redwire

0-30V Stabilized Power Supply

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Yep, i came also to the same calculations. There are heatsinks with 0.8K/W, but they are too huge and its not really possible to mount the 2n3055 on it.

I will later check my local dealer, ive got an idea ....


Today i was playing around a little bit with the Powersupply and burned some leds. Why: If you set the current to ~10mA and turn off the supply, u get a short, huge peak of current which kills your leds. My slow multimeter shows up to 30-40mA for a setting of 10mA. Because the multimeter is slow and averaing, i think its way more for a short time.
At the moment ive got like 3000uF only on my caps, so if i got up to 12000uF the peak will be longer and higher.
Is there any solution to keep up the current control "till the end"?

Also possible solution: Switch for output and switch for the supply itself. Or maybe i get a multiple-pole-switch (never saw it with more than 2) switch turn off the output and 220v input at the same time. One switch and 2 relays would be an idea too ...

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Hi fly3rman,
The original circuit used TL081 opamps that have a problem of "phase inversion" when an input voltage got within 3V of the negative supply. So when the power was turned off the negative supply voltage dropped and the output went as high as it could go. So transistor Q1 was added to short the drive to the output when the negative supply began to drop when the power was turned off.

The new circuit uses modern opamps that do not have the phase inversion problem so Q1 was removed. The output should not go high when the power is turned off.

post-1706-14279144413192_thumb.png

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Hmm.

Okay still it does happen, and i do use TI Sampled tle2141, so they should be fine.
Can anyone else who build the supply test this behaviour? Redwire maybe?

I dont think its something in the circuit like the multimeter?

I will test further later today. Will see what happens on U3 pins.

EDIT: Btw it does only affect current control. It does not overcome the set maximum voltage. But if voltage is to max and current is limited, i still has the effect. Ive uploaded a video showing the effect, also very interresting is the flickering effect, no idea where thats from.
http://share.ovi.com/media/fly3rman.videos/fly3rman.10007

Also at ON of the supply there is kind of the same effect: current limit jumps in after a flash of led (so its conducting for a short time)

EDIT2: testing with dc trafo now, i think the effect isnt there with it. Must be the big transformer, maybe i DO need the full 12000uF wrong
EDIT3: Exchanged u3, no effect.

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It looks like you have the output set for current regulation and the output voltage of your project increases when the power supply is turned off.
Then the output current also increases.

I think it is because the negative supply becomes zero volts quickly so D9 cannot keep holding the output voltage down.

You might fix it by increasing the value of C3.

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Hi.
Ive increased C3 to 47uF + 100uF. Same behaviour. Increased to 47uF + 470uF same. 47uF+2200uF is way better. But for this is took reduced the C3 for 2200uF, only a slight increase of voltage/current on OFF.
Couldnt i feed C3 from C1?
With 2200uF on C3: Negative Voltage of -1.5 on negative lane and it does not get higher than -1.1 while OFF process. So thats not the problem i think.

Also nice: fast off/on doesnt produce this behaviour, because caps are still loaded then. So how to delay the output ON after ON of powersupply itself? Its not an option to fully go down with the potentiometers before on/off of the supply.
The effect is still only there if i use current limit, not voltage. IF Voltagelimit is to zero, no flash of led on start or off.

Could be in next design update.
Iam also thinking a on/off switch for the output is a must. But mechanical it would be a problem, because we want an OFF state for Output for each ON of the supply.
Also maybe q1 should find his way back into the circuit because of the dont-have-to-wait-cap thing:
"It is a great advantage in experimental work to be able to kill the output of a power supply without having to wait for the capacitors to discharge and there is also an added protection because the output of many stabilised power supplies tends to rise instantaneously at switch off with disastrous results."
If someone provide me a reasonable R15 value for the REV2 Circuit, i could implement the Q1 into my actually cirtcuit for testing if whished


Is actually the ON behaviour (no limiting for a short time) normal? Cany anyone test it pease?
Btw i have to replace the rectifier bridge (600v, 4A at the moment, getting too hot).

