![]() In a battery-powered device where the load is variable and power supply is limited, for example, using a BJT would be a bad idea. Generally, A MOSFET is usually more efficient in power supplies. These include power level, drive voltage, efficiency, cost, and switching speed, amongst other things - this is where it really helps to know your project! When choosing which to use in a project, one must consider many different factors to arrive at a decision. There is not a straightforward and definitive answer to this question. Unfortunately, we cannot say which is “better” because the matter is highly subjective. Power electronics market 2020: Winners, losers and opportunities Which is better?īoth MOSFET and BJT have unique characteristics and their own pros and cons. A MOSFET’s structure is inherently more complex than a BJT’s structure.A BJT depends on the current at its base terminal whereas a MOSFET depends on the voltage at the oxide-insulated gate electrode.MOSFETs are ideal for high-power applications whereas BJTs are more commonly used in low-current applications.The MOSFET has a source, drain, and gate whereas the BJT has a base, emitter, and collector. ![]() While both have three terminals, these differ.The MOSFET (voltage controlled) is a metal-oxide semiconductor whereas the BJT (current controlled) is a bipolar junction transistor.There are many differences between the MOSFET and BJT. In either case, the current’s direction in the base is the same as the collector. In the NPN, the polarity is the opposite and current flows in the emitter and out the collector. Current flows in the collector of a PNP and out of the emitter. In between these structures is a small layer of the other doping agent called the “base”. Each type has a large collector element and a large emitter element which are doped in the same way. There are two types of BJT – PNP and NPN. A BJT has three pins – the base, collector, and emitter – and two junctions: a p-junction and n-junction. The Bipolar Junction Transistor (BJT) is a current-driven device (in contrast, MOSFET is voltage-driven) that is widely used as an amplifier, oscillator, or switch, amongst other things. Understanding the difference between n- and p-type semiconductors What is BJT? ![]() Because gate terminal voltage is positive or negative, channel conductivity is decreased.Įnhancement mode: when the gate terminal’s voltage is low, the device does not conduct unless more voltage is applied to the gate terminal. This often sees MOSFETs being used in low-power devices or as building blocks to reduce power consumption.ĭepletion mode: When the gate terminal’s voltage is low, the channel exhibits maximum conductance. This level of insulation roots low power consumption and is the primary benefit of this type of transistor. The gate terminal itself is made from metal and is detached from the source and drain terminals using a metal oxide. Likewise, in n-channel MOSFETs, the source and drain terminals are made of n-type semiconductor. These are saturation, active, inverted, and cutoff.In p-channel MOSFETs, the source and drain terminals are made of p-type semiconductor. The most commonly employed configuration is the common emitter configuration.Ī BJT can be biased into one of four possible modes. Hence we call the different circuit configurations common emitter, common base, and common collector to identify the lead common to both the input and the output. Since there are only three leads for a BJT, one of the leads must be common to both the input and the output circuitry. In most applications the input signal is across two of the BJT leads while the output signal is extracted from a second pair of leads. The vast majority of BJT applications are in analog electronics, but BJTs can also be employed in digital circuitry.Ī BJT can be used in several circuit configurations. The two p–n junctions are then formed between the emitter and base and collector and base. Thus for a pnp BJT, the emitter and collector regions are p-type while the base is n-type. The second layer is called the base and the third layer is called the collector. The first type of device is called a pnp BJT, while the second device is an npn BJT. These are alternating p, n, and p layers or n, p, and n layers. ![]() The device comprises three different doped layers. A bipolar junction transistor (BJT) consists of two p–n junctions with three terminals. ![]()
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