Skip to main content

There are four  types of automatic voltage regulators:  Ferroresonant, Tap Switching, Limited Range Variable Transformer. and Variable Transformer Buck-Boost.


Ferroresonant constant  Variable Transformers

These types of automatic voltage regulators use a capacitor in series with the transfer coil and tend to be high impedance devices that are sensitive to load changes and do not handle high input  loads very well. They can interact with switch mode power supplies to produce transient and electrical  noise on the output and their resonant circuits make them particularly sensitive to frequency changes. When applied cautiously these units can prove from  2-5 % output regulation, load isolation and noise attenuation.

Tap switching Transformer

TAP Switching Transformer based regulators monitor output voltage and  use solid state switching circuits for changing the transformer taps on a fixed ratio transformer. These units tend to provide only 3-5% output regulation as the number of taps used are minimized to control cost.  Although these regulators are extremely fast, this fast response time can often create instability when powering equipment with switch mode power supplies and their output waveform tends to produce harmonics and radio frequency interference.

Limited Range Variable  Transformers

Limited range variable transformer regulators use variable transformers to directly control the output voltage of the regulator. This places the variable transformer’s vulnerable brush and brush track directly in the power path of the regulator subjecting these critical components to system stresses which can lead to possible premature regulator failure. Applications with high overload cycling might require the unit to be over-sized, and with the variable transformer brushes in the power path electrical noise can be introduced  into the system. While limited range variable transformer  regulators can provide  +/- 1 to 3% output voltage regulation they tend to be larger than the Var Tx Buck-Boost Regulator, as manufactured by Staco, that offers  +/-1  % output regulation.

Variable Transformer  Buck-Boost  V

The buck-boost transformer is a fixed ratio isolation transformer capable of high current capacity at low voltage. The ratio of the buck boost transformer is determined by the amount of voltage needed to buck or boost the input line voltage to maintain the specified output level. The buck boost transformer secondary is wired in series with the load and the transformer primary winding is connected across the variable transformer’s “center tap” and brush terminals. Depending on which side of the center tap the variable transformer brush is positioned, the variable buck-boost transformer system will add to “boost” or subtract from “buck” the input line voltage.  The further the variable transformer is from the “center tap” the more bucking or boosting of voltage will occur.

The key to the proven reliability and long trouble free service life of a Staco Voltage Regulator is in the combination of a motor driven variable transformer with buck-boost transformer technology. The only active component in the main power path of the voltage regulator is the secondary winding of the buck-boost transformer. Staco Energy manufactures and supplies this type of voltage regulator. This gives the Staco Energy regulator the advantage of being able to withstand substantial current overloads while protecting the variable transformer brushes, which are the most vulnerable component in any variable transformer system, as they are completely isolated from overload conditions by the buck-boost transformer.

Due to transformer inefficiency above rated design, the amount of current that the buck-boost transformer can induce across to its primary winding and into the variable transformer circuit is dramatically decreased as regulator overload current increases. The controller monitors the regulator’s output voltage and then uses these feedback signals to determine drive commands for the variable transformer motor interface circuit. The controller is designed to adjust the motorized variable transformer to provide a 21% or better output voltage regulation over the entire input voltage range. Staco Energy offers two types of controllers. The solid state type LRC controller which is standard on type AVR (automatic voltage regulators) and the microprocessor type MP controller which is offered as standard on all MVR voltage regulators and is available as an option for Automatic Voltage Regulators.


Applications for Automatic Voltage Regulators

Broadcast: regulation for broadcasting transmitter sites and studios

Commercial: High rise building whole floor regulation or power condition, input voltage regulation for elevator control, large A/C chillers, lighting and other sensitive non-critical systems.

Industiral: industrial automation, process control, CNC, factory robotics, facility level of point- of -use , heavy load machinery regulations.

Marine: Deck sides or shipboard voltage regulation and power conditioning.

Medical Medical imaging: x-ray , CAT scans and MRI power conditioning: building or whole floor regulations.

Mobile: Commercial broadcast and military mobile communication trucks, trailers and shelters.


Staco Energy

Staco Energy has been in the AV Voltage control and regulation field since 1937. They are built for long term reliability and trouble free operation. The key to the proven reliability and long trouble free service life of a Staco Voltage regulator is the combination of motor driven variable transformer with buck boost transformer technology. Staco Energy transformers have an excellent accuracy: they maintain a constant output voltage within +/-1% or better regardless of input voltage variations from +10—20% and Staco regulators cause no waveform distortion and add no harmonics to the system. For further information call Peninsula Technical Sales at 650-965-3636 or visit our webpage. We are happy to assist you in any need you may have for power condition equipment.




Peninsula Technical Sales represents electronic equipment manufacturers and is proud to offer our services online and to the following cities and their surrounding areas: San Francisco, Santa Clara, San Jose, Fremont, Sacramento, Milpitas, and Santa Rosa.