Controlling an Adjustable Voltage Regulator with a prop?

laser-vector

Hi,

I was wondering if anyone may have any ideas on a way to use a prop to control an adjustable voltage regulator?

I would like to use some LM338 5 amp positive voltage regulators in a circuit that takes one of the propeller's outputs and converts it to an analog voltage which would then be used as a signal to the voltage regulators Adj pin.

I am playing around with some different setups and have been researching a little but i just cant seem to make the link between Propeller -- Adjustable Voltage Regulator (as in typical configurations the Vout of the regulator is connected to the Adj. through a voltage divider, im not sure how or where id introduce an analog voltage, nor the scale). i was thinking of using some digital potentiometers to make up the voltage divider but they're not cheap and only have so many bits of precision in them..

vreg input voltage = 24v
vreg output voltage = 0 - 12v

LM338 datasheet: http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000548.pdf


Just as an application note:
I plan on using the propeller to maintain a feedback loop of the output voltage of the devices after the voltage regulators. as those devices warm up they tend to drift a little, the propeller would see this drift and be able compensate by making changes to the voltage regulators output. furthermore this also adds the ability to control the voltage regulators via a serial/usb interface.

Thanks so much for any input!!

Leon

You could use a digitally controlled pot:

http://www.maxim-ic.com/datasheet/index.mvp/id/6410

Using it with an adjustable regulator is one of the applications suggested in the data sheet.

A better solution would be a switching power supply controlled by the Propeller, it will be a lot more efficient.

Phil Pilgrim (PhiPi)

You will not be able to get less than 1.2V from that regulator. The output voltage is always 1.2V + V_adj. If that's okay, this circuit might make a good starting point:



-Phil

Correction: In the above schematic, switch the plus and minus inputs.

laser-vector

thank you for that schematic! ill make that up and start playing with it tonight

Phil Pilgrim (PhiPi)

I just realized there's an error in the schematic. Switch the plus and minus inputs of the op-amp from what is shown above. If the DAC value is higher than the divider feedback, you want to sink less current with the NPN, not more.

-Phil