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Remote Trip.
A negative-going edge applied to terminal J3-30 ( TRIPREMOTE ) will shut down the power
supply, reducing the output voltage to near zero. For minimum pulse duration and timing considerations with respect
to
RESETREMOTE , see Table A-1. The following paragraph provides a brief circuit description (see schematic
diagram and Figure A-8).
A negative going edge at
TRIPREMOTE coupled through opto-isolator (U9) causes one-shot U13B to set the
TRIP/RESET latch (U5A) low. This sets terminal J1-13 (
INHIBIT ) low, thus inhibiting the Pulse Width Modulator
of the power supply. It also lights the unregulated indicator on the front panel and generates an unregulated signal
from the opto-isolator U3.
The low signal generated by the Trip/Reset Latch is also coupled through opto-isolator U2 and appears at J3-17 as
an
EOVERVOLTAG status signal. This signal does not affect the state of the power supply's OVP circuit.
Remote Reset. A negative-going edge applied to terminal J3-29 ( RESETREMOTE ) will return the supply to its
initial state following a system-initiated shutdown or an OVP shutdown caused by a temporary over voltage
condition. For minimum pulse duration and timing considerations with respect to
TRIPREMOTE see Table A-1
under Remote Control. The following paragraphs provide a brief description of this circuit (see schematic diagram
and Figure A-8).
A negative-going pulse applied to terminal J3-29 (
RESETREMOTE ) is coupled through opto-isolator U10.
One-Shot U13A then triggers and resets the TRIP/RESET latch output high. This sets terminal J1-13 (
INHIBIT )
high, thus enabling the power supply's Pulse Width Modulator.
The
RESETREMOTE signal will also reset the power supply OVP circuit in the event that an overvoltage
condition has shut down the supply. When a
RESETREMOTE signal is present, ONE SHOT U13A goes low, this
will produce an OV CLEAR pulse at terminal J1-12. The
CLEAROV pulse will cause the output of A2U2 to go
low thus, resetting the OV FLIP FLOP. When this occurs the output of A2U24D goes high and simultaneously
causes the front panel OV LED to turn off and the OV signal (J1-6) to go high. The
EOVERVOLTAG signal to
U4B also goes high and enables the PWM of the power supply .
Note By observing the EOVERVOLTAG status indicator or the power supply's output while applying
a reset pulse to RESETREMOTE , the user can determine the cause of shutdown. If the output
returns and
EOVERVOLTAG goes high immediately, this indicates a controller-initiated
shutdown. If the output takes about one second to return, this indicates that the output voltage had
exceeded the OVP trip point. If the OVP circuit trips continually, check the load and/or the trip
point setting.
Alternate Method of Remote Control. The INHIBITREMOTE input, J3-31, provides an alternate method of
remote shutdown. By maintaining a low logic level at this input, the supply's output will be inhibited until
INHIBITREMOTE is returned to its initial high state. The following paragraph provides a brief description of this
circuit (see schematic diagram and Figure A-8).
A low logic level applied to terminal J3-31 (
INHIBITREMOTE ) is coupled through opto-isolator U8 and causes
U4B to inhibit the power supply's (PWM) Pulse Width Modulator. If jumper W1 is used (see Figure A-8) while a
INHIBITREMOTE signal is applied, an EOVERVOLTAG signal will appear at terminal J3-17
EOVERVOLTAG thus, indicating the power supply shut down.