Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Designing a variable PSU

Status
Not open for further replies.

kybert

New Member
Right, this is a tricky one, so im gonna ask for the help of experts like you guys...

I need to design and build a variable power supply. Sounds easy? heres the specs...

Suppy voltage is from a 3V lithium battery.
Required output voltages is: 2.0VDC --> 14VDC @ 1mA continous, in 0.25V steps (48 steps)

The output must be able to turn on and off. (via a transistor i guess).


OK, so now your thinking "easy, use a charge/pump regulator and a variable resistor"... Well yes that would work, but it also needs to be controllable by a microprocessor, so the micro can change the voltage.


--
So i looked at the LM2623 device, looks ok to me, will do the job, but cannot be controlled by a processor without a digital pot?


Any ideas welcome. Needs to be really super cheep and easy to setup/calibrate.




Joe
 
I did not study the data sheet long enuf to do a detail design, but this should give you an idea. The boost converter output cannot go below the battery minus a diode, so a transformer is needed. The Vdd and BOOST pins cannot exceed 10 volts, so the yellow LED is used as a voltage control ( about 2 volts). Vdd has to exceed 1.1 volts in order to start. The EN pin will turn it on and off and the X9317 can control the output voltage.
 

Attachments

  • digital_ps.jpg
    digital_ps.jpg
    58.3 KB · Views: 405
You need a buck/boost converter. Or, alternately, simply a boost converter with a couple of diodes to reduce the lowest output voltage below 3v. You will have a big question of how good a regulation and how much ripple is tolerable.

Be aware a microcontroller alone might take 5-20mA of supply current.
 
Can't you use a DAC to generate the voltages? Used together with the higher boost voltage fixed at say 15V or so you could program the output voltages you want.
 
Thanks all.

I've had a good look at this, and i've decided to go for the (cheepest) option, the ADC.

The processor will be using about 100uA when in full opperation (no leds), so it should be ok.

I've looked at the DAC0800 8-bit convertor, and it looks like it is capable of being driven at 15V, so 15/256 = 50mV resolution which exceeds my spec -- Cool !

Are there any pitfulls i will need to be aware of before i get started on the design?
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top