ZLED7020

High Current 40V LED Driver with Internal Switch

Data Sheet

August 12, 2011

© 2011 Zentrum Mikroelektronik Dresden AG — Rev. 1.2

All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without

the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice.

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LX

MAX

LX

F

MAX

D

AVG

MIN

f

*

V

D

*

I

V

t

*

I

1

C

∆

=

∆

=

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

1

C

=

(9)

Where:

Symbol

Description

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

negligible.

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

Peak rectified supply voltage minus LED string forward voltage or minimum ZLED7x20 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 minimum bypass capacitor C1 of 220

µF 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

Average nominal LED string current.

On time of the internal MOSFET output switch.

Permissible voltage ripple on the supply voltage.