AN2317 - Application

External Circuit Design

23/27

●

requirements expressed in

Equation 36:

Equation 36

In fact, considering that the charge stored in the capacitor is:

Equation 37

where,

T = the AC sine wave period, and

the output ripple voltage is expressed as:

Equation 38

then the capacitor C value can be calculated by using a fixed voltage ripple value:

Equation 39

then, fixing our ripple to

ΔV=200mV we can calculate C value accordingly.

For the purposes of this application, C is calculated as follows:

Equation 40

seems to be enough to change the D3 diode (see

Equation 34) from the previously

selected ZMM SOD 80*5.1V G Zener Diode, if the output current is too high, then the

Note:

Usually it is not necessary to use resistor R1 in the circuit.

R

25

∼

()T

=

I

=

ΔV

Q

C

----

=

ΔV

I

C

--------

=

C

10mA

200mV 50Hz

⋅

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

1000

μF

==