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0-30V Stabilized Power Supply


redwire
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  • 3 weeks later...

So, I ended up getting the PCB:s from Repairman (great service there) and have put one together, I do have a weird issue someone might be able to help me with:

The circuit the PCB is based on is the Liquidbyte version from the top of page 88 of this thread (http://electronics-lab.com/community/index.php?/topic/29563-0-30v-stabilized-power-supply/&page=88). The things where I deviate a bit are:

  1. The ballast resistors for the 2N3055's are 0.1 Ohm rather than 0.33 since I didn't have those available at sufficient power rating
  2. The sense resistor is 0.46 Ohm: Rather, it's a small network of two 0.56 Resistors in parallell after which there is a single 0.18 one in series, yielding 0.56/2+0.18 = 0.46 Ohms, again for availability
  3. The single 10 uF Polyester cap was also lacking, so it's replaced by two 4.7 uF ones in parallell, they turn out to measure almost exactly 10 uF
  4. My rectifier bridge is only rated at 12 Amps at 250 V, this should be sufficient though
  5. The Transformer is a 30V/4A, yielding the same 120VA

Now, when I fire the thing up, I can adjust voltage fine from about zero (haven't been able to calibrate it yet) but only up to 17.56V (which may not be that exact given it's from my multimeter). Turning the trim pot adjusts down from this fine, but when adjusting up it goes to those 17.56 and stops. Now, if I disconnect the voltage adjust pot entirely the output shoots up to 40V, connecting it back makes things stop at 17.56 again. Have looked things over and can't find anything obviously wrong, maybe someone has an idea to what may be happening would be greatly appreciated!

Cheers

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Whats the voltage drop over your 0.46 ohm sense resistor?

It is past bedtime here, can think more tomorrow. But I think it could be current limit.

When you remove the voltage trim pot you get really high gain, which means that the input voltage at the rightmost op amp can be low (caused by current limit) and still provide a high output voltage.

If the 100k current limit trimpot is connected wrong it will always be 100k. This will mess up the current limit op amp.

So I hope the solution is to put a bridge/jumper/short between pin 1 and 2 on the 100k trim pot.

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Unloaded or loaded with a minimal load (a 1k resistor and a led) same thing. Voltage drop is about 180 mV, and I don't think it's the current limiting, the current limiting led doesn't turn on, which it does if I set it low enough to kick in on my small load, so that part of the circuit seems to work fine. And yes, the bridge on the 100k trimmer is in place.

I did notice something while probing the thing though. As expected, the voltage over D6 is 5.6V. However, and thus over R14, the non-inverting input to U2 is half, at 2.8V, making it's output 5.6 and thus the output of U3 roughly three times that at max voltage adjustment, which is those 17.5V I get at the output, and it can of course never go above that. Now, the reason for that U2 input beats me.

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The middle opamp in Liquibyte's schematic is the 11.2V reference because it uses a 5.6V zener diode and it has a gain of 2 times. The voltage setting pot R27 is simply a voltage divider that feeds 0V to 11.2V to the non-inverting input pin 3 on the opamp on the right side. The gain of this opamp is 1+ (56k/28.8k)= 2.9444 times so that the maximum output of the circuit is 11.2v x 2.9444= 30.0V. Your middle opamp is messed up since its output voltage is too low.

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Sorry for not getting back, been out of town. Turned out the Op-Amp was defect; put a fresh one in and it worked like a charm. Thanks for the help

Now, another question: As audioguru says above, the voltage pot just feeds 0-11.2 V to the right Op-Amp. I wanted to try to control the voltage from another source, which I can't really get to work as I want: From 11.2~8.2V it works fine and the output adjusts down perfectly. However, no matter how much lower I try to feed it, it won't get lower, actually stopping the input source from going any lower. As soon as I shut the supply off or disconnect it jumps back down. Interestingly, with a multimeter set for Voltage measuerment between pin 3 (Non-inverting in) and pin 4 (ground) it does suddenly work as expected and adjusts all the way down to 0, as soon as I remove it it's back to ~8.2. I'm sure I'm missing something obvious here..

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  • 5 months later...

