Specifications

4
Increase Safety with Remote Disable
Feature
Remote disable offers a safe way to
shut down a power supply to respond
to some particular operating condi-
tion or to protect system operators
(in response to a cabinet door being
opened unexpectedly or someone
pushing a panic button, for instance).
Remote inhibit (RI) is an input to the
power supply that disables the output
when the RI terminal is pulled low
(Figure 1). Shorting the normally open
switch turns off the supply’s output.
You could also use a logic chip with
an open collector transistor output
instead of the switch. Figure 1 also
shows the discrete fault indicator
(DFI), which you can use to signal
an operator or other components in
the system whenever the power sup-
ply detects a user-defined fault.
Almost any operating condition can
create a DFI signal. For example, to
generate a DFI signal when the load
draws excessive current, enable the
over current protection (OCP) mode,
program the unit to generate a DFI
signal when it enters constant current
mode, then program the maximum
current the load normally draws. If
the load current exceeds the maximum,
the DFI output goes low, disables the
power supply, and informs the opera-
tor of the over-current condition (or
performs another user-defined func-
tion), without tying up the system bus
or interrupting the system controller.
You can daisy chain DFI and RI as
shown in Figure 2. If one supply
detects a fault, all supplies in the
system are disabled. Using this
approach, you can chain together
an unlimited number of supplies.
Figure 1. Remote inhibit and discrete fault
indicator schematic
Figure 2. Daisy-chained DFI and RI
Tip
3