DN93

A Product Line of
Diodes Incorporated
DN93
Wide input voltage range SEPIC LED driver using ZXLD1321
with external power switch
Ray Liu, Applications Engineer, Diodes Incorporated
Introduction
Some LED lighting applications like the solar and automotive system, require an LED driver with
a wide input voltage range where the LED voltage falls between minimum and maximum input
voltage. In this case, neither boost nor buck topology would be a suitable solutions. SEPIC (Single
Ended Primary Inductance Converter) resolves this issue and provide reasonable efficiency with
relatively simple topology.
The following is a design example of a SEPIC LED driver which is capable of driving multi-chip
LEDs with forward voltage up to 17V and LED current of 1A . The input voltage is wide with range
from 8V to 30V.
1A Multi-chips LED driver with external SEPIC MOSFET switch
Figure 1 and Table 1 show the schematic and bill of materials of the design respectively.
R1*
1
10
M_LOAD
11
2
9
8
L ED1
C9
L ED2
C8
Q2
EMITTER1
EMITTER2
ISENSE
Q3
5
GND
L1
R6
C7
R7
C6
D1
L ED3
6
7
Exp'd Pad
COLLECTOR1
COLLECTOR2
CFB
N/C
TADJ
3
4
13
ADJ
D2
VREF
BIAS
14
M_VIN
VIN
12
R1
U1
ZXLD1321
R8
Q1
VI N
C5
C3
C4
R4
C15
Z1
C14
L 1'
L ED4
R5
Q4
C10 C11 C12 C13
R9
R3
C1
C2
R2
R2*
Z2
Figure 1 - Schematic
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Ref No.
Value
Part No.
Manufacturer
Note
U1
LED Driver IC
ZXLD1321
Diodes Zetex
Q1
60V 10A Mosfet
ZXMN6A25K
Diodes Zetex
Q2
Gate Driver Pairs
ZXTC2045
Diodes Zetex
Q3
50V NPN
ZXTN2031
Diodes Zetex
D1
PDS5100H
Diodes Zetex
D2
100V 5A Schottky
Rectifier
100V 1A Rectifier
S1B
Diodes Zetex
Z1
12V 350mW Zener
BZX84C12
Diodes Zetex
Z2
18V 350mW Zener
BZX84C18
Diodes Zetex
L1
22uH 5.2A SEPIC
Inductor
NPIS25DW220MTRF
744870220
MSD1278-223ML
NIC Components
Wurth Electronik
Coilcraft
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C1
10nF 50V
SMD 0603
47nF 50V
SMD 0603
470uF 50V
NMC0603X7R103K50TRPF
GRM188R71E103KA01
NMC0603X7R473K50TRPF
GRM188R71E473KA01
Generic Electrolytic
NIC Components
Murata
NIC Components
Murata
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4.7uF 50V X7R
SMD 1206
GRM31CR71H475KA12
Murata
www.murata.com
200mΩ
NIC Components
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C2 C15
C5
C3 C4
C6 C7
C8 C9
C10 C11
C12 C13
C14
R1 R1*
R2 R2*
20mΩ
NCST12GR200GTRF
SMD 1206
SMD 1206
R3
0Ω
SMD 0805 / 0603
R4
1.2KΩ
SMD 0805 / 0603
R5
33Ω
SMD 0805 / 0603
R6
18Ω
SMD 0805 / 0603
R7
10Ω
SMD 0805 / 0603
R8
4.7KΩ
SMD 0805 / 0603
R9
2.7KΩ
SMD 0805 / 0603
Table 1 - Bill of materials
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Circuit description
In this design, the ZXLD1321 is used as an LED driver controller to drive the MOSFET power
switch through a ZXTC2045 gate drive transistor pair.
Although the input voltage rating of ZXLD1321 is 12V, by using an external 60V Mosfet power
switch (ZXMN6A25K) and a simple 12V regulator formed by Q3 (ZXTN2031) and Z1, the system
could operate up to 30V supply voltage with absolute maximum rating of 40V.
The SEPIC power stage is formed by Q1, D1, L1, L1’ and C6 to C13. The same inductance is used
for both L1 and L1’ such that a coupled inductor can also be used. Instead of using two inductors
for the power stage, a single standard coupled inductor is used to minimize the component count.
The output of the SEPIC stage is connected to the LEDs through the current sensing resistor R1.
The voltage drop across R1 provides feedback to the LED controller IC and the sensing threshold
is 100mV. Since the rated voltage of ZXLD1321’s MVIN and MLOAD pin are limited to 18V, the
system is capable of driving LEDs with total LED voltage below 18V. To prevent MVIN and MLOAD
pins from over-voltage, Z2 and Q4 formed a voltage detection circuit which will pull down the ADJ
pin. This will shutdown the driver IC whenever the LED voltage is above 18V.
