STMicroelectronics EVALHVLED815W10 and EVALHVLED815W15 Evaluation Board for the Offline LED Driver with Primary-Sensing and High Power Fact EVALHVLED815W10 データシート
製品コード
EVALHVLED815W10
DocID023409 Rev 5
15/34
HVLED815PF
Device description
34
Moreover, the device is able to work in different modes depending on the LED's driver load
condition (see
condition (see
):
1. QR mode at heavy load. Quasi-resonant operation lies in synchronizing MOSFET's
turn-on to the transformer's demagnetization by detecting the resulting negative-going
edge of the voltage across any winding of the transformer. Then the system works
close to the boundary between discontinuous (DCM) and continuous conduction
(CCM) of the transformer. As a result, the switching frequency is different for different
line/load conditions (see the hyperbolic-like portion of the curves in
edge of the voltage across any winding of the transformer. Then the system works
close to the boundary between discontinuous (DCM) and continuous conduction
(CCM) of the transformer. As a result, the switching frequency is different for different
line/load conditions (see the hyperbolic-like portion of the curves in
Minimum turn-on losses, low EMI emission and safe behavior in short-circuit are the
main benefits of this kind of operation.
main benefits of this kind of operation.
2. Valley-skipping mode at medium/ light load. Depending on voltage on COMP pin, the
device defines the maximum operating frequency of the converter. As the load is
reduced, MOSFET's turn-on does not occur any more on the first valley but on the
second one, the third one and so on. In this way the switching frequency is no longer
increased (piecewise linear portion in
reduced, MOSFET's turn-on does not occur any more on the first valley but on the
second one, the third one and so on. In this way the switching frequency is no longer
increased (piecewise linear portion in
3. Burst mode with no or very light load. When the load is extremely light or disconnected,
the converter enters a controlled on/off operation with constant peak current.
Decreasing the load result in frequency reduction, which can go down even to few
hundred hertz, thus minimizing all frequency-related losses and making it easier to
comply with energy saving regulations or recommendations. Being the peak current
very low, no issue of audible noise arises.
Decreasing the load result in frequency reduction, which can go down even to few
hundred hertz, thus minimizing all frequency-related losses and making it easier to
comply with energy saving regulations or recommendations. Being the peak current
very low, no issue of audible noise arises.
Figure 11. Multi-mode operation of HVLED815PF (constant voltage operation)
4.2
Power section and gate driver
The power section guarantees safe avalanche operation within the specified energy rating
as well as high dv/dt capability. The Power MOSFET has a V
as well as high dv/dt capability. The Power MOSFET has a V
DSS
of 800 V min. and a typical
R
DS(on)
of 6
.
The internal gate driver of the Power MOSFET is designed to supply a controlled gate
current during both turn-on and turn-off in order to minimize common mode EMI. Under
UVLO conditions an internal pull-down circuit holds the gate low in order to ensure that the
Power MOSFET cannot be turned on accidentally.
current during both turn-on and turn-off in order to minimize common mode EMI. Under
UVLO conditions an internal pull-down circuit holds the gate low in order to ensure that the
Power MOSFET cannot be turned on accidentally.
AM13561v1
0
f
sw
Pinmax
Input voltage
P
in
f
osc
Burst-mode
Valley-skipping
mode
Quasi-resonant mode