THE ELECTROTHERMAL ANALYSIS OF A SWITCHED MODE VOLTAGE REGULATOR Krzysztof Górecki and Janusz Zarębski Department of Marine Electronics Gdynia Maritime University, POLAND

2 Outline  Introduction  The electrothermal model of the PWM controller (UC3842)  The electrothermal SPICE hybrid models (diode, MOS transistor)  Results of investigations of SMPS  Conclusions

3 Introduction SMPS Dc-dc converter RLC elements Semiconductor devices transistorsdiodes PWM controller

4 Introduction (cont.)   Selfheating – results from changing the electrical energy into the heat and non-ideal cooling conditions   Due to selfheating   Internal temperatures of semiconductor devices increase   Characteristics and parameters values of SMPS change   Electrothermal analysis – analysis with selfheating taken into account

5 In the paper   The new electrothermal models (ETM) of:   the current mode PWM controller   the diode   the MOS transistor dedicated for electrothermal analysis of SMPS in SPICE   Measurements and calculations of nonisothermal characteristics of SMPS Why the new models are needed?   the literature models are complicated   the time duration of calculations with these models is unacceptable long

6 The ETM of the UC3842 controller [1] Zarębski J., Górecki K.: Microelectronics Reliability, Vol. 47, No. 7, 2007, pp  The modified version of the model from [1]  The changes in description of the error amplifier block  In the model all terminals of IC, selfheating, nonlinear characteristics of semiconductor devices are taken into account

7 The ETMs of the diode and the MOSFET The general conception The general conception Only characteristics of the forward biased diode and switched-on transistor operating in SMPS are important Electrothermal hybrid model SPICE isothermal built-in model Controlled sources modelling the influence of selfheating Thermal model

8 The ETMs of the diode and the MOSFET (cont.)

9 Results of calculations and measurements  Transient analysis till the steady-state  One non-physical thermal time constant – to short the time of calculations

10 Results - opened feedback loop The calculations results The calculations results The measurements results The measurements results

11 Results - closed feedback loop The calculations results The calculations results The measurements results The measurements results

12 Conclusions   The presented calculations and measurements results confirm the correctness of the proposed by the authors electrothermal model of the controller UC3842 and the hybrid electrothermal models of the MOS transistor and of the diode.   The calculations and measurements results show the influence of both the input signals of the controller and the values of the boost converter elements on the output voltage.   The possibility of taking into account the phenomenon of selfheating enabled, among others, determining from the computer simulations the admissible values of load resistance and the regulator input voltage, at which the voltage regulator operates properly and the admissible temperature of its component elements is not exceeded.