This variable regulator circuit will provide an variable regulated output voltage, between 0 and 50 volts. The CA3140 operational amplifier compares the regulator output to a reference voltage, that depends on the R9 value.0V to 50 0VAC to 280VAC Variable Isolated AC Voltage - I designed and built this circuit about 25 years ago. It came in handy for many projects that were powered from 120 VAC, 240 VAC and 277 VAC. A tutorial on the LM317 voltage regulator. Shows you how to make a 1.25 to 25V adjustable voltage supply, or choose any other output voltage you want. An example of a fan speed controller is shown.
An integrated circuit voltage regulatorA voltage regulator is a system designed to automatically maintain a constant voltage level. A voltage regulator may use a simple feed-forward design or may include negative feedback.
It may use an electromechanical mechanism, or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.Electronic voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant. In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line.
Contents.Electronic voltage regulators A simple voltage/current regulator can be made from a resistor in series with a diode (or series of diodes). Due to the logarithmic shape of diode V-I curves, the voltage across the diode changes only slightly due to changes in current drawn or changes in the input.
When precise voltage control and efficiency are not important, this design may be fine. Since the forward voltage of a diode is small, this kind of voltage regulator is only suitable forlow voltage regulated output. When higher voltage output is needed, a or series of zener diodes may be employed. Zener diode regulators make use of the zener diode's fixed reverse voltage, which can be quite large.Feedback voltage regulators operate by comparing the actual output voltage to some fixed reference voltage. Any difference is amplified and used to control the regulation element in such a way as to reduce the voltage error. This forms a negative feedback control loop; increasing the open-loop gain tends to increase regulation accuracy but reduce stability.
(Stability is avoidance of oscillation, or ringing, during step changes.) There will also be a trade-off between stability and the speed of the response to changes. If the output voltage is too low (perhaps due to input voltage reducing or load current increasing), the regulation element is commanded, up to a point, to produce a higher output voltage–by dropping less of the input voltage (for linear series regulators and buck switching regulators), or to draw input current for longer periods (boost-type switching regulators); if the output voltage is too high, the regulation element will normally be commanded to produce a lower voltage.
However, many regulators have over-current protection, so that they will entirely stop sourcing current (or limit the current in some way) if the output current is too high, and some regulators may also shut down if the input voltage is outside a given range (see also: crowbar circuits).Electromechanical regulators. Graph of voltage output on a time scale.In electromechanical regulators, voltage regulation is easily accomplished by coiling the sensing wire to make an electromagnet.
The magnetic field produced by the current attracts a moving ferrous core held back under spring tension or gravitational pull. As voltage increases, so does the current, strengthening the magnetic field produced by the coil and pulling the core towards the field. The magnet is physically connected to a mechanical power switch, which opens as the magnet moves into the field. As voltage decreases, so does the current, releasing spring tension or the weight of the core and causing it to retract. Voltage regulator for generators.Generators, as used in power stations, ship electrical power production, or standby power systems, will have automatic voltage regulators (AVR) to stabilize their voltages as the load on the generators changes. The first AVRs for generators were electromechanical systems, but a modern AVR uses solid-state devices.
An AVR is a feedback control system that measures the output voltage of the generator, compares that output to a set point, and generates an error signal that is used to adjust the excitation of the generator. As the excitation current in the field winding of the generator increases, its terminal voltage will increase. The AVR will control current by using power electronic devices; generally a small part of the generator's output is used to provide current for the field winding.
Where a generator is connected in parallel with other sources such as an electrical transmission grid, changing the excitation has more of an effect on the produced by the generator than on its terminal voltage, which is mostly set by the connected power system. Where multiple generators are connected in parallel, the AVR system will have circuits to ensure all generators operate at the same power factor. AVRs on grid-connected power station generators may have additional control features to help stabilize the electrical grid against upsets due to sudden load loss or faults.AC voltage stabilizers Coil-rotation AC voltage regulator. Basic design principle and circuit diagram for the rotating-coil AC voltage regulator.This is an older type of regulator used in the 1920s that uses the principle of a fixed-position field coil and a second field coil that can be rotated on an axis in parallel with the fixed coil, similar to a variocoupler.When the movable coil is positioned perpendicular to the fixed coil, the magnetic forces acting on the movable coil balance each other out and voltage output is unchanged. Rotating the coil in one direction or the other away from the center position will increase or decrease voltage in the secondary movable coil.This type of regulator can be automated via a servo control mechanism to advance the movable coil position in order to provide voltage increase or decrease.
