L200 Linear PSU with adjustable output Voltage and Current

[MacIntoshCZ]

Without heatsink...

problem found

 

[Nigel Goodwin]

Without heatsink...

Your entire design is basically a toaster - you need large heatsinks.

 

[ChrisP58]

And the heatsinks need to be on all power semiconductors.

Depending on your settings and load conditions, the current control mosfet could easily dissipate more than your voltage control transistors.

Figure 23 of this datasheet shows a better way of doing a variable current limit. Instead of adding a separate current limit function, it uses the opamp to generate a current error signal that's feed back into the regulating engine of the L200. So no additional power devices are needed.

It does use the ancient LM741 opamp. If you change that, make sure that the replacement opamps inputs can operate near the positive rail. (Many can't)

https://www.mouser.com/Semiconducto...-Regulators/Datasheets/_/N-5cg9g?keyword=L200

 

[GiacomoPascon]

And the heatsinks need to be on all power semiconductors.

Depending on your settings and load conditions, the current control mosfet could easily dissipate more than your voltage control transistors.

Figure 23 of this datasheet shows a better way of doing a variable current limit. Instead of adding a separate current limit function, it uses the opamp to generate a current error signal that's feed back into the regulating engine of the L200. So no additional power devices are needed.

It does use the ancient LM741 opamp. If you change that, make sure that the replacement opamps inputs can operate near the positive rail. (Many can't)

https://www.mouser.com/Semiconducto...-Regulators/Datasheets/_/N-5cg9g?keyword=L200

"Connecting point A to a negative voltage (for example - 3V/10 mA) it is possible to extend the output voltage range down to 0 V and obtain the current limiting down to this level (output short-circuit condition)."

I chose to use the Mosfet because I need short circuit protection and this circuit doesn't provide it. At least, this is what I understood....

 

[MacIntoshCZ]

"Connecting point A to a negative voltage (for example - 3V/10 mA) it is possible to extend the output voltage range down to 0 V and obtain the current limiting down to this level (output short-circuit condition)."

I chose to use the Mosfet because I need short circuit protection and this circuit doesn't provide it. At least, this is what I understood....

Yes and no.
Your current will not rise to HIGH value becouse is limited to certain value.
Just add resistor for highest accetable reference voltage to adjust peak current...

 

[GiacomoPascon]

Yes and no.
Your current will not rise to HIGH value becouse is limited to certain value.
Just add resistor for highest accetable reference voltage to adjust peak current...

I watched again EEVBlog's video about opamps but I can't understand the circuit on fig.23.
I think it's a kind of Gain adjusting with P1, but I don't know why they put 1K resitor from pin 2 to pin 5...

 

[GiacomoPascon]

Hi to all, I'm back after making and testing the l200 board.
The voltage regulation works fine until I put a load on the output.
When the voltage is set to 2.66V, the minimum, and a light bulb is connected the voltage raises to about 5/6V (without touching the potentiometer!).

I initially tought that the problem was the current regulation circuit, but disconnecting it didn't changed anything.
Does anyone know the cause of this behaviour?

Thanks in advace.
Giacomo.

 

[MacIntoshCZ]

weak power supply?

 

[crutschow]

So with no heatsink, the MOSFET became a nice, high temperature heating element.
A MOSFET can generally tolerate no more than about 1W of dissipation without a heatsink.

 

[GiacomoPascon]

weak power supply?

I tought it, too, but I found that the problem was on the Emitter resistor. Apparently the value was too low and not enough to keep the voltage stable...

 

[GiacomoPascon]

So with no heatsink, the MOSFET became a nice, high temperature heating element.
A MOSFET can generally tolerate no more than about 1W of dissipation without a heatsink.

Are you referring to the Mosfet that blew up on the current regulation?

 

[crutschow]

Are you referring to the Mosfet that blew up on the current regulation?

Any MOSFET that dissipates power.