If the current is greater than 300ma the resistance should be 2ohm. I would like to build a voltage or digitally controlled resistor for controlling older analog equipment from a micro or pc. The wattage rating indicates the amount of power the resistor can safely dissipate as heat. My application needs to control a psu remote port which requires 1k ohm to produce 1v on the psu out put. For easy configuration of the ltc6990, use the timerblox ltc6990. Siliconix note an105 has some example circuits with jfets voltage control resistors. The field effect transistor as a voltage controlled resistor we consider the use of a nchannel fet as a voltage controlled resistor where the resistance between the drain and source is controlled by the gatesource voltage. The ltc6990 is part of the timerblox family of versatile silicon timing devices. An important aspect that students miss since it is not explicitly stated is that, on changing the voltage applied on the fets gate pin the resistance offered by the fets channel changes. A simple addition to the above resistor model gives you a voltagecontrolled resistor. The vcr is one of the numerous interesting circuit elements that can be produced by using a jfet junction fieldeffect transistor with simple biasing. The first thing that comes to someones mind when thinks of a dimmer, is a potentiometer that controls the light intensity. If we refer back to figure 2 in part 1, for a voltage controlled resistor without feedback resistors, we see that for vds 0 volt, the resistance is. A voltage controlled current source circuit, in accordance with another embodiment of the present invention, includes a first resistor, a first current mirror having a current terminal coupled to a first terminal of the first resistor, wherein the first current mirror generates a first reference current, a first voltage controlled impedance.
The nature of vcrs a voltagecontrolled resistor vcr may be defined as a threeterminal variable resistor where the resistance value between two of the terminals is controlled by a voltage potential applied to the third. This voltage is converted to a current signal and is applied to the capacitor. Methods of outputvoltage adjustment for dcdc converters introduction some systems benefit by adjusting the output voltage of one or more dcdc converters while the converters are enabled and the system is operating. There are many functions included within the free download of the software and available on the internet. I tried an normal resistor with an expression, but i discovered that i can only use expressions for voltage and current sources. A new grounded voltage controlled positive resistor gvcpr is proposed in this brief. While the value can be made to change for a set of simulations by using a parametric sweep to move through a fixed sequence of values, a voltagecontrolled resistor can be made to change dynamically during a. Voltage controlled resistor replacement ni community. I looked at the spec sheet for the above devices and its not clear how to read the salient specs. A voltagecontrolled amplifier can be realised by first creating a voltagecontrolled resistor vcr, which is used to set the amplifier gain. Sep 04, 2018 voltage controlled oscillator vco, from the name itself it is clear that the output instantaneous frequency of the oscillator is controlled by the input voltage. Figure 6 to include a jfet as a controlled resistor. Between each element and at either end are tap points accessible to the wiper element.
So, you can think in terms of building a programmable current sink, or you can measure the voltage at the pin with various resistances repeat your current test, but check voltage too and then make a circuit to drive the pin to. Us20050280376a1 transistorized, voltagecontrolled dimming. Im trying to draw out the schematic for a current controlled resistor that behaves as follows. While the value can be made to change for a set of simulations by using a parametric sweep to move through a fixed sequence of values, a voltage controlled resistor can be made to change dynamically during a simulation. Im not much on designing fancy transistor circuits, but i could imagine you could, in principle, design a circuit such that the current that a transistor draws across itself depends on the voltage presented at one of its terminals dont some fets sort of do that. Pbfree plus anneal available rohs compliant description the intersil x9511 is a push button controlled potentiometer that is ideal for push button controlled resistance trimming. Engineering and manufacturing amplifiers design and construction testing amplifiers electronics electric current regulators usage signal processing methods voltage regulators. This technical brief offers one simple way of making a vcr using ltspice. The voltage drop across resistor r2 122, v r2 is the sum of the voltage from circuit node b to circuit node e, v be, and the voltage from circuit node e to circuit node c, v ec, but v be may be approximated as the base to emitter voltage drop of switching transistor q1 114, e.
Pdf voltage controlled resistor using quasifloatinggate. For purposes of this discussion, the gatetosource voltage. Tons of different circuits can be found around the net. A simple addition to the above resistor model gives you a voltage controlled resistor. Ideally, something that has a 0 5v input swing with a linear resistance output from 0 10kohms, respectively. For a junction fieldeffect transistor jfet under certain operating conditions, the resistance of the. A voltage controlled resistor vcr is a threeterminal device that varies the resistance between two terminals relative to voltage in the third terminal. In general, this is a valid assumption that reduces the design complexity. Lm566c voltage controlled oscillator general description the lm566cn is a general purpose voltage controlled oscillator which may be used to generate square and triangular waves, the frequency of which is a very linear function of a control voltage. The resistance, r, provides the required reduction in current or the desired drop in voltage. With reversal of the dc voltage by the load, the flow of power is from the dc source to the ac supply. But if it is operated on the region prior to pinchoff that is where vds is small, say below 100 mv, it will behave as a voltagevariable resistor we.
