POSITIVE THERMISTORS "Posi-R"
APPLICATION GUIDELINES FOR POSITIVE THERMISTORS, "Posi-R"
General Observations
1. Do not use"Posi-R" in the presence of oil or water.The parts could fail.
2. Do not apply voltage in excess of the rated voltage
.
This could cause a short circuit or burn-out.
3. Do not use "Posi-R" with reactive gas,reducing gas, or oxygen-free environment
-
electrical characteristics may deteriorate or
burn-out may occur.
Notes on Usage
1. Please use the parts within the rated operating temperatures according to the catalog.
2. Please use the parts wihtin the maximum operating voltage and maximum inrush current as specified in the catalog.
3. The surface temperatures for the "Posi-R" during operation are :
for overcurrent protection 100 to 160˚C
Please take into consideration the effect of generated heat around the "Posi-R"
4. Excessive press or shock (ex. drop) should not be applied to the "Posi-R".
5. Do not apply more lead stress than specified.
6. Do not allow flux to come in contact with "Posi-R", it may cause failure.
7. The outer resin on the leads may be partially peeled off. This will not affect the function of products.
8. In case of gluing "Posi-R", the outer resin may be come off, please contact us in this case.
Notes on Storage
1. Packaged parts should be stored under the following conditions :
temperature :
–
10 to +40˚C
humidity : 85% or less
2. Storage of "Posi-R" devices may result in increased resistive characteristics. They will return to the initial value by applying
max. operating voltage prior to using the parts.
3. Shall be used shortly after opening the package. The prolonged exposure to the air may case to deteriorate the solderability.
CAT.8100B
POSITIVE THERMISTORS "Posi-R"
Characteristics of Positive Thermistors "Posi-R"
•
Switching Temperature (Resistance Anomaly Point)
At the resistance / temperature characteristics of positive thermistors "Posi-R", the temperature which the resistance value becomes
twice as high as that of at 25˚C, is called as "switching temperature" (Curie point)
Thermistors "Posi-R" show anomalous temperature characteristics of resistivity, and typical characteristics are represented in Fig. 1.
Optimum characteristics can be selected for each application.
•
Temperature Coefficient
The temperature coefficient is calculated from the linear range at the steepest portion of resistance (T
1
to T
2
) as illustrated in Fig. 2.
Temperature coefficient =
10
5
2.303 ( log
10
R
2
/ R
1
)
×100
(%/ ˚C)
t
2
– t
1
10
4
10
3
Resistance ratio (1 at 25˚C)
10
2
BL
BT CA CE CJ CN
10
1
10
-1
–50
0
50
100
150
200
250
Temperature (˚C)
Fig. 1 Resistance / Temperature Characteristics
Maximum Inrush Current
The maximum inrush current is the maximum allowable current (effective value) flowed into a Posi-R. No current higher than this shall
be flowed as it causes breakdown of a Posi-R.
Recovery Time
The recovery time is the time constant necessary for a Posi-R to quickly return to the switching temperature (resistance of twice as high
as the initial value) after the power source is cut off.
Dissipation Factor
When a power source is applied to Posi-R and thermal equilibrium will have been reached, the following equation is established.
V
•
I = C (T
1
–T
0
)
Where, V : Applied voltage (V)
I : Equilibrium current (A)
C : Dissipation factor (W/ ˚C)
T
1
: Equilibrium temperature of Posi-R (˚C)
T
0
: Ambient temperature (˚C)
In case that the dissipation factor is known by putting arbitrary values of voltage and current into the above equation, the equilibrium
temperature at the then voltage can be attained.
The temperature rise (T
1
– T
0
) of Posi-R due to voltage application can be also computed easily.
CAT.8100B
POSITIVE THERMISTORS "Posi-R"
R
2
Resistance
R
1
log
10
R
T
1
t
1
t
2
T
2
Temperature (˚C)
Fig. 2 Temperature Characteristics of "Posi-R"
•
Voltage / Current Characteristics
In the Fig. 3 circuit, the relationship between voltage and current is called as the voltage/current characteristics when the voltage is
applied to Posi-R and it gets the thermal equilibrium.
As seen in Fig. 4, the characteristic follows Ohm's law up to E
1
point. The current increases when the voltage is raised, provided that
the temperature characteristics is within the range of switching temperature or lower. The range between E
1
and E
2
is over the
switching temperature but within the constant range of power dissipation. However, beyond E
2
point, an excess power will run and
Posi-R will result in breakdown, accordingly.
Therefore, the operating voltage of Posi-R shall be lower than E
2
, and its rated voltage shall be defined to half of E
2
value or lower,
taking the safety into account.
A
"Posi-R"
V
Fig. 3 Measuring Circuit
1
1
long
10
1
Current
1
2
E
1
Voltage log
10
E
E
2
Fig. 4
Voltage / Current Characteristics
CAT.8100B
POSITIVE THERMISTORS "Posi-R"
•
Equilibrium Current, Equilibrium Resistance
The current, which Posi-R gets thermal equilibrium with an arbitrary voltage application (for 30 seconds or longer), is called as the
equilibrium current.
Besides, the quotient which the applied voltage is divided by the equilibrium current is specified as the equilibrium resistance.
•
Current , Time Characteristics
In the Fig. 5 circuit, when a load resistance (R) and a Posi-R are connected in series and an arbitrary voltage higher than E
1
in Fig. 4 is
applied, the Posi-R will have inherent temperature due to a current flowing through it. Its temperature rises as time passes by, and it
exceeds the switching temperature in a certain time, resulting in a rapid damp of the current. The trip time can be adjusted by the
current volume as shown in Fig. 6.
By making use of these characteristics, a Posi-R can be used for the following applications;
1. Timing circuit
2. Switching use for motor starting
3. Overcurrent protection
When the parameters of I
1
, t
1
, I
2
and t
2
in Fig. 6 are expressed in a logarithmic graph in the manner of Fig. 7, an almost linear graph is
formed and the relationship between the circuit current and the trip time can be obtained.
But, when a Posi-R is used for a timing application such as a timer, the voltage shall be appropriately applied for 30 seconds or less
as the changes of conditions may affect much more as time passes by.
A
Posi-R
R
Fig. 5
Measuring Circuit
I
1
Current
I
2
t
1
Time
t
2
Fig. 6
Current / Time Characteristics
log
10
I
Current
I
1
I
2
t
1
Time
log
10
t
t
2
Fig. 7
Current / Time Characteristics
CAT.8100B
POSITIVE THERMISTORS "Posi-R"
Type numbering system
(Example for overcurrent protection 12V. 2.2Ω)
1
2
3
4
5
6
7
8
9
10
11
Z P C 1 1 C E 2 R 2 A
Revision Code
Nominal Resistance
Switching Temperature (Example)
Configuration
Nominal resistance
0.5Ω
1.0Ω
2.2Ω
10Ω
100Ω
1kΩ
Code
0R5
1R0
2R2
100
101
102
Code
C
D
S
P
R
M
Z
Temperature
150˚C
160˚C
190˚C
110˚C
120˚C
135˚C
Usage
Code
BL
BN
BX
CC
CE
CH
Type (Posi-R)
Application
For overcurrent protection
Disc type
For square type temperature heater
For thermal sensing
For air conditioner
For refrigerator motor starting
Others Appliance
CAT.8100B
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