AN44 ZETEX [Zetex Semiconductors], AN44 Datasheet - Page 4

• Manufacturer Part Number: AN44
• Description: A high power LED driver for low voltage halogen replacement
• Manufacturer: ZETEX [Zetex Semiconductors]

AN44
As the T
is rather close to 1.7µs and it is possible that, over component tolerances, the coil current will not
reach zero, but this is not a big issue as the remaining current will be small. Note that, because of
the peak current measurement and switch-off, it is not possible to get the dangerous ‘inductor
staircasing’ which occurs in converters with fixed T
so even if it starts from a finite value (i.e. continuous mode) it will not exceed the I
current will therefore be approximately the average of 680mA and zero = 340mA (it will not be
exactly the average, because there is a 200ns period at zero current, but this is small compared
with the I
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Ref
U1
Q1
D1
D2
L1
R1
R2
C1
C2
C3
OFF
Value
1A / 40V
6V8
22 H
50m
1k2
100 F/25V
1 F/10V
2.2 F/25V
PEAK
period is nominally 1.7µs, the current should have time to reach zero. However, 1.5µs
and component tolerances).
Part number
ZXSC310E5
ZXMN6A07F
ZHCS1000
Generic
DO3316P-223 Coilcraft
Generic
Generic
Generic
Generic
Generic
Table 1 Bill of materials
Manufacturer Contact details
Zetex
Zetex
Zetex
Generic
Generic
Generic
Generic
Generic
Generic
4
ON
www.zetex.com
www.zetex.com
www.zetex.com
www.coilcraft.com
times. The current can never exceed I
Comments
LED Driver in SOT23-5
N-channel MOSFET in
SOT23
1A Schottky diode in
SOT23
6V8 Zener diode
0805 size
0805 size
© Zetex Semiconductors plc 2006
Issue 2 - July 2006
PEAK
. The LED
PEAK
,