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0-30 Vdc Stabilized Power Supply

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I think I found a possible replacement. Look at the MJE180 from Fairchild.
http://www.fairchildsemi.com/ds/MJ/MJE182.pdf

Good, Ft (50 MHz), gain (50 min) and Ic (3A)

Initial simulations look very good. Very stable with low ESR values and very fast loop load-step response (200nS).

I will analyze this further, but it looks good.

Mouser have them for $0.60 ea.

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Hi AN920,
Digikey don't have any MJE180 transistors, maybe because it is old and is hardly used anymore. It might become obsolete soon.

I haven't seen transistors with that old Motorola case since the '60s.

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Hello everybody

I finished building my modified project maybe a year ago and promised back then to post some pictures as soon as i could get my hands on a digicam :)
Well, here they are:

Outside:
RIMG0029k.jpg

The output can be shortened and switched off by two flick switches. This allows adjusting of voltage and current limiter before feeding it to the circuit.

In order to prevent heating problems, I used a sandwich design for the bottom of the case. The 92mm fan sits directly behind the filter on the bottom. It blows up to the mounting plate, which has several holes in it to allow fresh air to get to the board, the trafo, and some other places. The rest of the airflow goes to the back and is forced through the heatsink.

Inside:
RIMG0037k.jpg
Looks shocking, but at least there's no space wasting ;)

Both BD 241 and the 0,47R resistor are mounted on the sheet of aluminium bolted to the black heatsink.
The 10.000

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If you are referring to the bode plots of the PSU loop stability, that was injected with a current transformer inserted into the feedback path. I could have injected in the error amp's own feedback path as preferred by some people. In this case I don't think it will make much difference.

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The problem is that there is only one point in the feedback path that contains all the feedback information from both loops, and that would be between the R12, C6 & C9 node and the R11 and U2 pin 4 node... but I'm not sure it's a legitimate injection point. The same rules should apply here as for DC-DC's and per Dr Venable and Dr Ridley, specific criteria have to be met in regards to the injection point, and if not followed, the results are not exactly accurate.

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Somebody who has the project made with the slow TIP31A driver transistor could 'scope its output while it was loaded and unloaded with a 3A load.

IC voltage regulators have overshoot and ringing at their outputs but the capacitor to ground on their output reduces it very well.
The LM723 regulator has a horrible step in its response when it is loaded:

post-1706-14279143550141_thumb.png

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The current probe or current transformer method was suggested by Dr. Middlebrook long ago. Every injection point has its pros and cons. I think where a loop is very marginally stable various methods may make a small difference, but where it shows obvious instability it won't make much of a difference. By using the better driver we can get it unconditionally stable, so why not? The price is only $0.18

Someone who tests the supply for load switching may see no oscillation, because of high ESR output cap. He will see a voltage dip and overshoot when the load is removed. The real test will be with a high grade (switchmode type) electrolytic with low ESR.

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Hey all.... i'm  from brazil and here dont sell mc34071 and rs1506, someone can tell a website that i can buy this??
ty...

The TLE2141 opamps can also be used.

Go to www.farnell.com and click on the flag of Brasil. But they also don't have either opamp.
Maybe they can order them for you.
They are in many countries. The Canadian/American one has EVERYTHING.

post-1706-14279143879222_thumb.png

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Audioguru, thanks for good advices. I did measure U1 output and it is approximately constant (10.2V without load, and 10.1V with 3A load ). Also I realized that I need thicker wires on output. Now my supply really works good. There is negligible voltage drop. Thanks again!!!

Mayhem, maybe You should take same advices...

Best regards!

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Could someone please decsribe what Op Amp circuits U1, U2 and U3 are please just to get a better understanding. I have a fair idea what the are but just want to clarify it.

U1 is an 11.2V voltage reference. The opamp has a gain of 2 and it multiplies and feeds the 5.6V zener diode D8.
U2 is the main amplifier for the voltage regulator. It has a voltage gain of 3.074. It has a variable input voltage.
U3 is the current regulator. It compares the voltage drop across R7 caused by load current with the setting of the current pot. If the load current is higher than the current pot then U3 reduces the output voltage through D9 until it is the same as the current pot.

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Hello Mayhem!
I did make test to my unit and result is next: Output voltage is set to 1.50V and then when I put a 1.5A load voltage falls to 1.37V!!!
Accordingly, there is a voltage drop of about 0.13V!!! How much is Your voltage drop under this conditions?
P.s. My project is not entirely original. I did make a small changes in rectifier.


