![]() But BJTs are typically much closer to n=1 than diodes are so I haven't seen much practical use. Prior to Zetex, you had to get a big power transistor in TO-3 can to get this low. Transistors have a varying gain so we want to use the minimum. In either case, the functional dierence of a FET from a bipolar junction transistor is the extremely high input impedance of the. The current through the load at saturations is Ic VP/Rc. In some cases, the log-log, or linear graph of Ic vs Vce shows the linear property above 10 of Imax. Field eect transistors (FETs) come in a myriad of dierent congurations and types, but they generally belong to two broad classes: depletion-mode devices like JFETs or enhancement-mode devices like MOSFETs. saturation current temperature exponent and is used to BJT Circuits. Saturation in a transistor switch circuit is achieved when the voltage across the collector/ emitter (VCE(sat)) is less than or equal to. This collector-emitter saturation bulk resistance called RCE R C E is defined for VceVce (sat) at Ic/Ib10 at various currents. Something tells me that 10 -14 A happens to be the default for someone's SPICE.ĮDIT: you can step up your game just a little bit by including n≠1. model of SPICE models to LTspice Simulate in LTSpice the NPN BJT transistor. What makes you think that some random SPICE model you found on the internet is anything but dogshit? (This often includes straight from the manufacturer's website.) SPICE programs always have default values for any parameters you don't include in the model. It is in this region that the transistor can act as a fairly linear amplier. ![]() The nal region of operation of the BJT is the forward active region. I've also seen a SPICE model which has an Is=10-14 A but when i try to compute values with it i get pretty substantial deviance from the datasheet. Most of the power that must be dissipated by the transistor when used as a switch comes from the short time periods between between being fully saturated an fully cutoff. You can also use a MOSFET with a low gate-source voltage. ![]() ![]() My opinion is that for a transistor in SOT-89 at a current of 2A, you need to think about heat sink. Preferably as long as you can without guessing at the numbers. The saturation voltage at other currents can be obtained from the Collector-emitter saturation voltage diagram in the datasheet or measured experimentally. These three portions are called Emitter, Collector, and Base. Basically, transistors have three portions and two junctions. These transistors are known as PNP or NPN bipolar junction transistors depending on whether P or N-type is sandwiched. Also why does the graph deviate at a certain point from the diode equation Vbe = Vt*ln(Ic/Is) ?įind a nice straight section of the Ic vs Vbe log-plot. BJT transistors are formed after connecting two PN junctions back to back. ![]()
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