Designing a variable PSU - Electronic Circuits Projects Diagrams Free

kybert · 6th January 2005, 12:09 AM

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

Russlk · 6th January 2005, 02:27 AM

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.

Oznog · 6th January 2005, 03:59 AM

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.

TheOne · 6th January 2005, 05:12 AM

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.

kybert · 6th January 2005, 10:21 AM

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?

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6th January 2005, 12:09 AM	(permalink)
kybert	Designing a variable PSU 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

6th January 2005, 03:59 AM	(permalink)
Oznog	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.

6th January 2005, 05:12 AM	(permalink)
TheOne	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. __________________ \"You can\'t make a circuit fool-proof, cause fools are so ingenious!\"

6th January 2005, 10:21 AM	(permalink)
kybert	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?