NCP1236 Просмотр технического описания (PDF) - ON Semiconductor

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NCP1236

Fixed Frequency Current Mode Controller for Flyback Converters

ON Semiconductor 

VHV

VHV(start)

VHV(stop)

NCP1236

Brown-out

DRV

Starts at next

VCC(ON)

time

t HV

Figure 33. AC Input Brown−out Timing Diagram

time

Oscillator with Maximum Duty Cycle and Frequency

Jittering

The NCP1236 includes an oscillator that sets the

switching frequency with an accuracy of $7%. Two

frequency options can be ordered: 65 kHz and 100 kHz. The

maximum duty cycle of the DRV pin is 80%, with an

accuracy of $7%.

In order to improve the EMI signature, the switching

frequency jitters $6% around its nominal value, with a

triangle−wave shape and at a frequency of 125 Hz. This

frequency jittering is active even when the frequency is

decreased to improve the EMI in light load condition.

fOSC

fOSC + 6

Nominal fOSC

fOSC − 6

Clamped Driver

The supply voltage for the NCP1236 can be as high as

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

DRV pin cannot accept more than 20 V on their gate. The

driver pin is therefore clamped safely below 16 V. This

driver has a typical current capability of $500 mA.

VCC

Clamp

DRV signal

DRV

Figure 35. Clamped Driver

8%

(125 Hz)

Figure 34. Frequency Jittering

Time

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