Dear frirends,

I have to digitally control 35 volts by varying it from minimum to maximum by using 8051.

Basically I plan to use an NPN transistor by controlling its base voltage.

I intend to use R2R DtoA conversion by connecting the staircase of resistor network to the base of NPN transistor.

I connected the base of the transistor to +5 volts thru Variable. used +5 reg. because later
actually the output would be coming from 8051 which is +5 volts.

This does not vary the voltage at the emitter of the transistor much.

However, if I connect the variable directly to 35 volts then the output varies between Minimum and 35 volts as maximum.

( the circuit image I can send if required please )

Kindly help me.