HR2000 — FLUORESCENT LAMP HB DRIVER WITH PFC

HR2000 Rev. 1.0

www.MonolithicPower.com

15

2/20/2013

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© 2013 MPS. All Rights Reserved.

Preheat State

When Vvcc>Vvcc(start) & VPreFT<Vfault(reset),

HR2000 gets into Preheat state from the start up

state. During this state, Pre/FT pin’s detection

function will be disabled. High voltage will be sent

out in this state.

During this state, CP/EOL pin will disable EOL

detection function and only take the timing

function.

In this state, only CS pin has a current limit

function. If Vcs>Vcs(pre) in a switching period,

the FC pin will be discharged by an internal

current source IFC(disch) cycle-by-cycle. This

controls the working frequency.

Ignition State

Ignition state follows preheat state closely. In this

state, EOL protection and CS(pre) limit are

disabled. FC voltage increases which results in

frequency decreasing. Then the voltage on lamp

gets higher and higher to ignite the lamp.

CP/EOL pin also only takes timing function in this

state. Once preheat state is over, Pre/FT pin is

dropped to Vfault(reset2), and then the detection

function is active. If Pre/FT pin VPreFT>Vfault(ref)

& low side drive is high, then HR2000 will

consider it is fault state.

After

preheat

state,

CS

pin

over

current

protection is active and limits CS voltage (power

stage current).

When Vcs>Vcs(clamp) @ low side drive=high,

the impedance of CS pin will become very small

and a current flows into this pin. The koc of this

current will charge the CT pin to increase

frequency. The low side MOSFET will be turned

off quickly while high side MOSFET will not be

affected. This results in a narrow turn on time of

low side MOSFET and a relatively larger turn on

time of high side MOSFET. This asymmetric

operation of half bridge limits the output power.

Burn state

After ignition state, Burn state is entered. At the

beginning of burn state, CP/EOL pin will be

dropped to the middle level of the EOL detection

window Veol(middle). Then the EOL detection

function is active instead of the timing function.

Voltage on FC pin will continue to increase until it

reaches a clamping level. CS pin over current

protection mentioned in ignition state is still used

to limit CS voltage (power stage current).

Protection

In oscillation state, the half-bridge protection

includes:

EOL protection

Capacitive mode protection

Current limit

VCC low protection

Over temperature protection

EOL protection

‘End of Life’(EOL) protection is enabled after

CP/EOL is dropped to Veol(middle). There is a

window comparator for this protection. If the

voltage

on

CP/EOL

pin

get

out

of

Veol(low)~Veol(high), then the current source

Ifault(ch) will charge the capacitor at Pre/FT pin.

If VPreFT>Vfault(ref), then HR2000 will get into

fault state.

This protection is disabled in PFC Vo-low state.

Capacitive mode protection

The capacitive mode protection is active during

all oscillating states. It is detected by the voltage

on CS at the moment of turning on of low side

MOSFET. If at this moment, Vcs>Vcs(cap), then

capacitive mode is confirmed and FC pin is

discharged at this switching cycle. VFC will

decrease

towards

zero

which

means

the

maximum frequency if the capacitive mode

always exists. If capacitive mode @ fmax is

detected, then Ifault(ch) is actived to charge the

capacitor at Pre/FT pin.

Current limit

The current limit is realized on CS pin. There are

three kinds of limitation on CS pin.

Vcs(pre) in preheat state;

Vcs(clamp) of over current protection function in

oscillating states;