ZLED7x30 Datasheet

18

April 20, 2016

LX

MAX

LX

F

MAX

D

AVG

MIN

f

V

D

I

V

t

I

C

∗

∆

∗

=

∆

=

*

1

F

135

V

2

.

3

*

3

2

*

V

24

ms

10

*

A

33

.

0

1

C

MIN

µ

=

−

=

ripple

ON

AVG

MIN

V

t

I

C

*

1

=

(9)

Where:

Symbol

Description

IAVG

Average nominal LED string current assuming that the contribution of the IC supply current is

negligible.

tD

Discharge time at given AC frequency. Will be a maximum of 10ms (½ period duration) at 50Hz.

ΔVMAX

Peak rectified supply voltage minus LED string forward voltage or minimum ZLED7x30 supply

voltage, whichever is greater.

Example: For an application with 3 LEDs with 3.2V forward voltage each driven at 0.33A and supplied with rectified

24VAC, a mi

nimum bypass capacitor C1 of 220μF or 330μF might be adequate. Compared to the calculation, a

safety margin of about 50% must be added to consider temperature effects and aging.

(10)

A second function of C1 is to bypass the current ripple of the switching converter and thus prevent it from disturbing a

stable IC supply or backlash on the power supply circuit. For this reason even in DC-supplied applications, the use of

an adequate C1 might be useful. The defining parameters are now as shown in equation (11):

(11)

Where:

Symbol

Description

IAVG

Average nominal LED string current.

tON

ON time of the internal MOSFET output switch.

Note: tON must be longer than tONmin=200ns.

Vripple

Permissible voltage ripple on the supply voltage.