Calculating the base resistor is a common engineering task, which this calculator automates. Bjt circuit configurations, bjt design, base resistance and emitter current crowding in bjts, punchthrough breakdown in bjts, gummelpoon bjt equivalent circuit accounting for the leakage currents. Bjt biasing using a current source lecture ku ittc. Current source biasing integrated circuits have transistors which are manufactured simultaneously with the same device parameters parameters from chip to chip will vary as a result, different bias techniques are employed than in discrete designs one common technique is current source biasing, which allows the. A bipolar junction transistor is a solidstate device in which the current flow between two terminals the collector and. The beta and vd transistor parameters, can be measured, or gathered from a data sheet. Remember that a bipolar transistor is a current amplifier. Designing a single bjt transistor current source discrete design. Fb means forward current transfer ratio of the common, or grounded, base circuit, whereas fe means forward current transfer ratio of. My favorite so far is a voltage divider calculator that can do arbitrary seriesparallel networks. Pnp transistor tutorial the bipolar pnp transistor. The following circuits show some of the basic uses of the lm317 lm338 lm350 series of voltage regulators when configured as a current regulator or constant current source ccs. Bjt characteristic curves it is sometimes helpful to view the characteristic curves of the transistor in graphical form.
The algorithm makes use of ac and dc load line theory and formulas and is one of the most accurate you will find online. Pspice model library includes parameterized models such as bjts, jfets, mosfets, igbts, scrs, discretes, operational amplifiers, optocouplers, regulators, and pwm controllers from various ic vendors. Bjt ac analysis on the output side, the controlledcurrent source is connected between collector and emitter, i source i b. Two bjt current source figure 3 shows npn and pnp twotransistor bjt current sources that are simpler to design. Without this base current, the transistor cant turn on. A bjt transistor can be used as an electronic switch when it is driven into saturation, or alternatively driven to the cut off region. Bjt transistor bias voltage calculator calculates for. The lm4lm234lm334 are 3terminal adjustable current sources featuring 10,000. Bjt common emitter configuration design calculator. The humble transistor q1 emitter e collector c base b. Remember that a bipolar transistor is a current amplifier, because a small amount of current ib through the base controls a larger amount of current ic flowing through its collector.
Is is often called the saturation current, and it fits into the spice model equation for vbe for example along with another constant n variations on this. Constant current source calculator electronic products. You can pass your mouse or click on it over the blue underlined text in the calculator to obtain more information about that area. Voltage and current calculation free online math calculator. It is a semiconductor device and it comes in two general types. Here is a calculator for transistor base resistor values. Transistor simulator calculator, voltage and current. Normally, voltage gain a v and current gain a i are high. Transistor base resistor calculator kaizer power electronics. This calculator provides the required electrical power power output from the amplifier to produce a desired sound pressure level spl at a given distance, along with an amount of headroom to keep the amplifiers out of clip. This is frequently done with a simple resistor whose value is calculated using ohms law.
The base current, ib, of a transistor is a crucial current of a bipolar junction transistor. The bjt current source top of page produces a constant current out of q4 regardless of the voltage at its collector. This transistor simulator calculator is used to calculate the collector and emitter voltage, base current, emitter current, power and collector current using the given inputs. These values are responsible for enabling transistor. When re is theload, output resistance can be found by killing the source short vi and nd. Small signal equivalent circuits and parameters for the bjt r model when the ac portion of the input is small around the q point current source calculator. Electronics tutorial about the transistor as a switch and using the transistor as a. Transistor switch saturation calculator electronic products. Current source biasing integrated circuits have transistors which are manufactured simultaneously with the same device parameters parameters from chip to chip will vary as a result, different bias techniques are employed than in discrete designs one common technique is. These were the industry standard for a long time, but people are finally learning how much more efficient mosfets a voltage controlled device are over the more common bjt a current controlled device.
That is not correct, a bjt is basically a current amplifying device if a voltage comes out of a bjt based amplifier that voltage is either the bjts collector current which is turned into a voltage by a resistor connected to the bjts collector or the bjt is used as a voltage buffer common collector or emitter follower where it does not. Calculator vbe vce hfe first you must check the datasheet of the transistor in question and identify the values vbe, vce, and hfe. Note that it does require an external source of dc power supply to carry out the amplification process. Download pspice for free and get all the cadence pspice models.
The construction and terminal voltages for an npn transistor are shown above. The things you learned about biasing a transistor in chapter 5. Just fill the input fields below in given order from top to bottom. Twobjt current source figure 3 shows npn and pnp twotransistor bjt current sources that are simpler to design.