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Hey guys, sorry for putting pressure on this, but i/we do have fixing of this problem as a task on sunday ;]
Can someone give me some input if he has the same problem and if it would help to reimplement q1 again and how to impelent it into the REV2 circuity?
I need clean on/off behaviour on my supply.

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The problem of the output regulated current increasing when the power is turned off is caused by the -1.3V supply dropping too fast. In addition to increasing the value of C3 maybe the value of C2 should also be increased and the power rating of R2 should be increased.

You can add Q1 to short the output of U2 when the power is turned off like in the original circuit but it will be tricky to sense when the negative supply drops low enough to turn on Q1. R15 is not needed. But the max output of a TLE2141 is 80mA so there will be plenty of current in Q1!

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The problem of the output regulated current increasing when the power is turned off is caused by the -1.3V supply dropping too fast. In addition to increasing the value of C3 maybe the value of C2 should also be increased and the power rating of R2 should be increased.

Ive replaced C2 and C1 with 470uF. The negative voltage goed down to -1.6V now.
But the behaviour is different from just drop too fast. It does oscilate. In my case it does go up to +3V, and after some quick flashes of connected leds it goed down  again to -1.2 again and is slowly dropping.

I am also testing Q1 solution right now. Used parts:
Q1 BC548
R13 10kOhm
R14 1.5kOhm
I quicktested, the transistor is always on :/ But i also have to put D10 into. R14 value must be corrected too i think because of difference from -5.6V to -1.3V. I might use a potentiometer for testing.

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C1 must be a huge value to reduce ripple on the output. Therefore with a small load current it takes a long time to discharge. But the negative supply discharges quickly then U3 loses its negative supply and cannot hold the output voltage down through D9 when the power is turned off.

R13 andf R14 are a simple voltage divider. You can calculate values where Q1 is turned off normally but turns on when the negative supply reduces a little.

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I would like to build this circuit and I am looking for the best working solution..There are so many revisions I am not sure which is best.

Can anybody please advise me on  this?

The latest revision (schematic Rev2 and parts list Rev3) is reliable, inexpensive and works well.

post-1706-14279144413671_thumb.gif

post-1706-14279144413871_thumb.png

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I seem to be having a problem sourcing the parts. The closest the biggest supplier in the country can only offer is a 2x15VAC transformer. Can I use this? Otherwise, a 24VAC transformer is availible. Is there any good options for this voltage?

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I seem to be having a problem sourcing the parts. The closest the biggest supplier in the country can only offer is a 2x15VAC transformer. Can I use this? Otherwise, a 24VAC transformer is availible. Is there any good options for this voltage?

2x15VAC is fine (30VAC) if it is rated for 126VA or more or 4.2A AC or more.
With a 24VAC/102VA transformer the max output from the project is about + 25VDC at 3A.

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@ audioguru

Ive calculated the working point on my circuit (42v plus, -1.6 volt minus) to a voltage divider of 10k ohm and 440 ohm. Already did a dirty testing with 10k and 470 ohm, its better, but still problematic. Still the d10 isnt in so far.
I will do more testing with a potentiometer, but there is a flaw in the design with the voltage divider i think.
If plus voltage is kept up and minus voltage drops, the q1 can work. But there will be a point, where plus voltage is also very low, so the needed base voltage cant be kept up and it will be conduct again. Still, this can kill an LED.


The approach must be different, the complete ouput must be OFF as along as plus voltage is under 42V and minus voltage is over -1.3V.
I will try followin approach (maybe in addition): a closing mechanic relais:
http://www.produktinfo.conrad.com/datenblaetter/500000-524999/503605-da-01-en-RELAIS_ZETTLER_AZ762_1A_48DE.pdf
"Must operate DC" for 60 DC Coil is 42V. The difference between our plus and minus lanes is ~43.5V. Connected to this and if one lane drop voltage (off behaviour), the relais is open and output is OFF.

