DN-H01
Design Note
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
Introduction
In a few general lighting applications, there is a need to isolate
the LEDs from the AC input line. These are cases when
the driver terminals of the LED strings are exposed to the
external environmental conditions, or the LED strings are user
accessible for maintenance during operation. In these cases,
an isolated LED driver is needed for safety considerations.
This design note provides the circuit schematic, bill of
materials, and transformer design for an isolated LED driver
using Supertex’s HV9910B. The power stage is a flyback
converter with an isolated secondary side feedback, using an
opto coupler, to ensure a very good line and load regulation
(typically <1% over line and load). Below are the design
parameters which are the target specification for this LED
driver circuit. This LED driver will also meet CISPR-15 EMI
limits for general lighting.
The information in this datasheet also applies to the Supertex
HV9910.
Design Parameters
Parameter
Value
Input voltage
90 – 256VAC, 50/60Hz
LED string voltage
4.0 – 16V
LED current
350mA
Initial regulation
<5%
Line and load regulation
<1%
Over voltage protection
20V
Switching Frequency
100kHz
Isolated LED Driver
Using the HV9910B
Circuit Schematic
C3
10
uF
,
40
0V
C2
2.
2u
F
,
40
0V
1
2
3
4
L1
BU
9H
S-
15
3R
15
B
C4
0.01uF, 250VAC
C1
0.01uF, 250VAC
F1
2A, 250VAC
1
3
2
D9
LMV431
D7
9.1V
C12
1n, 250VAC
D2
B1100-13
D4
BAV2
0W-7
Q3
STD1NK60T4
R8
0.56
VIN
1
LD
13
PWMD
9
GN
D
5
CS
4
GATE
8
RT
14
VDD
12
U2
C9
1u
F
,
16
V
V
DD
V
DD
C8
1u
F
,
50
V
D1
1N4764ADO41
D3
MUR140RL
R5
228k
C5
4.
7u
F
,
25
V
C6
4.
7u
F
,
25
V
LED+1
LED-1
R2
1.78,1/4W
R1
1.78,1/4W
R7
20k
C11
0.1uF
R9
1k
U3
H11A817A
R13
100
D8
20V
R6
5.49k
R11
97.6k
R12
4.99k
R3
1k
Q1
MMBT2222A
t
RT1
CL-140
C13
2.
2u
F
,
40
0V
1
3
9
10
4
5
O
O
O
T1
J1
J2
A
C
1
A
C
2
PO
S
N
E
G
U1
HV9910B