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
Device description
HVLED815PF
16/34
DocID023409 Rev 5
4.3
High voltage startup generator
shows the internal schematic of the high voltage start-up generator (HV
generator). It includes an 800 V-rated N-channel MOSFET, whose gate is biased through
the series of a 12 M
the series of a 12 M
resistor and a 14 V Zener diode, with a controlled, temperature
compensated current generator connected to its source.
The HV generator input is in common with the DRAIN pins, while its output is the supply pin
of the device (VCC pin). A mains “UVLO” circuit (separated from the UVLO of the device
that sense VCC) keeps the HV generator off if the drain voltage is below V
of the device (VCC pin). A mains “UVLO” circuit (separated from the UVLO of the device
that sense VCC) keeps the HV generator off if the drain voltage is below V
START
(50 V
typical value).
Figure 12. High voltage start-up generator: internal schematic
With reference to the timing diagram of
, when power is applied to the circuit and
the voltage on the input bulk capacitor is high enough, the HV generator is sufficiently
biased to start operating, thus it will draw about 5.5 mA (typical) to the V
biased to start operating, thus it will draw about 5.5 mA (typical) to the V
CC
capacitor.
Most of this current will charge the bypass capacitor connected between the VCC pin and
ground and make its voltage rise linearly. As soon as the VCC pin voltage reaches the
V
ground and make its voltage rise linearly. As soon as the VCC pin voltage reaches the
V
CC_ON
turn on threshold (13 V typ.) the chip starts operating, the internal Power MOSFET
is enabled to switch and the HV generator is cut off by the Vcc_OK signal asserted high.
The IC is powered by the energy stored in the V
The IC is powered by the energy stored in the V
CC
capacitor.
The chip is able to power itself directly from the rectified mains: when the voltage on the
VCC pin falls below V
VCC pin falls below V
CC_RESTART
(10.5 V typ.), during each MOSFET's off-time the HV
current generator is turned on and charges the supply capacitor until it reaches the V
CC_ON
threshold.
In this way, the self-supply circuit develops a voltage high enough to sustain the operation of
the device. This feature is useful especially during constant current (CC) regulation, when
the flyback voltage generated by the auxiliary winding alone may not be able to keep VCC
pin above V
the device. This feature is useful especially during constant current (CC) regulation, when
the flyback voltage generated by the auxiliary winding alone may not be able to keep VCC
pin above V
CC_RESTART
.
AM13562v1
VCC
Icharge
CONTROL
Mains UVLO
IHV
DRAIN
12M
HV_EN
Vcc_OK
14V
GND