| Author | Message | | | eric | | Posted: Sun Aug 27, 2006 10:29 am Post subject: Pushbutton Switch | | | | Site Admin Joined: 01 Jan 1970 Posts: 311 | K. Lorenz
This circuit acts like a two-position switch but is operated
using a pushbutton. After power has been applied, the circuit
is in the following initial state: the bases of T1 and T2 are at
the positive supply potential and the base of T3 is at ground
potential. All transistors are cut off. The other contact of the
pushbutton is at ground potential. No current flows through
the relay coil and the status LED is off.
If the pushbutton is pressed, T2 and (after a slight delay due
the RC network) T3 switch on. The collector of T3 is now
nearly at ground potential, so current flows through the relay
coil and the function LED is illuminated. T1 can also switch on.
This situation is stable, since ground potential can reach the
base of T2 via R1, so nothing changes
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