PIC controlled adjustable voltage regulator

[tomskk]

Does anybody know of a simple schematic for a PIC controlled variable (trimpotentiometer adjustable) high current voltage regulator?

I need to lower a 2-cell (2.4V) Voltage (about 3-8A) with a trimmpotentiometer to between 0.8V to 1.8V.

[willfly]

Should be fairly simple. If you can code PIC, just connect an output line to a power MOSFET and drive PWM signal in your software. Some PIC's (16F87x) have PWM capability built in.

If you can't code PIC's then wire up a 555 timer IC into astable miltivibrator and drive a power MOSFET. A capacitor in output will smooth out switching ripples. A trimpot can change 555 duty cycle.

[tomskk]

I don't want to regulate current. Current must pass through. I want to regulate voltage.

I'am using a PIC to drive a POWER mosfet as a SWITCH, but I want to use it to regulate the output Voltage as well

Example:
input Voltage: 2.4V
input Current: 8A

output voltage: 0.8V - 2.0V
output current: 8A

Can it also be done with POWER mosfet without a lot of power discipation? I don't want to use a cooler.

[Acetronics]

Hi, Tomskk

What you're looking for is called a switching regulator ...

IF you really DO want a PIC in it, have a look to Microchip's Application Notes ...

There's just one for you !!!

Alain

[tomskk]

Can a switching regulator really handle so much current?

[Acetronics]

As much as your switching stage ,coil , diode and capacitors can Handle ... respect also to a "certain" weight !!!

Note such supplies are widely sold on the web ( Conrad.de ... i.e ) ...20, 40 and 60 Amps ...

Alain

[Comatose]

A switching regulator is what you want. You can make one with a PIC if you're okay with feedback control systems - its an easy system to model. There are a lot of good dedicated control chips that will do just this, though.

For any low-output buck converter use a synchronous rectification type topology, or the diode losses will eat you alive.

[Chippie]

For any low-output buck converter use a synchronous rectification type topology, or the diode losses will eat you alive.
I would have thought using Schottky diodes would be a better bet compared with a Synchronous rectifier, given that its easier to implement, having to wind an extra 'coil' .......but then I'm not a designer ;)

[Comatose]

Extra coil? A synchronous buck converter has a mosfet in place of the catch diode, often in parallel with a schottky. Still only one inductor.

Any low-voltage design (3v+ from less than 50v in) should use a schottky for the catch diode. But if you've only got .8 volts output, and 2.4v in, an 8A schottky is going to push your efficiency below 65% by itself. Your total efficiency is likely to be as bad as 50%.

[Chippie]

The attached cct shows what I meant to say..(not very explicitly I admit...)

The winding f-g provides the gate drive,while winding d-f provides the main power....

Maybe there is a more elegant way of doing this that I dont know of ? ;)

[Comatose]

Oh, I see what you're getting at. Thats a synchronous forward converter, not a buck converter. I'll agree thats a more complex beast, but usually reserved for highish input voltages.

http://focus.ti.com/lit/ug/slvu007/slvu007.pdf is more what I had in mind here, or something similar.

[tomskk]

A switching regulator is what you want. You can make one with a PIC if you're okay with feedback control systems - its an easy system to model. There are a lot of good dedicated control chips that will do just this, though.

What chips did you have in mind. I am looking for a low cost and small option, because the whole PCB should not consume a lot of place and weight, but should be able to withstand currents up to 30-40A, or at least 20A.

[ESC_RC]

A power with DC/DC ?