boosting output of oscillator

Audioguru

Joined Dec 20, 2007
11,249
The output high voltage if a 555 has a voltage loss of 1.3V at a low current. The transistor has a base-emitter voltage loss of 0.6V at low currents. So the output high voltage at the emitter of the transistor is only 10.1V when the supply is 12V.

The two transistors multivibrator should not use a supply voltage higher than the reverse breakdown voltage of the emitter-base of the transistors which is about 5V to 7V.
With a 12V supply then diodes should be added in series with the emitters to prevent avalanche breakdown.

This project explains the problem with avalanche breakdown:
http://hobby_elec.piclist.com/e_ckt7.htm
 
Top