If the threshold were just a bit lower, I would suggest putting the diode in series with the transistor base. Transistor would conduct when i/p was high enough to forward bias both the diode and the EB junction.

dear friends, plz help me design a simple electronic switch which is ON if the input voltage is in the range of 1.5volts to 2.0 volts and turns OFF if the input supply not in the above range.
thankyou.

 

dear friends, plz help me design a simple electronic switch which is ON if the input voltage is in the range of 1.5volts to 2.0 volts and turns OFF if the input supply not in the above range.
thankyou.

Although your request is somewhat similar, it's not quite the same as the O.P.'s original request. It is best to start a new thread in such circumstances.

However, see the attached; one-half of an LM339 comparator IC is used, along with some resistors, a couple potentiometers, and a Zener diode.

The inputs of the unused comparators should be connected to ground.

 

So moved. This link - http://forum.allaboutcircuits.com/showthread.php?t=7830 - points to the original thread.

 

What the Sarge has provided is called a "window comparator." Using that exact phrase in a search will turn up additional ideas.