When an npn bipolar transistor is used to control a motor, solenoid, relay or any other device containing an electromagnet, a protection diode is necessary to protect the transistor from the large back e.m.f. When current flows into the Base, the Collector-Emitter resistance drops and allows current to flow. When there is no Base current, the resistance between the Collector and Emitter is very high. With the button not pressed, no current flows into the Base and no current flows through the Collector to the Emitter. As a small current is flowing into the Base, a larger current is allowed to flow from the power rail, through the bulb, into the Collector and out through the Emitter to 0 V. The resistor is necessary to allow the Base-Emitter voltage to remain at 0.7 V. When the button is pressed the Base voltage is greater than 0.7 V and so current flows through the Base resistor and into the Base. The circuit shows an npn bipolar transistor connected as a transducer driver. Examples of power transistors include the well known 2N3055. Power transistors can handle large currents and are used in high power amplifiers and high current regulators.
BIPOLAR TRANSISTOR CIRCUITS DRIVERS
These are used as transducer drivers and low power amplifiers and are capable of handling currents of 1 or 2 amps. Again, the emitter is marked by a tag on the metal case and the metal case and metal heatsink tab are connected to the collector. Examples include 2N3053, BC441 and TIP41B. Medium sized transistors also come as a slightly larger metal can type or as a TO-220 style plastic type with a metal mounting tag. On the canister type, the tag on the case marks the emitter and the metal case is connected to the collector. They come in a small metal canister style package (e.g. Signal transistors are used for signal processing, logic operations and voltage amplifiers. The bipolar transistor is a current operated device.īipolar transistors come in different shapes and sizes depending on their intended use. To enable a Base current to flow, the Base potential must be 0.7 V higher than the Emitter potential. The emitter is identified by the arrow pointing outwards.īasic action: When a small current flows into the Base, a much larger current is allowed to flow from the Collector to the Emitter. These are called the Base, Collector and Emitter. A basic electronics course only considers this simple application as a transducer driver.Īn npn bipolar transistor has three terminals or, in other words, three legs. Used as a switch, or transducer driver, the transistor can be used to control powerful devices and switch large currents. The npn bipolar transistor can also be used as a straightforward electronic switch. The npn bipolar transistor is therefore a fundamental building block of modern electronics. The simple npn bipolar transistor can be used to construct all of the logic gates, and by extension all digital circuits, and also Op-Amps and all manner of analogue circuits. OverviewĪn npn bipolar transistor is an active circuit component with three legs and usually made from silicon. As transducer drivers, MOSFETs tend to be better at handling high currents than bipolar transistors but bipolar transistors are better suited to low voltage circuits.
MOSFETs are operated by voltages and can be either n-channel or p-channel MOSFETs. Bipolar transistors are devices that are operated by current. Bipolar transistors can be either npn type or pnp type. There are two distinct types of transistor, the bipolar transistor and the MOSFET, and for each type of transistor there are two varieties. Transistors are devices that require only small input currents or voltages but can handle large output currents. Something needs to allow the process devices to work with the output transducers and this is where transistors are used. The output transducers may, on the other hand, require larger currents (several Amps) and work at higher voltages. The devices used to perform the various processes are often small low power ICs that can only source or sink relatively small currents (several mA) and work at fairly low voltages. By considering a systems approach to electronics, processes such as counters and logic circuits often need to drive larger output devices such as bulbs, motors and heaters etc. The above is a fairly concise description of what transistors do.
They deal with electrical power in response to electrical signals. Transistors are devices that are used to drive output transducers.
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