The circuit shown consists of a power stage for relay excitation. 2N3053 can be a BD135 and 2N406 can be replaced with a BD136. R3 depends on the trigger voltage.
We found this circuit in an old documentation, using an operational of the time. The circuit...
This circuit shows how to use a 3-terminal voltage regulator as a low frequency oscillator by...
The circuit bellow uses two NPN transistor to drive heavy loads up to some amperes. The maximum...