A082804
Low Voltage, Buck Boost, High Brightness LED Driver Demo Board
Introduction
The Supertex HV9910DB4v.2 demo board is a
complete high current, high brightness (HB) LED
power driver to supply a string of LEDs using the
HV9910 IC from a low DC voltage. The demo board
can be used to test the performance of the HV9910 as
a constant current driver to power LEDs.
HV9910DB4v.2 can drive LED strings whose voltage
is less or more than the input voltage.
HV9910DB4v.2 can supply a maximum output current
of 620mA (adjustable using the on-board
potentiometer) to drive LED strings having a
maximum string voltage of 22V. HV9910DB4v.2 is
ideally suited to drive a string of 5 or 6 high brightness
LEDs at high efficiencies (typically greater than 85%).
This demo board is an improved version of the
HV9910DB4 v.2 with over-voltage protection and
output voltage feedback to maintain a constant LED
current (see Application note AN-H49 for details).
The power conversion stage of HV9910DB4v.2
consists of a current-controlled buck-boost converter
operating at a variable switching frequency. The
nominal output current of the demo board can be
adjusted to any value less than 780mA using the on-
board trimming potentiometer. PWM dimming can be
achieved by applying a pulse-width-modulated square
wave signal between the PWMD and GND pins.
Specifications
Input 9VDC – 30VDC
Load Current 780mA maximum
LED String Voltage 10V minimum
22V maximum
Switching Frequency Variable, depends on output
voltage
Overall Set Point 26V
Efficiency >85% (typ.)
Board Layout and Connections
HV9910DB4 v.2
8-30VDC
PWMDimming
(optional)
Enable
Connection
Actual Size: 53.5mm x 26.75mm
HV9910DB4 v.2
A0826804
2
Instructions
VIN+: Connect the positive terminal of the DC input
source to this pin.
VIN-: Connect the negative terminal of the DC input
source to this pin.
LED+: Connect the Anode of the LED string to this
pin.
LED-: Connect the Cathode of the LED string to this
pin.
VDD: This pin is connected to the VDD pin of the
HV9910. The typical voltage on the pin is 7.6V. This
voltage can be used to drive any additional circuitry
required. Please see the datasheet regarding the
output current capability at the VDD pin.
GND: This pin is connected to the Ground
connection of the buck converter.
PWMD: This terminal can be used to either
enable/disable the converter or to apply a PWM
dimming signal.
To just enable the converter, connect the PWMD pin
to the VDD pin. Disconnecting the PWMD pin will
cause the circuit to stop.
PWM dimming of the LED light can be achieved by
turning on and off the converter with a low frequency
50Hz to 1000Hz TTL logic level signal. Changing the
Duty Ratio of the signal changes the effective
average current via the LEDs, changing the light
emission.
Note: In the case of PWM dimming, the PWMD pin
should not be connected to the VDD pin!
Setting the Output Current
The output current of a peak-current-controlled buck-
boost converter is given by:
2
5.12 LDoVI×≈
where:
o
I: output current
LD
V: voltage at the dimming pin
Testing HV9910DB4v.2
Connect the LED string to the output terminals.
Check the polarity of the LED connection, anode end
of the string should be connected to the positive
output, cathode should be connected to the negative
output. Connect the DC input to the input terminals
(check the polarity). Short the PWMD pin to VDD.
Apply a DC voltage at the input terminals and the
LED string should start to glow.
An ammeter can be connected in series with the
LED(s) to measure the output current. The current
level can then be changed by adjusting the trimming
potentiometer.
Open LED Condition:
This power stage can be run under open LED
condition. When there are no LEDs connected at the
output, the converter will switch at a frequency of
about 2.5kHz and draw about 0.2 to 0.3W of power
from the input.
Linear Dimming Test:
Gradual change of current via LED(s) is possible by
using the trimming potentiometer placed on the demo
board. The HV9910 has a preset voltage reference
level of 250mV when the voltage at the LD pin of the
IC is above 250mV. The external resistor divider
consisting of R12 and potentiometer R11 can change
that level by pulling down the pin LD below 250mV,
reducing the LED string current in linear fashion.
