HF01B00/01/02/03/04–OFF LINE HIGH VOLTAGE QUASI RESONANT REGULATOR
OPERATION
The HF01B00/01/02/03/04 incorporates all the
necessary features to build a reliable Switch
Mode Power Supply. Its high level of integration
requires very few external components. Quasi-
Resonant operation over entire input/load range
results in high efficiency and better EMI
performance. It also has burst mode operation to
minimize the stand-by power consumption at light
load. Protection features such as latched shutdown
or auto-recovery for over-current, over-voltage or
over-temperature contribute to a safer converter
design without engendering additional circuitry
complexity.
Soft-Start
To reduce stress on the primary MOSFET and
the secondary diode during start-up and to
smoothly establish the output voltage, the
HF01B00/01/02/03/04 has an internal soft-start
circuit that gradually increases the primary
current sense threshold, which determines the
MOSFET peak current during start-up. The pulse
width of the power switching device is
progressively increased to establish correct
operating conditions until the feedback control
loop takes charge.
Start-up and VCC UVLO
Initially, the IC is driven by the internal high
voltage current source, which is drawn from the
D pin.
Soft Start
Primary Current
The IC starts switching and the internal high-
voltage current source turns off as soon as the
voltage on pin Vcc reaches 11.8V. At this point,
the supply of the IC is taken over by the auxiliary
winding of the transformer, when Vcc falls below
8V, the regulator stops switching and the internal
high-voltage current source turns on again.
Vcc
Regulation Occurs Here
Auxiliary Winding Takes Charge
Figure 4—Soft Start
11.8V
Valley Switching Detection
8V
The
HF01B00/01/02/03/04
operates
in
Discontinuous Conduction Mode (DCM). The
valley switching detector ensures minimum
Drain-Source voltage switching, per Quasi-
resonant operation.
Drain
Switching Pluses
Valley switching detection is accomplished
through monitoring the voltage of the auxiliary
winding at the VSD pin. The voltage presents a
flyback polarity and the valley switching detection
threshold is 45mV. When the voltage on auxiliary
winding falls below 45mV, the drain-source
voltage of the MOSFET become the lowest,
which is called ‘valley point’, at this point the
valley switching detector activates the controller
to switch on the MOSFET to ensure the minimum
High voltage
current source
On
Off
Figure 3—VCC UVLO
Drain-Source
voltage
switching,
which
The lower threshold of VCC UVLO decreases from
8V to 5.5V when fault conditions happen, such as
OLP, OVP, and OTP.
contributes to better efficiency and EMI
performance.
HF01B00/01/02/03/04 Rev. 1.2
4/9/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
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