PRF18BA471QB5RB Datasheet, PDF (8/104 Pages) Murata Manufacturing Co., Ltd. – POSISTOR for Circuit Protection

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Basic Characteristics of POSISTORr
R90E.pdf
Sep.24,2012
Technical Terms
1. Protective Threshold Current
The maximum current value is called the "Protective
Threshold Current" for Voltage vs. Current characteristics
(static).
When smaller than the protective threshold current flows
in POSISTORr, it reaches its stability (as shown in figure
on right) at the intersection (A) of the load curve (a) and
voltage-current characteristics of POSISTORr(c). And
POSISTORr works as a normal fixed resistor.
However, when larger than protective threshold current
flows, it stabilizes at the intersection (B) with the load
curve (b).
2. Protective Threshold Current Range
Protective threshold current varies depending on the
ambient temperature, resistance value, temperature
characteristics and shape. (see Figure on right) The
maximum value of trip current and the minimum value of
the hold current are in the range of ambient temperature
-10 to +60°C.
That is, when a current is smaller than the hold current,
POSISTORr works only as a fixed resistor. When larger
than the trip current flows, however, POSISTORr
protects the circuit from overload.
3. Operating Time
A period starting from the voltage input to the moment
current itself sharply attenuates is called "Operating
Time." Conventionally, operation time (t0) is determined
to be the period until inrush current (I0) decreases to a
level one half the original inrush current (I0/2).
Load Curve of Circuit and Voltage - Current Characteristics
of POSISTORr
Vp
a Load curve in normal state
(normal current)
b Load curve in abnormal state
(abnormal current)
c Voltage-current characteristics
of POSISTORr
b
c
E
RL
a
I
A
E - Vp
I = _RL
B
Voltage (log) ^E
Protective Threshold Current Range
1000
800
Trip Current
600
Protective Threshold Current
400
Hold Current
200
0 _{-20 0 20 40 60}
Ambient Temperature (°C)
Operating Current
I0
I0
2
Operating Time
t0
Time (sec.)
6