NCP1237 datasheet(16/34 Pages) ONSEMI

Part #	NCP1237

Description	Fixed Frequency Current Mode Controller for Flyback Converters

PDF	34 Pages

Scroll/Zoom	100%

Manufacturer	ONSEMI [ON Semiconductor]

Direct Link	http://www.onsemi.com

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16 / 34 page

NCP1237

http://onsemi.com

CURRENT−MODE CONTROL WITH OVERPOWER COMPENSATION AND SOFT−START

Current Sensing

NCP1237 is a current−mode controller, which means that

the FB voltage sets the peak current flowing in the

inductance and the MOSFET. This is done through a PWM

comparator: the current is sensed across a resistor and the

resulting voltage is applied to the CS pin. VCS is applied to

one input of the PWM comparator through the LEB block.

On the other input the FB voltage divided by KFB sets the

threshold: when VCS reaches this threshold, the output

driver is turned off.

The maximum value for the peak current, VILIM, is set by

a dedicated comparator.

Figure 11. Current Sense Block Schematic

−

tLEB

blanking

KFB

VDD

RFB(up)

−

VILIM

VCS(stop)

tSSTART

Soft−start ramp

Start

Reset

IC Start

IC Stop

Oscillator

DCMAX

Protection

Mode

UVLO

Jitter

HV stop

Latch

Soft−start

IC stop

TSD

Fault

DRV Stage

blanking

PWM

tBCS

NCP1237 Datasheet(PDF) 16 Page - ON Semiconductor

NCP1237 Datasheet(HTML) 16 Page - ON Semiconductor

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