How pnp transistor works pdf

Remember these circuits, and, hopefully, with a bit of pattern-matching, you can make sense of more complex amplifiers. Three of the most fundamental transistor amplifiers are: common emitter, common collector and common base. In each of the three configurations one of the three nodes is permanently tied to a common voltage usually ground , and the other two nodes are either an input or output of the amplifier. Common emitter is one of the more popular transistor arrangements. In this circuit the emitter is tied to a voltage common to both the base and collector usually ground.

The base becomes the signal input, and the collector becomes the output. The common emitter circuit is popular because it's well-suited for voltage amplification , especially at low frequencies. They're great for amplifying audio signals, for example. If you have a small 1. One quirk of the common emitter, though, is that it inverts the input signal compare it to the inverter from the last page!

If we tie the collector pin to a common voltage, use the base as an input, and the emitter as an output, we have a common collector. This configuration is also known as an emitter follower.

The common collector doesn't do any voltage amplification in fact, the voltage out will be 0. For that reason, this circuit is sometimes called a voltage follower. This circuit does have great potential as a current amplifier. In addition to that, the high current gain combined with near unity voltage gain makes this circuit a great voltage buffer. A voltage buffer prevents a load circuit from undesirably interfering with the circuit driving it.

For example, if you wanted to deliver 1V to a load, you could go the easy way and use a voltage divider , or you could use an emitter follower. As the load gets larger which, conversely, means the resistance is lower the output of the voltage divider circuit drops.

But the voltage output of the emitter follower remains steady, regardless of what the load is. Bigger loads can't "load down" an emitter follower, like they can circuits with larger output impedances. We'll talk about common base to provide some closure to this section, but this is the least popular of the three fundamental configurations. In a common base amplifier, the emitter is an input and the collector an output. The base is common to both.

Common base is like the anti-emitter-follower. It's a decent voltage amplifier, and current in is about equal to current out actually current in is slightly greater than current out. The common base circuit works best as a current buffer. It can take an input current at a low input impedance, and deliver nearly that same current to a higher impedance output.

These three amplifier configurations are at the heart of many more complicated transistor amplifiers. They each have applications where they shine, whether they're amplifying current, voltage, or buffering. We could go on and on about the great variety of transistor amplifiers out there. Here are a few quick examples to show off what happens when you combine the single-stage amplifiers above:.

The Darlington amplifier runs one common collector into another to create a high current gain amplifier. Voltage out is about the same as voltage in minus about 1.

The Darlington pair is a great tool if you need to drive a large load with a very small input current. A differential amplifier subtracts two input signals and amplifies that difference. It's a critical part of feedback circuits, where the input is compared against the output, to produce a future output.

This circuit is also called a long tailed pair. It's a pair of common-emitter circuits that are compared against each other to produce a differential output. Two inputs are applied to the bases of the transistors; the output is a differential voltage across the two collectors. A push-pull amplifier is a useful "final stage" in many multi-stage amplifiers.

It's an energy efficient power amplifier, often used to drive loudspeakers. The push-pull amp doesn't really amplify voltage voltage out will be slightly less than that in , but it does amplify current.

It's especially useful in bi-polar circuits those with positive and negative supplies , because it can both "push" current into the load from the positive supply, and "pull" current out and sink it into the negative supply. If you have a bi-polar supply or even if you don't , the push-pull is a great final stage to an amplifier, acting as a buffer for the load.

Let's look at a classic example of a multi-stage transistor circuit: an Op Amp. Being able to recognize common transistor circuits, and understanding their purpose can get you a long way! Here is the circuit inside an LM , a really simple op amp:.

The internals of an LM operational amplifier. Recognize some amplifiers? There's certainly more complexity here than you may be prepared to digest, however you might see some familiar topologies:. After this crash course in transistors, we wouldn't expect you to understand what's going on in this circuit, but if you can begin to identify common transistor circuits you're on the right track!

Now that you're in control of the source of control, we recommend a SparkFun Inventor's Kit to bring your newly found knowledge to life. We've also provided links to a semiconductor kit and single transistors to insert into your own projects. This is a ve…. With the Add-On Pack you will be able to incorporate some of the older parts that used to be included in the SIK that were re….

On top of that, our very own Director of Engineering, Pete, has produced a series of According to Pete videos with a focus on transistors and transistor amplifiers. Definitely check out his Diodes and Transistors video:. Great stuff! Or, if you're itching to learn more about electronics in general, check out some of these SparkFun tutorials:. See our Engineering Essentials page for a full list of cornerstone topics surrounding electrical engineering. Take me there! Need Help?

Mountain Time: Shopping Cart 0 items. Product Menu. Today's Deals Forum Desktop Site. All Categories. Development Single Board Comp. Home Tutorials Transistors Transistors. Contributors: jimblom. Introduction Transistors make our electronics world go 'round.

We've got you covered! Favorited Favorite 76 Wish List. Favorited Favorite 55 Wish List. Favorited Favorite 12 Wish List. Favorited Favorite 19 Wish List. See all transistors. Symbols, Pins, and Construction Transistors are fundamentally three-terminal devices. Extending the Water Analogy If you've been reading a lot of electricity concept tutorials lately, you're probably used to water analogies.

