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PDF HV9921 Data sheet ( Hoja de datos )
| Número de pieza | HV9921 | |
| Descripción | 3-Pin Switch-Mode LED Lamp Driver IC | |
| Fabricantes | Supertex | |
| Logotipo |  |
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Supertex inc.
HV9921
3-Pin Switch-Mode
LED Lamp Driver IC
Features
►► Constant output current: 20mA
►► Universal 85 - 265VAC operation
►► Fixed off-time buck converter
►► Internal 475V power MOSFET
Applications
►► Decorative lighting
►► Low power lighting fixtures
General Description
The HV9921 is a pulse width modulated (PWM) high-efficiency
LED driver control IC. It allows efficient operation of LED strings
from voltage sources ranging up to 400VDC. The HV9921
includes an internal high voltage switching MOSFET controlled
with fixed off-time (TOFF) of approximately 10.5μs. The LED
string is driven at constant current, thus providing constant light
output and enhanced reliability. The output current is internally
fixed at 20mA for HV9921. The peak current control scheme
provides good regulation of the output current throughout the
universal AC line voltage range of 85 to 265VAC or DC input
voltage of 20 to 400V.
Typical Application Circuit
AC
HV9921
3 VDD
DRAIN 1
GND
2
LED1
-
LEDn
Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
1 page  
HV9921
current is limited to about 150mA typically. However, it
may become lower at increased junction temperature. The
duration of the leading edge current spike can be estimated
as:
TSPIKE = ((VIN • CP) / (ISAT)) +trr
(4)
Conduction power loss in the HV9921 can be calculated as:
PCOND = (D • IO2 • RON) + [IDD • VIN • (1 - D)] (9)
where D = VO /ηVIN is the duty ratio, RON is the on-resistance,
IDD is the internal linear regulator current.
In order to avoid false triggering of the current sense
comparator, CP must be minimized in accordance with the
following expression:
CP <
ISAT
•
(TBLANK(MIN)
VIN(MAX)
-
trr
)
(5)
where TBLANK(MIN) is the minimum blanking time of 200ns, and
VIN(MAX) is the maximum instantaneous input voltage.
Estimating Power Loss
When the LED driver is powered from the full-wave
rectified AC line input, the exact equation for calculating the
conduction loss is more cumbersome. However, it can be
estimated using the following equation:
PCOND = (KC • IO2 • RON ) + (KD • IDD • VAC )
(10)
where VAC is the input AC line voltage. The coefficients KC
and Kd can be determined from the minimum duty ratio of
the HV9921.
0.7
Discharging the parasitic capacitance CP into the DRAIN pin of
the HV9921 is responsible for the bulk of the switching power
loss. It can be estimated using the following equation:
PSWITCH = [(VIN2 • CP ) / 2 + VIN • ISAT • trr ] • FS (6)
0.6
0.5
Kd(Dm)
0.4
Kc(Dm)
where FS is the switching frequency, ISAT is the saturated
DRAIN current of the HV9921. The switching loss is the
greatest at the maximum input voltage.
The switching frequency is given by the following:
0.3
0.2
FS = (VIN - η-1 • VO) / VIN • TOFF
(7)
where η is the efficiency of the power converter.
When the HV9921 LED driver is powered from the full-wave
rectified AC input, the switching power loss can be estimated
as:
2PS•W1TITOCFHF≈ (VAC • CP + 2 • ISAT • trr )(VAC - η-1 • VO )
(8)
VAC is the input AC line voltage.
The switching power loss associated with turn-off transitions
of the DRAIN pin can be disregarded. Due to the large amount
of parasitic capacitance connected to this switching node,
the turn-off transition occurs essentially at zero-voltage.
0.1
0
0.1 0.2
0.3 0.4 0.5 0.6
Dm
Fig. 1. Conduction Loss Coefficients KC and Kd
0.7
EMI Filter
As with all off-line converters, selecting an input filter is critical
to obtaining good EMI. A switching side capacitor, albeit of
small value, is necessary in order to ensure low impedance
to the high frequency switching currents of the converter. As
a rule of thumb, this capacitor should be approximately 0.1-
0.2 µF/W of LED output power. A recommended input filter is
shown in Figure 2 for the following design example.
Design Example
Let us design an HV9921 LED lamp driver meeting the
following specifications:
Input:
Universal AC, 85-265VAC
Output Current: 20mA
Load:
String of 10 LED (LW541C by OSRAM
VF = 4.1V max. each)
Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
5
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| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet HV9921.PDF ] | |
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