lobiastro.blogg.se - Npn darlington transistor switch configuration

With a positive signal applied to the Base of the transistor it turns “ON” acting like a closed switch and maximum circuit current flows through the device. With a zero signal applied to the Base of the transistor it turns “OFF” acting like an open switch and zero collector current flows.

Then the transistor operates as a “single-pole single-throw” (SPST) solid state switch. For a PNP transistor, the Emitter potential must be positive with respect to the Base. Then we can define the “saturation region” or “ON mode” when using a bipolar transistor as a switch as being, both junctions forward biased, V B > 0.7v and I C = Maximum. This means then that we can ignore the operating Q-point biasing and voltage divider circuitry required for amplification, and use the transistor as a switch by driving it back and forth between its “fully-OFF” (cut-off) and “fully-ON” (saturation) regions as shown below. The areas of operation for a transistor switch are known as the Saturation Region and the Cut-off Region.

If the circuit uses the Bipolar Transistor as a Switch, then the biasing of the transistor, either NPN or PNP is arranged to operate the transistor at both sides of the “ I-V ” characteristics curves we have seen previously. However, high power devices such as motors, solenoids or lamps, often require more power than that supplied by an ordinary logic gate so transistor switches are used. Some output devices, such as LED’s only require a few milliamps at logic level DC voltages and can therefore be driven directly by the output of a logic gate. Solid state switches are one of the main applications for the use of transistor to switch a DC output “ON” or “OFF”. However, both the NPN & PNP type bipolar transistors can be made to operate as “ON/OFF” type solid state switch by biasing the transistors Base terminal differently to that for a signal amplifier.

Used where high amplification is neededĢD dimensions will help you in placing this component at the time of making circuit on perf board or a PCB.When used as an AC signal amplifier, the transistors Base biasing voltage is applied in such a way that it always operates within its “active” region, that is the linear part of the output characteristics curves are used.

Can be used to switch high current (upto 5A) loads.

So, if you looking for a transistor that could be easily controlled by a Logic device to switch high power loads or to amplify high current then this Transistor might be an ideal choice for your application. Although care has to be taken to check if the logic device can source upto 120mA. This transistor has a low Base-Emitter Voltage of only 5V hence can be easily controlled by a Logic device like microcontrollers. TIP120 transistor is known for its high current gain (hfe = 1000) and high collector current (IC =5A) hence it is normally used to control loads with high current or in applications where high amplification is required. This increases the current gain and current rating of this transistor. The Darlington pair inside this transistor is shown clearly as its internal circuit schematic belowĪs you can see, there are two transistors inside this TO-220 package in which the emitter of first transistor is connected with the base of second transistor and the collector of both transistors are connected together to form a Darlington pair. If you need more voltage then you can check other transistor in the same family lit the TIP122. It can also withstand about 60V across its collector- Emitter hence can be used to drive heavy loads. It functions like a normal NPN transistor, but since it has a Darlington pair inside it has good collector current rating of about 5A and a gain of about 1000. The TIP122 is a Darlington pair NPN transistor. Note: Complete Technical Details can be found at the TIP120 datasheet given at the end of this page.

Continuous Collector current (IC) is 5A.

High DC Current Gain (hFE), typically 1000.This makes it suitable for medium and high power electronics like controlling motors, solenoids or high power LEDs.Ĭontrols the biasing of transistor, Used to turn ON or OFF the transistorĬurrent flows in through collector, normally connected to loadĬurrent Drains out through emitter, normally connected to ground It can switch loads upto 60V with a peak current of 8A and continuous current of 5A. The TIP120 is a NPN Darlington Power Transistor.