Motor control driver

Gentelmen and Ladies,

I am using a Cygnal development kit to drive several functions of a project I am working on. One of the DAC's will be driving a motor. The motor runs on a varying voltage from about 1.1 to 5V to vary the speed from off to max and pulls up to 400mA. The Cygnal device will supply about 300uA to drive the motor and has a maximum DAC output of 2.4V. I have put together the attached circuit and it seem to be close to what I need, although there are some things I would like to improve. Please refer to the schematic.

The input is very sensitive. I can only vary the input from 1.4 to 1.7V to acheive the full scale of off to max out of Q2.

My input current also is a little high. It runs from a few uA to 2mA at most.

I would like to decrease the voltage sensitivity and decrease the input current.

Any suggestions or comments would be greatly appriciated.

Thanks

Gerry


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You need more current gain and some variable voltage gain. The attached circuit should work, you will have to adjust the trim resistor, depending on the gain of the output transistor.

Russlk,

Thanks I will give it a try this morning,