Low ripple rectifier. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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Power supplies are usually assembled according to the classical scheme: AC voltage rectifier, filter capacitor, stabilizer. However, in some cases, you can do without a filter, which is often the most cumbersome part of the power source. It is known that a capacitor included in an alternating current circuit shifts its phase by 90 degrees. Such a phase-shifting capacitor is used, for example, when connecting a three-phase motor to a single-phase network.
The capacitive filter smoothes the output voltage ripple of single-phase rectifiers, creating an acceptable value of its constant component, and the larger the capacitance of the filter capacitors, the less the ripple and, accordingly, the greater the constant component.
In three-phase rectifiers, due to the mutual overlap of voltage half-waves, the constant component is larger, which in many cases makes it possible to do without a capacitive filter.
If a phase-shifting capacitor is used in a single-phase rectifier, which provides mutual overlapping of the half-waves of the rectified voltage, in many cases, at a constant load, a bulky capacitive filter can be dispensed with or its capacitance can be significantly reduced. A diagram of such a stabilized rectifier is shown in fig. 6.9.
A three-phase rectifier VD1...VD6 is connected to an AC voltage source through active (resistor R1) and capacitive (capacitor C1) resistance.
The output voltage of the rectifier stabilizes the Zener diode VD7. The capacitor (or several capacitors connected in parallel to obtain the required capacitance) must be rated for operation in AC circuits.
The described rectifier can be used where it is necessary to reduce the dimensions of the electronic device, since the dimensions of the oxide capacitors of the capacitive filter are usually larger than the phase-shifting capacitor of a relatively small capacity.
The gain in dimensions is especially noticeable in mains rectifiers, when the mains voltage is directly rectified without the use of a step-down transformer. Another advantage of the proposed option is that the consumed current is practically constant (in the case of a constant load), while in rectifiers with a capacitive filter at the moment of switching on, the starting current significantly exceeds the steady-state value (due to the charge of the filter capacitors), which in some cases is highly undesirable .
The described device can also be used with series voltage stabilizers with a constant load, as well as with a load that does not require voltage stabilization.
Author: Semyan A.P.
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