(Thermal resistance of infinite heat-sink : Rth(c-a) = ; then Rth(j-a) = Rth(j-c))For surface-mount devices, the heat-radiation path is mainly the part of a circuit board that's just beneath the device; which can make it quite difficult to measure the case temperature because of the location. Total absolute thermal resistance from junction to ambient = + where R θ B {\displaystyle R_{\theta {\rm {B}}}} is the absolute thermal resistance of the bond between the transistor's case and the metalwork. The ambient temperature shall be 25 [deg.C].Junction temperature is calculated by using the above thermal resistance.For a semiconductor device package used with a heat sink, in order to ensure more accurate calculations, thermal resistance of junction-to-case values should be used instead of thermal resistance of junction-to-ambient values.For calculation of junction temperature, please refer to âThermal Design and Attachment of a Thermal Fin: Power MOSFET Application NotesâToshiba Launches 100V N-channel Power MOSFETs in Compact Package for Automotive ApplicationsToshibaâs New Discrete IGBT for Voltage Resonance Circuits Contributes to Lower Power Consumption and Easier Design of EquipmentToshiba Launches General-Purpose System Power IC with Multiple Outputs for Automotive Functional SafetyToshibaâs New Three-Phase Brushless Motor Control Pre-Driver IC Features Sensorless Control and Closed Loop Speed ControlAbout information presented in this cross reference Please treat these only as reference data. Simply select an application and click through to the block diagram to discover our semiconductor solutions.At first, the value of âthermal resistance Rth(j-a)â is calculated by using the datasheet data below. That is 80% from 100% of its initial value (20% down), and then down to 0.2W which is 40% of its initial value (60% down).In the examples above, we discussed cases in which the current is applied to a device continuously. Junction-to-case thermal resistance (θ JC) is defined as the thermal resistance from the semiconductor junction to the case of the oscillator (junction-to-case). ΔT j [deg.C]＝ R th(j-a) [deg.C/W] × P LOSS [W] T j = ΔT j + T a ΔT j: Junction temperature rise R th(j-a): Thermal resistance, junction to ambient P LOSS Once junction temperature is known, another important parameter, thermal resistance (Rθ), may be calculated using the following equation: Rθ = ΔT/(V f *I f ) Junction temperature of LEDs and laser diodes [ edit ] The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. This means that the value goes down to 0.4W. RθJA Junction-to-ambient thermal resistance 42.5 C/W RθJC (top) Junction-to-case (top) thermal resistance 56.1 C/W RθJB Junction-to-board thermal resistance 25.5 C/W ΨJT Junction-to-top characterization parameter 9.9 C * Rth ( j-a ) varies depending on the circuit board, the heat-dissipation conditions involving soldering methods and the method of temperature measurement.By continuing to browse this website without changing your web-browser cookie settings, you are agreeing to our use of cookies.