NCP1027 データシートの表示（PDF） - ON Semiconductor

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NCP1027

High−Voltage Switcher for Medium Power Offline SMPS Featuring Low Standby Power

ON Semiconductor 

NCP1027

The bridge power dissipation is 3302/3.018 Meg =

36 mW in nominal high−line operation. Figure 30b

simulation result confirms our calculations.

Figure 31 describes signal variations during a brown−out

condition. Please note that output pulses only reappear

when VCC reaches VCC(ON), ensuring a clean startup

sequence. As in fault mode conditions, the startup source

is activated on and off and self−supplies the controller in a

Dynamic Self−Supply (DSS) mode.

Figure 31. Signal Evolution During a Brown−Out Condition

Depending on input surge tests, it might be necessary to

wire a filtering capacitor between BO and GND (close to

the circuit) to avoid adversely triggering the internal latch

(unless this is a wanted feature) when the pulse train

appears.

Latchoff Protection

There are some situations where the converter shall be

fully turned−off and stay latched. This can happen in the

presence of a secondary overvoltage (the feedback loop is

drifting) or when an overtemperature is detected.

Secondary monitoring is usually implemented when the

coupling between auxiliary and power windings does not

lead to a precise primary detection, hence the

auto−recovery OVP on pin 1 would not satisfy the precision

requirements. Due to the addition of a comparator on the

BO pin, a simple external circuit can lift up this pin above

VLATCH and permanently disable pulses. The VCC needs

to be cycled down below 3.5 V typically to reset the

controller.

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