External Circuit Design

AN2317 - Application

20/27

and

Equation 29), and is expressed as:

Equation 27

where,

Note:

By adding a low-cost half-wave rectifier, current is allowed to be supplied by the source

during the positive half, where,

●

Equation 28

where,

Europe = 220V/50Hz), and

●

Equation 29

By substituting the values expressed in

Equation 27 with those in Equation 28 and Equation

29, the results are as follows:

Equation 30

Assuming that the voltage drop across each diode is 0.7V, then the total voltage drop is

expressed as:

Equation 31

I

IN

V

IN R MS

()

X

C2

R

1

+

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

=

V

IN RM S

()

1

2

---

V

PEAK

V

Z

–

2

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

⋅

=

X

C2

1

2

πfC

2

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

=

I

IN

V

PEAK

V

Z

–

22 X

C2

R

1

+

()

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

2V

mains

V

Z

–

22 X

C2

R

1

+

()

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

==

V

Z

V

D1

V

D3

5

0.7 2

6.4V

=

⋅

+

=

+

=