A braking mechanism or high ratio gearing is used to hold the rotating coil in place against the powerful magnetic forces acting on the moving coil. Magnetic mains regulator Electromechanical Electromechanical regulators called voltage stabilizers or tap-changers, have also been used to regulate the voltage on AC power distribution lines.
These regulators operate by using a servomechanism to select the appropriate tap on an autotransformer with multiple taps, or by moving the wiper on a continuously variable auto transfomer. If the output voltage is not in the acceptable range, the servomechanism switches the tap, changing the turns ratio of the transformer, to move the secondary voltage into the acceptable region.
The controls provide a dead band wherein the controller will not act, preventing the controller from constantly adjusting the voltage ('hunting') as it varies by an acceptably small amount.Constant-voltage transformer The ferroresonant transformer, ferroresonant regulator or constant-voltage transformer is a type of saturating transformer used as a voltage regulator. These transformers use a composed of a high-voltage resonant winding and a to produce a nearly constant average output voltage with a varying input current or varying load. The circuit has a primary on one side of a magnet shunt and the tuned circuit coil and secondary on the other side.
The regulation is due to magnetic saturation in the section around the secondary.The ferroresonant approach is attractive due to its lack of active components, relying on the square loop saturation characteristics of the tank circuit to absorb variations in average input voltage. Saturating transformers provide a simple rugged method to stabilize an AC power supply.Older designs of ferroresonant transformers had an output with high harmonic content, leading to a distorted output waveform. Modern devices are used to construct a perfect sine wave.
A bank of voltage regulators used to control the voltage on long AC power distribution lines. This bank is mounted on a wooden pole structure. Each regulator weighs about 1200 kg and is rated 576 kVA. DC voltage stabilizers Many simple DC power supplies regulate the voltage using either series or shunt regulators, but most apply a voltage reference using a shunt regulator such as a,. Each of these devices begins conducting at a specified voltage and will conduct as much current as required to hold its terminal voltage to that specified voltage by diverting excess current from a non-ideal power source to ground, often through a relatively low-value to dissipate the excess energy. The power supply is designed to only supply a maximum amount of current that is within the safe operating capability of the shunt regulating device.If the stabilizer must provide more power, the shunt regulator output is only used to provide the standard voltage reference for the electronic device, known as the voltage stabilizer.
The voltage stabilizer is the electronic device, able to deliver much larger currents on demand.Active regulators Active regulators employ at least one active (amplifying) component such as a transistor or operational amplifier. Shunt regulators are often (but not always) passive and simple, but always inefficient because they (essentially) dump the excess current which is not available to the load.
When more power must be supplied, more sophisticated circuits are used. In general, these active regulators can be divided into several classes:. Linear series regulators.
Switching regulators. SCR regulatorsLinear regulators.
Main article:Linear regulators are based on devices that operate in their linear region (in contrast, a switching regulator is based on a device forced to act as an on/off switch). Linear regulators are also classified in two types:. series regulators. shunt regulatorsIn the past, one or more were commonly used as the variable resistance. Modern designs use one or more instead, perhaps within an. Linear designs have the advantage of very 'clean' output with little noise introduced into their DC output, but are most often much less efficient and unable to step-up or invert the input voltage like switched supplies.
All linear regulators require a higher input than the output. If the input voltage approaches the desired output voltage, the regulator will 'drop out'. The input to output voltage differential at which this occurs is known as the regulator's drop-out voltage. (LDOs) allow an input voltage that can be much lower (i.e., they waste less energy than conventional linear regulators).Entire linear regulators are available as. These chips come in either fixed or adjustable voltage types.Examples of some are the 723 general purpose regulator and 78 XX/79 XX seriesSwitching regulators. Switching regulator integrated circuit LM2676, 3 A step-down converter.Switching regulators rapidly switch a series device on and off.
The of the switch sets how much is transferred to the load. This is controlled by a similar feedback mechanism as in a linear regulator. Because the series element is either fully conducting, or switched off, it dissipates almost no power; this is what gives the switching design its efficiency. Switching regulators are also able to generate output voltages which are higher than the input, or of opposite polarity — something not possible with a linear design. In switched regulators, the pass transistor is used as a 'controlled switch' and is operated at either cutoff or saturated state. Hence the power transmitted across the pass device is in discrete pulses rather than a steady current flow. Greater efficiency is achieved since the pass device is operated as a low impedance switch.