As the control voltage decreases from nominal voltage, the frequency also decreases and as the nominal control voltage increases, the frequency also gets higher. But the control of this dimmer is a dc voltage level. The proposed gvcpr with a single control voltage is composed of only six mos transistors operated in. Apr 20, 2018 voltage controlled resistor is there any way to get a voltage controlled resistor. A resistor voltage divider at the vco pin programs the desired vco voltage levels. Im on the hunt for some sort of analog voltage controlled potentiometer. Voltage controlled oscillators tuning a voltage controlled oscillator vco is an oscillator whose frequency can be varied by a voltage or current. Fet as a vvrvoltage variable resistor circuitstoday. The frequency is also a function of an external resistor and capacitor. A voltagecontrolled resistor vcr may be defined as a threeterminal variable resistor where the resistance val ue between two of the terminals.
That is, the load current drainsource current of a fet is controlled by the voltage applied on the gate pin. During the positive halfcycle of the supply voltage, the scr is forwardbiased and will conduct if a trigger is applied to the gate. A voltagecontrolled resistor vcr is a threeterminal active device with one input port and two. The nature of vcrs a voltage controlled resistor vcr may be defined as a threeterminal variable resistor where the resistance value between two of the terminals is controlled by a voltage potential applied to the third. The input is given in form a voltage that can be controlled. Mosfet as a voltage controlled resistor electrical. The inputport voltage controls the value of the resistor between the output ports. Smith, member, ieee, sima dimitrijev, member, ieee, and h. Vcrs are commonly used in the following electronics. Controlling a dcdc converter by using the power mosfet as a. Simple control circuits for electronic ballast design. Pdf the paper discusses an application of the field effected transistor fet as a voltage controlled resistance which can be done in undergraduate.
Snosbw2f november 1999revised november 2015 lm700 dual. D continuous voltagecontrolled resistance d high offisolation d high input impedance. Voltage variable attenuators macoms voltage variable attenuators vvas are used in various applications for automotive and wireless markets. Frequency tx or rx range voltage tuning range linear tuning nonlinear tuning fig. Single voltage controlled cmos grounded resistors and their.
Jfet as voltage controlled resistor topics covered. In local oscillator applications, the vco frequency must be able to be varied over the rx or tx range quickly. These voltage levels control the frequency of the internal voltagecontrolled oscillator figure 2. Furthermore, the same textbook says that fet voltage controlled atenuators were commonly used as automatic gain control devices dynamic range compression for example by dolby. Jan 26, 2009 i know this was a long time ago but i have a similar need for a variable resistance 0240 ohms at 12 volts, which can be controlled with a varying voltage from a micro. Voltage controlled oscillator webbased design tool. Voltage controlled resistor is there any way to get a voltage controlled resistor. A simple voltage controlled resistance would be a light dependant resistor controlled by a led. Avoltage controlled attenuator as one example, the circuit in fig. One such function that has been difficult to find is a voltage.
The proposed gvcpr with a single control voltage is composed. Also, a gvcr with a single control voltage comprising 17 transistors is reported in ref. The x9511 is a resistor array composed of 31 resistive elements. Its applications can be found in telecommunications, electronics and measurements such as active rc filters with variable cutoff frequencies, con. Modeling voltagecontrolled and temperaturedependent. A voltagecontrolled resistor redgarden engineering llc. All you need is a controlling voltage to multiply the resistor value. Figure 1a shows a halfwave controlled rectifier circuit with a resistive load. An32 fet circuit applications pdf, 254 kb texas instruments. A single resistor, rset, programs the ltc6990s internal master oscillator frequency. Types of resistors the two main characteristics of a resistor are its resistance, r, in ohms and its power rating, p, in watts. Power mosfet as a voltage controlled resistor physics forums. The only methods i know of that can get this done is using digipots, jfetsmosfets, or relay controlled resistors. D continuous voltage controlled resistance d high offisolation d high input impedance.
