# (Sharing bulk materials) Short description of the rectifier circuit

2023-11-18Archive

A stable DC power supply is an important part of electronic devices and usually consists of alternating current through stabilized, rectified and filtered circuits. Introduction: The function of rectifier circuit is to convert low-voltage AC output from AC step-down circuit into unidirectional pulsating DC current. This is process of AC rectification. The rectifier circuit is mainly composed of rectifier diodes. The voltage after rectifier circuit is no longer an alternating voltage, but a mixed voltage containing direct and alternating voltage, which is commonly called unidirectional pulsating direct voltage. Here I will summarize information obtained from other messages and my own opinion, and present following contents:1: The basic working principle and simple calculation of rectifier circuit2 : How filter works

One: A basic introduction to three common rectification schemes

1: Classification of rectifier circuitsThe rectification circuits in power circuit mainly include half-wave rectification circuits, full-wave rectification circuits and bridge rectifier circuits. A voltage doubling circuit is used for rectification. other AC signals, such as in LED level meters circuits, to correct audio signals. 2: Characteristics of three common rectification circuitsThe first three rectification circuits have different characteristics of unidirectional pulsating DC, and output voltage of half-wave rectification circuit is only half a cycle. , so it's Fundamental unidirectional ripple DC is still 50Hz, because AC input frequency is 50Hz, half-wave rectifier circuit removes AC half-cycle, and does not change frequency Just like in rectifier circuit, positive and negative half-cycles of input AC voltage are used to double frequency up to 100Hz, so fundamental component of AC component of this unidirectional pulsating DC current is 100Hz, because rectifier circuit will inject AC voltage One and a half cycles of polarity are converted so that frequency of output ripple DC voltage is double that of input AC voltage. This increase in frequency is useful in filtering filter circuit. 3: Difference between three common rectification circuitsAmong three power circuit rectification circuits, only full-wave rectification circuit requires a secondary winding of power transformer with a center tap, and other two There is no tap requirement in this circuit for power transformer. In addition, in single-half schemeIodine rectification uses only one diode, full-wave rectification uses two diodes, and bridge rectification uses four diodes. According to above two characteristics, it is easy to distinguish between types of three rectifier circuits, but it should be noted that it is more accurate to distinguish three rectifier circuits by whether power transformer has taps or not. 4: Requirements for diodes in three common rectification schemesOn one hand, this is maximum operating voltage, and on other hand, this is maximum forward average current In In circuit half-wave rectifier, when rectifier diode is off, peak value of AC voltage is added to both ends of diode. The same is true for full-wave rectifier circuits: when one diode is on, other diode is off to handle full peak AC voltage. Therefore, these two rectification circuits require rectifier diodes of circuit to have a higher reverse peak withstand capability, for bridge rectifier circuit, two diodes are on and other two diodes are off, and they are connected in series to withstand reverse peak voltage is only half of reverse peak voltage at both ends of each diode, so requirement for rectifier diode's ability to withstand reverse peak voltage in this circuit is relatively low. One more note: in rectifier circuit, amplitude of input AC voltage is much larger than voltage drop across diode conductive tube, so voltage drop across rectifier diode tube can be neglected.

Second: imagine three kinds of rectifier circuits

1: Schematic of half-wave rectifier

Above is circuit diagram of a single-phase half-wave rectifier and circuit voltage waveformFirst, convert U1 (common mains voltage 220V) to U2. Because of unidirectional conduction of diode D, when U2 is a positive half cycle, ideally waveforms at both ends of RL are equal to U2; when U2 is a negative half-cycle, D is cut off and U0 = 0. Therefore, polarity of output voltage of rectifier circuit is constant, and its magnitude changes with time. The average value of U0 can be obtained using appropriate formula, ie U0 = 0.45U2, and then average value of I0 can be obtained. The current ID flowing through diode is rectified current I0, so maximum forward average diode current ID = I0;When diode D is turned off, an AC voltage U2 is added to two sides of end of D. Therefore, maximum output voltage that diode can withstand is U2, which is twice square root;2: single-phase full-wave rectification circuit

Above is circuit diagram of a single-phase half-wave rectifier circuit and voltage waveform of circuitThe working principle of a full-wave rectifier circuit is actually a combination of two half-wave phase half-wave rectifier circuits. , D1 - positive voltage, for D1 on and D2 off, voltage on RL is positive and negative. In second half cycle, D2 is forward voltage, D2 is on, D1 is off, and RL What you see at top is positive and negative voltage at bottom. This is repeated because two rectifying elements D1 and D2 not only use positive half-cycle, but also intelligently use negative half-cycle, which greatly improves rectification efficiencyso that U0 = 0.9U2. The average value of I0 can then also be calculated. The current flowing through each diode is half I0;When one diode is on, other diode is off and carries full AC peak voltage, which is highest transmission direction U2, whose voltage is in twice root sign;3: Diagram of a single-phase bridge full-wave rectifierThe above is a circuit diagram of a single-phase bridge full-wave rectifier First half In first cycle, D1 and D3 are on, and D2 and D4 are off, and top positive and bottom negative voltages are applied to RL In second half cycle, D2 and D4 are on, while D1 and D3 are off, and what is added to RL is still a positive and negative voltage. This circuit is similar to full wave rectification circuit, it makes full use of entire current process. So U0= 0.9U2. Then you can get average value of I0;The current flowing through each diode is equal to half of I0;Ignoring voltage drop when turning on a group of diodes, another group of diodesdov is disabled and withstands full peak AC voltage, i.e. U2, whose maximum inrush voltage is twice root sign