HR2000 — FLUORESCENT LAMP HB DRIVER WITH PFC

HR2000 Rev. 1.0

www.MonolithicPower.com

16

2/20/2013

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Capacitive protection in oscillating states.

They have been described in the related states

above.

VCC low protection

It is mentioned in VCC under voltage state.

Over temperature protection (OTP)

It is described in OTP state.

PFC part

In the typical application, PFC can be defined to

3 states:

Normal state;

VO-low state;

OVC state;

Normal state

PFC works at boundary conduction mode (BCM)

with Ton control. Fig3 shows the internal block.

Figure 3— PFC part block

The Ton is set by the voltage at Vo pin. Higher

Vvo, shorter Ton. The circuit in Fig1 shows the

example. ZCD pin detects the inductor current

zero-crossing point. When The Vzcd<Vzcdref,

Gate will be high and the external MOSFET will

be turned on.

In the range of Vvo(low)~Vvo(off), Ton varies

linearly from Ton(max) to zero. When Vvo>

Vvo(off), Ton is zero, and GATE pin is low.

The minimum turn off time is set internally to

1.4µs.

Vo-low state

In case of main voltage too low, PFC may not

maintain its intended output voltage. In order to

keep on working, the current sunk into Vo pin

is monitored. If it is lower than Ivo(low) the IC will

get into Vo-low state.

In Vo-low state:

There is a current Ifault(disch) to discharge

Pre/FT pin. This can increase the protection level.

EOL protection is disabled.

Vovc<Vovc(low) will overrule Vo-low condition.

OVC state

OVC pin monitors PFC output voltage and Boost

PFC MOSFET current. Fig1 shows the example.

If Vovc>Vovcref or Vovc<Vovclow, then PFC will

stop immediately.

Vovclow is set to prevent the absence of PFC

output detection.