Microchip HV9931DB1 Handleiding

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Supertex inc.
Supertex inc.
www.supertex.com
HV9931DB1
Doc.# DSDB-HV9931DB1
A032713
The HV9931 LED driver is primarily targeted at low to
medium power LED lighting applications where galvanic
isolation of the LED string is not an essential requirement.
The driver provides near unity power factor and constant
current regulation using a two stage topology driven by
a single MOSFET and control IC. Triac dimming of this
design is possible with the addition of some components for
preloading and inrush current shaping.
The DB1 and DB2 Demoboards were designed for a xed
string current of 350mA and a string voltage of 40V for a load
power of about 14W. The boards will regulate current for an
output voltage down to 0V.
Nominal input voltage for the DB1 is 120VAC, for the DB2
230VAC. Design for universal input (85 to 265VAC) is by
all means possible but does increase cost and size while
lowering efciency.
The input EMI lter was designed to suppress the differential
mode switching noise to meet CISPR15 requirements.
No specic components were added to suppress currents
of common mode nature. Common mode current can be
controlled in many ways to satisfy CISPR 15 requirements.
The board is tted with a number of optional circuits; a
schematic of a simplied driver is given as well. The circuits
featured are output current soft start and protections from
line overvoltage, load overvoltage and open circuit. The
driver is inherently short circuit proof by virtue of the peak
current regulation method.
Board Layout and Connections
LED Driver Demoboard
Input 120VAC // Output 350mA, 40V (14W)
Specications
Input voltage: 100VRMS to 135VRMS, 60Hz
Output voltage: 0 to 40V
Output current: 350mA +/-5%
Output power: 14W, Max
Power factor 98%
Total harmonic distortion EN61000-3-2 Class C
EMI limits CISPR 15 (see text)
Efciency 83%
Output current ripple 30%PP
Input overvoltage
protection 140VRMS, Latching
Output overvoltage
protection 43V, Latching
Switching frequency 73kHz
Dimensions: 3.5” x 3.0” x 1.25”
General Description
V
A
V
A
2
Supertex inc.
www.supertex.com
HV9931DB1
Doc.# DSDB-HV9931DB1
A032713
Step 1.
Carefully inspect the board for shipping damage, loose
components, etc, before making connections.
Step 2.
Attach the board to the line and load as shown in the diagram.
Be sure to check for correct polarity when connecting the
LED string to avoid damage to the string. The board is short
circuit and open circuit proof. The LED string voltage can
be anything between zero and 40V, though performance will
suffer when the string voltage is substantially lower than the
target of 40V. See the typical performance graphs.
Step 3.
Energize the mains supply. The board can be connected to
mains directly. Alternatively voltage can be raised gradually
from zero to full line voltage with the aid of an adjustable AC
supply such as a Variac or a programmable AC source.
Principles of Operation
The HV9931 topology can be viewed as a series connection
of two basic power supply topologies, (1) a buck-boost
stage as rst or input stage, for purpose of converting AC
line power into a source of DC power, commonly known as
the DC bus, having sufcient capacitive energy storage to
maintain the bus voltage more or less constant throughout
the AC line cycle, and (2) a buck stage as second or output
stage for powering the LED string, stepping down the DC
bus voltage to the LED string voltage in order to produce a
steady LED string current.
The output or buck stage is designed for operation in
continuous conduction mode (CCM), operating with about 20
to 30% inductor current ripple. This amount of ripple serves
the needs of the HV9931 peak current controller which relies
on a sloping inductor current for setting ON time, and is of an
acceptable level to high brightness LEDs. Duty cycle is more
or less constant throughout the line cycle as the DC bus
voltage and LED string voltage are more or less constant
as well. Duty cycle and bus voltage do adjust in response to
changes in line or load voltage but are otherwise constant
over the course of a line cycle. With the HV9931, OFF time is
xed by design, being programmed by an external resistor,
whereas ON time adjusts to a more or less constant value,
being under control of the HV9931 peak current regulator.
The input or buck-boost stage is designed for operation
in discontinuous conduction mode (DCM) throughout the
range of line and load voltage anticipated. This can be
accomplished by making the input inductor sufciently small.
A well known property of the DCM buck-boost stage, when
operated with constant ON time and constant OFF time, is
that input current is proportional to input voltage, whether
in peak value or average value. This results in sinusoidal
input current when the input voltage is sinusoidal, thereby
giving unity power factor operation when operating from the
rectied AC line voltage.
When operated in the anticipated range of line and load
voltage, the MOSFET ON time will be under control of the
output stage current controller, which turns the MOSFET
off when sensing that the output inductor current has
reached the desired peak current level as programmed by
a resistive divider at the CS2 pin. Under certain abnormal
