HV9910
Application Information
AC/DC Off-Line Applications
The HV9910 is a low-cost off-line buck, boost or
buck-boost converter control IC specifically
designed for driving multi-LED stings or arrays. It
can be operated from either universal AC line or
any DC voltage between 8-450V. Optionally, a
passive power factor correction circuit can be used
in order to pass the AC harmonic limits set by EN
61000-3-2 Class C for lighting equipment having
input power less than 25W. The HV9910 can drive
up to hundreds of High-Brightness (HB) LEDs or
multiple strings of HB LEDs. The LED arrays can
be configured as a series or series/parallel
connection. The HV9910 regulates constant current
that ensures controlled brightness and spectrum of
the LEDs, and extends their lifetime. The HV9910
features an enable pin (PWM_D) that allows PWM
control of brightness.
The HV9910 can also control brightness of LEDs
by programming continuous output current of the
LED driver (so-called linear dimming) when a
control voltage is applied to the LD pin.
The HV9910 is offered in standard 8-pin SOIC and
DIP packages. It is also available in a high voltage
rated SO-16 package for applications that require
V
IN
greater than 250V.
The HV9910 includes an internal high-voltage
linear regulator that powers all internal circuits and
can also serve as a bias supply for low voltage
external circuitry.
the sense resistor is applied to the CS pin of the
HV9910. When the voltage at CS pin exceeds a
peak current sense voltage threshold, the gate
drive signal terminates, and the power MOSFET
turns off. The threshold is internally set to 250mV,
or it can be programmed externally by applying
voltage to the LD pin. When soft start is required, a
capacitor can be connected to the LD pin to allow
this voltage to ramp at a desired rate, therefore,
assuring that output current of the LED ramps
gradually.
Optionally, a simple passive power factor correction
circuit, consisting of 3 diodes and 2 capacitors, can
be added as shown in the application circuit
diagram of Figure 1.
Supply Current
A current of 1mA is needed to start the HV9910. As
shown in block diagram, this current is internally
generated in HV9910 without using bulky startup
resistors typically required in the offline
applications. Moreover, in many applications the
HV9910 can be continuously powered using its
internal linear regulator that provides a regulated
voltage of 7.5V for all internal circuits.
Setting Light Output
When the buck converter topology of Figure 1 is
selected, the peak CS voltage is a good
representation of the average current in the LED.
However, there is a certain error associated with
this current sensing method that needs to be
accounted for. This error is introduced by the
difference between the peak and the average
current in the inductor. For example if the peak-to-
peak ripple current in the inductor is 150mA, to get
a 500mA LED current, the sense resistor should be
250mV/(500mA+ 0.5*150mA)=0.43Ω.
LED Driver Operation
The HV9910 can control all basic types of
converters, isolated or non-isolated, operating in
continuous or discontinuous conduction mode.
When the gate signal enhances the external power
MOSFET, the LED driver stores the input energy in
an inductor or in the primary inductance of a
transformer and, depending on the converter type,
may partially deliver the energy directly to LEDs
The energy stored in the magnetic component is
further delivered to the output during the off-cycle of
the power MOSFET producing current through the
string of LEDs (Flyback mode of operation).
When the voltage at the V
DD
pin exceeds the UVLO
threshold the gate drive is enabled. The output
current is controlled by means of limiting peak
current in the external power MOSFET. A current
sense resistor is connected in series with the
source terminal of the MOSFET. The voltage from
4
Dimming
Dimming can be accomplished in two ways,
separately or combined, depending on the
application. Light output of the LED can be
controlled either by linear change of its current, or
by switching the current on and off while
maintaining it constant. The second dimming
method (so-called PWM dimming) controls the LED
brightness by varying the duty ratio of the output
current.
The linear dimming can be implemented by
applying a control voltage from 0 to 250mV to the
LD pin. This control voltage overrides the internally
set 250mV threshold level of the CS pin and
programs the output current accordingly. For
C110504
SUPERTEX [ Supertex, Inc ]
