Electric energy converters, which are semiconductor or electrovacuum devices that convert an alternating input current to a constant output, are called rectifiers. A half-wave rectifier is built according to a half-bridge or bridge circuit, the detailed formation of which we will consider.
The essence and structure of half-wave rectifiers
Most of these devices produce unidirectional ripple voltage. To smooth the ripple, use special filters.
To improve the parameters of the rectifier, it is necessary to ensure the flow of current to both half-periods of the input voltage. For this purpose, two types of half-wave rectification schemes are used , which operate both out of phase and synchronously with a single load.
With this inclusion, you will need two sources of primary voltage, which will have a common point. Such a circuit is called a “half-wave rectifier with a midpoint”. In this case, the average value of the voltage current in the load resistors with half-wave rectification will exceed such indicators of a half-wave circuit by half.
It should be noted that the two-half-wave scheme, which has a midpoint, has its own negative points. When the current passes one diode, on the opposite, the reverse voltage in the peak phase reaches its doubled input maximum voltage, which must be remembered when choosing diodes for the rectifier.
In this regard, we consider in more detail a two-half-wave rectifier with a metal-intensive circuit having a large active equivalent internal resistance. This leads to the presence of large losses associated with significant heating of the transformer winding.
When constructing such a circuit with a smoothing capacitor, it is necessary to take into account that the measurement of alternating voltage is always carried out in effective values, which are much less than the maximum amplitude. When there is no load on the capacitor, the rectified voltage is always equal to the amplitude. This means that a half-wave rectifier having a single-phase alternating current of 12 V on the capacitor, when there is no load, will receive a voltage of 17 V. Based on this, we can conclude that under load the rectified voltage decreases, but does not become less than the existing variable voltage currents and will be determined by the capacity of the smoothing capacitor.
The circuit of such a rectifier can be described as follows. In order to suppress interference, the primary winding of the transformer is connected to a filter, which includes two capacitors with an attached midpoint to the ground. They are necessarily unipolar, and in order to reduce the probability of breakdown, their rated voltage is 200 V.
As a rule, the switch is installed in front of the capacitor, which is necessary to prevent the supply of mains voltage when the rectifier is working on the capacitors. A half-wave rectifier has a secondary winding of the transformer with a central terminal, but with a bridge circuit, this terminal is not necessary. The filter for the rectifier is two capacitors and a series resistor. However, with a low ripple, it is permissible to add another capacitor and resistor at the output.
Since electric machines operate in accordance with the principle of reversibility, voltage rectifiers together with the inverter are two types of electric machine. An inverter is a device that converts direct voltage to alternating voltage.