NCP1237 datasheet(19/34 Pages) ONSEMI

Part #	NCP1237

Description	Fixed Frequency Current Mode Controller for Flyback Converters

PDF	34 Pages

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Manufacturer	ONSEMI [ON Semiconductor]

Direct Link	http://www.onsemi.com

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19 / 34 page

NCP1237

http://onsemi.com

Figure 15. Overpower Compensation Current Relation to Feedback Voltage and Input Voltage

VFB

IOPC

VFB(fold)

VFB(OPC)

VHV

Feedback with Slope Compensation

The ratio from the FB voltage to the current sense setpoint

is typically 5. This means that the FB voltage corresponding

to VILIM is 3.5 V. There is a pullup resistor of 20 kW

(typical) from FB pin to the internal reference VFB(ref).

Figure 16. FB Circuitry

−

t LEB

blanking

VDD

Oscillator

20 kW

K FB

slope

comp.

PWM

In order to allow the NCP1237 to operate in CCM with a

duty cycle above 50%, a fixed slope compensation is

internally applied to the current−mode control. The slope

appearing on the internal voltage setpoint for the PWM

comparator is −32.5 mV/

ms typical for the 65 kHz version

(and respectively −50 mV/

ms and −67 mV/ms for the

100 kHz and 133 kHz versions).

NCP1237 Datasheet(PDF) 19 Page - ON Semiconductor