HFC0100—QUASI RESONANT CONTROLLER
OPERATION
The HFC0100 incorporates all the necessary
features needed to a reliable Switch Mode Power
Supply. Its valley detector ensures minimum
Drain-Source voltage switching (Quasi-Resonant
operation). When the output power falls below a
given level, the regulator enters the burst mode.
An internal minimum off time limiter prevents the
free running frequency to exceed 150kHz.
Start-Up
Initially, the IC is self supplying from the internal
high voltage current source unit which drawn
from the HV pin.
The IC starts switching and the internal high
voltage current source unit is stopped as soon as
the voltage on Pin Vcc reaches the threshold
V
CCH
—11.8V.
Before the supply is taken over by the auxiliary
winding of the transformer, the Vcc capacitor
supplies HFC0100 to maintain Vcc.
Quasi-Resonant Operation
The HFC0100 operates in Discontinuous
Conduction Mode (DCM). The valley detector
ensures
minimum
Drain-Source
voltage
switching (Quasi-Resonant operation)
As a result, there are virtually no primary switch
turn on losses and no secondary diode recovery
losses. It ensures the reduction of the EMI noise.
Figure2 shows the valley detector unit.
When the voltage:
(V
DS
−
V
in
)x
N
aux
24k
Ω
x
<
55mV
N
pri
24k
Ω +
R
VSD
Figure 2—Valley Detector
V
DS
100V/div
Valley Switching
4us/div
Figure 3—Valley Switching
To ensure the switching frequency below the
EN55022 start limit---150kHz, HFC0100 employs
an internal minimum off time limiter---7.8μS,
shows as figure 4.
V
DS
—Drain Source Voltage of the primary FET
V
IN
—Input Voltage
N
aux
—Auxiliary Winding Turns of the transformer
N
pri
—Primary Winding Turns of the transformer
The valley detector sends out a valley signal to
turn on the primary FET.
Figure3 shows a typical drain source voltage
waveform with valley switching.
V
DS
100V/div
T
off
≥7.8uS
2us/div
Figure 4—Minimum Off Time Limit
HFC0100 Rev. 1.01
www.MonolithicPower.com
9/23/2011
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
9
MPS [ MONOLITHIC POWER SYSTEMS ]