D gain ranging capabilitywide range signal attenuation d no circuit interaction d simplified drive. Im aware of fets acting as voltage controlled resistors in their linear region, but the characteristic has too small of an operating window and is not as. A voltage controlled amplifier can be realised by first creating a voltage controlled resistor vcr, which is used to set the amplifier gain. I know this was a long time ago but i have a similar need for a variable resistance 0240 ohms at 12 volts, which can be controlled with a varying voltage from a micro. In the ohmic region1, the draintosource current, i ds, depends on the gatetosource. The disabled output can be configured to be high impedance or forced low. Controlling a dcdc converter by using the power mosfet as. Here, we can see that at nominal control voltage represented by v cnom, the oscillator works at its free running or normal frequency, f cnom.
Our vvas operate from 10 mhz to 45 ghz and are ideal for cellular infrastructure, handset gain control, radar systems, satellite radios and. The output frequency is determined by this master oscillator and an internal. If the current through the resistor is less than 300ma then the resistance should be close to 0. Voltage controlled resistor emulated resistor all about.
The mosfet as a voltage controlled resistor example a mosfet l 1 m m, t ox 10 nm, v t 1 v and m n 300 cm 2 vsec is to be used as 50 w terminating resistor when applying a gatesource voltage, v gs 5 volt. Methods of outputvoltage adjustment for dcdc converters. The field effect transistor as a voltage controlled resistor. Voltage controlled oscillator usage of vco, working and. For a voltage controlled oscillator generating a sawtooth waveform, the main component is the capacitor whos charging and discharging decides the formation of the output waveform. Us6388507b1 voltage to current converter with variation. Electrical symbols for android free download and software. Rds \v red v iv rer where vrer is assumed to be between 0 and vc. In such applications the fet is also referred to as a voltagevariable resistor or volatile dependent resistor. The mosfet as a voltage controlled resistor example.
Floating resistor, voltagecontrolled resistor, cmos, differential difference current conveyor ddcc 1. Introduction the voltagecontrolled resistor vcr is widely used in analog signal processing. The figure above represents the basic working of voltage controlled oscillator. One such function that has been difficult to find is a. C information furnished by analog devices is believed to be accurate and reliable. Voltage controlled amplifier with linearized response to the controlling voltage. When you add an external resistor, that creates a voltage divider and the speedometer reads the resulting voltage. The 2n3685 acts as a voltage variable resistor with an. Fet is a device that is usually operated in the constantcurrent portion of its output characteristics. In most circuits the value of a resistor is fixed during a simulation. If a potentiometer is used, things can be very easy.
Solidstate drives, smartphones and optical modules adjust the core voltage usually through i2c communication to the main proces. Barry harrison abstract most converter designs assume that a closed power switch has zero volts across it. Jfet draintosource voltage variation to follow the development in your text, the first effect were going to look at is the variation of the draintosource voltage through the applied voltage v dd. A voltage controlled resistor vcr is a threeterminal active device with one input port and two output ports. A voltagecontrolled resistor vcr is a threeterminal device that varies the resistance between two terminals relative to voltage in the third terminal.
The jfet has long been used as a voltage controlled. Im aware of fets acting as voltagecontrolled resistors in their linear region, but the characteristic has too small of an operating window and is not as. Modeling voltagecontrolled and temperaturedependent resistors. Pdf fgmos based voltagecontrolled grounded resistor. Half wave controlled rectifiers with a resistive load. Im on the hunt for some sort of analog voltagecontrolled potentiometer.
Wow, what a concept, a voltage controlled resistor. A guide to using fets for voltage controlled circuits, part 2 edn. But if it is operated on the region prior to pinchoff that is where vds is small, say below 100 mv, it will behave as a voltage variable resistor we. Voltage controlled resistor using quasifloatinggate mosfets article pdf available in maejo international journal of science and technology 71. Vcrs are most often built with fieldeffect transistors fets. In this article we will discuss halfwave controlled rectifiers. A wirewound resistor can have a smaller physical size for a given power rating than carbon composition or film resistors, compare this 5w resistor with the 1w resistor at labelled 3 in fig. The figure to the right is a modified version of figure 6. Technology voltagecontrolled resistor device based on phase. Voltage dependent resistor article about voltage dependent. It means that now the mosfet is acting as a openload with infinite resistance. Methods of output voltage adjustment for dcdc converters introduction some systems benefit by adjusting the output voltage of one or more dcdc converters while the converters are enabled and the system is operating. However, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. The vcr is one of the numerous interesting circuit elements that can be produced by using a jfet junction field.
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