Hey Kvakva, thanks for doing the tests. My voltage drop is much higher. When i put a load of 1.5A the voltage drops nearly to 0V. I did what audioguru suggested concerning the voltage in the output of U1. I have a steady voltage of 11V, even under load conditions. I'm almost giving up this project, i measured everything that i thought could cause the problem and i found nothing that seems to be wrong. Kvakva, can you tell me what were the modifications that you did in the original project? What transistors did you use for Q1 and Q3? The only thing that i can't understand is the voltage between base and emitter of Q2 and Q4. I measure none voltage drop. I believe i should be measuring 0,7V but i can find the problem. Can you measure also these voltages on your ckt?

Thanks for helping me Kvakva and congratulations for your success!!!!!

Is this the project that you build?

post-45379-14279143881667_thumb.gif

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Hi Mayhem,
Of course Q2 and Q4 should have a base-emitter voltage drop of 0.7V to 1.2V when there is a load. They are emitter-followers. Yours must be shorted from base to emitter.

Opamp U2 has an open-loop voltage gain of about 200,000 so it should amplify the small error to keep the output voltage from dropping when there is a load.

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Hi No Worries,
At a DC current of 3A, a 6800uF filter capacitor of a 60Hz mains that is full-wave rectified produces a ripple voltage of 1.85V peak which is a fluctuating loss of voltage which might cause hum at the output.
If the mains frequency is 50Hz then the peak ripple voltage is 2.2V.
Use two 6800uF capacitors in parallel.

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Hi Mayhem,
Of course Q2 and Q4 should have a base-emitter voltage drop of 0.7V to 1.2V when there is a load. They are emitter-followers. Yours must be shorted from base to emitter.

Opamp U2 has an open-loop voltage gain of about 200,000 so it should amplify the small error to keep the output voltage from dropping when there is a load.


Hey Audioguru. I allready replaced both Q2 and Q4. Before the replacement i did a diode test with a multimeter on both transistors to verify if they had any problems. They had none. No shorts and only two voltage drops. I believe my problem is in this area because the output (pin6) of U2 varies according to the load, but i don't know where. Is there any other component (or problem in the pcb) that could cause this problem?  What is the function of R1?

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with the voltage adjusted to 1,5V and connecting a load of 3,7 ohms i get the following table:
                         with load                   without a load
pin 3 of U2            0,5V                             0,5V
pin 2 of U2            0,49V                           30mV
pin 6 of U2            1,52V                           25,4V

I measured Vbe of Q2 and Q3 and i have always 0V, with and withoud the load connected. The only voltage drop i have is 66mV in Q2 when the load is connected.

1) Pin 3's voltages are normal because U2 and the output transistors have a voltage gain of 3.07.
2) Pin 2's voltage without a load is way too low. If the output transistors are working properly then the output voltage would be pinned as high as it can go. When the output voltage is 1.5V without a load then pin2 and pin3 voltages should be almost the same. If the output voltage tries to go a little too high then the negative feedback through voltage divider R11 and R12 increases the pin2 voltage slightly that causes U2 to reduce the output voltage. If the output voltage tries to be too low then the negative feedback reduces the pin2 voltage slightly that causes U2 to increase the output voltage.
3) The pin6 voltages are both wrong.
a) With a 405mA load the voltage should be 1.5V plus 0.7V for the base-emitter for Q4 plus 0.6V for the base-emitter voltage for Q2 plus a little voltage for R15. Then the pin6 voltage should be about  2.9V, not 1.52V.
b) Without a load the output voltage is way too high. It should be 1.5V plus 0.4V for Q4 plus 0.3V for Q2. Then the pin6 voltage should be about 2.2V, not 25.4V.

Check the transistor datasheets to see which pin is which.

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hey ppl!!
i buyed today some commponents but i have some problems... the zener diodes is bzx55c5v6 and bzx55c10, is it the same of bzx79c5v6 and bzx79c10???

and the diodes 1N4148 is all like zener diodes.. is correct or i buyed the wrong diode??

ty all XD now if all is correct i just have to buy trimpots, ics, bridge and capactors

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rcakto    For the large cap you have lots of options to use,  one, two  or parallel several.  On one build I used 3  of these  661-EKMH630VNN562MR (mouser part #)    It doesn't need to be exactly 12,000uf.

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Hi all! Can anyone help me?

I've built this power supply. All worked fine. But when I try to load it (15-20 V, 1.5-2 A), C7 explodes. The load itself is a flyback (its primary winding, 5 turns of 1mm wire), which is driven by a power MOSFET. Could this be because of self-induction impulses?

post-46700-14279143920256_thumb.jpg

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