STMicroelectronics HVLED805 Evaluation Board EVALHVLED805 EVALHVLED805 Data Sheet

Doc ID 18077 Rev 1

13/29

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.

 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 
generator off if the drain voltage is below V

START

 (50 V typical value).

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) from the bulk capacitor. 

         

Ic ha rge

IHV

CO NTRO L

Mai ns  UV LO

Vc c _O K

H V_ EN

12M

14 V

S OURCE

DRAIN

Vcc