Mosfets as voltage dividers.

[roughshawd]

I see a lot of yootoob videos where a guy wires up some pots and some resistors and diodes to some mosfets, and builds a voltage and amperage controller.

I am rebuilding a bench ps and was wondering if this would be a good circuit to put in for variable power and current?

 

[crutschow]

I am rebuilding a bench ps and was wondering if this would be a good circuit to put in for variable power and current?

Rebuilding it why?
Can't tell about adding variable voltage (power) and current control unless we see the schematic of the supply.

 

[AnalogKid]

this

What this?

 

[roughshawd]

Ok. Sorry.

 

[roughshawd]

Oh.. the reason why..... Lost my photos of the board...dismantled it... It needs a new transistor, and the OEM posted only an upgrade schematic for the model.

 

[AnalogKid]

That is not much information to work with. Make and model of the bench power supply? Reason it needs to be rebuilt? In what way is it not working normally? Link to one of the videos you describe? Supply, its front panel, the board - anything?

ak

 

[Delta Prime]

the OEM posted only an upgrade schematic for the model

Can you post the upgraded schematic along with your model number? Thank You.

 

[danadak]

One way of doing it is a front end to a bare power supply :

https://www.aliexpress.us/item/3256804869918495.html?spm=a2g0o.productlist.main.69.38dfjXCzjXCzvB&algo_pvid=4ec7dfa5-4576-4247-9c1b-bd9edd77b822&algo_exp_id=4ec7dfa5-4576-4247-9c1b-bd9edd77b822-34&pdp_npi=4%40dis%21USD%2113.50%2111.74%21%21%2113.50%2111.74%21%402101dedf17139650475891979e26b7%2112000032414294525%21sea%21US%21784751897%21&curPageLogUid=9xgWZjfdiI9j&utparam-url=scene%3Asearch%7Cquery_from%3A

There are other variants of the above, range, power.....


Regards, Dana.

 

[roughshawd]

Yes I have copied the schematic... Now to paste it...ok.
The board that was in the device was not this one, but had many of the same components. I tested the transistor...two diodes. Don't know what that means.

 

[roughshawd]

Yes I have copied the schematic... Now to paste it...ok.
The board that was in the device was not this one, but had many of the same components. I tested the transistor...two diodes. Don't know what that means.

The 2N3055 transistor. I will probably need a few other components.

 

[Harald Kapp]

This particular circuit relies on properties of the bipolar transistor, e.g. the base-emitter voltage V_BE, Simply replacing the bipolar transistors with MOSFETs will not work. To use MOSFETS you'll have to do a major redesign of the circuit. Basically replace everything to the right of C1.
The circuit also seems to use the LED as a voltage reference. The regulation will therefore not be very stable as the output voltage depends on the current through the LED, temperature etc,

If you want to keep this power supply, replace the faulty components (C1 is a very good candidate).
Other wise it may be more practical you build a new power supply from scratch, reusing only the transformer, rectifier and (a new) C1.

 

[AnalogKid]

That is an all linear supply, with the output current limited to around 2 to 2.5 A (not the 7 A stated on the drawing.) Also, D1 - D4 are rated for only 3 A. The circuit output voltage is adjustable from 10 V to 19 V -ish, it the power transformer can support it.

You can replace the combination of TR1 and TR4 with a single power MOSFET, but the result might have issues. The max output voltage might be less. Also, a power MOSFET will have more gain and bandwidth that a 2N3055, so the circuit might break into oscillation.

ak