SCY99079ADR2G 데이터 시트보기 (PDF) - ON Semiconductor

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SCY99079ADR2G

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

ON Semiconductor 

VCC

VCC(on)

VCC(min)

VCClatch

VCCreset

Vbulk

BO

signal

Drv

DAP018A/B/C/D/F

Controller waits for the next VCC(on) event (fresh re−start)

restart

VBO(on)

Mains interruption

VBO(off)

The BO information is latched. The next re−start

occurs when VCC hits VCC(on) again

Figure 45. A Brown−out Event Immediately Stops the Driving Pulses

When the bulk comes back to its normal level, the

controller waits for the next VCC(on) event to re−start

pulsing. In this case, the BO re−appears while VCC was still

ok but the controller waits for VCC to ramp down to VCClatch

then performs a fresh re−start before pulsing again.

The bridge resistors can be evaluated using the following

equations:

Rupper

+

VBO,on * VBO,off

IBO

(eq. 1)

Rlower

+

VBORupper

VBO,off * VBO

(eq. 2)

Where VBO = 1 V typical and IBO = 10 mA typical.

Suppose the adapter designer needs a turn−on voltage of

100 Vdc and a turn−off voltage of 50 Vdc, then the upper

resistor would be 4.9 MW and the lower side resistor 100 kW.

The total dissipation for a 330 Vdc bulk rail would amount

to 22 mW.

* Please note that the current source arrangement brings

un−precision to the turn−on voltage only, whereas the

turn−off voltage is only dependent on the VBO reference

voltage.

Frequency Foldback and Skip Cycle

Unlike its predecessor, Speedking II implements a

frequency reduction in low power mode. Also called

frequency foldback, this technique has proven to offer a

good performance, especially in the middle of the power

range. On this controller, the foldback occurs when the peak

current reaches a level set via the original skip pin (pin 5).

Once the peak current reaches this value, via a decrease in

the feedback voltage, the controller freezes it and the only

way to further reduce the output power is to fold the

frequency back. The frequency variation is ensured over a

delta feedback voltage of around 500 mV. When the

frequency hits the frequency limit (Ftrans), the frequency

reduction is stopped. At this point, if the load goes further

down, the feedback voltage drops and when it reaches

300 mV, the controller enters traditional skip−cycle (no

soft−burst).

At full power, the peak current varies according to the

power demand, the switching frequency being fixed to

65 kHz. The feedback voltage is allowed to move between

300 mV and 3.4 V which is the upper feedback limit beyond

which a fault is detected. When the load starts to decrease,

the feedback voltage goes down to impose lower peak

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