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0-30 Vdc Stabilized Power Supply

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Let's try something different, let's "back into" the circuit to find DC gain (the circuit has AC gain as well).



Hello Again!

Took me a little while to digest the latest post but I think now that I am set!  The equations made it all clear and helped tremedously!

One of the most confusing aspects to my understand went away when I (finally) realized that the Q2/Q4 transistors were configured as a Darlington pair and therefore had a Vgain near unity!

Thanks so much for the patience and guidance offered!

I'm off to build a power supply!

Kevin

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Hi,

I am using HA17741 op amps which are rated at below the almost 40V supplied to them. for a 36V op amp. tho replacing them for the TL081 wouldn't really fix that would it, they are 36V also? 

Which is why they failed. or so i think they did. not sure how to test that. U1 and U3 have voltage but point 3 and 4

and U2 ther is no voltage. maybe i can trace the circut back from U3 untill i find the voltage?, donno heh

OPA445 are $34.10 each. thats around $15 - 20 USD. does anyone know of somthing rated between TL081

and OPA445. thats between 36V and 50V? I did find some US suppliers for cheaper then that but then the postage kinda makes it pointless

If not i guess its the OPA445, in the end i don't want somthing thats going to just melt.

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yea im not sure,

im in new zealand, but even things like TL081 which i found in the end. for $1.61NZD. thats less then $1 US and the 2n3055 for $2.20NZD. maybe the OPA445 is just rare

and thx. ill try one of the 44V op amps

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has someone redesign PCB for duble operational amplifier like MC34072 ? or even quad ? I can't find 34071 or TLE2141 in my place and OPA is to much expensive here ... but I have a few 34072 ...

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U2 needs to be a single high voltage opamp because it has input offset voltage adjustment pins for RV1. Then the value of RV1 and R10 must be adjusted to match different opamps. Some opamps need RV1 to connect to the positive supply instead of the negative supply.

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You can look up the spec's for those old opamps to see if they will fail with a supply voltage from this project that is higher than the max voltage allowed for them.
The OP37 and NE5534 are de-compensated and therefore would oscillate in this circuit.

Since you cannot get modern parts then use a transformer with a lower voltage like 20VAC which would give a unregulated positive supply to the opamps of 29VDC without a load, plus the negative supply of 5.6VDC so they will have a total supply of 34.6V which is less than the 36V max allowed for ordinary opamps.
The project will then have a max output voltage at 3A of current of only about 20VDC.


EDIT: I find UA741 OP Amp, it is 44V, its not decompensated....

Ok I try it with some 44V OPAmp.  I can buy OPA445 now, but for $14.11 per unit :-D Its wery expensive, so its better to buy professional lab power supply.

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Hi
I've got a bridge rectifier module GBPC2502P 25A 200V. Can I use it in this circuit?

Also can I make some measurements on the circuit before placing the op-amps 445AP. It was very difficult to get them so I don't want to burn them. I'm looking for expected voltages at different test points in the circuit.

Thank you for your help.

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I've got a bridge rectifier module GBPC2502P 25A 200V. Can I use it in this circuit?

It is bigger than is needed but it will work fine.

Also can I make some measurements on the circuit before placing the op-amps 445AP. It was very difficult to get them so I don't want to burn them. I'm looking for expected voltages at different test points in the circuit.

The 30VAC transformer will be about 31.5VAC without a load. Then its peak voltage is 44.5VDC and the rectifier bridge will charge C1 to +43.1V which is the positive supply for the opamps.
The negative supply should be close to -5.6VDC.

If anything shorts the output of an opamp then it will get pretty hot. Double check which pin is which on the Q2 and Q4 transistors.

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I'm Kinda confused :-\...... though this seems to be a good project!
Can somebody gimme the Block diagram!

It is just a power supply that has voltage regulation and current regulation.
Here is a simple block diagram. What is confusing you?

post-1706-14279143415943_thumb.png

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hi everyone,
its me again. I have a ques, can the 12,000uF, 63V is replaced with a 18,000uF, 50V. i cant find one with 63V. and the other i can find is 8000uF at 50v and 100V.
u suggest parallel-ing the 8000uF o use a single 18,000uF 50v? but i feel the 50V would do good enough.
i would like to thank for any comment or suggestion. Im cant access the forums the office in PC. so, Thanks again in advance.

