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0-30 Vdc Stabilized Power Supply

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•Thank you for the help. That doesn't sound really good for me then, i will try to make it hopefully work, i won't mind ripple at the high end as much, (since i will not be pushing it to the limits), with these facts in mind, if i would go for more powerfull transistors and  put them idealy all on a heatsink, and air cool them, they should not get too hot hopefully, in worst case, i could put them in pararel. for the transformer, i alredy have it which is small issue, since i'm starting i can not get diffrent one any time soon, i might actualy eventualy go back, redesign few stuff on it, and maybe order more suitable transformer, once i get better knowledge about electronic in general,
•Also will putting back the Q1 with the rezistors&diode (if it is needed for it, seen latest version of this circuit without it at the 5A mod page Link), keep the other parts cooler or have no effect and make it a bit more dumbprof (let's face it, if i make stupid mistake as i usualy do by acident, i would not like to kill the power suply at it's 1st year of use :lol:)?

•Also could Full wave rectifier like this one, replace the full bridge rectifier, considering i have CT transforer, that could allow me to get enought current in the low output voltage, and at high voltage, it will remain with big ripple affect sadly (i don't mind it as much) Ripple measured by Tintin

•Thanks for help&understanding i appreciate it a lot ^_^

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One 2N3055 transistor overheats in the original circuit that used a 24VAC transformer and produces 25VDC at 3A. Therefore I used higher voltage opamps, a 28V 4.2A transformer, a more modern driver transistor Q2 that can be cooled well and two 2N3055 transistors to share the heat on a very large heatsink. Some people added a fan and a smaller heatsink instead of a huge heatsink.

If you connect the two 24V windings of your transformer in series and use the centertap as 0V then its output voltage will be 24VAC x 1.414= 34V minus the 1V for the two rectifiers then the supply voltage will be too low because the circuit needs a 28VAC transformer. 

Your transformer voltage is too high so it cannot be used for this project. Or you could parallel the two 24VAC windings or with the centertap as above then the maximum regulated output voltage will be 25VDC at 3A.

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•Thank you for the help. i  will try to do same as you did for the higher input voltage and make it work, and for the cooling solution i will probably go for fan air cooling+medium size heatsink (or the biggest one i will find) (TLE2141 might need one too, i will try to make something for it if it heats up a lot).
•I know i'm not using proper transformer, but thats all i have, if i connect it to the 48 VAC transformer (it will be a bit lower, we have 230 VAC here, and the transformer has input "pins" only for 220 VAC, and 240 Vac (100VAC and 120VAC will be pointless in my case)) should i worry about the TLE2141 getting too much voltage/current, and if is there an solution (without changing the transformer) ? Thanks in advance <3

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The original project used a 24VAC transformer and TL081 opamps that have a maximum allowed supply of 36V. Since the project was not able to produce 30VDC at 3A because the supply voltage was too low, I changed the transformer to 28VAC and changed the opamps to TLE2141 that have a maximum allowed supply of 44VDC.

Please post a video of your TLE2141 opamps blowing up if you power them from the 66VDC produced from rectifying the 48VAC from your wrong transformer. Or just parallel the two 24VAC secondaries which produces a rectified 32VDC so that the maximum regulated output from the project will be about 25VDC at 3A.

The TLE2141 U2 gets warm, not hot because its output current is fairly low since it drives the driver transistor Q2 that drives the output transistors to 3A.   

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Did you know that Chinese companies (ebay, Aliexpress, Banggood, Amazon and others) have copied the original defective Greek kit and used the wrong opamps and resistors that burn up? Their kits of the original project are very cheap. They use some Oriental transistors instead of the original ones.

  

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The OPA541 shows in its datasheet that if its positive supply is your 48VAC rectified to make +66VDC, its required negative supply is -6V and its output is 0V (shorted or set to a low voltage) then the output transistor in it has a voltage of 66V across it and figure 11 shows a max allowed output current of only 0.35A if it has a huge heatsink.

If it has a positive supply of +36V and a negative supply of -6V and its output voltage is set low then its maximum allowed output current is 2.5A if it has a huge heatsink.

If it has the +36V, -6V supply and its output is set to +26V then its max allowed output current will be 7.5A if it has a huge heatsink.  