Therefore collector current and emitter current are again i c 99i b 2. Hi, i agree that this is a little unusual because they seem to give some spice data, yet they spec the vbe voltage at the same time, and the gain given would be a typical actual beta not bf in the spice model sense, which would probably be higher. How to calculate the base current, i b, of a transistor. The voltage sources are connected to a pnp transistor are as shown. The simple use of a transistor enables a far more effective current source to be made. Bjt amplifier circuits pdf 23p this note covers the following topics. This tool calculates the current flow through each of up to 10 parallelconnected resistances connected to a current source. Home tools transistor switch saturation calculator transistor switch saturation calculator. A bipolar junction transistor is a solidstate device in which the current flow between two terminals the collector and the emitter is controlled by the amount of current that. Bipolar junction transistors bjt general configuration and definitions the transistor is the main building block element of electronics. This calculator will compute the values of the biasing resistors required to provide the maximum output voltage swing in a npn bipolar junction transistor bjt amplifier circuit. Design a npn transistor current source with a base supply voltage of 5 v, a collector supply voltage of 10 v, and a target constant current of 10 ma. Cir download the spice file one of the less glamorous but equally important circuits in audio amplifiers is the current source. The following calculators, will compute all of the bias values of the transistor circuit, given the supply voltage, and the base voltage, and all of the resistor values.
For convenience, you can change the baseemitter voltage, which is set to 0. Although transistor switching circuits operate without bias, it is unusual for analog circuits to operate without bias. The current source operates because of the fact that the collector current in a transistor circuit is. In this case, little current ows in rl which is ne because we are using this con guration as a bu er and not to amplify the current and power. Ohms law states the relationship between current, voltage and resistance. Home tools constant current source calculator constant current source calculator. Base resistence needed to drive transistor into saturation. Bjt ampli er circuits as we have developed di erent models for dc signals simple largesignal model and ac. Ive had a little project on the back burner for some time ive been meaning to write up a whole bunch of little useful electronics calculators not just like the little ones you see scattered around that are no more convenient than a pocket calculator and put them in a collection online. It can be used when it is desired to have a much lower output current than input current. This is very similar to the graphical approach used with diodes, but now we have three possible points where something could be happening base, emitter, collector. I wonder about bjt maximum collector current, maximum base current, and maximum emiter current, or maximum voltage,and whether or not these values can be use to calculate the needed minimum current or voltage to find all resistors and other parts.
Nov 20, 2017 i wonder about bjt maximum collector current, maximum base current, and maximum emiter current, or maximum voltage,and whether or not these values can be use to calculate the needed minimum current or voltage to find all resistors and other parts. The key to maximizing led life is limiting the current that runs through it. A bipolar junction transistor is a solidstate device in which the current flow between two terminals the collector and the emitter is controlled by the amount of current that flows through a third terminal the base. Select the bjt you want to use, from its datasheet lookup the current gain factor and place it here as a parameter. Here we will describe the system characteristics of the bjt. I b and i c current goes into the transistor the sign of the current is taken as positive and if current goes out from the transistor then the sign is taken as negative. But since they already give the vbe then there doesnt seem to be any. And it all depends on what information is already known about the transistor. The fet constantcurrent sourcelimiter introduction the combination of low associated operating voltage and high output impedance makes the fet attractive as a constantcurrent source. An oftenused circuit applying the bipolar junction transistor is the socalled current mirror, which serves as a simple current regulator, supplying nearly constant current to a load over a wide range of load resistances.
This biasing scheme has a number of important advantages. I think you should use the average current, lets say 0. Lm317 lm338 lm350 current regulator calculator and. Also, the internal resistance of the signal source should be given. Consider a base resistor that controls the amount of current entering the base junction of a bipolar junction transistor bjt to cause it to conduct in the saturation region. That is not correct, a bjt is basically a current amplifying device if a voltage comes out of a bjt based amplifier that voltage is either the bjt s collector current which is turned into a voltage by a resistor connected to the bjt s collector or the bjt is used as a voltage buffer common collector or emitter follower where it does not. The output current in each is the collector current io. The pnp transistor has very similar characteristics to their npn bipolar cousins, except that the polarities or biasing of the current and voltage directions are reversed for any one of the possible three configurations looked at in the first tutorial, common base, common emitter and common collector. The fusion of these two diodes produces a three layer, two junction, three terminal device forming the basis of a bipolar junction transistor, or bjt for short. Lm317 lm338 lm350 current regulator calculator and circuits. Our default conditions are calculated on loading of the calculator but can be changed and recalculated. Solve for voltage and current transfer functions and input and output impedances nodevoltage method is the best. Bjt ac analysis on the output side, the controlled current source is connected between collector and emitter, i source i b.
Sound that is radiated from a point source drops in level at 6 db per doubling of distance. Why is bjt called as current controlled current source and. Calculating current limiting resistor values for led circuits. Current is established with one external resistor and no other parts are required. This time the emitter is connected to the supply voltage vcc with the load resistor, rl which. There are several ways to find the base current, ib, of a transistor. One of the less glamorous but equally important circuits in audio. There are many ways to create a current source, most of which use some form of transistor based current mirror. Data entry is on the left, a representative schematic is in. This is a simple design tool for calculating bias resistor values, smallsignal gain and inputoutput resistances of a commonemitter bjt amplifier. Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage.