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HF01B00

Off Line High Voltage Quasi Resonant Regulator

Monolithic Power Systems 

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.

Start-up and VCC UVLO

Initially, the IC is driven by the internal high

voltage current source, which is drawn from the

D pin.

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

11.8V

Regulation Occurs Here

Auxiliary Winding Takes Charge

8V

Drain

Switching Pluses

High voltage

current source

On

Off

Figure 3—VCC UVLO

The lower threshold of VCC UVLO decreases from

8V to 5.5V when fault conditions happen, such as

OLP, OVP, and OTP.

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.

Soft Start

Primary Current

Figure 4—Soft Start

Valley Switching Detection

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.

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

Drain-Source voltage switching, which

contributes to better efficiency and EMI

performance.

HF01B00/01/02/03/04 Rev. 1.2

www.MonolithicPower.com

9

4/9/2013

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© 2013 MPS. All Rights Reserved.

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