EGR220 Than & Bhavin Lab #6

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Introduction and Objectives

One of the most applications of diodes are rectifier

circuits, which converts AC to DC, and these designs

are used in power-supply. In fact, diodes rectifier forms

the fundamental building block of the DC power

supplies for electronic devices [1]. However, in

instrumentation applications, the signal to be rectified

can be very small, and needs very precise transfer

characteristics. For this purpose, we need super- diode.

Therefore, in this lab, we were instructed to measure

and analyze behavior of rectifier circuits, both half-

wave and full wave (bridge) rectifier and peak rectifier.

The primary objectives of this lab are:

1. To analyze and understand the nature of half-

wave super-diode rectifier

2. To be able to implement AC Volt Meter with

super-diode

3. To be able to understand the nature of full-

wave rectifier with super-diode.

Equipments and Components used

In this lab, the equipments and components we used

are:- ICs: L M 1458 (x2), Diodes: 1N914 (x2)

Resistors: 1KΩ (x3), l0KΩ (x5), Capacitor: 47μF

(x1), a breadboard, a waveform generator, ±20V

power supply, a multi-meter, an Oscilloscope to

capture the I-V curve, wires and cords.

Procedures

Procedure 1: Analyzing the Nature of of Half-

Wave Super-Diode Rectifier

R=1k

+

-vin=

2sin2(100)t

vout

Figure 1

By giving input voltage (2Sin2π 100t), we tried to get

the transfer function of super-diode in XY mode.

Figure 2: Transfer Function of Circuit 1(100Hz)

The advantage of this circuit design (precision

half-wave rectifier) over regular half-wave

rectifier design was its precision. Since the

voltage drop in Si diode is around 0.7V, if we

provided the input voltage around 0.7V, we could

not get the proper transfer function in regular

rectifier. However, this is not the case in

precision rectifier.

But the circuit design in figure 1 has its own

drawback. The transfer function is also limited

by the input signal frequency. At 600 Hz, because

of time delay, we could see the distortion of

transfer function.

Figure 3: Transfer Function of Circuit 1 (600Hz)

In oder to overcome this, we implement the

circuit design in figure 3.

EGR220 Than & Bhavin Lab #6

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Figure 3: Alternative Circuit Desing

In this design, we can also control the slop line of

the transfer function by varying R1 and R2. If R1

and R2 are equal, we got Vout = -Vin .

Figure 4: Transfer Function of Circuit 2 (100Hz)

Figure 5: Transfer Function of Circuit 2 (600Hz)

We could see that at 600Hz, the transfer function

was still linear enough even though there existed

some distortion because of Op-Amp Saturation.

Procedure 2: Implementing AC Volt Meter

with Super Diode

Figure 6

In this circuit design, the precision rectifier was

followed by low pass filter. The average output

voltage of rectifier is (Vp/π) (R2/R1) and

harmonics of the frequency. The low pass filter

remove those harmonics and the final output

voltage will become DC with a value

Vout = -(Vp/π)(R2/R1)(R4/R3) (3)

Therefore, the above circuit can be used to read

rms value for input sinusoids.

Figure 7: Transfer Function of Circuit 3 (4Vp

1kHz)

When we measured the output voltage, we got -

1.28V. We calculated the input peak voltage and

got 4.01V. When we measured the input voltage

EGR220 Than & Bhavin Lab #6

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directly, we got 2.82V. Therefore, the error is

1.54V.

Procedure 3: Analyzing the Nature of of Full-

Wave Super-Diode Rectifier

Figure 8

We built the circuit the by providing Vin = 5V

with frequency of 200Hz, R1 = R2 = 1kΩ and RL

= 10KΩ. After than, we captured the screen image

of V1, V2 and Vo.

Figure 9: V1 (Transfer Function)

Figure 10: V2 (Transfer Function)

Figure 11: Vout (Tranfer Function)

To put it simply, the circuit in figure 8 operates as

an absolute value circuit, as in absolute value

function. By measurement, we found that V1 =

Vin and V2 = -Vin, and Vo is the summation of

V1 and V2.

1 2 3 4 5 6 7 8 9

0

0.5

1

1.5

2

2.5

3

3.5

Error Vs. Input Voltage

Error

Vin

Err

or

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Discussion

The super diodes are very useful in building

rectifier circuits for instrumentation applications,

although regular rectifiers are useful in power

supply applications. In addition to that, we could

even built AC Voltmeter with super diode and low

pass filter. We can also build peak precision

rectifier with super diodes.

References [1] Sedra, Adel S., and Smith. Kenneth C. “Microelectronics

Circuits”. 5th. New York: Oxford University Press, 2004.