerance can i give to the R1 and to R7

Most resistors today are 5%. See my list.

post-1706-14279142593425_thumb.png

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I am sorry I missed your question before. In this thread we discuss problems with the original design for this project and fixes for them. The voltage and current of the original spec'd transformer were too small. Increasing the transformer's voltage means that special high voltage opamps must be used. See my recommended parts list.


People who built the original project reported that these little diodes get too hot. A 1000V 1N5408 diode will also get too hot. I recommend using a high-current rectifier bridge module bolted to a metal chassis.


A 1N752A zener diode is tested and designed to operate at 20mA. D8 is the project's main voltage reference and R4 in the original project supplies only 1.2mA to it. The 1N752A's datasheet shows that its voltage is low and it barely regulates at such a low current.
I recommend using a BZX79C5V6 zener diode for D8 that is tested and designed to operate at 5mA, and changing R4 for 5.6mA.
D7 can be nearly any 5.6V zener diode.


A 1N4001 is rated for 50V and a 1N4002 is 100V but cheaper. A 1N4007 is rated at 1000V and is more expensive. The output of this project is only 30V so any of them will work.


Most resistors today are 5%. See my list.


oooo
i just came from the store  :'( any way can you tell me more about the changed parts why changing them and in what are they better?

and one thing more i can install a cooling system (2 computer fans, intake and outtake) that will help?

Ron

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ammm
what wre the pots and trimpots?

The voltage adjust pot is P1 and the current adjust pot is P2.
Pots are made with a 20% tolerance so if their values are 20% low then the voltage or current max will be 20% high unless a trimpot (small preset pot) is added in series to increase the total resistance to the correct value.

and about the Tolerance
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Connect your voltmeter directly to the output terminals because the internal wiring has some voltage loss.
A current meter in series with the load has a resistance that ruins the fabulous voltage regulation of this project.

This is very good advice by the way  ;D I blow around 10 or more fuses when tried to connect a good ampermeter in series with the load.
When me and my friend tried the PSU it worked good except when we tried to test its current limit with a low resistence ampermeter we got one big problem - the main fuse at transformer's input was unusable anymore.We thought the PSU doesnt have working current limiter because the ampermeter showed current above 3A and then the fuse blew,but it seems that was the problem - the ampermeter in series with the load.
I was going to ask about this "bug" but after some time i got the answer myself.The strange thing is that with some no-name chinese ampermeter it showed some results and the current protection/regulation was OK.But when tried to connect a better device the fuse blew.Which i guess means the first "noname" ampermeter has higher resistance and therefore the results were wrong.
Anyway,the PSU is somehow working and did the job it was supposed to do  ;D
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Hi Gruber,
The current-setting pot in this project has a tolerance of 20% and the values of the resistors were chosen so it provides 3A if the pot's resistance is 20% high. If your pot's resistance is 20% low then with it set to max, the project will try to produce 4.2A.
Such a high current will overload the transformer and cause its core to saturate. A transformer with a saturated core isn't a transformer anymore, it is a piece of wire across the mains, blowing fuses.

You should add a trimpot in series with the current-setting pot. Adjust the trimpot so the project supplies a max of exactly 3A when the current-setting pot is at max.

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Hi,
I have built this PSU few months ago with modified parts (with no casing). :P
Few hours ago I have plugged it and spark came out near C1.
Now output is ~0.42V and I cannot set any voltage. :'(
I Have done few measurments:

Q4:
Ucb = 39.5V
Uce = 39.5V
Ube = 0V

U1 (pin4-6) = 11.35V
U2 (pin4-6) = -0.5V
U3 (pin4-6) = 37.9V

voltage across r7 is few mV

I wonder what could be wrong and if you can help me.
I hope OPamps aren't damaged, because it is really hard to get them ???

Thanks!

(sorry for my bad english)

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Hi Tedy,
Maybe the spark was caused by a poor solder joint or fused pcb trace to C1. It has a huge surge of current to charge it.

Doesn't your project use two 2N3055 transistors with emitter resistors as Q4?

Turn off the project quickly if U2 gets hot. Q1 might be turned on all the time shorting its output to ground, because something might not be working in the negative -5.6V supply.
If Q1 is normally turned off, the output of U2 should increase as you adjust the voltage pot.

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Yes, but R2 and C2 feed the negative -5.6V supply circuit.
Q1 is designed to short the output of U2 to ground at the moment that the power to the project is turned off, to prevent the output voltage from rising. The negative supply has a small filter cap that discharges much quicker than the main positive filter cap when the power is turned off. When the negative -5.6V disappears, Q1 turns on.

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