0

50

100

150

200

250

300

350

400

0

20

40

60

80

100

% Total Rated Output Power

Discontinuous conduction mode (DCM)

Boundary conduction mode (BCM)

Frequency

foldback mode

(FFM)

V

OUT

SW

FB

VIN

EN/UVLO

TC

GND

SS/BIAS

RSET

LM25183

C

OUT

C

IN

T

1

V

IN

N

D

FLY

R

SET

R

FB

R

TC

C

SS

R

UV1

R

UV2

D

CLAMP

D

F

D

OUT

10

LM25183

SNVSBJ3 – APRIL 2020

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Feature Description (continued)

Figure 15. LM25183 Flyback Converter Schematic (Optional Components in Red)

7.3.2 PSR Flyback Modes of Operation

The LM25183 uses a variable-frequency, peak current-mode (VFPCM) control architecture with three possible

modes of operation as illustrated in Figure 16.

Figure 16. Three Modes of Operation Illustrated by Variation of Switching Frequency With Load

The LM25183 operates in boundary conduction mode (BCM) at heavy loads. The power MOSFET turns on when

the current in the secondary winding reaches zero, and the MOSFET turns off when the peak primary current

reaches the level dictated by the output of the internal error amplifier. As the load is decreased, the frequency

increases to maintain BCM operation. Equation 1 gives the duty cycle of the flyback converter in BCM.