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I have a question about the sizing of the resistor divider for Q1 on the revised schematic.   Currently it is listed as 12K and 160 Ohms.  When the negative rail (-1.3V) is operating, the base voltage on Q1 will be approx. -0.7V assuming a Vdc of 39.6 on the top rail.   When the power is shutting off and the negative rail collapses and goes to 0V, the transistor base will be 0.5 volts.  The minimum on voltage for typical transistor( 2n2222) is 0.6V.  Q1 will not have the minimum voltage to switch.  Using a 12K resistor the current may not saturate the transistor to operate like a switch.   The original design utilized a  5.1 zener  for the negative rail  with (10K and 1.5K) divider on Q1 resulted in a operating voltage on the base of the transistor of -0.01 V, but when the negative rail collapsed it resulted in 5.1V on the base of Q1.  Do I have an error in my math?

post-107142-14279144730853.gif

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When the negative supply collapses to 0V when the positive supply is still 37.8V then the current in both resistors in series is 37.8V/(12k + 160 ohms)= 3.1mA. If the base is +0.65V then the current in the 160 ohms needs to be 0.65V/160 ohms= 4.1mA so the 160 ohms resistor value and the negative supply voltage are too low.

I removed Q1 and somebody else later added it back in wrongly.

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I'm planning to build (another) power supply with Q1 to see if it clamps down the output to prevent spikes when the power is shut down.   I plan on using 7.5K and 240 ohm divider.  With power on, the base of the transistor will be -0.03V.  When the negative rail collapses, the base of Q1 will be 1.23V with approx.  5.1mA.    Now I just need to pick out a good transistor for Q1.

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On 12/26/2018 at 2:40 AM, audioguru said:

The TIP31 is 83 times slower than the BD139 that I recommend that has almost the same speed as the original 2N2219 that got too hot as Q2. Then the TIP31 will probably cause oscillation. 

I discovered ...

The problem has nothing to do with the power supply.

I was using a voltmeter based on the ICL 7107 to make the measurements, and when I put another meter I did not find any variation in the output voltages.

The readings of my small home-mounted voltmeter go up only when the source has loads on the output, otherwise these metaphysical follies do not happen.

When using a common multimeter with a scale of 6,000 counts I did not find any variation in the different loads and voltages that I put in the output of the power supply.

Even so, I switched TIP31 to BD139.

I am just a hobbyist in electronics and here in Brazil people like me can not afford professional or sophisticated equipment to study and experiment, we need to build our bench equipment by dismantling old appliances and taking advantage of the pieces taken from these scraps. That's why all the information about this project is very important to people like me.

Thanks again for the help and information.

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Hi!

I've seen the updated schematic, and I'm wondering if it is viable to keep everything like the original project (including the transformer) and just change the OpAmps (and add bypass caps) for the hypothetical case where I don't want to supply more than 15V at 0.5A (or 1A if it can reach that high). I already bought the kit from banggood, as well as their janky heatsink+fan addon for a total of 5USD, and I can buy the TLE2141IP (not CP, but seems the same apart from temperature ratings) for another 5USD. The idea is that I'm almost starting my vacations, and would like the PSU to work for 2 weeks so that I can do something with it right now (a mix of analog and digital stuff, hence the need for an adjustable PSU), and buy the "upgrades" during the next couple of months and then overhaul the PSU entirely in one go. I'm perfectly aware that I should do all the modifications that where suggested, and that the resistor power ratings are too low for the intended use of this power supply. This is just a stopgap measure for a month or two, not something definitive.

 

Also, would there be any problem in implementing the corrected circuit in a perfboard instead of creating a custom PCB? I belive I won't be able to mod the existing PCB that came with the kit, but at the same time don't want to go all out and do a proper PCB, which ends up being somewhat expensive.

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The original circuit should work fine up to 15V at 1A if you replace the old opamps with the newer higher voltage ones. You probably should recalculate the resistors that set the maximum voltage and current outputs. If the Chinese kit uses the transistor that shorts the opamp output when the power is turned off then the resistors that feed the transistor need to be recalculated for the reduced voltage.

I have used perforated stripboard for many projects including very complicated ones. The copper strips are cut to length with a drill-bit and become almost half the wiring of a pcb. The parts and a few short jumper wires become the remainder of the wiring. Only one wire is in each hole so changing a part is easy like on a pcb.

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Hi everyone!, i've been following this project for a while now and i finally settled on for building it, however i was unable to find the required op-amps, i even searched for various with similar specs but still couldn't find anything (where i live is pretty hard to find especific electronic components). Doing a little research i found that is possible to "increase" the voltage range of a low voltage op amp by bootstrapping, and i was wondering if i could use a lower voltage rail to rail op amp with this method instead. i'll link a great article from EDN magazine about it.

24127-45890.pdf

EDN_BootStrapDiag_small.PNG

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