Design Considerations
Since the voltage spike caused by the high switching current and stray inductance of PCB’s
copper track would be high compared to the low ISENSE voltage threshold of ZXLD1321 which is
below 55mV, RC filter formed by C2 and R5 is used to prevent false triggering of ISENSE pin. i.e.
C2 should be placed as close as possible between the ISENSE pin and the exposed GND pad of
the IC.
In SEPIC design, high ripple current appears at the output filtering capacitor (C10 – C13) and the
SEPIC coupling capacitor (C6 - C9). Hence, a low ESR capacitor with an appropriate ripple current
rating should be used. In this design, we recommend use of a standard X7R ceramic SMD
capacitor working in parallel rather than the specialized pulse capacitor.
Performance
The typical efficiency throughout the input voltage range is shown in Figure 2 with average
efficiency of 85%.
The line regulation of LED current is shown in Figure 3 with line regulation better than 3%.
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Typical performance graphs
100
90
80
E ffic ienc y (% )
70
60
50
40
30
20
V F = 16V or 4 LEDs
V F = 13V or 3 LEDs
10
0
8
10
12
14
16
18
20
22
24
26
28
30
LE D V oltage (V )
E ffic ie n c y v s L E D V o lta g e
Figure 2
1200
LE D Current (m A )
1000
800
600
400
V F =1 6 V or 4 LEDs
V F =1 3 V or 3 LEDs
200
0
8
10
12
14
16
18
20
22
24
26
28
30
Input V oltage (V )
L E D C u r r e n t v s In p u t V o lta g e
Figure 3
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Conclusion
The ZXLD1321 can be used in SEPIC mode to produce a high buck-boost LED driver with scalable
output current capability at an efficiency of around 85%. The input voltage can be between 8 and
30V but the number of LEDs must be limited to ensure the output voltage is less than 17V.
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Definitions
Product change
Diodes Incorporated the right to alter, without notice, specifications, design, price or conditions of supply of any product or service.
Customers are solely responsible for obtaining the latest relevant information before placing orders.
Applications disclaimer
The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for
the user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is
assumed by Diodes Inc. with respect to the accuracy or use of such information, or infringement of patents or other intellectual property
rights arising from such use or otherwise. Diodes Inc. does not assume any legal responsibility or will not be held legally liable (whether
in contract, tort (including negligence), breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business,
contract, opportunity or consequential loss in the use of these circuit applications, under any circumstances.
Life support
Diodes Zetex products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body
or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labelling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to
cause the failure of the life support device or to affect its safety or effectiveness.
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company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a
representation relating to the products or services concerned.
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All products are sold subjects to Diodes Inc. terms and conditions of sale, and this disclaimer (save in the event of a conflict between the
two when the terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement.
For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Diodes’ sales office .
Quality of product
Diodes Zetex Semiconductors Limited is an ISO 9001 and TS16949 certified semiconductor manufacturer.
To ensure quality of service and products we strongly advise the purchase of parts directly from Diodes Inc. or one of our regionally
authorized distributors. For a complete listing of authorized distributors please visit: www.diodes.com
Diodes Zetex does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales channels.
ESD (Electrostatic discharge)
Semiconductor devices are susceptible to damage by ESD. Suitable precautions should be taken when handling and transporting devices.
The possible damage to devices depends on the circumstances of the handling and transporting, and the nature of the device. The extent
of damage can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time.
Devices suspected of being affected should be replaced.
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Diodes Zetex Semiconductors is committed to environmental excellence in all aspects of its operations which includes meeting or
exceeding regulatory requirements with respect to the use of hazardous substances. Numerous successful programs have been implemented to reduce the use of hazardous substances and/or emissions.
All Diodes Zetex components are compliant with the RoHS directive, and through this it is supporting its customers in their compliance
with WEEE and ELV directives.
Product status key:
“Preview”
Future device intended for production at some point. Samples may be available
“Active”
Product status recommended for new designs
“Last time buy (LTB)”
Device will be discontinued and last time buy period and delivery is in effect
“Not recommended for new designs” Device is still in production to support existing designs and production
“Obsolete”
Production has been discontinued
Datasheet status key:
“Draft version”
This term denotes a very early datasheet version and contains highly provisional information, which
may change in any manner without notice.
“Provisional version”
This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance.
However, changes to the test conditions and specifications may occur, at any time and without notice.
“Issue”
This term denotes an issued datasheet containing finalized specifications. However, changes to
specifications may occur, at any time and without notice.
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