![]() These parasitic elements introduce a delay on the device switching speed somehow. These are input capacitance, gate charge, output capacitance, and rise and fall times to name some. MOSFET has parasitic elements defined in the datasheet. MOSFET Efficiency Factors for Switching Converters The added losses due to switching is not enough to offset the loss of the BJT due to higher VCEsat. Despite of this, MOSFET is still overall has the advantage. In other words, the switching losses of a BJT is could be negligible. Ploss_MOSFET_switching = Ploss_gatecharge + Ploss_COSS + Ploss_rise_fallīy looking at the BJT datasheet, there is no information about input capacitance, output capacitance or the rise time and fall time. These losses are directly proportional to the switching frequency. It has also losses due to the output capacitance (COSS) and due to rise and fall times. In applications like switching converters and power supplies, the MOSFET will have power loss on the gate that is caused by the gate charge or input capacitance. Comparing Switching Losses of MOSFET and BJT On the other hand, VCEsat value of BJT is high.Ĩ. This is because RDSon value nowadays is reaching very small value. Pdiss_BJT = Ibase X VBE + Icollector X VCEĬomparing the loss of MOSFET due to the RDSon and the loss of BJT due to VCE saturation voltage, MOSFET is very small. The power loss in the collector-emitter is due to the voltage drop and the collector current. The power loss on the base is due to the VBE and the base current. MOSFET RDSon Temperature Coefficient Usage and InterpretationīJT on the other hand has losses on both the base and the collector-emitter. How to Use MOSFET RDSon Data from the Datasheet It has no power loss on the gate ideally when the circuit is design only for on/off switch. MOSFET power dissipation or power loss is due to the drain to source on state resistance. MOSFET and BJT Static Power Dissipation/Power Loss To drive it to saturation, the applied voltage level must be far above the gate to source threshold voltage (VGSth).īoth devices are comparable in terms of voltage rating. To turn on a MOSFET, it needs to apply voltage on the gate to source. MOSFET Advantages Over BJT in Switching Converters 4. On the other hand, current controlled means that to set the BJT operation, it needed an amount of current on the base. Voltage controlled means that to set the MOSFET operation, it needs to have adequate voltage across gate to source. MOSFET is a voltage-controlled device while BJT is a current controlled device. This is also the case for a BJT, there is a voltage drop across collector-emitter. At this operation, MOSFET drain-source voltage is not zero but there is a value depending to the circuit biasing. In this operation mode, both devices will operate in the linear region. Also, the same manner to BJT the voltage across collector-emitter is ideally zero.īoth devices are useful as signal amplifier. At saturation, MOSFET drain to source voltage drop is ideally zero. MOSFET is popular as a switch in which it will operate in cut-off and saturation. ![]() ![]() MOSFET and BJT Comparison in Terms of Operation Below are circuit symbols for the MOSFET.ģ. It has gate (G), drain (D), and source (S). MOSFET is a three terminal semiconductor device. ![]() NMOS is commonly used as low side driver while PMOS is common in high side driving. This is something related to the dominant charge carriers. MOSFET is also either N channel (NMOS) or P channel (PMOS). MOSFET is either depletion or enhancement per construction. In terms of construction, MOSFET and BJT comparison is very different. Comparing MOSFET and BJT in terms of Construction How to Use MOSFET as Reverse Battery ProtectionĢ. On the other hand, MOSFET is widely used as a switch because of easier circuit requirement and analysis required. However, BJT is very much famous compared to MOSFETs. They are both useful as relay drivers, signal inverters, power switch to name few.īoth are also famous in signal amplifiers. Application of MOSFET and BJTīoth MOSFET and BJT are good to use as electronic switches. It is worth to discuss MOSFET and BJT comparison to understand which part to use. BJT on the other hand is bipolar junction transistor. MOSFET is metal oxide semiconductor field effect transistor. Two of the most common three terminal semiconductor nowadays are MOSFET and BJT.
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