2. npn transistor can work properly even if it is put reversely but the performance ... I think is a mix of luck in here in choosing the correct components to make this circuit work as a latch.

By using dual bipolar devices in one case, the manufacturer nearly perfectly matches the two devices. Although this Design Idea describes a positive power supply, you can realize a similar ...

In the circuit, I actually used MPSA15 (NPN) and 2N5087 (PNP) transistors. Oscillographs I had another interesting oscillograph with a 5mS /div timebase, but lost it due to buggy Tektronix Wavestar ...

NPN transistors are key components in electronics, ... An NPN transistor has three legs. In circuit diagrams or symbols, ... This makes it a latching device, ideal for alarm circuits.

In circuit diagrams or symbols, the legs of an NPN transistor can be identified as follows: Base (B) : Usually located in the middle. Collector (C) : Often connected to the positive voltage.