AN4165 datasheet(24/37 Pages) STMICROELECTRONICS

Part #	AN4165

Description	This document describes a 12 V - 1 A power supply set in non-isolated flyback topology

PDF	37 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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24 / 37 page

Feedback loop calculation guidelines

AN4165

24/37

Doc ID 023661 Rev 1

Feedback loop calculation guidelines

11.1

Transfer function

The set PWM modulator + power stage is indicated with G1(f), while C(f) is the “controller”,

i.e. the network which is in charge of ensuring the stability of the system.

Figure 34.

Control loop block diagram

The mathematical expression of the power plant G1(f) is the following:

Equation 2

where VOUT is the output voltage, Ipkp is the primary peak current, fp is the frequency of the

pole due to the output load:

Equation 3

and fz the frequency of the zero due to the ESR of the output capacitor:

Equation 4

AM11582v1

)

(

)

(

)

(f)

OUT

Vdc

fsw

Ipkp

Vdc

fsw

Ipkp

⋅

2ESR)

·(R

OUT

⋅

·ESR

OUT

⋅

AN4165 Datasheet(PDF) 24 Page - STMicroelectronics