HF01B00/01/02/03/04

–OFF LINE HIGH VOLTAGE QUASI RESONANT REGULATOR

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

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4/9/2013

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winding.

The plateau voltage of the auxiliary winding is

sampled at the VSD pin with a 3.5us delay after

the turn-off sequence. Otherwise, the ringing

cause by transformer leakage inductance may

unintentional trigger the OVP.

3.5us

OVP Sample

Figure 9

—OVP Sample Delay

Over Load Protection (OLP)

In a flyback converter, the maximum output

power is limited by the maximum switching

frequency and primary peak current. If the load

consumes more than the maximum output power,

output voltage will drop below the set point. This

reduces the current through the optocoupler LED

by the negative feedback control loop, and thus

FB voltage goes up.

The voltage at the FB Pin is continuously

monitored. When the feedback voltage exceeds

and enters a safe low-power operating mode that

prevents from any lethal thermal or stress

damage. As soon as the fault disappears, the IC

resumes switching. Thus the circuit operates in a

burst manner, called auto-recovery. During fault

down from 8V to 5.5V.

During the start-up phase or load transient, the

FB voltage stays high enough temporarily to

mis-trigger the OLP, to prevent this undesired

protection, OLP circuit is designed to be triggered

after Vcc is decreased below 8.5V.

Burst Operation

To minimize stand-by power consumption, the

HF01B00/01/02/03/04 implement burst mode at

no load or light load. As the load decreases, the

FB voltage decreases. The IC stops switching

when the FB voltage drops below the lower

starts to drop at a rate dependent on the load.

This causes the FB voltage to rise again due to

the negative feedback control loop. Once the FB

switching pulse resumes. The FB voltage then

decreases and the whole process repeats. Burst-

mode operation alternately enables and disables

the switching pulse of the MOSFET. Hence

switching loss at no load or light load conditions

is greatly reduced.

Figure 10 shows the burst mode operation of

HF01B00/01/02/03/04

0.7V

0.5V

Figure 10

—Burst Mode Operation

Thermal shutdown (TSD)

To prevents from any lethal thermal damage, the

HF01B00/01/02/03/04

shuts

down

switching

cycle when the junction temperature exceeds

150 ℃ . As soon as the junction temperature

drops below 110℃, the power supply resumes

operation. During OTP, the lower threshold of the