0-30 Vdc Stabilized Power Supply

[mixos1]

Hello FireFly

You can buy a plastic insulator that is made exactly for the dimentions of TO-3 package transistor and has good heat transfer characteristics. The clear plastic you have is old type. You can also find other kind of matterials that are like rubber . Almost all electronics parts stores has it.

I attach you also an image that saws how to use it.

Regarding the "Heat Transfer Compound" you can put it both sides of the mica isulator for better performance.

 

[Shahriar]

Hi,

I want to use the pcb of the 30V power supply but when i print it, it Becomes too much big, Can anybody tell me how i can fit it in actual size (12.5cm x 8.7cm)

your help is appreciated in advance

 

[mixos1]

The best way to print it out correctly is to make some test prints to find the correct ratio. Take a part with fixed dimensions (like an IC) and try to fit it on the print out paper. Then change accordingly the ratio (resize scale) to achieve the correct dimensions. It is better to use a program that allows you to change the percentage (%) of the print out.

 

[Shahriar]

Thanks a lot for your help...

 

[Kevin Weddle]

This power supply looks a little simple. I would design my own and forget about the opamp, most likely. With so many possibilities, you have to wonder what the ideal operation is. This is the circuit I use presently, but I need a better one.

 

[ante1]

Hi mastrila,
If C7 gets hot you probably got oscillation. The only way C7 can get hot is if it

 

[Ani1]

Hi everybody,

Can I place LF351 in place of TL081 in this project. I checked the datasheet, both of them are almost similar.

Regards,
Ani

 

[audioguru2]

Do not use a 2N2222 instead of a 2N2219 for Q2 since it must dissipate up to 5W and therefore is shown with a heatsink.
The 2N2219 has a larger metal case and is designed for use with a heatsink. The 2N2222 has a small plastic case and cannot dissipate more than about 1/3W. With 5W in a 2N2222 it will smoke then burn.
Although the two transistors have the same voltage and current ratings, the little 2N2222 is designed to SWITCH current (when switched-on it has very little voltage across it and therefore low power).

 

[audioguru2]

Hello Tom and others,
You CANNOT put stabilized power supplies in parallel since you cannot ensure that they have EXACTLY the same output voltage. The supply with the slightly higher voltage will carry the whole load while the lower voltage one(s) will tell its regulator that the voltage is high enough or is too high and therefore to shut-down.

Although you CAN isolate parallelled supplies with a series resistor from each one's output to the load, so that the supply with the slightly higher voltage carries enough current to allow its voltage at the output of its series resistor to drop to the level of the slightly lower voltage one(s) so that this one (these ones) carry the remaining current. But those series resistors ruin the voltage stabilization since the output voltage will fluctuate with load current changes.

 

[MP1]

audioguru, what are you referring to in this post? Multiple regulators in parallel? Complete supplies in parallel? Which post are you replying to?

MP

 

[audioguru2]

MP, I was replying to Tom in his reply #9 in this post where he asked if he could parallel 2 of these Stabilized Power Supplies to get more output current.
My reply refers to paralleling these supplies, any other regulated supplies and IC regulators in general.

 

[MP1]

Thanks, the post ended up out of place and it was not clear to whom you were answering.

I agree that it is not good practice to parallel the power supplies, but you should know that it is general practice to parallel regulators such as the 78XX or 79XX series to get more current rating from them. In this case, it does work. When doing this, you should use a small resistance like 0.1 or 0.22 ohm between the output pins because all regulators are going to be a little different and this will keep the current flowing equally between them. This is the same practice as paralleling power transistors.

MP

 

[audioguru2]

MP, to boost the current output of a regulator, a power PNP transistor and input sense resistor is recommended to be wired across the regulator, as shown at fig. 10 in the datasheet of the MC78XX series by ON Semi here:

http://www.onsemi.com/pub/Collateral/MC7800-D.PDF

This way, their superb load regulation (the output drops only 1.3mV typ. with output changes of 5mA to 1.5A) is kept.
If you parallel regulators as you mentioned with 0.22 ohm resistors on their outputs, the output will drop up to 330mV.

You are correct that transistors can be paralleled this way and are equalized with minimal consequence.

 

[MP1]

The boost with transistor(s) is how I do it, also. Although I use a NPN instead. Either method can be used. The reason I jumped in was your statement "CANNOT". And as you see, it CAN be done.

