NCP1336 데이터 시트보기 (PDF) - ON Semiconductor

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NCP1336

Quasi-Resonant Current Mode Controller for High Power Universal Off-Line Supplies

ON Semiconductor 

NCP1336A/B

VCO Mode

VCO operation occurs for FB voltage lower than 0.8 V

(FB decreasing), or lower than 1.6 V (FB increasing). This

corresponds to low output power.

During VCO operation, the peak current is fixed to 25%

of its maximum value and the frequency is variable and

expands as the output power decreases.

The frequency is set by the end of charge of Ct capacitor.

This capacitor is charged with a constant current source and

1 iout

800m

600m

400m

200m

0

2 vct

3 v(fbint:x1) 5 drv

7.00

5.00

3.00

1.00

−1.00

the capacitor voltage is compared to an internal threshold

fixed by FB voltage (see Figure 6). When this capacitor

voltage reaches the threshold, the capacitor is rapidly

discharged down to 0 V and a new period start. The internal

threshold is inversely proportional to the FB voltage. The

relationship between VFBth and VFB is: VFBth = 6.5 − (10/3)

VFB. When VFB is lower than 0.3 V, Ct voltage is clamped to

VCTmax = 5.5 V. Figure 17 shows the VCO mode at works.

IOUT

1

Ct,

FB threshold

23

30.0

20.0

DRV

10.0

0

5

−10.0

7.57m

7.78m

7.99m

8.20m

8.40m

time in seconds

Figure 17. In VCO Mode, as the Power Output Decreases the Frequency Expands

S

Q

Q

R

Vcc Management

DRV

PNOK

Fault

HV

Vcc

Vdd

ItimerC

CS

FB/4

PWM

PWM

Reset

Comparator

+

-

OPP

Max Ip

Comparator

+

+

-

Ilimit + Vopp

+

Ilimit

IpFlag

R

Q

Q

S

+

-

VtimFault

ItimerD

+

Figure 18. Fault Timer Schematic

Timer

Ctimer

http://onsemi.com

18

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