SPICE modelling of PFC controller Krzysztof Górecki, Janusz Zarębski Department of Marine Electronics Gdynia Maritime University, POLAND

Outline Introduction Structure and principle of operation of the device UC3853 Model of the device UC3853 Results Conclusions

Introduction (1) Switched mode power supplies commonly used in electronic installations cause changes for worse of the quality of energy in the line. This phenomenon results from the fact that switched mode power supplies absorb a current from the line in the pulses form. Power supplies can be treated as the nonlinear RLC load of the line and the power consumed by switched mode power supplies comprises: active and reactive powers. The second quality of energy influences disadvantageously the operation of many installations connected to the power network, e.g. electrical machines, causing an additional increment of their winding temperature.

Introduction (2) The important parameter characterizing the electrical installation influencing the electrical energy quality is the power factor (PF). To obtain a high value of PF, a switched mode power supply input current should be formed in such a way as to get the sinusoidal course of current synchronized with the course of the line voltage. To get the proper shape of the input current, special circuits of power factor correction (PFC) are used.

Introduction (3) Currently, the predominant role is played by active PFC consisting of dc-dc converters and special integrated circuits working as a PFC controller. Today, a lot of concerns offer such circuits, that realize different algorithms of power factor corrections. Designing and analysing electronic circuits demand the use of credible models of circuit elements, acceptable by the proper software, e.g. SPICE. There is no information about the models of PFC controllers for SPICE.

In the paper In this paper the authors present a new model of a PFC controller realizing the control of the average value of current. For the considerations the device UC3853 (Texas Instruments) has been chosen.

Structure and principle of operation of the device UC3853 The considered device consists of nine blocks enabling the control of the average value of the input current and the output voltage as well as two protection blocks. The control of the current and voltage is realized by the error amplifier (EA), the multiplier (MULT), the squaring circuit (X2), the current amplifier (CA), the PWM comparator (COMP), the oscillator (OSC), the RS flip-flop (FF) and the output stage (OS). The device also includes the blocks protecting the overvoltage at the device output and too low value of the supply voltage.

Model of the device UC3853 The model of the device UC3853 has developed according to the principles of formulating integrated circuits models for SPICE and the catalogue data. The presented model consists of 2 controlled current sources, 6 controlled voltage sources, 2 independent voltage sources, 5 resistors and 2 NAND gates. The detailed description of the sources efficiency – see proceedings

Results (1) The tested switched-mode power supply containing the controller UC3853

Results (2) Vin = 150 V The nominal value of Vout is 130 ms after switching on this device The input current is sinusoidal, but its amplitude is changing with time. In the steady state, this amplitude slightly exceeds 1 A

Results (3) Vin = 310 V The results of switching-on the overvoltage protection circuit at the beginning of the power supply operation is shown. Not before reaching 110 ms, the power supply input current is of the desirable sinusoidal form. In the steady state the measured characteristics are qualitatively similar to the calculated ones

Conclusions In the paper the new SPICE model of the monolithic PFC controller UC3853 is proposed. The results of the analysis of the power supply with this PFC device, confirm the correctness of the model. The presented results of the analysis confirm the proper description of all the blocks of the device responsible for regulation of the output voltage and the input current of the device as well as the overvoltage protection circuit. The model can be useful for designers of power supply systems, especially such systems with the PFC circuit. In spite of the fact that the model was investigated for the device UC3853 only, it can be used for other PFC controllers based on the conception of controlling the current average value. The drawback of the model is long time of an analysis to get the steady state, which can reaches even a few hours In further investigations the authors will elaborate a special algorithm, which will enable shorting the analysis of the considered class of the power supply systems.