From: "Saved by Internet Explorer 11" Subject: The Full-Wave Rectifier and Averaging Filter - Freecircuits.net Date: Fri, 1 Aug 2014 16:04:56 -0700 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_0000_01CFADA2.567EEE20" X-MimeOLE: Produced By Microsoft MimeOLE V6.1.7601.17609 This is a multi-part message in MIME format. ------=_NextPart_000_0000_01CFADA2.567EEE20 Content-Type: text/html; charset="windows-1251" Content-Transfer-Encoding: quoted-printable Content-Location: http://www.freecircuits.net/circuit-61.html
The circuit shown in Figure 1 is the heart of an average reading, rms = calibrated AC voltmeter. As shown, it is a rectifier and averaging = filter.=20 Deletion of C2 removes the averaging function and provides a precision=20 full-wave rectifier, and deletion of C1 provides an absolute value=20 generator.
Figure 1. Full-Wave Rectifier and Averaging =
Filter
Circuit operation may be understood by following the signal path for = negative=20 and then for positive inputs. For negative signals, the output of = amplifier A1=20 is clamped to +0.7V by D1 and disconnected from the summing point of A2 = by D2.=20 A2 then functions as a simple unity-gain inverter with input resistor, = R1, and=20 feedback resistor, R2, giving a positive going output.
For positive inputs, A1 operates as a normal amplifier connected to = the A2=20 summing point through resistor, R5. Amplifier A1 then acts as a simple=20 unity-gain inverter with input resistor, R3, and feedback resistor, R5. = A1 gain=20 accuracy is not affected by D2 since it is inside the feedback loop. = Positive=20 current enters the A2 summing point through resistor, R1, and negative = current=20 is drawn from the A2 summing point through resistor, R5. Since the = voltages=20 across R1 and R5 are equal and opposite, and R5 is one-half the value = of R1,=20 the net input current at the A2 summing point is equal to and opposite = from the=20 current through R1 and amplifier A2 operates as a summing inverter with = unity=20 gain, again giving a positive output.
The circuit becomes an averaging filter when C2 is connected across = R2.=20 Operation of A2 then is similar to the Simple Low Pass Filter = previously=20 described. The time constant R2C2 should be chosen to be much larger = than the=20 maximum period of the input voltage which is to be averaged.
Capacitor C1 may be deleted if the circuit is to be used as an = absolute value=20 generator. When this is done, the circuit output will be the positive = absolute=20 value of the input voltage.
The amplifiers chosen must be compensated for unity-gain operation = and R6 and=20 R7 must be chosen to minimize output errors due to input offset = current.
=20 2965 10=20 December 2007