![]() It covers the basics in an easy to follow way but also addresses a lot of other things, and walks you through a lot of neat stuff. I highly recommend buying that book if you intend to learn any electronics, by the way. ![]() Read this for more information, more lucidly written than what I have put here: The exact values depend on what you're trying to switch and what transistors you're using. Typically this means making the base current about 1/10 or so (as a rule of thumb) of the collector-emitter current. To turn it on, you want to put enough current into its base to get its collector-emitter current as high as you need. ![]() To turn an NPN off, you want to put very little (preferably no) current into its base. This is the region where the current flowing from the drain to the source is at. The transistor is now in saturation.įor switching, you're not interested in the active region (amplification), you just want to slam the transistor between saturation and cutoff. This is an article explaining what the saturation region of a transistor is. You are now in the active region, which means that the current flow on the collector-emitter is an amplified version of the base current.Īs you keep raising the current into the base, the collector-emitter rises (falls, for a PNP) even more rapidly, until at some point the transistor can no longer allow more current to flow and the collector-emitter current levels off. If you provide some more current to the base, then at some point more current will be able to flow on the collector-emitter. For a PNP, it means that as much current as is available will flow across the collector-emitter. For an NPN, this means that no current will flow across the collector-emitter. If you provide no (or very little) current to the base compared to the collector-emitter, then the transistor will be in cutoff. The ratio between the base current and the collector-emitter current depends on the transistor's 'beta', or gain (also called its hfe-imagine the 'fe' is written in subscript). Typically you arrange resistors to provide the needed amounts of current into each terminal. If you don't, check out (actually, check out that whole online book-it's a great resource and easy to follow).Ī transistor uses a small amount of current flowing into its base to control a larger current flowing between its collector and emitter. Nothing else will make sense unless you know that V = IR (V means voltage, I means current, and R means resistance). A transistor goes into saturation when both the base-emitter and base-collector junctions are forward biased, basically. I'm just a hobbyist but I use it every time I have to think about electronics. I should probably say that you really, really want to learn Ohm's Law if you're going to mess with this stuff. ![]() NPN and PNP are opposites (mostly) so 'cutoff' and 'saturation' mean the opposite things for them. Yes, those are basically the three states for a transistor. In the active region, the transistor acts as an amplifier. In the active state, the collector current is β times the base current, i.e.(If you are a female, can we call you 'Miss Demeanor'?) In the active region, emitter to the base junction is forward biased and the base to collector junction is reverse biased. In the saturation region, the B-E and B-C junction are forward biased and IC=IE ACTIVE REGION: TRANSISTOR AS AN AMPLIFIER: In cut off region the output of the transistor VCE, IC, IB and IE=0 SATURATION REGION: In the saturation region, both the junctions are in forwarding bias,and the transistor acts as a closed switch. In cut off region, both emitter to base and base to collector junction is in the reverse bias and no current flows through the transistor. Based on biasing, the transistor can be operated in cut off, active and saturation region of the transfer characteristics of the transistor.In this post, we will discuss operation of BJT in Active, Saturation and Cutoff Region TRANSISTOR AS A SWITCH : CUT OFF REGION: Saturation (in a transistor): The state of a transistor at which the collector current has reached its maximum value for the present collector-emitter voltage, and cannot increase further by only increasing the base current IB. The transistor can be used as a switch or as an amplifier by forward/reverse biasing the emitter to base and base to collector junctions.
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