0-30V Stabilized Power Supply

[lighty]

I have checked Emmitter voltage of the Q2 and it is same as the base voltage of the 2N3055's, when Voltage pot set to 0V as per previous post, but I will check again at say 12V.

I will go through the board again with a fine tooth comb, Like I always say "if it wasn't for bad luck, I wouldn't have any luck at all"  ;D

 

[audioguru2]

The BD139 will take the entire load if the base and emitter of one 2N3055 is shorted together or if both 2N3055 transistors do not have their collectors (their metal cases) connected to +35V.

 

[lighty]

I feel like a idiot now >,  you have hit the nail on the head, only one of the 2N3055 cases where connected to the +35V.

Will connect both and test!

 

[audioguru2]

only one of the 2N3055 cases was connected to the +35V

Then the 2N3055 transistor that was connected to +35V does not work.

 

[lighty]

Thanks for all your patient help.

Tested to 3amps! all ok

 

[audioguru2]

Goodie! I am glad you fixed it.

 

[lighty]

Ok, now that I have eventually got my PSU unit working 100%, I'm wanting to build a  LCD Display for it.

I'm hope to have the following displayed on it.

Actual Voltage
Set voltage
Actual current
Set current
Temp of heatsink

So here is my question, once calibrated, are the voltages from the wipers of P1 and P2 linear to the voltage and current limits, Or would the voltages change as the circuit regulates the voltage/current? The reason I ask is I'm wanting the use the ADC to read the voltages (through voltage divider resistor) from the the wiper to show the "set" V and I.

Would this work?

 

[lighty]

Mmmmm

Ok, the "SET" values don't look like it will work, the voltages change when circuit goes into CC.

 

[PicMaster]

Mmmmm

Ok, the "SET" values don't look like it will work, the voltages change when circuit goes into CC.

You could not have set voltage anyway, You could set the voltage with the wiper but you would have no way of limiting it, if you where to move the pot. The only way would be remove pots and use PWM from the pic. The same goes for the current control. You can read real time voltage,current and temp of the heatsink,
I did sometime time ago remove the pots and used pic to control the PSU but never got around to finishing it may be I will blow the cob webs off it and start again.

 

[lighty]

Hi PicMaster

I wasn't intending to control the PSU with a pic, but rather just use the voltages of the wiper to show where the Voltage and Current pots are situated.

Eg, lets say the Vpot is set to 12 and current to 1 Amp, it would show this on the LCD, along with the realtime Volts and Amps. but at least you know the PSU wouldn't deliver More than 1 amp should something go wrong, wouldn't be nice to find out that the pot was set at 2 Amp... similarly for the voltage, to pervent over voltage should the load drop from the PSU, while you have something else connected to... If you know what I mean?

I suppose you could use a tandem ganged Pot, using the second Pot to drive the "SET" voltages to the pic.

 

[lighty]

I'm wanting to add a Fine Adjustments pots to the circuit for the vltage and current, as I find the Pots are very sensitive.

I was thinking of putting a 1K Pot between P2 and R18, and P1 and the output od U1.

Would this work?

View attachment 41370

 

[audioguru2]

A pot used for "fine" adjustment is always in the wrong position and might be forgotten.
Simply use a very big knob on one pot then it can be turned a lot or turned a little.

 

[lighty]

Ok, thanks

good advise!

 

[morpheous87]

Could be used a 31V transformer for the PSU, ot it needs some changes?

 

[audioguru2]

A 31V transformer might produce 32VAC without a load. Then its peak voltage is 45.3V and the bridge rectifier reduces it to 44.1V. Opamps U1 and U2 will operate or will blow up with the 44.1V supply which is higher than their max allowed supply of 44.0V. The voltage will be even higher when the mains voltage is higher and with mains voltage spikes.

Maybe a couple of back-to-back zener diodes can be added in series with one transformer wire to reduce its AC voltage.

 

[redwire]

Hi  Lighty   

Is this what you were thinking of making?

View attachment 41398

 

[surubel]

Hello again.
I managed to finish the PSU. It worked perfectly from the first time. (except the GND trace under-dimensioned, but I fixed it  ;D)
Some pictures:
       
     
       

 

[morpheous87]

For the 3A PSU version (PicMater's veersion), can two potenciometers be usedin series for coarse and fine adjustment? I saw somewhere they should be in 1:10 propotions, so 1k and 10k ?

 

[audioguru2]

You can use 10k and 1k pots in series.
I would just use a big knob on one pot.

 

[morpheous87]

The biggest knob I found is 30mm in diameter. I'm wondering what would be better, this big knob or two potenciometers in series.