[R-390] Correction NTC resistor

[Tisha Hayes]

Roy, K1LKY caught an error I made. The CL-90 is a NTC (negative temperature
coefficient) device.

Here is an excerpt from a CL-90 datasheet;

"Energy Surge at Turn-On
At the moment the circuit is energized, the filter caps in a switcher
appear like a short circuit which, in a relatively short period of time,
will store an amount of energy equal to 1/2CV2. All of the charge that the
filter capacitors store must flow through the thermistor. The net effect of
this large current surge is to increase the temperature of the thermistor
very rapidly during the period the capacitors are charging. The amount of
energy generated in the thermistor during this capacitor-charging period
is dependent on the voltage waveform of the source charging the capacitors.
However, a good approximation for the energy generated by the thermistor
during thisperiod is 1/2CV2 (energy stored in the filter capacitor). The
ability of the NTC thermistor to handle this energy surge is largely a
function of the mass of the device. This logic can be seen in the energy
balaPositive

http://www.ge-mcs.com/download/temperature/920-325D-LR.pdf

And for PTC devices here is an excerpt from a Cooper Industries datasheet
on the "Polyfuse";

A PTC device is a resettable fuse, where high curent causes the resistor to
go open. This is a positive-temperature-coefficient device.

Positive Temperature Coefficient (PTC) devices are simple, inexpensive, but
critical circuit components that protect against overload or short-circuit
(fault) conditions. Although multiple differences exist between PTCs and
traditional one-time fuses, probably the most notable is that PTCs can
allow current to flow after the fault is cleared without replacing the
fuse, often
referred to as resettable.

PTC exhibit a positive temperature coefficient (resistance increases
exponentially with increased temperature) allowing them to protect circuits
exposed to increased currents or temperature. The Positive Temperature the
circuit by increasing its internal resistance in the event of a
short-circuit or overcurrent.

-
Ms. Tisha Hayes. AA4HA