Hi everyone. I've built one of the early 3A versions of this project several years ago. Its has worked very well after making the upgrades recommended by Liquibyte and audioguru (Thanks very much).

I am planning to build a 5A version with a few additions of my own. I have added an arduino NANO which will measure and display AMPS and VOLTS, a cooling fan control which uses 2 CPU fans and heatsinks to cool output transistors, a bar graph display for current limit setting, buzzer for current limit warning and a relay to enable/disable power supply output.

Using the output relay avoids needing the soft start delay to avoid the output transients and can disable outputs with press of a button.

I've attached schematics of my current version for anyone interested.

After seeing design by Imester using 2 transformers to step up or down the output voltage, I would like to integrate something similar into my design using 2 12V center tapped transformers instead of a single 24V. Could easily use arduino and relays to control which transformer secondary windings to use depending on Volt Adj pot setting.

Does the opamps need their own separate supply voltage for this to work properly or could it simply use Vin as it does now?

Any ideas and suggestions for a dual transformer setup or the overall design are welcome.

power supply 30V 5A v5 page2.pdf

power supply 30V 5A v5.pdf

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  • 1 month later...
On ‎11‎/‎20‎/‎2016 at 8:48 AM, lmester said:

I finally have my power supply finished! It's on the shelf! I'm doing some full power tests.

I Started with a pair of the Chinese circuit board kits.  Lucky that I found this thread. I made the mods to the boards and added higher power components and  PWM fan control.

My transformers have multiple primary voltage taps. I Used a comparator to select a higher transformer input voltage tap when the power supply  output voltage is low. This greatly lowered the power Dissipation. With commercial power supplies this transformer voltage selection is done on the secondary of the transformer.  With the transformers that I got for free, I could only switch primary winding taps. This required triac switching circuits.

Pictures are attached.

 

PS4 001s.jpg

PS4 002s.jpg

PS4 004s.jpg

PS4 006s.jpg

PS4 007s.jpg

PS4 009s.jpg

PS4 010s.jpg

Hi imester, nice work by the way, can you tell me where did you find voltmeter and ammeter with decimal point accuracy? or did you build yourselfe,

and can you post any links to buy those voltmeter and ammeters?

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On 3/19/2018 at 2:52 PM, pooter1 said:

After seeing design by Imester using 2 transformers to step up or down the output voltage, I would like to integrate something similar into my design using 2 12V center tapped transformers instead of a single 24V. Could easily use arduino and relays to control which transformer secondary windings to use depending on Volt Adj pot setting.

Does the opamps need their own separate supply voltage for this to work properly or could it simply use Vin as it does now?

Any ideas and suggestions for a dual transformer setup or the overall design are welcome.

 

You'll need to keep the supply voltage high enough so that the zener voltage reference does not drop out. This was not a problem for me as the minimum voltage that I appliy is about 15V.  Also, for input voltage switching to work porperly, you'll want to monitor the supply output voltage and not the volt adjust pot. If the supply is operating in constant current mode the output voltage may not match the pot position.

 

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  • 2 weeks later...
On 27.09.2014 at 8:08 PM, Guest liquibyte said:


Point taken, I modified the schematic to have the parts list on the image.  Attached is a zip file of the .sch and .brd for Eagle as well.  Just in case anyone wants to play around with it or have boards made.

What do you use for your schematics and boards?  I'm just curious.

Edit: added the parts list as a text file and a pdf.  These have the Digikey part numbers on them.

0-30V-0-3A.zip

parts.txt

parts.pdf

Hello liquibyte,

Can you provide gerber files for that board revision (7)

Thank you

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On 11/14/2014 at 2:19 AM, Guest liquibyte said:

Cuối cùng tôi đã có những hành động tăng đột biến. Tôi đã đặt U1, U2, và U3 đằng sau mạch khởi động mềm MOSFET và để lại các bóng bán dẫn vượt qua bên ngoài. Đây là kết quả và mô phỏng để bạn có thể tự chạy nó.

Chỉnh sửa: Tôi đã chỉ duyệt quanh trang web của TI và đi qua Taming tuyến điều chỉnh dòng inrush . ; D Hình 2 cho thấy tôi đã đi đúng hướng ở đây. Tôi nghĩ rằng chúng tôi có thể có một giải pháp khả thi với điều này.

