INCREASING OUTPUT PUSH-PULL CURRENT Circuit
Some 555's do not swing
rail-to-rail when 200mA is being delivered and the chip gets very
hot when trying to deliver 200mA.
The solution is to add a push-pull output. The following arrangement
has been chosen as it swings almost rail-to-rail but two faults need
to be addressed.
Both transistors turn on during the brief interval when pin 3 is
travelling from high to low or low to high.
This means the two transistors will put a "short" across the power
rail.
The addition of the 4R4 will allow a high current to flow but the
transistors will not be damaged. In addition, diodes on the base of
each transistor allows alternate ones to turn off when output pin 3 is HIGH or
LOW.
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