Electronics > Beginners

DIY 0-30V 0-3A ...Again

<< < (4/13) > >>

Jwillis:

--- Quote from: IanB on January 06, 2019, 12:51:50 am ---
--- Quote from: Jwillis on January 06, 2019, 12:25:41 am ---Still have full range of voltage without load but it still drops to 200mV at load full available current (30mA).
--- End quote ---

I do not think you have not clarified whether this restriction in current applies at all selected voltages, or just at the maximum voltage?

--- End quote ---

Oh Sorry Ian .The restriction is is the same at all positions of the voltage pot.At maximum load with the current 30mA of the voltage can be adjusted between 0 and and around 200mV
It's acting like Q2 and Q4 aren't  turning on at all and all the current is being drawn from U2 which just doesn't make sense .
I have some 3055 s to replace the  2SD1047 if need be.
I'll take a fresh look at it again tomorrow .It's probably something stupid .

IanB:

--- Quote from: Jwillis on January 06, 2019, 01:17:08 am ---Oh Sorry Ian .The restriction is is the same at all positions of the voltage pot.At maximum load with the current 30mA of the voltage can be adjusted between 0 and and around 200mV
It's acting like Q2 and Q4 aren't  turning on at all and all the current is being drawn from U2 which just doesn't make sense .
I have some 3055 s to replace the  2SD1047 if need be.
I'll take a fresh look at it again tomorrow .It's probably something stupid .

--- End quote ---

OK, thanks for the clarification. But I'm still having a little trouble following what you are doing.

The normal way to test such a power supply would be to set the voltage with no load, set the current limit to maximum, and then increase the load gradually and watch what happens to the voltage. When the voltage starts to dip or lose regulation you have reached the limit on how much current can be supplied.

A common way to adjust the current limit would be to short the output terminals and then turn the current adjustment until it is at the current you want. When doing this it would be normal for the output voltage to be close to zero (since the output is shorted).

Audioguru:
The driver and output transistors are simple emitter-followers. The output transistor has an hFE of at least 25 and the driver transistor's hFE is at least 80. Then the total current gain is 2000 and only 3A/2000= 1.5V will appear across R15 if Q1 is properly turned off. U2 will have a max output current of only 1.5mA.

Maybe the voltage at pin 3 of U3 is not about 1.5V when the current-setting pot P2 is set to 3A to match the 3A x 0.5 ohms= 1.5V of your R7. Because any current more than 3A will cause the output of U3 to go low enough to reduce the output voltage and current.   

Cliff Matthews:
Note: the garbage pots from Banggood could be a source of a lot trouble (at least they were for me).
I cut-and-pasted a side-by-side schematic to help future modders.

Mate_Well:
•Actually, i was very interested in this project some time ago, after digging into it, i found there is a great document ( in French and it is not idealy translated but it is understandable into english), it has very nice measurements, facts, and additions to it https://drive.google.com/open?id=1qaKc0H9951NUQiRNrA4dNyz8iehMwrSn (it has the most stable part list/diagram from all that are floating arround, i hope this will help out (also  i did not tryed to build it yet) :D


•I will also try to make it much more powerfull with more powerfull transformer, which leads to more powerfull opamps, and other parts, air coling and such, i will do it long time from now on (i need to save up for the parts sadly)  :scared:

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod