power switches with programmable trip characteristics designed for
use as solid-state replacements for 3- to 20-ampere circuit breakers.
· Externally programmable for trip delay and current trip prints.
· Status reporting permits remote sensing of trip, over-temperature,
· Low junction-to-case thermal resistance--achieved through
require low cost and high reliability power control.
functions, including power control, fall under its command. Since
mechanical circuit breakers do not lend themselves to this type of
control, a solid-state solution was developed. Solid-State Power
Controllers (SSPCs) were the result.
the mechanical circuit breaker. These devices protect wire harnesses
from overheating, which may result from abnormally high current
drains due to a malfunctioning system component.
on and off. Turning on into capacitive loads results in high inrush
currents that may be more than 10 times their rated currents.
Conversely, turning off highly inductive loads results in a large
voltage, or inductive kick, which can exceed their voltage rating.
Contact erosion caused by arcing in these load types severely
limits circuit breaker life and produces severe EMI problems.
When this strip heats, due to I
portional to the temperature, and the temperature is proportional
to the length of time it has dissipated its I
contact closure. The soft turn-on feature of SSPCs reduces the peak
inrush current into capacitive loads, reducing EMI emissions greatly.
In addition, during turn-off of inductive loads, stored energy can be
dissipated in the pass element as well as a shunt diode.
rated current. This forms the upper limit of the I
400% of rated load. With decreasing current, the trip time increases.
At rated current, the unit will trip in 10 seconds. As a convenience
to our customers, NHI has designed its SSPC to allow external pro-
gramming of both the instant trip point and the trip time.
lowest possible thermal resistance. Being a matched TCE system, the
package will withstand stringent environmental conditions. The flexibility
of the unique construction of the Series 90000 package allows for quick
and inexpensive custom configurations.
feature. If the load current exceeds 400% of nominal rating, the
unit will trip in less than 25µ seconds.*
The temperature of the switching elements is constantly moni-
tored. If their temperature exceeds a safe limit, the unit will turn
off and report an "over temperature" fault on its status outputs.
Restart is automatic when the unit cools down approximately
15°C. For certain applications involving "battle override" require-
ments, the unit can be supplied such that an over-temperature
condition is reported on the status output, without protecting
itself by turning off.
status reporting functions, ensuring complete isolation of these
"TTL"-compatible functions from the power line. The control
input is a diode-protected schmitt trigger gate for maximum noise
immunity. The status outputs are "HC" CMOS compatible and
can sink or source a minimum of 4 mA.
est overloads, while severe overloads will trip in milliseconds. By
the addition of an external resistor, the actual trip point can be
lowered to as low as 30% of its nominal rating. This allows a sin-
gle type to be utilized in multiple applications, reducing inventory
ments of MIL-STD-704. The off-state voltage blocking rating
between the power and control/status pins is 100 VDC, with
500V minimum isolation for the 28V models. The 270V models
exhibit 600VDC voltage blocking with a minimum of 1000V isolation.
VDC units use low Vsat IGBTs (<1.2 Volts max.) as the pass
elements. The unique construction of Series 90000 SSPCs utilizes
the high-current input/output tabs as the mounting mechanism,
and the heat sink for the high-power switching elements. The
direct metallurgical bond between the switching elements and
these tabs ensures extremely low electrical ON resistance and a
minimum Øjc for the switching elements.
transients during Off switching of SSPCs. NHI SSPCs are
equipped with an internal shunt diode for negative transients on
the load side. On the Line side, the user is required to place a
transient voltage suppressor. The transients at this terminal are
positive and add to the line voltage. To prevent voltage break-
down of the switch elements, a Transorb of proper voltage and
energy rating is utilized. Voltages on 28 VDC units should never
exceed 100 VDC, and 600 VDC on 270 VDC units. Transorb
should be installed as close as possible to the SSPC. Any induc-
tance between the two compromises Transorb effectiveness.
limited only by wire impedances. If the capacitance value is too
great, the instant trip circuit might trip the SSPC. Soft turn-on of
the MOSFET or IGBT reduces the effect of this condition.
However, the design engineer shall carefully examine his system
to ensure that high capacitive loads are minimized and that there
is a reasonable resistance in the wiring to limit high surge currents.
TTL/CMOS - compatible status lines report SSPC operating conditions to the system.
Eight different states are possible, as described above.
A resistor between pins 6 and 7 allows the user to set the trip point to any value
between 3 and 10 Amps. The chart shows the relationship between the resistor value
Leaving Pin 8 open sets trip to 40 Amps. Connecting it to Pin 6 sets it to 120 Amps.
(80 Amps for 270-Volt units.) Placing a resistor between pins 6 and 8 allows the user
to set the INSTANT trip point to any value between 40 and 120 Amps (40 and 80
Amps for 270-Volt Units). The chart shows the relationship between the resistor value
and the INSTANT trip current.