AC Good Circuit
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Described is a hardware implementation to provide an AC good signal for power supplies. The circuit described may be used in power supplies which use active power factor correction circuits as well as conventional VAC input power supplies.
AC Good Circuit
a hardware implementation to provide an AC good
signal for power supplies. The circuit described may be used in
power supplies which use active power factor correction circuits as
well as conventional VAC input power supplies.
shows the circuit representation for sensing the AC
voltage and generating a positive AC good signal. The AC good
circuit consists of bi-polar transistors Q1 and Q2, resistors R1
through R11, diodes D1 through D6, optical isolator ZM1, voltage
comparator ZM2, and capacitors C1 and C2. Bias voltage Vcc
a positive source voltage for the isolated portion of the circuit.
The AC good
circuit described functions in two modes: Normal
Turn-on Sequence and Turn-off Sequence.
Figure, diodes D1 through D4 are connected to the input
VAC line is such a way to form a full wave rectification of the AC
voltage. This generates a positive voltage at A with respect to B.
The voltage at A is filtered by capacitor C1 and divided down by the
voltage divider resistors R1 and R2. Capacitor C2 along with
resistor R1 provides a time delay and second filtering before
applying the voltage to the cathode of zener diode D5.
voltage at the cathode of D5 increases to the
breakdown voltage of D5, D5 begins to conduct. This action allows
current to flow into the base of transistor Q1 turning Q1 on. When
Q1 turns on, current is pulled through the light emitting diode of
optical isolator ZM1 which turns on the isolated transistor within
internal transistor of ZM1 turns on, current is pulled
through resistor R6 and the voltage at the ZM1 transistor collector
is pulled toward ground. Once the voltage at...