L6561

4/13

3

OVER VOLTAGE PROTECTION OVP

The output voltage is expected to be kept by the operation of the PFC circuit close to its nominal value.

This is set by the ratio of the two external resistors R1 and R2 (see fig. 5), taking into consideration that

the non inverting input of the error amplifier is biased inside the L6561 at 2.5V.

In steady state conditions, the current through R1 and R2 is:

equals zero.When the output voltage increases abruptly the current through R1 becomes:

Since the current through R2 does not change,

error amplifier.

This current is monitored inside the L6561 and when reaches about 37

µA the output voltage of the multi-

plier is forced to decrease, thus reducing the energy drawn from the mains. If the current exceeds 40

µA,

the OVP protection is triggered (Dynamic OVP), and the external power transistor is switched off until the

current falls approximately below 10

µA.

However, if the overvoltage persists, an internal comparator (Static OVP) confirms the OVP condition

keeping the external power switch turned off (see fig. 4).Finally, the overvoltage that triggers the OVP

function is:

5

Lower Clamp Voltage

0.3

0.65

1

V

5

Sink Bias Current

1V

2

µA

5

Source Current Capability

-3

-10

mA

5

Sink Current Capability

3

10

mA

5

Disable threshold

150

200

250

mV

5

Restart Current After Disable

-100

-200

-300

µA

OUTPUT SECTION

7

Dropout Voltage

1.2

2

V

0.7

1

V

1.5

V

0.3

V

7

Output Voltage Rise Time

40

100

ns

7

Output Voltage Fall Time

40

100

ns

7

IGD Sink Current

5

10

-

mA

OUTPUT OVERVOLTAGE SECTION

2

OVP Triggering Current

35

40

45

µA

Static OVP Threshold

2.1

2.25

2.4

V

RESTART TIMER

Start Timer

70

150

400

µs

Table 5. Electrical Characteristics (continued)

Symbol

Pin

Parameter

Test Condition

Min.

Typ.

Max.

Unit

I

R1sc

V

out

2.5

–

R1

--------------------------

I

R2

2.5V

R2

------------

==

=

I

R1

V

outsc

V

out

2.5

–

∆

+

R1

-----------------------------------------------------

I

R1sc

I

R1

∆

+

==