NCP1237 datasheet(15/34 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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15 / 34 page

NCP1237

http://onsemi.com

Oscillator with Maximum Duty Ratio and Frequency

Jittering

The NCP1237 includes an oscillator that sets the

switching frequency with an accuracy of

$7%. The

maximum duty ratio of the DRV pin is 80% (typical), with

an accuracy of

$7%.

In order to improve the EMI signature, the switching

frequency jitters around its nominal value, with a

triangle−wave shape.

Figure 9. Frequency Jittering

Time

fOSC

fOSC + Ajitter

Nominal fOSC

fOSC - Ajitter

1 / Fjitter

Clamped Driver

The supply voltage for the NCP1237 can be as high as

28 V, but most of the MOSFETs that will be connected to the

DRV pin cannot tolerate a gate−to−source voltage greater

than 20 V on their gate. The driver pin is therefore clamped

safely below 16 V.

Figure 10. Clamped Driver

DRV

Clamp

DRV signal

VCC

This driver has a typical current capability of

±1.0 A.

NCP1237 Datasheet(PDF) 15 Page - ON Semiconductor