Precision Rectifier Circuits: Design and Application, Study Guides, Projects, Research of Design

Download Precision Rectifier Circuits: Design and Application and more Study Guides, Projects, Research Design in PDF only on Docsity! Precision Rectifier Circuits Rectifier circuits are used in the design of power supply circuits. In such applications, the voltage being rectified are usually much greater than the diode voltage drop, rendering the exact value of the diode drop unimportant to the proper operation of the rectifier. Other applications exists, however, where this is not the case. For example, in instrumentation applications, the signal to be rectified can be of very small amplitude, say 0.1 V, making it impossible to employ the conventional rectifier circuits. Also the need arises for very precise transfer characteristics. Precision Half-Wave Rectifier- The Superdiode There are many applications for precision rectifiers, and most are suitable for use in audio circuits. A half wave precision rectifier is implemented using an op amp, and includes the diode in the feedback loop. This effectively cancels the forward voltage drop of the diode, so very low level signals (well below the diode's forward voltage) can still be rectified with minimal error. Another Circuit The circuit below accepts an incomimng waveform and as usual with op amps, inverts it. However, only the positive-going portions of the output waveform, which correspond to the negative-going portions of the input signal, actually reach the output. The direct feedback diode shunts any negative-going output back to the "-" input directly, preventing it from being reproduced. The slight voltage drop across the diode itself is blocked from the output by the second diode. D1 allows positive-going output voltage to reach the output. An Application: Measuring AC Voltages What is the DC output voltage of the following circuit if R1 = 3.24 kΩ, R2 = 10.2 kΩ, R3 = 20 kΩ and R4 = 20 kΩ. Assume Vp = 2 V Filter rectifier waveHalf − 3 4 1 22 R R R RpVv π −= Design Task: Based on the circuit of the AC voltmeter and for a sinusoidal input signal with an amplitude Vp at a frequency ωo, find the output voltage vI described by its Fourier series (average value plus the harmonics of the frequency ωo . State when the output signal can be described by the DC voltage components (this means reducing the amplitudes of these harmonics to very small level). Precision Bridge Rectifier for Instrumentation Applications AC Voltmeter A Precision Peak Rectifier The capacitor retains a voltage equal to the positive peak of the input A Precision Peak Detector When the peak detector required to hold the value of the peak for a long time, the capacitor should be buffered. An op amp A2, which should have high input impedance and low input bias current, is connected as a voltage follower. The rest of the circuit is similar to the half-wave rectifier.