Newport New Focus 8703, Руководство пользователя

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14 Theory of Operation
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Over-voltage protection: If the power input voltage exceeds 16.7 to 18.5 V,
a transient voltage suppressor (TVS) shunts the power input to ground. The
internal 2-A fuse will then open. The TVS will also shunt the power input
to ground if an internal fault shorts any high voltage to the power input.
The input fuse will also open if the input power voltage is reversed. Brief
power supply transients will not blow the fuse.
•
Inrush resistor: A 5.6
Ω
resistor handles all input current until the power
supply is operating. This resistor will over-heat and open if an internal
fault occurs before the power supply starts operating.
Over-temperature protection: If the case temperature reaches 80 °C (4 V at
temperature monitor pin 21), the unit will pull LFAULT low to tell the user
that the case, which acts as a heatsink, reached the maximum allowed
temperature. The user is expected to take some measures like decreasing the
pulse rate, air force cool the 8712 case, or use a heatsink. If the case
temperature continues to rise, at 85 °C (4.12 V at temperature monitor) the
output will be turned off. The output will remain off until the case
temperature will decrease to 75 °C (3.86 V at temperature monitor), when the
output will be turned on automatically. If left unattended, the unit will
protect itself cycling between 85 °C and 75 °C.
If a heatsink is needed, 8712 has 4 threaded holes on top (see Figure 14) to
accommodate a standard half brick heatsink. Examples of heatsinks are
Wakefield 528-24AB and 517-95AB. When Wakefield 528-24AB is
mounted on 8712 the unit temperature time constant becomes 10 minutes.
For 517-95AB heatsink the unit temperature time constant becomes 16
minutes.
Heatsink mounting holes
3.4.2 Power Connections
Special emphasis on proper power-trace routing is needed due to the high
static and dynamic currents demanded by the 8712. Ideally the 8712 will be
placed physically close to its power source. The optically isolated control
interface makes it possible to place 8712 close to the power supply without
Heatsink
mounting
holes