The simplest of all rectifier classes is the diode rectifier. In its simplest form, diode rectifiers do not provide any means of controlling the magnitude of the output current and voltage. To be suitable for industrial processes, the output value must be controllable within a certain range. This control can be accomplished by applying mechanical so-called on-load tap-changers. As a typical case, the on-load tap changer controls the input AC voltage on the primary side of the rectifier transformer, so it can also control the output DC value within a certain range. Usually on-load tap-changers are used in combination with saturable reactors in series in the rectifier output circuit. By introducing a DC current in the reactor, a variable impedance is generated in the line. Therefore, by controlling the voltage drop across the reactor, the output value can be controlled within a relatively narrow range. The simplest voltage-doubling rectification (double) method is to use two groups of simple half-wave rectifiers to generate two positive and negative power outputs with opposite diodes, and filter them respectively. Connect the positive and negative terminals to obtain an output voltage twice the AC input voltage. Such circuits are called Delon circuits (German: Delon-Schaltung). If desired, this circuit can also provide intermediate voltage, or be used as a positive and negative dual voltage power supply.
Another variant of the above circuit can be derived: use two capacitors connected in series as filter capacitors at the output end of the bridge rectifier, and connect a switch between the midpoint of the filter capacitor and one end of the AC input. When the switch is turned off, this circuit will act like a normal bridge rectifier; when the switch is turned on, it will become the aforementioned Delong circuit, which acts as a voltage doubling rectifier. For example, when the AC input is 100120V, the switch can be turned on; when the AC input is 220240V, the switch can be turned off; this makes it easy to switch between any power supply in the world, producing approximately 320V (±15 percent or so) DC voltage to feed a relatively simple switch mode power supply.
Although such a voltage doubler circuit can provide several times the voltage of the input AC peak value, the current output and voltage stability are limited. Such voltage multiplier circuits are often used to supply high voltages to cathode ray tubes (CRTs), photomultiplier tubes, or electric mosquito swatters in older TV sets.