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Hi Adian,
The peak voltage from the 30VAC transformer is only 44VDC when there is no load. A 50V capacitor should be fine. I selected a 63V capacitor because it was available on Farnell's site.

You can use any value over 10,000uF. You can parallel capacitors for a total over 10,000uF if you want.

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Also read this: http://www.electronics-lab.com/forum/attachments/Digital_Panel_Meter.pdf

It's true that you need to connect a load to the output. Read this to understund how to current limiter works.



I can't access to this file http://www.electronics-lab.com/forum/attachments/Digital_Panel_Meter.pdf

Regards,

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can i change the 0.47ohm 10W resistor with a 0.05ohm 9w instead. reduces the overall power consumed.

You mean a 1W resistor.
Sure, but unless you also change a few other resistors then the max output current will try to be 32A. Also, U3 opamp will need to have its input offset voltage adjusted to zero.

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Hello. I'm ready to do this power supply  :)
And I have some questions....
Ps. I'm sorry for my English language. it isint very well.
1. Can I use MJE3055 tranzistor instead 2N3055 ?
2. Can I use 2200uF 50V electrolytic capacitor instead 3300uF 50V ?
3. In this circuit said that need 0.47Ohm 5W rezistor, can I put  two 0.22Ohm 3W rezistors?
Thankyou for the answer  ;)

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Hi Aqmas,
Welcome to our forum. ;D
Are you going to make the original project? It has problems.
Its transformer is too small and gets too hot.
Its Q2 and Q4 transistors get too hot.
Its rectifier diodes get too hot.
Some resistors get too hot.
Its opamps operate with a supply voltage higher than their maximum allowed voltage.
Its max output is only 25V/2.5A.

I have made a parts list with improvements and it is posted in this thread many times. Then the improved project will have a well-regulated 30V/3A and nothing gets too hot.

1) An MJE3055 is small and can dissipate only 65% as much heat as a metal case 2N3055. I recommend two 2N3055 transistors. Each transistor needs an emitter resistor to equalize their gain.
2) 2200uF and 3300uF are much too small. I recommend 12,000uF.
3) I recommend 0.47/10W since 3A x 3A x 0.47= 4.23W and a 5W resistor would be extremely hot. 

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Can 2N3055 be replaced with 2N3773 as it was mentioned in other forum?

The 2N3773 is a little bit better than a 2N3055 but it is not twice as good so two still must be used in the improved project.
With a 30VAC transformer, the unregulated positive supply voltage is 40.4VDC. If the output is set to a low voltage or if it is shorted then the output transistor must dissipate 121W. The 2N3055 is rated for 115W max and the 2n3773 is rated for 150W max but only with a "perfect" heatsink. There is no such thing as a perfect heatsink unless it has a high velocity fan.

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hmmmm........
I thougt, that I put a fan to freeze a radiator. May it would be better? I really want to put a mje3055, would fan help that it dont overheat  ???
Hmmm, o if I do with old part list, but put 12'000uF capacitor, 0.47/10W rezistor, and bigger transformer ?
I think I could put transformer near mje 3055 and freeze it together. and if I put some rezistors with more W, ant then they wont be so hot...
and instead  1N4001 diode put 1N4007.

Maybe then everything would be okey?

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I thougt, that I put a fan to freeze a radiator. May it would be better? I really want to put a mje3055, would fan help that it dont overheat   ???

An MJE3055 is in a little TO-220 plastic case that is too small to dissipate all the heat from this powerful project.

if I do with old part list, but put 12'000uF capacitor, 0.47/10W rezistor, and bigger transformer ?

Many more parts need to be upgraded.

1N4001 diode put 1N4007.

1N4001 and 1N4007 diodes have a max current allowed of only 1A which is too low. The 1N5402 diodes in the original parts list are rated for 3A max but get too hot. A 6A to 10A rectifier bridge module should be bolted to the metal chassis for cooling.

Maybe then everything would be okey?

No. Many things will still be wrong.

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I have jus one mje3055  ;D
Then ok.  persuaded  ;D
I found a new list of components  ;D
Then I  will have to bought all components, but ok :)
But I cant find a new pcb... can help someone? thankyou
If we need to use two 2N3055, then how connect them?

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