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The "must operate" voltage of a relay is the maximum coil voltage to activate it. Its maximum must operate voltage is 42V and its minimum might be only 30V or less.

Its "dropout" voltage is a minimum of 10% of its nominal 60V rating which is only 6V.
So it is useless to detect when the supply voltage drops.

A comparator is a device that accurately detects when a voltage has dropped to a certain amount.

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hello everyone ( specially audioguru ":D")

I'm from Croatia, and i can't anywhere buy tle2141 or mc34071, so i will buy it on ebay. Now, i want to know is this right one tle2141cp (or is it possible to buy some substitue?) ( http://www.ebay.com/itm/Single-Operational-Amplifier-TLE2141CP-/330629861183?pt=LH_DefaultDomain_2&hash=item4cfb134f3f#ht_1331wt_1110 )

thank you in advance

PS. Sry for my english. :/

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hello everyone ( specially audioguru ":D")

I'm from Croatia, and i can't anywhere buy tle2141 or mc34071, so i will buy it on ebay. Now, i want to know is this right one tle2141cp (or is it possible to buy some substitue?) ( http://www.ebay.com/itm/Single-Operational-Amplifier-TLE2141CP-/330629861183?pt=LH_DefaultDomain_2&hash=item4cfb134f3f#ht_1331wt_1110 )

Yes that is the correct IC. The E-Bay seller is in my country and sells it at almost double its normal cost here. I don't know how much the shipping will cost to your far away country.

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I found some interestin solution about original sheme here http://www.electronics-lab.com/projects/power/001/index.html

Received the following email from Ivan on 02/2010:

Ok. I bulid your project about a day ago. Mounted all the parts on the pcb and then concluded that there is some serious problems in this schematics. First, 2N3055 will overheat, so you have to connect two of them in parallel with emitter resistors 0.1ohm/5w. Second, maximal voltage between '+' and '-' of TL081 is 36VDC.If you connect them as it is shown in this circuit diagram that voltage will be about 45VDC, so they will burn down immediately. To fix this problem you have to reconnect all pins number 7 of U1, U2 and U3, emitter of Q3 and 'upper' end of R19 to out of an 7809 with 18V zener diode between 'common' pin and '-' of 3300uF cap, and input of 7809 connect to '+' of the same cap. Now, on pin number 7 and mentioned parts you'll have 27VDC, and total voltage will be 32.6VDC. Third, instead of using 3300uF, use 4700 or 6800uF/63VDC to reduce the ripple on higher currents (2-3A). The rest of the circuit is perfect. I like it cause it is so inexpensive and easy to make with those simple reconstructions i mentioned.


What think about this???

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I found some interestin solution about original sheme here http://www.electronics-lab.com/projects/power/001/index.html



What think about this???

With 27V on the output opamp then the max output of the project will be only about 21V, not 30V.
You would have the same 21V max output if you used a 21V transformer. Then only a single 2N3055 output transistor is needed and the driver transistor will be cooler.

Why not use the newer 44V opamps and a -1.3V negative supply instead so that the output can be 30V?

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With 27V on the output opamp then the max output of the project will be only about 21V, not 30V.
You would have the same 21V max output if you used a 21V transformer. Then only a single 2N3055 output transistor is needed and the driver transistor will be cooler.

Why not use the newer 44V opamps and a -1.3V negative supply instead so that the output can be 30V?

I'am from Bulgaria and i can't find the newer opamps. I need to find some other solution.....

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A 120VA transformer is slightly too small. Then when the project is supplying 3A continuously the transformer will be slightly warmer than its max allowed temperature.
Inside a box it might get too hot.


Many thanks.  As I do not anticipate using the supply at 3A a lot, nor for long periods I think I will go for this option and just be sensible about suitable cooling.

You do a great job on here, I am sure that many other appreciate your advice as well.

All the best

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