HF01B00/01/02/03/04

–OFF LINE HIGH VOLTAGE QUASI RESONANT REGULATOR

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

www.MonolithicPower.com

9

4/9/2013

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© 2013 MPS. All Rights Reserved.

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.

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.

11.8V

8V

Vcc

Drain

Switching Pluses

Regulation Occurs Here

Auxiliary Winding Takes Charge

High voltage

current source

On

Off

Figure 3

—V

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.