Date Sheet

AD8510/AD8512/AD8513

Rev. K | Page 17 of 21

PRECISION RECTIFIERS

Rectifying circuits are used in a multitude of applications. One

of the most popular uses is in the design of regulated power

supplies, where a rectifier circuit is used to convert an input

sinusoid to a unipolar output voltage.

However, there are some potential problems with amplifiers

used in this manner. When the input voltage (VIN) is negative,

the output is zero, and the magnitude of VIN is doubled at the

inputs of the op amp. If this voltage exceeds the power supply

voltage, it can permanently damage some amplifiers. In addition,

the op amp must come out of saturation when VIN is negative.

This delays the output signal because the amplifier requires

time to enter its linear region.

Although the AD8510/AD8512/AD8513 have a very fast

overdrive recovery time, which makes them great choices for the

rectification of transient signals, the symmetry of the positive

and negative recovery times is also important to keep the output

signal undistorted.

Figure 49 shows the test circuit of the rectifier. The first stage of

the circuit is a half-wave rectifier. When the sine wave applied at

the input is positive, the output follows the input response.

During the negative cycle of the input, the output tries to swing

negative to follow the input, but the power supply restrains it to

zero. In a similar fashion, the second stage is a follower during

the positive cycle of the sine wave and an inverter during the

negative cycle.

8

4

2

1

3

1/2

AD8512

4

8

5

7

6

2/2

AD8512

R2

10kΩ

R3

10kΩ

R1

1kΩ

OUT A

(HALF WAVE)

OUT B

(FULL WAVE)

10V

10V

VIN

3V p-p

Figure 49. Half-Wave and Full-Wave Rectifiers

TIME (1ms/DIV)

Figure 50. Half-Wave Rectifier Signal (OUT A in Figure 49)

TIME (1ms/DIV)

Figure 51. Full-Wave Rectifier Signal (OUT B in Figure 49)