NCP1216A 데이터 시트보기 (PDF) - ON Semiconductor

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NCP1216A

PWM Current-Mode Controller for High-Power Universal Off-Line Supplies

ON Semiconductor 

NCP1216, NCP1216A

the nominal switching frequency whose sweep is

synchronized with the VCC ripple. For instance, with a 2.2 V

peak−to−peak ripple, the NCP1216P065 frequency will

equal 65 kHz in the middle of the ripple and will increase as

VCC rises or decrease as VCC ramps down. Figure 20

portrays the behavior we have adopted:

To better understand how this skip cycle mode takes place,

a look at the operation mode versus the FB level

immediately gives the necessary insight:

FB

VCCOFF

VCC Ripple

68 kHz

4.2 V, FB Pin Open

65 kHz

62 kHz

VCCON

Figure 20. VCC Ripple is Used to Introduce a

Frequency Jittering on the Internal Oscillator

Sawtooth

Skipping Cycle Mode

The NCP1216 automatically skips switching cycles when

the output power demand drops below a given level. This is

accomplished by monitoring the FB pin. In normal

operation, pin 2 imposes a peak current accordingly to the

load value. If the load demand decreases, the internal loop

asks for less peak current. When this setpoint reaches a

determined level, the IC prevents the current from

decreasing further down and starts to blank the output

pulses: the IC enters the so−called skip cycle mode, also

named controlled burst operation. The power transfer now

depends upon the width of the pulse bunches (Figure 22).

Suppose we have the following component values:

Lp, primary inductance = 350 mH

Fsw, switching frequency = 65 kHz

Ip skip = 600 mA (or 333 mV / Rsense)

The theoretical power transfer is therefore:

1

2

Lp

Ip2

Fsw + 4 W.

(eq. 8)

If this IC enters skip cycle mode with a bunch length of

10 ms over a recurrent period of 100 ms, then the total power

transfer is:

4 0.1 + 400 mW.

(eq. 9)

Normal Current Mode Operation

Skip Cycle Operation

IpMIN = 333 mV / Rsense

3.2 V, Upper

Dynamic Range

1V

Figure 21.

When FB is above the skip cycle threshold (1.0 V by

default), the peak current cannot exceed 1.0 V/Rsense. When

the IC enters the skip cycle mode, the peak current cannot go

below Vpin1 / 3.3. The user still has the flexibility to alter this

1.0 V by either shunting pin 1 to ground through a resistor

or raising it through a resistor up to the desired level.

Grounding pin 1 permanently invalidates the skip cycle

operation.

Power P1

Power

P2

Power

P3

Figure 22. Output Pulses at Various Power Levels

(X = 5 ms/div) P1 < P2 < P3

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