ALGUNAS REFERENCIAS AL PRINCIPADO DE ASTURIAS

Two TC1411N MOSFET drivers are used to drive the MOSFETs of the converter. Maximum output current of the driver is 1A with the possibility of 5V to 15V supply. This driver is used with +15V biasing supply. PWM outputs from the DSP at pins GPIO-00 and GPIO-02 are provided to the drivers as an input. Outputs of this driver is connected to the Gate terminal of the MOSFETs. Functional block diagram and PIN out of the driver are shown in Figure 7.14.

(a) SiC MOSFET (SCT2120AF) (b) SiC Schottky barrier diode (SCS220AE2)

Fig. 7.13 Schematic diagram of MOSFET and diode

85 7.5.5 Programing in DSP

TMS320F28335 Digital Signal Controller (DSC) is used for the implementation of control algorithm for the interleaved boost PFC. Code Composer Studio (CCS) v5, which is provided by Texas Instruments (TIs), is used for the programming. Code Composer Studio is an integrated development environment (IDE) that supports TI's Microcontroller and Embedded Processors portfolio. Code Composer Studio comprises a suite of tools used to develop and debug embedded applications. It includes an optimizing C/C++ compiler, source code editor, project build environment, debugger, profiler, and many other features. Code Composer Studio combines the advantages of the Eclipse software framework with advanced embedded debug capabilities from TI resulting in a compelling feature-rich development environment for embedded developers. The code debugging can be done with the simulator software that is part of CCS. The control algorithms are implemented in the interrupt service routine at the end of the ADC conversion. The schematic diagram of TMS320F28335 board is shown in Fig. 7.15. Assignments of input/output variables to GPIO (General Purpose Input Output) pins are listed in Table 7.2.

Fig. 7.15 DSP development board of the Texas F282335

Table 7.2: Input/output variables and GPIO connections

Variables GPIO/ADC Input/output

VAC A6 Input

VDC B6 Input

Im1 A7 Input

Im2 B7 Input

Relay command GPIO-10 Output

d GPIO-02 Output

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7.6

Summary

The active power factor correction technique has been discussed in details in this work, which has number of advantages over passive power factor correction method in terms of size, volume and weight of the circuit elements. The active power factor correction circuit is more compact and weighs less compared to passive power factor correction circuit. A single phase interleaved PFC has been investigated very closely. The circuit operation for the CCM mode is discussed in detail and the power losses in the devices and rectifier are calculated. The circuit has been simulated with the help of PSIM software and simulation results are presented. A prototype of interleaved boost PFC circuit is designed with using SiC MOSFET and SiC diode. The procedure of design is discussed in details. To control the circuit, computer assisted DSP interface is adopted. For the DSP programming, Code Composer Studio (CCS) v5, provided by Texas Instruments is used.

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Chapter 8

Synchronous Rectifier

8.1

Introduction

An SR is able to reduce the conversion losses due to the device conduction, thus leading to improvement in efficiency. The conduction losses contribute significantly to the overall power loss of a diode rectification circuit, especially in low output-voltage applications. In the diode, the conduction losses depend on the forward voltage drop, the diode resistance and the magnitude of current that passes through the devices while in a MOSFET the conduction losses depend on the on resistance (RDS,on) of the MOSFET and the current that

passes through the devices. Moreover, driving losses are also a part of the losses in a MOSFET but they are negligible compared to the total power losses up to frequencies of hundreds of kHz. Therefore, the MOSFET-based SR is widely adopted in low output voltage applications. Another possibility is the use of Schottky diodes as they have low forward voltage drop as compared to pn-junction diode but they are suffering from a number of limitations like high leakage current and lower temperature operation. Hence, a MOSFET- based SR is commonly used in place of Schottky diode-based SR. Besides being attractive for efficiency, a MOSFET-based SR is also attractive in applications sensitive to converter size (higher power densities) such as portable or handheld equipment, and thermal performance (higher operating temperature).

The on resistance (RDS,on) of a MOSFETs can be lowered, either by increasing the size of

the die or by paralleling more devices. Moreover, RDS,on has a positive temperature

coefficient. The paralleled MOSFETs will automatically tend to share current equally, facilitating optimal thermal distribution among the devices. This improves the ability to remove heat from the components and the PCB, directly improving the thermal performance of the design. MOSFET manufacturers like Cree, Rohm, and Infineon are constantly introducing new MOSFET technologies that have lower RDS,on and total gate charge (QG),

which makes it easier to implement SR in power converters.

The major difficulty in synchronous rectification is to design the driving circuit. The SR driving signal can be obtained through two ways, self-derived and external-controlled. Self- derived method develops SR driving signal by detecting either the current flowing through SR or the voltage drop across a SR. External-controlled method develops a SR drive signal from the voltage signal that exists in the switching topology and coincides with the desired drive timing [48]-[52]. Moreover, in self-derived method, the voltage driven is more attractive for its simplicity and low cost but it is topology dependent and usually only suitable for voltage feed topologies. Instead, current-driven method senses the current entering into

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the SR to turn on or off the SR devices properly and hence it is topology-independent. Therefore, a current-driven SR can directly replace a diode rectifier in any topology.