You are correct that you will have some loss due to the resistors, but overall, you will have a boost in current handling. If a 12 volt regulator is rated at 1 amp, then this would mean the internal resistance can be resembled as 12 ohms. 12/12 = 1 amp. If you add the 0.22 resistance, then 12/12.22 = 0.98 amps. If you have two regulators in parallel in this manner, you will now have the capability of 1.96 amps, which is not double, but is close. If someone is needing to get exactly 2 amps out of 1 amp regulators, then this will not quite get them there. But if they need to get more than 1 amp or need to push this regulator a little over it's limit, then it is certainly a solution. Especially for a beginner who is not up on transistor formulas and cannot build a device with transistors. All they need is ohms law, a couple of resistors and another regulator.

I am not telling you your method is wrong. Just that the other might be an option for some.

MP

 

[mastrila]

I had an earlier problem with some componemts getting very hot which I eventually traced to a broken trace (pun not intended).
Everything is "cool" now but I have another problem that I cannot figure out.
I(max) varies with the load. For example, the supply will crank out more than 3.5A with a 5R resistor across the DC output. However, with 15R I(max) drops to abot 1.6A; 20R=1.2A; 32R=0.8; 75R=0.36A. AS it can be seen the relationship is not linear but follows a parabolic curve.
The V(max) is "approached" with increasing R but never reached.
I am using a 24V 8A tansformer, so the problem is not here. Any idea? I am lost and ready to give up.
Thank you,
Mastrila. ???

 

[audioguru2]

Hi Mastrila,
Maybe when your parts got hot they were damaged.
The guys who are talking about modifying this power supply to get 5A of current output are having problems similar to yours with the original circuit. Their post is here:
http://www.electronics-lab.com/forum/index.php?board=13;action=display;threadid=196
Those guys and I believe that the circuit depends too much on "selected" parts as follows:
1) A transformer that has really good regulation (low resistance windings) so that its voltage doesn't sag too much at the voltage peak when it is sourcing many amps to charge the filter cap.
2) Rectifiers that have a low voltage drop during #1 above.
3) A filter cap. that is at its extreme max. tolerance (+100% is double its rated value) and has a very low ESR.
4) Q1 and Q2 with more hFE than minimum or typical spec.
5) A power utility that provides 120VAC at all times (don't your lights dim when your computer is turned-on?).
6) Good luck.
Such a circuit can be described as having a "minimal" design.
A 2N3055 might be older than me. A newer PNP output transistor or power FET might be better.
I haven't built this circuit and won't unless it is upgraded so that it can meet its own specs.

 

[bigpetespc]

Hello all, I hope someone can help. Im new to electronics, but want to build this power supply as a first project.
I have studied the circuit and Im beggining to understand bits of it, but I want to build the PSU with a fitted moving coil volt and ammeter. Please can someone point me in the right direction as to where and how to connect these items to the power supply PCB?
I know this subject hes been looked at by a few people in this thread, but I need a few clear instructions....Im a newbee.
Thanks
Ian

 

[audioguru2]

Hi Ian, welcome to Electronics-Lab and to the hobby.
1) Connect the positive terminal of a 3A DC ammeter to the positive output of the circuit.
2) Connect the positive terminal of a 30V DC voltmeter to the negative terminal of the ammeter. This junction becomes the positive connection of the power supply to your load.
3) Connect the negative terminal of the voltmeter to the negative output of the circuit. This junction is the negative connection of the power supply to your load.
This way, the voltmeter shows the voltage across your load. The voltage will drop a little when the load current is increased due to the voltage-drop across the ammeter.
In order to avoid the voltage-drop across the ammeter, a low-current ammeter in series with a resistor can be connected across R7 to indicate the output current. But the resistor must be correctly calculated to match the ratings of the low-current ammeter. Also its scale markings will require changing to "amps".

 

[MP1]

Ian, do you really need this old technology? Mixos has posted a diagram of the current meter and voltmeter connection on page 2 of this post. This is with the 7107 IC, which will give you a much better digital display. Just a suggestion.


MP

 

[bigpetespc]

Hi, thanks for the info. I re read the posts, and was thinking along those lines myself this afternoon. I think it was just a nostalgic thought on my part wanting to see the old 'moving needle'...lol.
Im going to start hunting for parts to make this up, and I will have a go at the digital meter as well. Ive made simple things in the past, but this is a bit of a challange for me. Hope no one thinks Im being a pain with the Newbee questions.
Ian