KA7525B 查看數據表（PDF） - Fairchild Semiconductor

零件编号

产品描述 (功能)

生产厂家

KA7525B

Power Factor Correction Controller

Fairchild Semiconductor 

KA7525B

Zero Current Detector

KA7525B operates as a critical conduction current mode controller. The power MOSFET is turned on by the zero current

detector and turned off when the peak inductor current reaches the threshold level established by the multiplier output. The

slope of the inductor current is indirectly detected by monitoring the voltage across a separate winding and connecting it to the

zero current detector Pin 5.

Once the inductor current reaches ground level, the voltage across the winding reverses polarity. When the Idet input falls

below 1.8V, the comparator output is triggered to the low state.

To prevent false tripping, 240mV of hysteresis is provided. The zero current detector input is internally protected by two

clamps.

The upper 7.5V clamp prevents input over voltage breakdown while the lower 0.75V clamp prevents substrate injection. An

internal current limit resistor protects the lower clamp transistor in case the Idet pin is accidently shorted to ground.

A watchdog timer function was added to the IC to eliminate the need for an external oscillator when used in stand-alone

applications. The timer provides a means to automatically start or restart the preconverter if the drive output has been off for

more than 300us after the inductor current reaches zero.

Drive Output

The KA7525B contains a single totem-pole output stage specifically designed for direct drive of power MOSFET. The drive

output is capable of up to 500mA peak current with a typical rise and fall time of 130ns, 50ns each with a 1.0nF load.

Additional internal circuitry has been added to keep the drive output in a sinking mode whenever the UVLO is active. This

characteristic eliminates the need for an external gate pull-down resistor. Internal voltage clamping ensures that output driver

is always lower than 13V when supply voltage variation exceeds more than rated Vgs threshold (typ 20V) of the external

MOSFET. This eliminates an external zener diode and extra power dissipation associated with it that otherwise is required for

reliable circuit operation.

12

Share Link: