L200 Linear PSU with adjustable output Voltage and Current

[GiacomoPascon]

There are some nice cheap modules available from China, which will exceed what you can build - such as this one:

RIDEN® DPS5020 Constant Voltage Current Step Down Communication Digital Power Supply Buck Voltage Converter LCD Voltmeter 50V 20A

Only US$49.99, buy best riden® dps5020 constant voltage current step down communication digital power supply buck voltage converter lcd voltmeter 50v 20a sale online store at wholesale price.

www.banggood.com

I saw those modules before but I want to build one on my own, spending as little money as possible. That's why I started thinking to a L200 Ic.

 

[GiacomoPascon]

Now I'm undecided about what to build.
Maybe I should go back to a linear psu limiting the current at 5 amps...

 

[MacIntoshCZ]

Thank you for the links, but at the moment I haven't anything to solder SMD components, and I'm a bit afraid seeing all those pins for a voltage regulator.

Then use tl494

 

[Nigel Goodwin]

Now I'm undecided about what to build.
Maybe I should go back to a linear psu limiting the current at 5 amps...

You're still talking lot's of heat and BIG heatsinks. The module I mentioned above, or the smaller 5A ones will be alot cheaper than anything you're likely to build, and far out perform it.

If you want to build a linear supply, and money isn't an issue, then you should use a tapped transformer and automatically switch different taps in as the voltage changes - this greatly reduces the waste heat - and is what commercial supplies usually do.

 

[GiacomoPascon]

You're still talking lot's of heat and BIG heatsinks. The module I mentioned above, or the smaller 5A ones will be alot cheaper than anything you're likely to build, and far out perform it.

If you want to build a linear supply, and money isn't an issue, then you should use a tapped transformer and automatically switch different taps in as the voltage changes - this greatly reduces the waste heat - and is what commercial supplies usually do.

I want to try using what I have: 24v Trafo, 3 BD648, L200; to build a 30v 5A PSU.
I'm still searching a way to limit the current from 0 to 5A...
If anyone has any idea please tell me.
Thanks in advace.

 

[GiacomoPascon]

Then use tl494

That would be the 2nd choice if there isn't a possibility to adjust the output current on a L200.
Thank you very much for the advice.
Giacomo.

 

[MacIntoshCZ]

I want to try using what I have: 24v Trafo, 3 BD648, L200; to build a 30v 5A PSU.
I'm still searching a way to limit the current from 0 to 5A...
If anyone has any idea please tell me.
Thanks in advace.

I used to use mosfet with sense current resistor. Op amp sense voltage on resistor and regulate gate of mosfet.

 

[GiacomoPascon]

I used to use mosfet with sense current resistor. Op amp sense voltage on resistor and regulate gate of mosfet.

Thanks,
this is an amazing idea!

I'm going to try adding this to my circuit, but I can't understand why you put one pin of the resistor to ground...

 

[MacIntoshCZ]

0,1R with 1A -> U = R*I -> 0,1V.
If you put 0,1V on pin 3 (+) of om amp, OpA will try to have same voltage on pin 2 (-).
Since you are sensing voltage on resistor, ground is yours reference.
Ploss on resistor is = R*I*I keep it in mind

 

[GiacomoPascon]

0,1R with 1A -> U = R*I -> 0,1V.
If you put 0,1V on pin 3 (+) of om amp, OpA will try to have same voltage on pin 2 (-).
Since you are sensing voltage on resistor, ground is yours reference.
Ploss on resistor is = R*I*I keep it in mind

Ok, thanks for the explanation, now I understand.
I have to buy an opamp to test this. I think LM324 will work well, right?

 

[MacIntoshCZ]

yes
In linear operation you should probably care about operating votlage range and input offsets
In this case 3mV. That means with 0,1R sense resistor you can adjust to 3mV drop -> I = U/R = 3mV/0,1R -> 0,3mA
frequency response parameter is for fast reading. -> switching topology

 

[GiacomoPascon]

yes
In linear operation you should probably care about operating votlage range and input offsets
In this case 3mV. That means with 0,1R sense resistor you can adjust to 3mV drop -> I = U/R = 3mV/0,1R -> 0,3mA
frequency response parameter is for fast reading. -> switching topology
View attachment 130841
View attachment 130842
View attachment 130843

I searched for some good mosfets in my "collection" and I chose the IRFB20N50K. I also modified the schematic and added all the new components.
Thanks again for your help.
I'll try this as soon as possible.

PS. Here are attached the schematic and the mosfet datasheet.

 

[MacIntoshCZ]

I searched for some good mosfets in my "collection" and I chose the IRFB20N50K. I also modified the schematic and added all the new components.
Thanks again for your help.
I'll try this as soon as possible.

PS. Here are attached the schematic and the mosfet datasheet.

Load needs to be before mosfet.

 

[GiacomoPascon]

Load needs to be before mosfet.

Thanks now I should have correct it.

 

[GiacomoPascon]

I'm back after trying the limitation circuit on bredboard.
I used an LM358D recovered from a board.
It worked until the MOSFET blew up.
The load was a resistor of about 2 ohm, and the circuit was delivering 2.5 amps to it.
Does anyone know why this happened?
Thanks in advance,
Giacomo.

 

[MacIntoshCZ]

I assume your mosfet does not like power losses.
(Vin-Vout)*Current or Vds*current
post values voltage current so on

 

[Nigel Goodwin]

I'm back after trying the limitation circuit on bredboard.
I used an LM358D recovered from a board.
It worked until the MOSFET blew up.

What sort of FET was it?, and how large a heatsink was it on?.

 

[GiacomoPascon]

I assume your mosfet does not like power losses.
(Vin-Vout)*Current or Vds*current
post values voltage current so on

I measured the voltage between Drain and Source:
About 10v with 1 amp flowing in the circuit, so 10w of dissipated power.

What sort of FET was it?

The Mosfet is a irfb20n50k, here's attached the datasheet.

 

[MacIntoshCZ]

with or without heatsink

 

[GiacomoPascon]

with or without heatsink

Without heatsink...