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

sideration 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:

=

− 2.5

R1

=

2.5V

R2

and, if the external compensation network is

When the output voltage increases abruptly the

current through R1 becomes:

R1

Since the current through R2 does not change,

enter the 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 condi-

tion keeping the external power switch turned off

(see fig. 1).

Finally, the overvoltage that triggers

the OVP

function is:

application circuits. The overvoltage can be set inde-

pendently from the average output voltage. The pre-

cision in setting the overvoltage threshold is 7% of

ELECTRICAL CHARACTERISTICS (continued)

ZERO CURRENT DETECTOR

Symbol

Pin

Parameter

Test Condition

Min.

Typ.

Max.

Unit

5

Input Threshold Voltage

Rising Edge

(1)

2.1

V

Hysteresis

(1)

0.3

0.5

0.7

V

5

Upper Clamp Voltage

µA

4.5

5.1

5.9

V

5

Upper Clamp Voltage

4.7

5.2

6.1

V

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

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

(1) Parameter guaranteed by design, not tested in production.

L6561

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