HV9931 Supertex, Inc., HV9931 Datasheet - Page 4

• Manufacturer Part Number: HV9931
• Description: Hv9931 Unity Power Factor Led Lamp Driver
• Manufacturer: Supertex, Inc.

Functional Description
Power Topology
The HV9931 is optimized to drive Supertex’s proprietary
single-stage, single-switch, non-isolated topology, cascading
an input power factor correction (PFC) buck-boost stage
and an output buck converter power stage. This power
converter topology offers numerous advantages useful
for driving high-brightness light emitting diodes (HB LED).
These advantages include unity power factor, low harmonic
distortion of the input AC line current, and low output current
ripple. The output load is decoupled from the input voltage
with a capacitor making the driver inherently failure-safe for
the output load. The power converter topology also permits
reducing the size of a fi lter capacitor needed, enabling use
of non-electrolytic capacitors. The latter advantage greatly
improves reliability of the overall solution.
specifi cally designed to drive a constant current buck-
boost-buck power converter. This patent pending control
scheme features two identical current sense comparators
for detecting negative current signal levels. One of the
comparators regulates the output LED current, while the
other is used for sensing the input inductor current. The
second comparator is mainly responsible for the converter
start-up. The control scheme inherently features low inrush
current and input under-voltage protection. The HV9931 can
operate with programmable constant frequency or constant
off-time. In many cases, the constant off-time operating mode
is preferred, since it improves line regulation of the output
current, reduces voltage stress of the power components
and simplifi es regulatory EMI compliance. (See Application
Note AN-H52.)
Input Voltage Regulator
The HV9931 can be powered directly from its VIN pin, and
takes a voltage from 8V to 450V. When a voltage is applied
at the VIN pin, the HV9931 seeks to maintain a constant
7.5V at the VDD pin. The V
reference for the current sense comparators. The regulator
is equipped with an under-voltage protection circuit which
shuts off the HV9931 when the voltage at the VDD pin falls
below 6.2V.
The VDD pin must be bypassed by a low ESR capacitor
(≥ 0.1µF) to provide a low impedance path for the high
frequency current of the output GATE driver.
The HV9931 is a peak current-mode controller that is
DD
voltage can be also used as a
4
The HV9931 can also be operated by supplying a voltage
at the VDD pin greater than the internally regulated voltage.
This will turn off the internal linear regulator and the HV9931
will function by drawing power from the external voltage
source connected to the VDD pin.
PWM Dimming and
Wall Dimmer Compatibility
PWM Dimming can be achieved by applying a TTL-
compatible square wave signal at the PWMD pin. When the
PWMD pin is pulled high, the GATE driver is enabled and the
circuit operates normally. When the PWMD pin is left open
or connected to GND, the GATE driver is disabled and the
external MOSFET turns off. The HV9931 is designed so that
the signal at the PWMD pin inhibits the driver only, and the
IC need not go through the entire start-up cycle each time
ensuring a quick response time for the output current.
The power topology requires little fi lter capacitance at
the output, since the output current of the buck stage is
continuous, and since AC line fi ltering is accomplished
through the middle capacitor rather than the output one.
Therefore, disabling the HV9931 via its PWMD or VIN pins
can interrupt the output LED current in accordance with
the phase-controlled voltage waveform of a standard wall
dimmer.
Oscillator
Connecting an external resistor from RT pin to GND programs
switching frequency:
Connecting the resistor from RT pin to GATE programs
constant off-time:
T
F kHz
OFF
S
[
[ ]
µ
s
]
=
=
R K
R K
T
T
[
[
25000
Ω
25
Ω
]
]
+
+
22
22
HV9931