When the pass device is at cutoff, there is no current and dissipates no power. Again when the pass device is in saturation, a negligible voltage drop appears across it and thus dissipates only a small amount of average power, providing maximum current to the load. In either case, the power wasted in the pass device is very little and almost all the power is transmitted to the load. Thus the efficiency of a switched-mode power supply is remarkably high-in the range of 70-90%.Switched mode regulators rely on pulse width modulation to control the average value of the output voltage. The average value of a repetitive pulse waveform depends on the area under the waveform. If the duty cycle is varied, the average value of the voltage changes proportionally.Like linear regulators, nearly complete switching regulators are also available as integrated circuits. Unlike linear regulators, these usually require an that acts as the energy storage element.
The IC regulators combine the reference voltage source, error op-amp, pass transistor with short circuit current limiting and thermal overload protection.Comparing linear versus switching regulators. This section does not any. Unsourced material may be challenged. In this case, the operational amplifier drives the transistor with more current if the voltage at its inverting input drops below the output of the voltage reference at the non-inverting input. Using the (R1, R2 and R3) allows choice of the arbitrary output voltage between U z and U in.Regulator specification The output voltage can only be held constant within specified limits.
Understanding How a Voltage Regulator WorksA voltage regulator generates a fixed output voltage of a preset magnitude that remains constant regardless of changes to its input voltage or load conditions. There are two types of voltage regulators: linear and switching.A linear regulator employs an active (BJT or MOSFET) pass device (series or shunt) controlled by a high gain differential amplifier. It compares the output voltage with a precise reference voltage and adjusts the pass device to maintain a constant output voltage.A switching regulator converts the dc input voltage to a switched voltage applied to a power MOSFET or BJT switch. The filtered power switch output voltage is fed back to a circuit that controls the power switch on and off times so that the output voltage remains constant regardless of input voltage or load current changes. What are some of the switching regulator topologies?There are three common topologies: buck (step-down), boost (step-up) and buck-boost(step-up/stepdown). Other topologies include the flyback, SEPIC, Cuk, push-pull, forward, full-bridge, and half-bridge topologies.
How does switching frequency impact regulator designs?Higher switching frequencies mean the voltage regulator can use smaller inductors and capacitors. It also means higher switching losses and greater noise in the circuit.
What losses occur with the switching regulator?Losses occur as a result of the power needed to turn the MOSFET on and off, which are associated with the MOSFET’s gate driver. Also, MOSFET power losses occur because it takes a finite time to switch to/from the conduction to nonconduction states. Losses are also due to the energy needed to charge and discharge the capacitance of the MOSFET gate between the threshold voltage and gate voltage.
What are the usual applications for linear and switching regulators?The linear regulator’s power dissipation is directly proportional to its output current for a given input and output voltage, so typical efficiencies can be 50% or even lower. Using the optimum components, a switching regulator can achieve efficiencies in the 90% range. However, the noise output from a linear regulator is much lower than a switching regulator with the same output voltage and current requirements. Typically, the switching regulator can drive higher current loads than a linear regulator. How does a switching regulator control its output?Switching regulators require a means to vary their output voltage in response to input and output voltage changes.
One approach is to use PWM that controls the input to the associated power switch, which controls its on and off time (duty cycle). In operation, the regulator’s filtered output voltage is fed back to the PWM controller to control the duty cycle. If the filtered output tends to change, the feedback applied to the PWM controller varies the duty cycle to maintain a constant output voltage. What design specifications are important for a voltage regulator IC?Among the basic parameters are input voltage, output voltage, and output current.
Depending on the application, other parameters may be important, such as output ripple voltage, load transient response, output noise, and efficiency. Important parameters for the linear regulator are dropout voltage, PSRR (power supply rejection ratio), and output noise.ReferencesRelated Categories.Related Markets & Technology. The cookies we use can be categorized as follows: Strictly Necessary Cookies: These are cookies that are required for the operation of analog.com or specific functionality offered.
They either serve the sole purpose of carrying out network transmissions or are strictly necessary to provide an online service explicitly requested by you. Analytics/Performance Cookies: These cookies allow us to carry out web analytics or other forms of audience measuring such as recognizing and counting the number of visitors and seeing how visitors move around our website. This helps us to improve the way the website works, for example, by ensuring that users are easily finding what they are looking for.
Functionality Cookies: These cookies are used to recognize you when you return to our website. This enables us to personalize our content for you, greet you by name and remember your preferences (for example, your choice of language or region). Loss of the information in these cookies may make our services less functional, but would not prevent the website from working. Targeting/Profiling Cookies: These cookies record your visit to our website and/or your use of the services, the pages you have visited and the links you have followed. We will use this information to make the website and the advertising displayed on it more relevant to your interests.
We may also share this information with third parties for this purpose.
Comments are closed.
|
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |