Datasheet

HVLED805 Application information
Doc ID 18077 Rev 1 13/29
5.1 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(BR)DSS of 800V min. and a
typical R
DSon
of 11 Ω.
The 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.
5.2 High voltage startup generator
Figure 10 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 MΩ 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 pin, while its output is the supply pin of the device (Vcc). 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).
With reference to the timing diagram of Figure 11, 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) from the bulk capacitor.
Figure 10. High-voltage start-up generator: internal schematic
Icharge
IHV
CO NT RO L
Mai ns UV LO
Vcc_OK
HV_EN
12 M14 V
S OURCE
DR AIN
Vcc