Operation Modes Unlike resistors , which enforce a linear relationship between voltage and current, transistors are non-linear devices.

The four transistor operation modes are: Saturation -- The transistor acts like a short circuit. Current freely flows from collector to emitter. Cut-off -- The transistor acts like an open circuit. No current flows from collector to emitter. Active -- The current from collector to emitter is proportional to the current flowing into the base. Reverse-Active -- Like active mode, the current is proportional to the base current, but it flows in reverse. Current flows from emitter to collector not, exactly, the purpose transistors were designed for.

Applications I: Switches One of the most fundamental applications of a transistor is using it to control the flow of power to another part of the circuit -- using it as an electric switch. Applications II: Amplifiers Some of the most powerful transistor applications involve amplification: turning a low power signal into one of higher power.

Common Configurations Three of the most fundamental transistor amplifiers are: common emitter, common collector and common base. Common Emitter Common emitter is one of the more popular transistor arrangements. Purchasing Transistors Now that you're in control of the source of control, we recommend a SparkFun Inventor's Kit to bring your newly found knowledge to life.

Our Recommendations:. Favorited Favorite 46 Wish List. Resources and Going Further If you're looking to get deeper into transistors, here are some resources we'd recommend: Getting Started in Electronics by Forrest Mims -- Mims is a master of explaining electronics in an easy-to-understand highly applicable manner. Definitely check this book out if you want a more in-depth introduction to transistors.

Digitally experimenting with circuits is a great way to learn. Besides, the current from emitter to collector starts to flow, provided the voltage VCE is applied at collector terminal. The PNP transistor can act as a switch and an amplifier. The application of an PNP transistor is to work as a high side switch. The first important thing to bear in mind to use a current limiting resistor at base. Higher base currents will damage a BJT. The corresponding saturation voltages and base currents are also available.

Find the collector current wiz the current consumed by your load. In order to drive the transistor into saturation condition sufficient base current has to be drawn out such that the transistor is completely ON. Calculating the base current and the corresponding resistor to be used. For complete saturation the base current is approximated to 2. Thus below is the circuit with 12V to base same as that to emitter with respect to ground during which the switch is OFF state.

Theoretically the switch is completely open but practically a leakage current flow can be observed. This current is negligible since they are in pA or nA. For better understanding on current control, a transistor can be considered as a variable resistor across collector C and emitter E whose resistance varies based on the current through the base B. Initially when no current is flowing through base, the resistance across CE is very high that no current flows through it.

When an potential difference of 0. Now current flows from emitter to collector proportionately to that of current flow from emitter to base, also the gain. Now let us see how to control the output current by controlling the base current.

The variation of practical value from calculated value is because of the voltage drop across transistor and the resistive load that is used. Also, we have used a standard resistor value of 13kOhm instead of Amplification is the converting a weak signal into usable form. To get current running from emitter to base, you need a voltage difference of about 0. Since the current goes from emitter to base, the base needs to be 0. By setting the base voltage of a PNP transistor to 0.

I know this can sound a bit confusing, so read on to see how you can design a circuit with the PNP transistor. With this circuit you can use to turn on an LED when it gets dark.

First of all, to turn on the PNP transistor, you need the voltage on the base to be lower than the emitter. This way, you know what voltage you have on the emitter. When the transistor turns on, the current can flow from the emitter to the collector. To turn on the LED, you need to turn on the transistor so that the channel from emitter to collector opens. To turn on the transistor you need to get the voltage on the base to be 0. For example, you can now make the LED turn on when it gets dark by using a photoresistor and a standard resistor set up as a voltage divider.

This is because the transistor affects the voltage too. But in general, when the photoresistor value is large no light present the voltage will be close to 8. When the value of the photoresistor is low a lot of light present the voltage will be close to 9V and turn off the transistor which turns off the LED.

And a diode always try to get its diode voltage over itself. This particular diode has a diode-voltage of about 0. And 8. Do you mean where to buy one? Or do you mean how to find the value of a resistor? It turns fully on and off now. But are you looking for a sharper transition between on and off to avoid the half-on state? Thanks a lot for such tremendous effort in explaining such a difficult question in an easier way.

Pls explain. Thanks a lot. The semi-off would dim the LED, not fluctuate. But if you somehow had a high-frequency signal and you want to fix the signal instead of the source of the problem then you can use a low-pass filter. There is either a problem with my Math or your Circuit. Your circuit works according to your video.

What did I do wrong? The part between the emitter and the base of the transistor behaves as a diode of 0. Taking that resistance into account makes the calculations very complex. So, for this type of circuit — it makes more sense to make a simplified calculation like you did above to make a first guess of the correct resistor value.

Then test it in real life and adjust the value according to your needs. Does it mean when you apply a voltage at the emitter you automatically get a voltage less than 0. No, but if you connect a resistor to the base, and the other end of the resistor to a lower voltage for example 0V , then you get a voltage on the base 0.

This brings about a few problems, i. Firstly, how much power does the flashing light component need? Second, how much power can the Transistor Switch deliver?

Third, how much power does it take to power the circuit? I would like to build a circuit similar, but with a thermistor, and different LED lights for various temperatures.