Full-wave rectifier circuit diagram and working principle description

The names of the precision full-wave circuits in the figure are purely personal names; unless otherwise specified, the gain is designed as 1.

Figure 1 is the most classic circuit . The advantage is that the filter capacitor can be connected in parallel to the resistor R5 . The resistor matching relationship is R1=R2, R4=R5=2R3; the gain can be adjusted by changing R5. The advantage of Figure 2 is that there are fewer matching resistors, and only R1=R2 is required. The advantage of Figure 3 is that the input impedance is high, and the matching resistors require R1=R2, R4=2R3. The matching resistors of Figure 4 are all equal, and the gain can also be changed by changing the resistor R1. The disadvantage is that in the negative half cycle of the input signal, the negative feedback of A1 is composed of two paths, one of which is R5, and the other is composed of the operational amplifier A2, which also has the disadvantages of the composite operational amplifier. Figures 5 and 6 It is required that R1=2R2=2R3, and the gain is 1/2. The disadvantage is that when the input signal is in the positive half cycle, the output impedance is relatively high. A common-mode amplifier with a gain of 2 can be added to the output for isolation. Another disadvantage is that the input impedance of the positive half cycle and the negative half cycle are not equal, and the internal resistance of the input signal is required to be negligible. Figure 7 Positive half cycle, D2 is on, gain = 1 + (R2 + R3) / R1; negative half cycle gain = -R3 / R2; the absolute value of the positive and negative half cycle gains is required to be equal. For example, if the gain is 2, R1 = 30K, R2 = 10K, and R3 = 20K can be selected. The resistance matching relationship of Figure 8 is R1 = R2. Figure 9 requires R1 = R2, and R4 can be used to adjust the gain, which is equal to 1 + R4 / R2; if R4 = 0, the gain is equal to 1; the disadvantage is that the input impedance of the positive and negative half waves is not equal, and the internal resistance of the input signal is required to be small, otherwise the output waveform will be asymmetric. Figure 10 is designed using the characteristics of the follower of a single power supply op amp, single Power supply Follower, when the input signal is greater than 0, the output is a follower; when the input signal is less than 0, the output is 0. Be careful of the nonlinearity of the single-power supply amplifier when the signal is very small. Moreover, the single-power follower also has nonlinearity when the negative signal is input. In the three circuits of Figures 7, 8, and 9, when the output of op amp A1 is positive, the negative feedback of A1 is formed by a composite amplifier composed of diode D2 and op amp A2. Due to the composite (product) effect of the two op amps, the gain of the loop may be too high, which is easy to oscillate. There are some precision full-wave circuits that are not recorded, such as the high-impedance type. There is also a type that connects the in-phase input of A2 to the inverting input of A1. In fact, it is the same principle as this high-impedance type, so it is not specially included. Others use the output of A1 to connect only a two The diode is not included, because when this diode is cut off, A1 is in an open loop state. Although there are ten kinds of precision full-wave circuits here, after careful analysis, it is found that there are not many excellent ones. To be exact, there are only three kinds, which are the three kinds mentioned above. Although the classic circuit in Figure 1 has many matching resistors, it can be completely realized with 6 equal value resistors R, among which resistor R3 can be connected in parallel with two R. The gain can be adjusted by R5, and the gain can be greater than 1 or less than 1. The most advantageous thing is that the capacitor filtering can be connected to R5. The advantage of the circuit in Figure 2 is that there are fewer matching resistors, and only one pair of matching resistors is needed. The advantage of Figure 3 is high input impedance. For some other types, in the half cycle when D2 is turned on, the negative feedback of A1 is realized through the compound of A2, which will cause self-excitation for some op amps. Some of the two half-waves have unequal input impedances, which places high demands on the signal source. Although two single op amps can achieve the purpose of rectification, the input and output characteristics are very poor. Followers or in-phase amplifiers are required for input and output isolation. Each circuit has its own design features. I hope we can learn useful things from the clever design of its circuit. For example, the design of a single-power full-wave circuit and a composite feedback circuit are both very useful design ideas and methods. If you can analyze the circuit principles of each figure and derive each formula, you will benefit.