External Circuit Design

AN2317 - Application

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1.1

Current Sensing Circuit

The STPM01 has two external current sensing circuits (see

Figure 1 on page 5):

1.

Primary channel, and

2.

Secondary channel.

1.1.1

Primary Current Sensing

The primary channel uses a current transformer to couple the mains current (see

Figure 2).

filter (LPF) is used to filter out the high frequency interference and has little influence on the

Figure 2.

Primary Current Sensing Circuit

2

12

12

1

2

1

R1

1.0k

R2

I2

VIN1

VIP1

U0

+

–

Burden Resistor

LPF

I1

1.0k

2

1

AI12297