0-30V Stabilized Power Supply

[denci]

I finally made this PS and except for a few necessary values of element changes work fine.
I think that I should change the transistor 2N3055 with other alternative transistor with same spacification because is very hot by increasing the current to 5A. I can also add the 4. 2N3055, i bought heatsink with 4 TO-3 hole but i don't see the point in this.
Maybe have anyone some advice for this?
Which element in circuit must be changed due the transistor replacement?

 

[audioguru2]

I think that I should change the transistor 2N3055 with other alternative transistor with same spacification because is very hot by increasing the current to 5A. I can also add the 4. 2N3055, i bought heatsink with 4 TO-3 hole but i don't see the point in this.
Maybe have anyone some advice for this?

With a 30VAC transformer, the positive supply is 42.4VDC. If the output is shorted or is at a low voltage and the current is set to 5A then the output transistors dissipate 42.4V x 5A= 212W! 70.7W each is too much.
Three 2N3055 transistors can do it if they are cooled so that their case is at 25 degrees C. A huge heatsink plus a fan can do i if it is big enough. Maybe your heatsink for four transistor is too small.

Which element in circuit must be changed due the transistor replacement?

Many of the parts in the original circuit were overloaded and were wrong.  Look at the new parts list and new schematic to see.

 

[denci]

Yes, i made PSU with new part list for 5A (redwire) and use new circuit with three 2N3055 transistor, but i thinking about replacing this transistor with better one, maybe with MJ15003, which have better thermal resistance (0.7°C/W) therefore dont,t need cooler to decreasing the temperature on heatsink and transistor case.
In this case, which element must be change in circuit if I want to use this alternative?
That's what I am thinking about...

 

[redwire]

The MJ15003 is a good power transistor.      The thermal Resistance, junction to case is about the lowest you can get but getting that to transfer to the heat sink is more difficult.  The power derating of 1.43 W/C is high if you are running hot but when you start at 250W you've got plently of  headroom.    Have you checked out the MJ11016 it is a darlington transistor and if you don't mind a 1v drop (or less) in the total output, it has a gain of 1000 and will reduce the load on the BD139. The thermal Resistance, junction to case is close to the MJ15003.  I did a test with only one MJ11016 driving a 5A-12v  load on a large heat sink (outside a case) with no fan for about 5 minutes without failure. The BD139 only had a small heat sink and did not get that hot.    I would feel very confortable with 3 transistors no matter what type (MJ15003, 2N5886 or MJ11016), running 5-7 amps.

 

[denci]

Therefore i can use three transistor any of MJ series on my heatsink but which element in circuit must be changed before running the PSU??

 

[redwire]

denci,  none

 

[helium_ninja]

If I wanted to make a dual supply with constant 5 volt terminal, would I need 3 transformers or could I build 3 circuits and tap right from the rectified signal?

 

[denci]

denci,  none

You mean "none" about changing elements in circuit or you said that i can't use the three MJ series and decrease temperature on heatsink and transistor case due the better thermal resistance (0.7)?

 

[redwire]

denci,  You should not need to change any parts to use the 3 MJ series transistors

 

[PETROS1308]

I have a tranformer 28Vac/5A.. It's ok to use it for the last version of power supply 0-30v 0-3A???

 

[mendimano1]

It is perfect for that.
;D

 

[darthtony]

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.

 

[ram2010mech]

Hi Friends,

I have bought all the components in the list except one, I could not get the capacitor C1 = 12000uF/63V in the market . Can any one please suggest the alternate for this or please help me to get this component.

Thanks
Ram

 

[thenr.]

I've bought mine on eBay, but it's 10000uf not 12000uf... good price, fast ship.

http://www.ebay.com/itm/2PCS-AUDIO-Electrolytic-Capacitor-30-41mm-10000UF-63V-63V-10000UF-/251121225080?pt=LH_DefaultDomain_0&hash=item3a77fdcd78

 

[audioguru2]

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. 

 

[ram2010mech]

Thanks guys....

 

[redwire]

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.

 

[audioguru2]

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.

 

[audioguru2]

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.

 

[audioguru2]

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.