[SOLVED] voltage insensitive to temperature

[z_mx]

Hello,,,
I just hope i am not going against the rules of this site.
I am young engineer after college. I don't know if anybody here had experience this problem and should please guide me through..

I need to stabilize voltage between points A and B in temperature range from -45 to +85. Haw can I do this (minimal change in the circuit)?
Thanks very much

 

[chuckey]

First of all you must test the circuit to see what its doing over the temperature range. The reason for changes are likely to be the change in Vbe of the transistors first then the values of the resistors changing, second.
Depending on what is required one form of compensation would be to put a forward biassed diode in series with R8, so as the temperature increases, the voltage drop across the diode decreases and reduces the current through the transistor Q3. if the effect is too great then you can put a resistor in parallel with the diode. You can experiment using thermistors across a resistor. In circuits that I have worked on the current through the resistor bleed chain (like R8), with its diode would be set the same as the Ic of the transistor ( good for -55 -> + 50 ).
Frank

 

[z_mx]

thanks you very much for the reply)))