|
|
PDF HV9925 Data sheet ( Hoja de datos )
| Número de pieza | HV9925 | |
| Descripción | Programmable-Current LED Lamp Driver IC | |
| Fabricantes | Supertex | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de HV9925 (archivo pdf) en la parte inferior de esta página. Total 10 Páginas | ||
|
No Preview Available !
HV9925
Initial Release
Programmable-Current LED Lamp Driver IC
with PWM Dimming
Features
Programmable Output Current to 50mA
PWM Dimming / Enable
Universal 85-264VAC Operation
Fixed OFF-Time Buck Converter
Internal 500V Power MOSFET
www.DataSheeOt4vUe.croTmemperature Protection with Hysteresis
Applications
Decorative Lighting
Low Power Lighting Fixtures
Typical Application Circuit
General Description
The HV9925 is a pulse width modulated (PWM) high-efficiency
LED driver control IC with PWM dimming capabilities. It
allows efficient operation of high brightness LED strings from
voltage sources ranging up to 400VDC. The HV9925 includes
an internal high-voltage switching MOSFET controlled with a
fixed off-time TOFF of approximately 10µs. The LED string is
driven at constant current, thus providing constant light output
and enhanced reliability. Selecting a value of a current sense
resistor can externally program the output LED current of the
HV9925. The peak current control scheme provides good
regulation of the output current throughout the universal AC
line voltage range of 85 to 264VAC or DC input voltage of
20 to 400V. The HV9925 is designed with a built in thermal
shutdown to prevent excessive power dissipation in the IC.
~
AC
~
BR1
CIN
CO
LED1
LEDN
D1
L1
Enable
CDD
678
3
Drain
PWMD
Drain
Drain
HV9925
4 VDD
U1
RSENSE
1
GND
2
RSENSE
NR021506
1
1 page  
HV9925
Functional Description
The HV9925 is a PWM peak current control IC for driving
a buck converter topology in continuous conduction mode
(CCM). The HV9925 controls the output current (rather than
output voltage) of the converter that can be programmed by
a single external resistor (RSENSE), for the purpose of driving a
string of light emitting diodes (LED). An external enable input
(PWMD) is provided that can be utilized for PWM dimming of
an LED string. The typical rising and falling edge transitions
of the LED current when using the PWM dimming feature of
the HV9925 are shown in Fig. 6 and Fig. 7.
When the input voltage of 20 to 400V appears at the DRAIN
pin, the internal linear regulator seeks to maintain a voltage
www.DataoSfhe7e.t54UV.DcoCm at the VDD pin. Until this voltage exceeds the
internally programmed under-voltage threshold, no output
switching occurs. When the threshold is exceeded, the
integrated high-voltage switch turns on, pulling the DRAIN
low. A 200mV hysteresis is incorporated with the under-
voltage comparator to prevent oscillation.
When the voltage at RSENSE exceeds 0.47V, the switch turns
off and the DRAIN output becomes high impedance. At the
same time, a one-shot circuit is activated that determines
the off-time of the switch (10µs typ.).
A “blanking” delay of 300ns is provided upon the turn-on of
the switch that prevents false triggering of the current sense
comparator due to the leading edge spike caused by circuit
parasitics.
Application Information
Selecting L1 and D1
variation. Therefore, the output current will remain unaffected
by the varying input voltage.
Adding a filter capacitor across the LED string can reduce
the output current ripple even further, thus permitting a
reduced value of L1. However, one must keep in mind that
the peak-to-average current error is affected by the variation
of TOFF. Therefore, the initial output current accuracy might
be sacrificed at large ripple current in L1.
Another important aspect of designing an LED driver with
HV9925 is related to certain parasitic elements of the
circuit, including distributed coil capacitance of L1, junction
capacitance, and reverse recovery of the rectifier diode D1,
capacitance of the printed circuit board traces CPCB and output
capacitance CDRAIN of the controller itself. These parasitic
elements affect the efficiency of the switching converter and
could potentially cause false triggering of the current sense
comparator if not properly managed. Minimizing these
parasitics is essential for efficient and reliable operation of
HV9925.
Coil capacitance of inductors is typically provided in the
manufacturer’s data books either directly or in terms of the
self-resonant frequency (SRF).
SRF = 1/(2π L ⋅ CL )
where L is the inductance value, and CL is the coil capacitance.
Charging and discharging this capacitance every switching
cycle causes high-current spikes in the LED string. Therefore,
connecting a small capacitor CO (~10nF) is recommended to
bypass these spikes.
The required value of L1 is inversely proportional to the ripple
current ∆IO in it. Setting the relative peak-to-peak ripple to
20~30% is a good practice to ensure noise immunity of the
current sense comparator.
L1 =
VO ⋅ TOFF
∆IO
(1)
Using an ultra-fast rectifier diode for D1 is recommended to
achieve high efficiency and reduce the risk of false triggering
of the current sense comparator. Using diodes with shorter
reverse recovery time trr, and lower junction capacitance CJ,
achieves better performance. The reverse voltage rating VR
of the diode must be greater than the maximum input voltage
of the LED lamp.
VO is the forward voltage of the LED string. TOFF is the off-
time of the HV9925. The output current in the LED string (IO)
is calculated then as:
IO
=
VTH
RSENSE
−
1
2
⋅
∆IO
(2)
where VTH is the current sense comparator threshold, and
RSENSE is the current sense resistor. The ripple current
introduces a peak-to-average error in the output current
setting that needs to be accounted for. Due to the constant
off-time control technique used in the HV9925, the ripple
current is nearly independent of the input AC or DC voltage
The total parasitic capacitance present at the DRAIN output
of the HV9925 can be calculated as:
CP = CDRAIN + CPCB + CL + CJ
(3)
When the switch turns on, the capacitance CP is discharged
into the DRAIN output of the IC. The discharge 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)
NR021506
5
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet HV9925.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| HV9921 | 3-Pin Switch-Mode LED Lamp Driver ICs |  Microchip |
| HV9921 | 3-Pin Switch-Mode LED Lamp Driver IC | Supertex |
| HV9922 | 3-Pin Switch-Mode LED Lamp Driver ICs | Microchip |
| HV9922 | (HV9921 - HV9923) 3-Pin Switch-Mode LED Lamp Driver ICs | Supertex |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |