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DC Regulator
A 3.3VDC linear regulator is used in order to feed the microcontroller, oscillator and LED indicators.
Control signals
Upon the arrival of the AC Monitor signal to the microprocessor, it is the firmware that defines if this signal
meets the necessary requirements to generate and maintain the control signals ACFAIL/POWERDOWN,
POWERUP/SYSTEMRESET and LINESYNC. All these lines are generated by the microprocessor and go
to the control signals’ output stage.
The ACFAIL/POWER DOWN output lines transition to High at Power Restoration; these lines go Low
(ground true) immediately upon Power Failure. These lines are driven separately.
The SYSRESET/POWERUP output Lines go to High 225 ± 25ms after power restoration and the supply
is fully recovered; these lines go Low 525 ± 25ms after ACFAIL goes Low.
Power up sequence
After detecting the presence of the AC signal the microcontroller set the ACFAIL/PWR DOWN
line to high; if there is no power failure within a 225ms period then the PWR UP/SYS RESET line
is set to high.
Power down sequence:
During a power failure, the ACFAIL/PWR DOWN signal is set to Low immediately, if the power
failure lasts more than 525 ± 25ms then the PWR UP/SYS RESET line is set to Low.
The LINESYNC signal is a continuous square wave signal of +5VDC amplitude, 8.333 ms half-cycle pulse
duration, and 50 ± 1 % duty cycle; it is synchronized to the 60Hz VAC incoming power line at 120 and 300
degree. The LINESYNC signal begins when SYSTEMRESET signal transitions to High; this signal
continues until SYSRESET transitions to Low. The microprocessor compensates for missing pulses
during normal operation.
Control signals output stage
It is used for supplying the appropriate drive sink capability to the control signals on the PS connectors.
This stage consists of two FET’s and three resistors for each control signal, it is arranged for giving an
output of the same logic level as the input; this is, if the control signal coming from the microcontrollers is
HIGH then the output of this stage is also HIGH.
The Linesync output has a drive sink capability of 16 mA. A 2K ohm pull-up resistor is connected between
the output and +5 VDC.
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