The maximum recommended output current of the
HV9910DB4 v.2 is 780mA.
PWM Dimming Test:
By applying a PWM TTL level signal between pins
PWMD and GND, the output current through the
LEDs can be changed in PWM fashion in a 0 to
100% range. In this dimming mode, the output
current has normally two levels – zero and nominal
current, except at very low duty ratios where the LED
current cannot ramp up to the nominal value within
the short time.
HV9910DB4 v.2
A082804
3
Q2
MMBT2907A
GND
1
2
L1
15uH
D1
B360A-13
R6
100K
R7
100k
C3
10uF, 25V
R8
1k
R9
340K
Q3
Open Circuit
Protection
U2
Q1
NDT3055
Output Voltage
Feedback
R5
0.05, 1/4W
C9
10uF, 25V
R10
10Meg
Vin 1
LD
7
PWMD
5
Gnd
3
CS 2
Gate 4
Rosc 8
Vdd
6
HV9910
U3
D3
BZX84C24-7
VDD
PWMD
R11
5k
C5
2.2uF, 16V
VIN+
VIN-
LED+
LED-
R12
178k
C2
10uF,35V
C1
10uF, 35V
C8
10uF, 25V
HV9910DB4 v.2 – Bill of Materials
Quantity
RefDes
Description
Manufacturer
Manufacturer's Part Number
2C1, C2 10uF, 35V SMD 1812 Multilayer Ceramic Chip capacitors Panasonic ECJ-5YF1V106Z
3C3,C8,C9 10uF, 25V SMD 1206 Multilayer Ceramic Chip capacitor Panasonic ECJ-3YB1E106M
1C5 2.2uF, 25V SMD 0805 Ceramic Capacitor Panasonic ECJ-3YB1E106M
1D1 60V, 3A SMA schottky diode Diodes, Inc. B360A-13
1D3 24V, 350mW SOT-23 zener diode Diodes, Inc. BZX84C24-7
7VIN-,VIN+,VDD,PWMD, 7 Position Breakaway Header Molex/ Waldom 22-28-4070
LED-,LED+,GND
1 L1 15uH, 4.5A inductor Coilcraft MSS1278-153MXB
1Q1 60V, 4A SOT-223 N-channel Mosfet Fairchild NDT3055
2Q2,Q3 -60V, 0.6A SOT-23 PNP transistor Diodes, Inc. MMBT2907A
1R5 0.05, 1/4W, 1% SMD1210chip resistor Panasonic ERJ-L14KF50MU
2R6,R7 100k, 1/10W, 1% SMD0805 chip resistor Panasonic ERJ-6ENF1003V
1R8 1k, 1/8W, 5% SMD0805 chip resistor Panasonic ERJ-6GEYJ102V
1R9 340K, 1/10W, SMD0805 1% chip resistor Panasonic ERJ-6ENF3403V
1R10 10Meg, 1/8W, SMD0805 5% chip resistor Panasonic ERJ-6GEYJ106V
1R11 5K surface mount trim pot Murata PVG3A502A01R00
1R12 178k, 1/10W, 1% SMD0805 chip resistor Panasonic ERJ-6ENF1783V
1U2 40V, 600mA dual NPN transistor Diodes, Inc. MMDT4401-7
1
U3
Universal LED Driver
Supertex
HV9910LG
Schematic Diagram
HV9910DB4 v.2
A082804
4
HV9910DB4 v.2 – Top Layer
HV9910DB4 v.2 – Bottom Layer
HV9910DB4 v.2 – Top Silk Screen
Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receive
s an adequate
"products liability indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices
determined to be defective due to workmanship. No responsibi
lity is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For
the latest product specifications, refer to the Supertex website: http://www.supertex.com. For complete liability information on
all Supertex products, refer to the most current data book or to
the Legal/Disclaimer page on the Supertex website.
A082804
