AN4205 datasheet(18/23 Pages) STMICROELECTRONICS

Part #	AN4205

Description	The most recent developments in energy savings fit perfectly

PDF	23 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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18 / 23 page

Output stage setting

AN4205

18/23

Doc ID 023929 Rev 1

Figure 12.

Operating point of the Power MOSFET

4.1

Switching regulation

The switching regulation adjusts the VDS voltage of the Power MOSFET (M2) device in order

to decrease the power losses during the linear regulation. In particular this type of regulation

first reads the VDS voltage of the Power MOSFET in series to the LED components and then

controls the out voltage (VBus) in order to fix VDS in order to minimize the power losses in the

power transistor. When the VDS voltage reaches the maximum threshold (fixed by the

specification), the IDS (IOUT) current has already reached the 350 mA value, thus triggering

the switching regulation.

Vds

Ids(Iout)

Ids=350mA

Vds=300 mV

Vgs

Vds [V]

Ids(Iout) [ A]

AM16378v1

AN4205 Datasheet(PDF) 18 Page - STMicroelectronics