| 摘要 |
A power failure indicator circuit (8) for a pulse width modulated power supply (10) compares the averaged voltage of the pulse width modulated signal to an input reference voltage (42) to determine if power failure of the supply will occur. The reference voltage corresponds to a predetermined proportion of the maximum average voltage of the pulse width modulated signal. In a preferred embodiment, the pulse width modulated signal is inverted (38) and filtered (40) to generate an averaged signal corresponding to the DC input voltage to the modulator within the pulse width modulated power supply (10). A comparator (44) compares the averaged signal voltage to the reference voltage to determine if the averaged signal voltage level has fallen below the reference voltage level. If the averaged signal voltage level does drop below the reference voltage level, the comparator (44) generates a signal warning of power failure of the power supply (10). |
