Single transistor voltage amplifier

[darryl_co]

Hi,
I am using two 555 to create a sweep oscillator.The range of voltage on control voltage pin of IC2 swings from 4.6 to 8.6 volts.How do I increase the range using additional transistor from 1 to 11 volts?

 

[MikeMl]

You cant. If you try, the second 555 will stop oscillating. Try it with a 1K or 5K Pot first.

Ps, I just checked it. It looks the 555 will oscillate if the control voltage is from 0.1 to 11.9V when the Vdd = 12.0V.

Here is how I would do it: The amplifier has to both source and sink current from the Control input to 555. It is easier to do this with an opamp than it is with a transistor. The voltage gain of the opamp is just under 3, and the two 100Ks bias the input midway with respect to V(rc). The opamp does not load the RC timing network of the first 555 like the base current of a transistor would.

 

[darryl_co]

if not 1 to 11 volts then as much as possible less than 4.6 and higher than 8.6.I cannot use a pot as I want it automatic not manual

 

[ronv]

Might be easier to use a rail to rail op amp.

 

[MikeMl]

Might be easier to use a rail to rail op amp.

Great minds, and all that... (look at the addition to my previous post)

The LM358 will pull close to ground, but only pulls to about 1V less than its Vdd of 12V. Modern CMOS opamps would do better.

 

[darryl_co]

What software are you using Mike ?

 

[MikeMl]

What software are you using Mike ?

LTSpice, free download at Linear.com

 

[darryl_co]

Thanks Mike the schematic works perfect.I am getting voltage as low as 0 volts and high as 11 volts.As 0 is too low I retained the pnp transistor T1 and fed the non inverting input if the opamp with the emitter of the transistor.Now the range is 2V to 11V.