The transistor 188 is one of my favorites, simply because even being so tiny it's able to handle currents as high as 1 Amp.
Understanding BEL188 Transistor Specification/Datasheet
The transistor BEL188 is a general purpose transistor, and due to its wide voltage and current rating can be used for almost all small to medium power circuit applications.
The pin-out of the transistor BEL188 is given in the following data:
Looking at the figure we see that it's pin configuration is similar to the small signal general purpose transistors like BC547 etc.
Holding the printed surface toward you, the right pin becomes the emitter, the center is the base and the left pin may be identified as the collector.
Other important specifications:
The material inside it is silicon (Si)
Polarity is PNP type
Maximum collector to emitter current handling capacity of BEL188 is around 1 Amp which constitutes to a power of around o.6 watts.
Maximum collector to base voltage or UCB is 25V,
Maximum safe voltage that may be applied across collector to emitter must not exceed 15 volts.
Maximum base to emitter saturation voltage must not exceed 1V.
Maximum tolerable junction temperature of BEL188 should not cross 150 degree Celsius.
The hfE of this transistor is very impressive, at around 150, it pretty well suits high gain circuit applications also.
Frequency handling capacity is at 250 MHz, again a very high range, that's double of the esteemed BC547, which is rated at just 100MHz.
NTE 188 is another general power transistor having higher voltage and current specs.
However unlike BEL 188 it's a PNP transistor and not NPN
Its Absolute Maximum Ratings are:
Collector to Emitter breakdown Voltage, VCEO = 80V
Collector to Base breakdown Voltage, VCB = 80V
Emitter to Base breakdown Voltage, VEB = 4V
Continuous sustainable Collector Current, IC = 2A
Total Power Dissipation (TA = +25°C), PD = 1W
Derate Above 25°C 8mW/°C
Total Power Dissipation (TC = +25°C), PD = 10W
With a current handling capacity that's as high as 1Amp, the transistor may be used in circuits which involve relatively higher output currents, for example for switching lamps, in amplifiers, for switching small solenoids or for operating DC motors etc.
Configuring BEL188 is very similar to the standard wiring used with general purpose small signal transistors, you may want to read this relay driver article for knowing the exact details.