Driving optimization

AN3973

14/24

Doc ID 022164 Rev 1

4

Driving optimization

The driving circuit optimization has been done in order to have the best performance of the

lighting system. Basically, this circuit concerns MOSFET and BJT transistors and it has

been realized in order to have thermal and electrical behavior of devices compliant to the

system features.

4.1

MOSFET circuit optimization

The elements of circuit optimization are shown below.

Figure 12.

Snubber and driving circuit of MOSFET

A small RC snubber circuit (C=680 pF and R=180

Ω) has been used to prevent voltage

spikes and voltage oscillation across the MOSFET during device turn-off. This means

limiting the rate of rise (

ΔV

current and to have less switching losses during turn-off. The driving circuit (R7=47

Ω and

diode) allows the MOSFET to not turn on too quickly in order to reduce the discharge of

snubber circuit capacitance and consequently to guarantee negligible switch-on losses and,

thanks to the diode, it allows the fastest discharge of parasitic capacitance of the MOSFET

and therefore speeds up switch-off.