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0-30V Stabilized Power Supply


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  • 2 weeks later...

Hi, i am a beginner in electronics, and i decided tobuild this power supply. Unfortunately, i built the original design(here: http://www.electronics-lab.com/projects/power/001/index.html)(i didnt check out this topic). It seemed to work fine , but while i was testing it before finishing the enclosure, it started to have problems. Anyway, after a couple of burnt transistors, now i have a contsant(non-adjustable) output of 30V, howver the current limiting seems to work just fine. If i disconnect the middle wire from the voltage adjustment pot, the output will "float" around 1-4V, howver if i touch it to either of the other wires that go to the pot, it will shoot up to 30V again. Any ideas of what  could be wrong?Are the corrections that i have seen necessary?(it really took me alot of time to make the pcb(twice, beacause once i printed it upside down) and to make it work, so i really dont want to start over again. thanks in advance

I should note that it is not exacltly the original design: i am using a larger bridge rectifier, a 10,000uf cap, a second R7 i parallel with the first one, and 2x2n3772 in order to get 5-6A that my transformer(24VAC secondary) can supply.Howver right now i am testing it with only 1 2n3055.

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12000uF is a common value in The West. Use 10000uF or 15000uF instead.
Use a 10000uF parallel with a 1000uF, 2200uF, 3300uF or 4700uF.

Most of us do not buy electronic parts in a "market", instead we go to an electronics parts distributor store or buy them online where they have millions of values for everything. 

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Yes,  Some of the benefits:

1.  Develop skills in making pcbs, and using software such as Eagle.
2.  Learn troubleshooting
3.  Utilizing a design (as revised) that is probably the best available
4.  Ability to ensure quality parts are used
5.  Satisfaction and pride in successfuly completing a project
6.  Develop skills in understanding programming AVR chips (LCD Display project)
7.  leveraging these skills to build other project using servos, lcd displays, flashing lights, etc  http://www.youtube.com/watch?v=ryhK9xIUcrQ 
      (sorry about the poor film quality)

If price and time are your primary concerns then buying one a commercial unit would be your best option.

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Hey, I have a few questions (about the schematic, posted in the first post of this topic):

1) There is diode D10 (1N4148) written in the parts list, but it isn't in the schematic. So I do not need it at all (it is just a mistake in the parts list)?

I started modifying this project. My latest schematic and parts list do not have D10 that I deleted from the original defective version.

Also, I don't know where C10 came for, but in original nor remade version schematics the is no C10 at all.[

I added C10 to filter the supply for U3 when I added the 10V zener diode. It is shown on my latest schematic but it is not called D10 and is not called anything. It is on my parts list.
The 10V zenewr diode is not called anything on my schematic but is called D12 on my parts list.

2) Do I need to use a silicone isolator for 2N3055 transistors of TO3 package type?

The output transistors have their collectors connected together and their metal case is the collector. If no insulators are used then the entire heatsink should be insulated from the chassis. With insulators for the transistors then the heatsink can be connected to 0V.

3) About the power supply: for example I will use digital ampermeter module. When will the chosen value of current limit will be seen? Only when a load will be connected to the power supply? If yes, then current limit value changing with linear potentiometer will be not available to see when no load is connected?

The amp-meter will reduce the voltage regulation a little.
The project has current regulation, not simple current limiting. Current regulation reduces the output voltage (and lights the red LED) so that the current cannot increase when it occurs. Make a scale of current for the current-setting pot. Minimum is a few mA, halfway is 1.50A and maximum is 3.0A.
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Why should the heatsink be connected to 0V?

When metal parts are connected to 0V then they provide shielding from interference to the circuit.

And more, do those 0.33 Ohm 2W resistors (thay are connected to power transistor emitters) must be with heatsinks? or can be used simple ceramic ones?

The maximum load for the project is 3A. Then each 0.33 ohm resistor has 1.5A (plus some small base current).
The power in each resistor is (1.5A squared) x 0.33 ohms= 0.74W so an ordinary 2W resistor or a 5W ceramic resistor can be used.
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  • 2 weeks later...

The parts on your perforated circuit board are too far apart. Then the wiring resistance will be too high and the stray capacitance between wires will be too high.
Then the circuit will probably oscillate at a high frequency and work very poorly.
We recommend using a pcb with a compact layout.
Wires that carry high current are obvious and should be large.

The rectified and filtered DC will be about 38V without a load which will not harm you. If you are sweating then 38V might let you feel a little tingle.

Here in Canada the regulations say that the wiring voltage for sound systems in schools must not exceed 25V so that sweating little kids who crawl around in the ceiling and touch the wires will not be killed.

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Hello, Can you tell me what changes should i make for 12amps??
The power supply is http://www.electronics-lab.com/projects/power/001/index.html

The project you copied is not reliable, does not produce 30V at 3A and has many parts overloaded.
I fixed it and the new schematic and parts list are in these threads.
The fixed version uses a newer real power transistor for the driver Q2 and two output transistors (each with an emitter resistor) instead of one transistor. I made a 5A version that uses three output transistors.

For an output of 12A then you will need 8 output transistors, 3 driver transistors plus additional pre-driver transistors.
But it will need to be re-designed for the output voltage to be as high as 30V.
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Six TIP35 output transistors on a HUGE heatsink and fan will be able to have a maximum continuous output current of 9A or 10A. Then the BD139 driver transistor Q2 will melt. If you use two or three BD139 driver transistors in parallel then opamp U2 that drives them will melt. It is difficult to parallel opamps so a pre-driver transistor is needed but then the output will not reach 30VDC. If the transformer has a higher voltage then many resistors will get too hot.

The original circuit has many problems that were fixed in my fixed version that uses a higher transformer voltage and TLE2141 or MC34071 opamps that have inputs that work at the negative supply voltage.
OPA604 opamps will not work in the fixed version unless their negative power supply voltage is increased, but then they might get too hot.

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I am sorry, but can you answer, please, this question. Thanks.

I answered this question on Feb 19:
"Most people's problems with this project are ICs or transistors with their pins connected backwards.
Double check the pins with the pictures in the datasheets."

The pots set the output to 0V and 30.0V, a few mA to 3.0A.
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