SCY99079BDR2G 查看數據表（PDF） - ON Semiconductor

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SCY99079BDR2G

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

ON Semiconductor 

DAP018A/B/C/D/F

RoppU

Rbias

This point will

be adjusted to

reduce the ref

at hi line to the

desired level.

Iopp

RoppL

OPP

Dz

VCC aux

+

Swings to:

N1Vout during toff

−N2Vout during ton

VDD

from FB

K1 SUM2

ref

K2

0.8 V ±5%

ref = 0.8 V + VOPP

(VOPP is negative)

Reset

-

+

CS

Figure 54. The Zener Diode can Introduce a Threshold which

Disables OPP at Low Line for Maximum Power Capability

Suppose we need a threshold placed at 150 Vdc. In that

case, give the turn ratio, we need to install a zener diode

featuring the following breakdown voltage:

Vz + 150 0.16 + 24 V

(eq. 8)

In high line conditions (Vbulk = 375 Vdc), the voltage on the

zener diode voltage will now swing to:

(eq. 9)

Vaux + −N2Vin,max ) 24 + −0.16 375 ) 24 + −36 V

Applying Equation 6 again, we have:

ROPPU

+

36 * 0.16

0.16ń1 k

+

224

kW

(eq. 10)

The new compensation now looks like what Figure 55

shows:

Peak current

setpoint

100%

20%

150

375

Vbulk

Figure 55. The Addition of the Zener Diode

Introduces a Threshold at 150 Vdc

The bias resistor Rbias, makes sure that enough current

circulates in the zener diode to make it work far enough from

its knee. The tradeoff includes the power consumption

brought by the addition of this new component. Further

reduction can be obtained by inserting a standard diode in

series with the zener to block the positive excursion.

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