Why Darlington pair has high input impedance?
As a result, a smaller base current can be used to switch a much larger load current as the DC current gains of the two transistors are multiplied together. Then the two transistor combination can be regarded as one single transistor with a very high value of β and consequently a high input resistance.
What is the input impedance of Darlington pair transistor?
A typical Darlington transistor has a current gain of 1000 or more, so that only a small base current is needed to make the pair switch on higher switching currents. Another advantage involves providing a very high input impedance for the circuit which also translates into an equal decrease in output impedance.
Which circuit uses photo Darlington devices?
The photo-transistor and photo-darlington devices are mainly for use in DC circuits while the photo-SCR and photo-triac allow AC powered circuits to be controlled. There are many other kinds of source-sensor combinations, such as LED-photodiode, LED-LASER, lamp-photoresistor pairs, reflective and slotted optocouplers.
What is the current gain of a Darlington pair?
If the current gain of a transistor is β1 and β2, the overall current gain of Darlington pair is β1β2. The current gain of this transistor is very high compared to the normal transistor.
Why does a Darlington pair have higher voltage than a transistor?
Base emitter voltage: The Darlington pair exhibits a higher voltage between the input base and the output emitter than a single transistor. As there are two base emitter junctions the turn on voltage for the overall Darlington Pair is twice that of a single transistor.
How is the Darlington pair used in electronics?
The Darlington transistor pair is a very useful circuit in many applications. It provides a high level of current gain which can be used in many power applications. Although the Darlington pair has some limitations, it is nevertheless used in many areas, especially where high frequency response in not needed.
What are the disadvantages of a Darlington pair?
The disadvantages of a Darlington transistor (i.e. a Darlington pair) have been summarized in the list below: It has a slow switching speed. The base-emitter voltage is almost two times compared to a normal transistor. Due to high saturation voltage]