Fairchild FPS Series, Design Manual

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www.fairchildsemi.com/fps
FPS
™
Design Guide
Green FPS™ Feature – Burst Mode Operation
Current
Waveform
Feedback
Waveform
Burst
Operation
Normal Operation
Not
Switching
Not
Switching
V
BURSTH
V
BURSTL
(Refer to schematic in Typical Application Circuit 40W Isolated Flyback Power Supply on page 24)
• In standby mode, outputs draw very little to no load current
• Output voltages increase causing the feedback voltage to decrease
• When the feedback voltage goes below VBURSTL threshold, switching stops in the FPS device
saving considerable power
• Depending on load current, the output voltages will eventually fall causing the feedback voltage to increase
• Once the feedback voltage crosses VBURSTH threshold, switching starts again
• A 5V output FSD210 board at 265V in no load standby consumes a mere 92mW
Below shows the waveforms of both normal and standby modes at the voltage extremes for the universal
voltage range.
standby normal
standby normal
Burst Operation @ 85VAC Burst Operation @ 265VAC