[introduction]Commutator of accurate active complete wave is a kind of classical imitate application. This one theme has a lot of different implementation methods, every kinds of method has his so-called advantage. But, (Almost) design of commutator of all active complete wave needs a circuit element, that contains the inverter that matchs resistor namely, it is with installing its gain accurate – 1. Attack in this kind of develop in, the symmetry of rectification relies on the precision that resistor place matchs, and compare its impossibly better. For example, graph 1 be well-known (true classical! ) design, among them appropriative inverter of operation amplifier U1b, r1 and R2 are appropriative the gain that its match installs resistor. Unless R1=R2, output of the commutator when losing Vin deflection otherwise is equal to unlikely the output of Vin deflection.

Commutator of accurate active complete wave is a kind of classical imitate application. This one theme has a lot of different implementation methods, every kinds of method has his so-called advantage. But, (Almost) design of commutator of all active complete wave needs a circuit element, that contains the inverter that matchs resistor namely, it is with installing its gain accurate – 1. Attack in this kind of develop in, the symmetry of rectification relies on the precision that resistor place matchs, and compare its impossibly better. For example, graph 1 be well-known (true classical! ) design, among them appropriative inverter of operation amplifier U1b, r1 and R2 are appropriative the gain that its match installs resistor. Unless R1=R2, output of the commutator when losing Vin deflection otherwise is equal to unlikely the output of Vin deflection.

Graph 1: Traditional and accurate commutator is designed, among them R1 and R2 are the symmetrical resistor that matchs.

To Vin input, d1 is shut and D2 guides, build the blame that does not suffer resistance effect to counter photograph unit gain for circuit: Vout/Vin=+1.

To losing an input, become only when R2=R1, d1 guides, d2 is shut, u1b turns into inverter, gain Vout/Vin= – R2/R1=-1. Otherwise, won’t produce the problem with rectification poor symmetry.

Graph 2 showed another kind (not quite groovy) design. But no matter whether be not convention, appropriative inverter of here Q2 and Q3, the run mode of the R1 of gain semmetry resistor that match and R2 and graph 1 in same.

Graph 2: The blame tradition commutator that uses schism circuit inverter still uses the resistor of symmetrical setting: R1 and R2.

But now, plant to break this machine-made, let us see a picture 3. Ask an attention, it did not match resistor. The working principle of this commutator is below.

Graph 3: Accurate without the special rule that matchs symmetrical resistor commutator is designed.

Q1 and Q2 provide simple alternate compensation, in order to offset the Vbe of Q3 and Q4 drops. Accordingly, negative Vin deflection is turned over by A1, output filter R3C3 by Q4. In the meantime, vin deflection makes Q3 guides, accumulative charge is with voltage form memory on C2, this voltage is added in half-period of subsequently contrary polarity, the pump of complete wave charge with Q3 and appropriative and simple Q4. Final result is:

Vout = Avg(Abs(Vin)) R3 / R2 / R1

Accordingly, want transistor Vbe to match only proper, have mathematical rectification symmetry.

(Textual publish at edition of EDN United States, referenced link: Peculiar Precision Full-wave Rectifier Needs No Matched Resistors, compile by Ricardo Xie)

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