Voltage Regulator

[mlt57sooner]

I need to be able to vary a dc voltage from about .5 mV to 3 V using a micrprosser output. I dont not want to use PWM I just would like to use 3 or 4 bits from the mircoprossor to vary the voltage. Anyone know of a good way to accomplish this?

 

[ljcox]

Use a D to A (Digital to Analogue) converter IC. They usually are 8 bit devices, but just use the 3 or 4 most significant bits.

However, with so few bits, the graduations will be large.

Len

 

[Nigel Goodwin]

A simple and cheap way is to use an R2R ladder network, this is simply a handfull of resistors that make up a D2A - there are various examples in the MicroChip application notes - or a web search should find you details.

Depending on your load impedance, you will probably have to buffer the output with an opamp or similar.

 

[pittuck]

I have been looking into making a smart charger for low voltage nicad packs using LM317's

I am planning to use digital potentiometers to vary the voltage/current supply.

Maxim and ST do samples of i2c and spi resistors in the 5k, 10k, 100k regions, parallel resistors can be used to get the correct resistance range. U must also make sure they dont get more than 5mA of juice.... u can get 256 steps over a 5V range giving the lowest voltage of about 20mV

(BTW i am planning to have some feedback on the output voltage(s) and compare it to the 2.5V reference described in nigels analog tutorial)

 

[mlt57sooner]

Op Amp as buffer

If I use the LM324 as the buffer how would the circuit be connected?

 

[Nigel Goodwin]

Re: Op Amp as buffer

If I use the LM324 as the buffer how would the circuit be connected?

Simply use one section of it as a unity gain non-inverting amplifier.