AN4164 datasheet(14/38 Pages) STMICROELECTRONICS

Part #	AN4164

Description	This document describes a 12 V-350 mA power supply set in non-isolated flyback topology

PDF	38 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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14 / 38 page

Testing the board

AN4164

14/38

Doc ID 023660 Rev 1

5.3

Burst mode and output voltage ripple

When the converter is lightly loaded, the COMP pin voltage decreases. As it reaches the

shutdown threshold, VCOMPL (1.1 V, typical), the switching is disabled and the energy is

not transferred to the secondary side anymore. At this point, the feedback reaction to the

stop of the energy delivery makes the COMP pin voltage increase again. As it rises 40 mV

above the VCOMPL threshold, the normal switching operation is resumed. This results in a

controlled on/off operation which is referred to as “burst mode”. This mode of operation

keeps the frequency-related losses low when the load is very light or disconnected, making

it easier to comply with energy saving regulations.

The figures below show the output voltage ripple when the converter is no/lightly loaded and

supplied with 115 VAC and with 230 VAC respectively.

Figure 17.

Output voltage ripple at 115 VAC

no load

Figure 18.

Output voltage ripple at 230 VAC

no load

AM11692v1

AM11693v1

Figure 19.

Output voltage ripple at 115 VAC

25 mA

Figure 20.

Output voltage ripple at 230 VAC

25 mA

AM11694v1

AM11695v1

AN4164 Datasheet(PDF) 14 Page - STMicroelectronics