KA7526D View Datasheet(PDF) - Fairchild Semiconductor

Part Name

Description

Manufacturer

KA7526D

Power Factor Correction Controller

Fairchild Semiconductor 

KA7526

Current Sense

Comparator

CS

+

-

4

+

1.65V

Vref

3

MULT

Vm1

Vmo

Error Amp.

- Vm2 +

++

-

1

INV

2

EA OUT

Fig.3.1 Multiplier Block

Current Sense Comparator

The current sense comparator adopt the RS latch configuration to ensure that only a single pulse appears at the drive output

during a given cycle. MOSFET drain current is converted to voltage using an external sense resistor in series with the external

power MOSFET. When sense voltage exceeds the threshold set by the multiplier output, the current sense comparator termi-

nates the gate drive to the MOSFET and resets the PWM latch. The latch insures that the output remains in a low state after the

MOSFET drain current falls back to zero.

The peak inductor current under normal operating conditions is controlled by the multiplier output, Vmo.

Abnormal operating conditions occur during preconverter start-up at extremely high line or as output voltage sensing is lost.

Under these conditions, the multiplier output and current sense threshold will be internally clamped to 1.65V. Therefore, the

maximum peak switch current is limited to:

Ipk(max) = 1.65V / Rsense

An internal R/C filter has been included to attenuate any high frequency noise that may be present on the current waveform.

This circuit block eliminates the need for an external R/C filter otherwise required for proper operation of the circuit.

+

-

1.65V

cs

4

Rsense

Multiplier

Output

External R/C Filter

can be eliminated

Fig. 4.1 Current Sense Circuit

12

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