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

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 M

Ω 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

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

Ic ha rge

IHV

CO NTRO L

Mai ns UV LO

Vcc_O K

HV_EN

12M

14 V

S OURCE

DRAIN

Vcc