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 160C 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 +40C 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 25C, 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 (T1 to T2) as illustrated in Fig. 2. Temperature coefficient = 2.303 ( log10 R2 / R1) x100 (%/ C) t2 - t1 105 104 Resistance ratio (1 at 25C) 103 BL 102 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 (T1-T0) Where, V : Applied voltage (V) I : Equilibrium current (A) C : Dissipation factor (W/ C) T1 : Equilibrium temperature of Posi-R (C) T0 : 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 (T1 - T0) of Posi-R due to voltage application can be also computed easily. CAT.8100B POSITIVE THERMISTORS "Posi-R" Resistance log10R R2 R1 T1 t2 t1 T2 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 E1 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 E1 and E2 is over the switching temperature but within the constant range of power dissipation. However, beyond E2 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 E2, and its rated voltage shall be defined to half of E2 value or lower, taking the safety into account. A "Posi-R" V Fig. 3 Measuring Circuit Current long101 11 12 E1 E2 Voltage log10E 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 E1 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 I1, t1, I2 and t2 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. Posi-R A R Fig. 5 Measuring Circuit Current I1 I2 t1 t2 Time Current log10I Fig. 6 Current / Time Characteristics I1 I2 t1 t2 Time Fig. 7 log10t Current / Time Characteristics CAT.8100B POSITIVE THERMISTORS "Posi-R" Type numbering system (Example for overcurrent protection 12V. 2.2) 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 Nominal resistance Code 0.5 0R5 1.0 1R0 190C BN BX 2.2 2R2 110C CC 10 100 120C 135C CE CH 100 101 1k 102 Switching Temperature (Example) Configuration Temperature 150C Code BL 160C Usage Type (Posi-R) Application Code For overcurrent protection C Disc type D For square type temperature heater S For thermal sensing P For air conditioner R For refrigerator motor starting M Others Appliance Z CAT.8100B POSITIVE THERMISTORS "Posi-R" For Overcurrent Protection When something abnormal occurs at the load such as a transistor circuit or a small-type motor, an abnormal current rushes into the power source circuit. Then, a power transistor at the transformer or the switching power supply generates heat in an abnormal level and causes breakdown. If a Posi-R for overcurrent protection is used in such a circuit, it can make the temperature compensation and protection for the power source and the load. An example is as shown in Fig. 8. As to the temperature protection, it can be perfectly made in use of this Posi-R owing to the excellent characteristics of resistance anomaly, that is, a current is reduced by the increased resistance due to the selfheating of Posi-R. At the voltage/current characteristics in Fig. 9, there is a peak current. If a current larger than this peak current flows, a Posi-R acts. But if a current less than the peak current flows, a Posi-R does not act. The peak current varies depending upon the size of Posi-R, resistance and ambient temperature. Fig. 10 shows an example of current characteristics. At the current higher than the upper limit of fluctuation range, a Posi-R acts. Contrary, at the current less than the lower limit, it does not act. But the fluctuation range varies owing to ambient temperature. For instance, if the operating temperature range is supposed to be at -10 to +60C, the lower limit at +60C becomes the maximum value for a normal current (non-acting) and the upper limit at -10C becomes the minimum value for a limiting current (acting), respectively. Judging from the above explained relations, a Posi-R can be suited for the circuit where the ratio of a limiting current to a normal current is more than 2.5 to 3 times. Power source circuit (Primary) Power source circuit (Secondary) Posi-R Posi-R Load Load power source power source Motor circuit Transistor circuit Posi-R Posi-R Load M Motor power source Fig. 8 Examples of applications Characteristics of ZPC4MCE100D 1000 Peak current 500 Current (mA) -10C 25C 300 60C 200 100 50 1 2 3 5 10 20 Voltage (VAC) Fig. 9 Voltage / Current Characteristics CAT.8100B POSITIVE THERMISTORS "Posi-R" Characteristic of ZPC4MCE100D 600 Limiting current (Acting) 400 Fluctuation range 300 Normal current (Non-acting) 200 100 25C -10C 60C Ambient temperature Fig. 10 Current Characteristics 104 103 Resistance ratio (1 at 25C) Current (mA) 500 102 10 1 0.1 0 50 100 150 200 Temperature (C) Fig. 11 Resistance / Temperature Characteristics CAT.8100B