circumstances such as initial run-up and line undervoltage,
which both could lead to the draw of abnormally high line
current, ON time is further curtailed by the action of the CS1
comparator, which monitors the input stage inductor current
against a threshold. This threshold can be a simple DC level
or be shaped in time as is performed on the Demoboard. In
particular, when shaping the CS1 threshold with the shape of
the rectied AC line input voltage waveform, the line current
will be bounded by a more or less sinusoidal line current
envelope which results in sinusoidal input current for low line
and other abnormal conditions.
The design exercise of an HV9931 LED driver revolves
around establishing component values for (1) the input and
Connection Instructions
Warning!
Working with this board can cause serious bodily harm or
death. Connecting the board to a source of line voltage will
result in the presence of hazardous voltage throughout the
system including the LED load.
The board should only be handled by persons well aware of
the dangers involved with working on live electrical equip-
ment. Extreme care should be taken to protect against elec-
tric shock. Disconnect the board before attempting to make
any changes to the system conguration. Always work with
another person nearby who can offer assistance in case of
an emergency. Wear safety glasses for eye protection.
Special Note:
The electrolytic capacitor carries a hazardous voltage for an
extended time after the board is disconnected. The board
includes a 1MΩ resistor placed across the electrolytic ca-
pacitor which will slowly discharge the capacitor after dis-
connection from line voltage. The voltage will fall more or
less exponentially to zero with a time constant of about 100
seconds. Check the capacitor voltage before handling the
board.
3
Supertex inc.
www.supertex.com
HV9931DB1
Doc.# DSDB-HV9931DB1
A032713
Simplied Schematic Diagram
output stage inductors, (2) a value for the bus capacitor, and
(3) a value for switching cycle OFF time, which together
result in (1) acceptable current ripple at the output stage
(say 30%), (2) an acceptable bus voltage ripple (say 5%),
and (3) an input stage which maintains DCM operation over
the desired line and load voltage range.
For a given HV9931 design, the bus voltage rises and falls
with like changes in line and load voltage. This is unlike a
two stage design having two transistors and control ICs,
where the bus voltage can be set independent of line and
load voltage variation. If the desired ranges of line and load
voltage are particularly large then the latter topology may be
preferable so as to avoid large variation in bus voltage.
The design of an HV9931 based LED driver is not further
discussed here, except for noting that a semi-automatic
design tool is available in Mathcad form, based on behavioral
simulation, which, allows components to be adjusted in an
iterative manner, starting from an initial guess. The tool allows
quick evaluation of nine standard test cases, exercising the
design over line voltage variation and tolerance variation of
three component parameters.
Mathcad design data can be found at the end of this
document. The data tends to be in good agreement with the
actual Demoboard despite the omission of switching losses
in the model. For this design we can see that the calculated
efciency is off by say 5 percent likely due underestimation
of switching losses and inductor core and winding losses.
A Simplied Version of the Design
The Demoboard can be simplied signicantly. Below is a
schematic showing the essential elements of the driver.
L11
1mH
BR11
RH06-T
R72
2.67kΩ
2
L31
560μH
M31
SPA04N50C3
L41
3.3mH
R71
680mΩ
E31
47μF
C51
10µF
D31
STTH1L06A
R51
196kΩ
R37
6.8kΩ
C37
100pF
F11
250mA
L21
1mH
C12
100nF
5
IC51
HV9931LG
ZOV
BZX84C43
ROV
10kΩ
THROV
BT168GW
Optional Output
Overvoltage Protection
AC1
C21
100nF
+
D32
STTH1L06A
D41
STTH1R06A
D42
STTH102A
R61
180mΩ
R73
75kΩ
C11
100nF
R62
2.43kΩ
R68
75kΩ
AC2
3
1
4
2
ANO
CAT
1 4 8
7
63
VIN GATE RT
CS2
CS1
GND VDD PWM
C
A
C
A
Contact Supertex Applications Engineering for guidance in
simplifying the design or for adding functions such as triac
dimmability.
Note on Inductors:
This board was tted with standard (COTS) inductors. These
are not necessarily an optimal choice but present an expedi-
ent way to go when evaluating a design. Custom engineered
parts generally give better performance, particularly with re-
spect to efciency.
Drum core style inductors, whether in radial or axial leaded
versions, are popular for their ready availability and low cost.
Drum core styles have particularly simple construction and
can be wound for lowest cost without coil former (bobbin).
They may serve well during the development stage, but may
not be the best choice for nal design. Keep these type of
inductors away form any metallic surface such as heatsinks,
PCB copper planes, metallic enclosures, and capacitors, as
these unshielded parts can create high eddy current losses
in these parts. For tightly packaged designs or where induc-
tor losses are an issue, drum core style inductors are not
recommended.

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: HV9931DB1

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