Chỉnh sửa thứ hai: Tôi đang đính kèm một mô phỏng riêng biệt để chèn nhiễu vào đầu vào ngoài việc tăng đột biến. Điều này mất một lúc để chạy nhưng kết quả là tuyệt vời theo ý kiến của tôi. Đầu ra của nguồn cung cấp rất trơn tru mặc dù đầu vào là thô như địa ngục.

post-107142-1427914482349_thumb.png

Let me know your gmail.

 

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On 20/10/2015 at 6:46 PM, liquibyte said:

Many, many questions keep getting asked about this thing and people keep attempting to build it without even knowing the basics, why I don't know.  The power supply suffers from a couple of issues that have never really been adequately addressed so this is going to be my attempt at bringing this thing into the modern age.  What follows is just preliminary work to right several wrongs I've noticed with the design.  It's not complete but I'm posting it to get opinions and suggestions.

This paragraph is for the newbies:  DO NOT ATTEMPT TO BUILD THIS YET.  If you don't know what you're doing, do not even try and breadboard this.  Once I have a final design, I promise that I'll post it.

Now, onward.  I'm posting my spice simulation for anyone that wants to try and give this a go.  One of the things that concerns me is the power dissipation in the op amps but I'm not sure how to get this down to a more acceptable level because I don't think 150mW at load is very good so suggestions are most welcome.

First, the voltage reference in the old version was an extremely odd thing to me so what I wanted to do was get a precision reference in there to work with.  10V seemed like a nice round number so that's what I went with and I actually have one on hand to use.

Second, the sense resistor.  0.47 ohms?  Once again, odd.  Plus, it suffers from extreme power dissipation as well.  My idea is to have a nice 0.1 ohm 3W 4 wire resistor in there to hook a meter to so I adjusted things around the reference to get me to where I wanted to be and I also have some of these.

What I'd like to eventually do is design the meters along with the supply so that what we end up with is a relatively complete project with all the nice bits people seem to be after.  No one, I repeat, no one ever offers a suggestion as to what to build to replace this, not one single engineer.  They will, however, be the first people to tell you how bad the design is but never offer any sort of advice as to why.  I know, I've asked and so have many other people.

0-30V-0-3A-redesign.zip

0-30V-0-3A-redesign.png

Hi All,

I saw this post by Liquibyte, and decided to take up the challenge of offering suggestions.  First, I'd like to say that I've enjoyed looking through this thread, and am very impressed with the work that has been done here by Liquibyte, Audioguru and others.  I have made some alterations to this new design, BUT I've not yet constructed it.  However, there are a number of things that I discovered when simulating with LTspice.

In the attached, I've made a number of alterations - rather than using a diode to ensure that the voltage reference is pulled down only when U1 is active, I've used a transistor.  The reason is that if the output were short circuited, then the inverting input of U3 would be zero, so U3 can never get the inverting and non-inverting outputs equal.  Hence the current is only limited by the output transistor drive capabilities since the minimum of the non-inverting input is the diode voltage drop plus the minimum output of U1.  Instead, I've used a transistor which can pull the non-inverting input of U3 very close to 0V (VIN-), which will be less than VOUT-, so the output of U3 will drop, and cut the voltage at VOUT+.

The second major difference is to remove the unnecessary output transistor Q4.  A single 2N3055 can drive up to 15A, so doubling up is not necessary.  (In fact, unless the transistors are well matched, it may have no effect whatsoever as at these "low" currents one transistor would carry the bulk of current if the matching were not perfect).  I was puzzled by the need for R13 until I realised that this is supposed to be part of circuitry to limit the current output of Q3.  I'm assuming that at some point in the past, the diodes that make this work were dropped - perhaps to keep the voltage up under high drive conditions?  In the redesign I've added three diodes from VOUT+ to the base of Q2.  If U3 tries to drive too much current through Q3, then the excess drive current will be routed through the diode chain, effectively limiting the drive current into Q3.  If the voltage is dipping under heavy load currents (less than the limit of 3A), then the output resistor can be reduced in size.  However, the consequence is that the maximum output current spike will be higher.

