0-30V Stabilized Power Supply

[audioguru2]

ok.. how about this?

MC33071/72/74, MC34071/72/74. Are they all the same?

Their datasheet show that thew xxxxx1 is a single opamp, the xxxxx2 is a dual opamp and the xxxxx4 is a quad opamp.
The datasdheet shows that the MC33xxxx has a very wide spec'd ambient temperature range for NASA but the MC34xxxxx has a tempreature range that is reasonable on earth. Guess why the MC33xxxx costs much more?

i cant find a 12000uF 63V.. can i just put a 10000uF+1000uF+1000uF in a parallel as substitution?

It is a simple filter so 10,000uF in parallel with one 2200uf or 3300uf capacitor is good. You can use one 15,000uF capacitor or 10,000uF plus two 1000uF capacitors to make 12,000uF if you want.

 

[iBOLIT]

Hello.
Can I use MC33171? It's slower (1.8MHz, 2.1V/uS) and has less Capacitance Drive Capability (500pF).
Thank's.

 

[audioguru2]

Can I use MC33171? It's slower (1.8MHz, 2.1V/uS) and has less Capacitance Drive Capability (500pF).

The MC33171 is low power so its idling power supply current is 1/9th the current of an MC34071 (I use them in low power battery-powered circuits) and its output high current is too low for this project at 1/9th as much as from an MC34071.

 

[zulcao]

audioguru, you can tell me what the special features mc34071 have?

I noticed that when the current control operates (at minimum), still have 0.7 volts in the input of oamp (due to the diode), multiplying by the gain, we have ~ 1.8 V, so in case of short-circuit 0.6A pass because of the output resistor of the 2n3055. is there any way to reduce it?

 

[audioguru2]

audioguru, you can tell me what the special features mc34071 have?

Unlike most opamps, the MC34071 and the TLE2141 have inputs that work as low as the negative supply which can be ground in some circuits. So U1 and U2 do not use a negaive supply and the negative supply for U3 is only -1.3V.
Their max allowed supply is 44V.

I noticed that when the current control operates (at minimum), still have 0.7 volts in the input of oamp (due to the diode), multiplying by the gain, we have ~ 1.8 V, so in case of short-circuit 0.6A pass because of the output resistor of the 2n3055. is there any way to reduce it?

No.
When the current control is set to maximum then 3A flows through R7 which is 0.47 ohms so it has a voltage of 1.41V across it which is one input to U3. The other input to U3 is a voltage from the current-setting pot. If more than 3A tries to flow then U3 reduces its output voltage which reduces the output voltage of the project until exactly 3A flows. If the output is shorted then the output is reduced to 0V with 3A flowing.

When the current control is set to minimum then only the idle current of the U1 (a few milliamps) and the low current of the feedback for U2 flows in the output of the project.

 

[zulcao]

well, I do not know if it's because I changed the oamp, i have not found anyone here in Brazil, but still have a 0.6 A flowing when I short, maybe if I use a germanium diode instead of a silicon?

 

[audioguru2]

well, I do not know if it's because I changed the oamp, i have not found anyone here in Brazil, but still have a 0.6 A flowing when I short, maybe if I use a germanium diode instead of a silicon?

Which opamp did you use?

 

[zulcao]

I used the UA741. With the tension he'd never zero, so I put a third diode to the negative input is -2.1 V and also linked to the negative pin of u2, This worked perfectly for the tension, but not to the current, I was wondering if u3 can put a negative output? let say -0.7 V? this could solve the problem I think.

 

[zulcao]

I made these changes and seems to be working  ;D ;D ;D

Obs: OAmp: UA741

View attachment 41533

 

[audioguru2]

The uA741C opamp is 43 years old. Its max supply is only 36V but the supply for U1 and U2 in this fixed project is 40VDC when it has no load and is higher if the mains voltage is a little high so it will fail soon. Its inputs must be 3V above its negative supply so your -2.7V negative supply is too low. The output of U2 must go down to about 1V but the 741 opamp cannot. It is much too slow which results in undershoots and overshoots when the load current quickly changes.

If you used an MC34071 or TLE2141 opamp for U3 then with a -1.3V negative supply its output can go as low as -0.9V to -1V to make the output voltage exactly zero. Your old 741 opamp cannot do that even when its negative supply is -2.8V.

Every opamp is different. Maybe you are lucky to find an old 741 opamp that works with your changes. But I design circuits that work properly with any passing opamp. 

 

[zulcao]

Thanks for your help, it was very useful. I really was lucky because the PSU is working  ;D. But as soon as I can I'll change for the MC34071.

Thank you very much

 

[morpheous87]

I have two working PCBs for the PSU. Now I'm trying to make LCDs which will display the voltage and the current. I'm going to use Arduino for measurment and voltage deviders. My question is, could I use only one Arduino board to measure voltage and current from both PCBs (because of the common ground, which I should use for the Arduino board)?

 

[zulcao]

if you DONT put Them in series, I think ther isnt any problem

 

[morpheous87]

if you DONT put Them in series, I think ther isnt any problem

That's the problem, I thnk to use it in series and parallel also.

 

[zulcao]

So if you join the both comon, when you out put them in series, it will short.

 

[nzo]

Could one of the smarties here point me to the page in this thread that has a final working version of this power supply? Could this final version be made into a sticky so the less electronically endowed of us don't have to wade through 78 possibly problem-filled pages to get to the bits that are accurate and valid?

This looks like a great project. Thanks.

 

[zulcao]

Page 55

 

[audioguru2]

This website does not have "stickies" like most other electronics chat sites.
This website does not allow you to key in a page number so you must go back only 2 pages at a time which takes a long time to get to page 55.

 

[nzo]

Ok thanks. I didn't mind clicking to page 55, but when I got there the train had already left What am I looking for on page 55? A new circuit diagram, parts list, a link to the info? There is nothing there like that from audioguru. Am I in a time warp?

 

[zulcao]

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