Functional description

AN1336

Figure 2: Supply hold-up

This is a result of the RC time constant inherent to most power supplies (see Figure 3: "Typical power

slew rate. Thus when the AC input fails, this capacitance will continue to power the circuit for several

milliseconds, typically in the order of 10 ms or more.

Figure 3: Typical power supply

Power-Fail Warning

Supply Hold-up

Power-Fail Output

Regulated Output Voltage

AC Input

AI04223

VUNREG

VCC

C1

C2

C3

REGUL ATOR

AI042222

2/10

DocID007594 Rev 2