One other final structural modification is to separate the voltage sense and current sense parts of the circuit to allow the common Voltage/Ammeter module to be installed.  As I've not built the circuit yet, I don't know what the internal resistance of the ammeter is, so I've put a nominal 0.15Ohm resistor in there.  Obviously this should be changed to whatever is appropriate.

With a little reorganisation in the drawing, which includes some test circuits: a 555 astable which has power spikes as it is not decoupled, a resistor that is suddenly shorted out at 0.5s, and a resistor that varies between an almost infinite resistance to zero in a way that should make the current rise linearly up to 0.5s, and then the voltage drop linearly.  Also, I've included a period after 1s when the supply is switched off.  When I did this, I found it necessary to modify the power supply to U1 to ensure that it continued to limit current, otherwise I ended up with a large current spike after the power source had been removed.  I've also added a few notes discussing things I've discovered when changing things around.  I'm offering this revised (but note UNTESTED) design to the forum.

Just one note, I've seen pictures of some builds, and am slightly concerned that the casing of 2N3055 is not covered by everyone.  The case of the 2N3055 is the collector, which will be at around 38V.  If someone connects VOUT- to earth, then the full 38V will be present on the case, with whatever current the transformer can supply.  Under the right (i.e. wrong!) conditions, this could be fatal.  Please make sure the case is covered!

If anyone builds this, then I'd be really interested to hear how they get on.  If you do, please try to understand how the design works first - working with high currents with an untested circuit is not something that should be taken on by those not very familiar with circuit design/construction.  My plan is to build a lower current/voltage version of the supply (I really don't need 30V, nor 3A), but finding the time to do this is my biggest problem...

Dave.

0-30V-0-3A-redesign-DL.zip

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Your idea to use only one 2N3055 output transistor will have it burning hot (38V x 3A= 114A!) if the current is set to 3A and the output is shorted or has a very low voltage. Two output transistors share the heat. Their emitter resistors match them pretty well. Two output transistors at b1.5A each will have a higher hFE than only one transistor at 3A then the driver transistor does not need to supply a higher current and it also stays cooler. 

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6 hours ago, audioguru said:

Your idea to use only one 2N3055 output transistor will have it burning hot (38V x 3A= 114A!) if the current is set to 3A and the output is shorted or has a very low voltage. Two output transistors share the heat. Their emitter resistors match them pretty well. Two output transistors at b1.5A each will have a higher hFE than only one transistor at 3A then the driver transistor does not need to supply a higher current and it also stays cooler. 

Agreed - the 2N3055 is rated at 115W maximum, and as the voltage drop also depends on what the ammeter internal resistance will be, it shouldn't be running so close to its limit.  The hFE parameter of the 2N3055 is very loosely defined (as is the case with most BJTs), so one of the transistors could be carrying in excess of 2A, and will run quite a bit hotter than the other, but not a big problem.

Of course, the alternative is to use a single transistor rated with a higher wattage!  I wondered about the 2N3771, but couldn't find a spice model for that.  I did find a spice model for the FJL4315, which is rated at 230V, 15A and 150W, and has an hFE of 60, so pretty much a drop-in replacement for the 2N3055, and would handle everything the supply could throw at it.

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I wrongly typed 114A instead of 114W. A single 2N3055 will be at its maximum allowed chip temperature of 200 degrees C when it dissipates 115W and its case is cooled to no more than 25 degrees C with liquid nitrogen or something. A heatsink also gets hot even when it is huge and has a fan blowing on it.

I never operate a transistor anywhere near its maximum temperature, voltage or current. Then it is reliable. 

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1 hour ago, audioguru said:

I wrongly typed 114A instead of 114W. A single 2N3055 will be at its maximum allowed chip temperature of 200 degrees C when it dissipates 115W and its case is cooled to no more than 25 degrees C with liquid nitrogen or something. A heatsink also gets hot even when it is huge and has a fan blowing on it.

I never operate a transistor anywhere near its maximum temperature, voltage or current. Then it is reliable. 

Yes, I did realise the mis-type, and agreed that it wasn't right to operate so close to the maximum.  Do you have any comments regarding the use of the 150W rated transistor instead?  After all, we are talking about a margin of around 30%...

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