555 ON 24v Circuit
If you need to operate a
555 on 24v, you will need to reduce the voltage to less than 18v.
The following circuits reduce the voltage to 12v:
30mA:
If the 555 circuit takes less than 30mA (the 555 takes 10mA) you can
use a 400mW zener diode to drop the 24v supply to 12v for the 555.
In other words, 12v is dropped across the zener.
Up to 500mA:
The next circuit will allow up
to 500mA. The transistor will need to be placed on a large heatsink.
It is
an emitter-follower-regulator transistor
and can be used with a 400mW
zener. The output voltage is 0.6v lower than the zener voltage.
Up to 500mA with "Amplifier Zener"
A 400mW zener can be
converted to a "Power Zener" by combining with a transistor as shown
in the following circuit: 12.6v will be dropped across the rails. In
other words, if the top rail is 24v, the bottom rail will be 11.4v.
Up to 1A:
Using the next circuit will allow the 555 to
take 200mA and the load to take 800mA. The 7812 will need to be
placed on a large heatsink. The 7812 is called a 3-terminal VOLTAGE
REGULATOR.
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