Found in the July 1994 Electronics Now magazine, this circuit drives a relay up to 12 V depending on the power supply. The transistor can be general purpose.
The instrument of this field strength meter, from a 1970s publication, can be a 200 uA...
We found this circuit in the ON Semiconductor Thyristor Manual although similar configuration can be found...
A very interesting integrated circuit for step-down converter designs (voltage reducers) with an...