AN2288

Meter hardware

11/29

Figure 6.

2.5V reference circuit

4.1.3

Current transformer block

The current transformer used has a turn ratio of 1:5000 and ~350 Ohm resistance, the shunt

resistance used is 36 Ohms (refer fig. 2), so, the effective resistance will be:

be:

minimum multiplication factor is x2. The MAX current is chosen such that the operational

The peak to peak voltage is 2.03V. There is safe margin of ~0.47V for a gain factor of x2.

4.1.4

Voltage divider block

The voltage is reduced using a potentiometer and referenced at 3.75V.

Figure 7.

Voltage divider circuit

5V

3.75V - R5*I2

I2

I1

I1+I2

R5

R6

+

-

3.75Vref

3.75V

R

shunt

350

36

×

350

36

+

-----------------------

32.64E

==

V

shunt

55A

5000

-------------

R

shunt

×

359mV

==

V

()

359mV

2

×

2

×

1.015V

==

2.5V

Neutral line

Phase

R28

R30

R26

R29

R31

C12

Analog input to ADC

C20