FS9721_LP3

Rev. 2.1

25/39

15.8

Mode Switch and Function Control Circuit

Diagram 20

Mode Switch and Function Control Circuit

S3~S4, S10~S13 and S15~S16 are the mode switches. For the functions of S3~S4, please refer to 10.3. For

the functions of S15~S16, please refer to 10.4. For the functions of S10~S13, please refer to 10.1. S14 is

RS232 output control switch. S2 and S5~S9 are the function select switches which are the trigger switches. For

their functions, please refer to “Keys Definition” and “Other Functions”.

In practice application, to use which switches or keys depend on the actual situation.

15.9

AC Rectifier Circuit

Diagram 21 is FS9721_LP3 average rectification circuitry. In the circuitry, AC signals enters IC through

R26, then divided the voltage by R26, R25, R24, R23 and R22. After voltage division, the AC signals come out

from OP1O pin, and enter the IC via AD IP pin and ADIN pin after rectifying. VR2 can adjust the size of the

signal to be the calibration of AC measurement.

400mV mode is amplified 10 times by OP.

Diagram 22 is the peak value rectification circuitry. Diagram 23 is the true valid value rectification circuitry.

User can decide which rectification circuitry to use according to the demand of oneself.