In this article, you’ll learn how to characterize a voltage controlled current source (VCCS). In this article, we’ll cover such topics as Diode compensation, Static voltage drop, Common emitter, and source. These are all fundamental aspects of a voltage-controlled current source.
A voltage controlled current source (VCCS) is a circuit that converts a known voltage into a known current. Among its most significant features is its ability to maintain a constant injection current over a wide frequency range. This is achieved by designing the current source with a high output impedance.
The DC forward voltage of a PIN diode changes with changes in its bias current, and a diode compensation circuit can help to eliminate this effect by balancing the voltage across the diode. A diode is the same material as a transistor, and its voltage VD is essentially identical to the voltage VBE. A diode is forward biased by a resistor RD and source VDD, so that the voltage across the diode is the same as the voltage VBE. This compensation allows the voltage to stay constant, thereby maintaining the current IC.
Voltage compensation is achieved by regulating the voltage across Element 2. In a voltage controlled current source, this compensation occurs when the voltage source’s input voltage drops below the voltage level of Element 2. In such a circuit, the voltage drop across the Element is called the compliance voltage. The voltage difference between Element 2 and Element 1 determines the current.
In a voltage controlled current source, diode compensation reduces the voltage difference between the emitter and collector of the regulated input voltage. By reducing the output voltage, the current reaches the ground through the diodes and resistors. When the current level reaches the nominal value, the output voltage returns to the nominal regulated level.
A voltage controlled current source can be implemented using bipolar junction transistors. The emitter follows the source. The collector is connected to an external load. The emitter resistor senses the load current and drives the emitter follower Q1. The output current is adjusted by the transistor Q1 through the voltage drop across the load resistor R2.
Voltage controlled current sources are devices that produce an output voltage from an input signal. The output voltage is determined by the voltage across the common emitter. These devices are also known as voltage controlled amplifiers. They work by utilizing a common emitter and a load resistor. The common emitter carries the current from the source to the load.
One of the most fundamental properties of voltage controlled current sources is their ability to regulate current. This is accomplished by varying the resistance of the base-to-collector region. The resistance of the base-to-collector terminal is equal to the resistance of the common emitter. It is important to use a biasing component to ensure that the output impedance is not too high.
Voltage controlled current sources are often used in circuits with a common base. They are typically connected in series with a load to control current flow. For example, a 5 V source coupled with a 4.7 kO resistor will provide a constant current of one mA to a load with a resistance of 50 to 450 O.
Both voltage controlled current sources use DC servos to maintain the base voltage. This is necessary because the gain is too high without feedback. Without feedback, the output voltage would be only half the voltage of the supply. This is necessary to maintain the correct voltage and current. The base-emitter voltage will set the collector current. The output impedance will change with temperature.
Common emitter amplifiers also share the emitter lead with a load. The difference in resistance between the two sources determines the voltage gain. The larger the load resistance, the more gain it will produce.
A common source of voltage controlled current is a device that amplifies an input signal at the source terminal, and a voltage or current is then produced at the output terminal. These devices also are called voltage amplifiers or transconductance amplifiers. The output voltage and current of these devices depend on the input impedance, and these devices are typically used for modeling operational amplifiers and transistors.
While many current sources are available, this one has some major advantages. For one, the output current can be bilateral, a huge advantage over other current sources, such as the Howland type. Other current sources require a large number of resistors that must be matched and stable. In contrast, the current source shown in Figure 2-30 has no matched resistors, and is precise over a broad current range.
A common source of voltage controlled current can be defined using the Schematic Editor. This tool allows you to define the component labels and the control gain. The control gain must be the same length as the output voltage. The Y(t) variable represents the output voltage or current. The X1 and Xn are the respective control label vectors with corresponding gain values g1 and gn. The value of g1 and gn must be real numbers.
Common sources of voltage controlled current are used to control a large voltage across an output. The output voltage of a voltage controlled current source can be wide enough to vary a load’s voltage across a large range. A single positive power supply is usually applied to the source for control. The inputs are terminals 14 and 16 for the differential amplifier. The negative feedback from junction 12 is also present.
Power dissipation is a function of the current absorbed and delivered by a voltage controlled current source. An ideal source will plot a horizontal line on the I-V characteristic, but a practical source will have an internal source resistance (R P) that reduces the resulting current. This decrease is due to the splitting of the current. A part of the current flows into the parallel resistance R P, while the rest flows to the output terminals.
Power dissipation of a volumetric voltage controlled current source can be calculated using the following equations. Note that the values for the resistors have to be calculated at minimum supply voltage and maximum load current. In this way, the power dissipation is equal to the total voltage across the load. However, the efficiency of this kind of voltage controlled current source is poor and is therefore impractical for most applications.
The output of a voltage controlled current source varies with its temperature and geometry. Hence, it is important to control the temperature of the current source chip to maintain predictable current output. However, changing the temperature will change the output current and introduce errors in the circuit. As a result, the power dissipation of a voltage controlled current source must be carefully controlled. A simple model of this type of voltage controlled current source is represented in FIG. 1.
In addition to heat dissipation, voltage controlled current sources can also produce heat. A good example of this is an electric heater using resistance wire. Nichrome is a unique heating element with characteristics that include high cost-effectiveness, oxidation resistance, and high flexibility. Another example of a voltage controlled current source is a light bulb.