Power Electronics AssignmentGate Drives You have y Custom Research Paper Assistance

Power Electronics AssignmentGate Drives You have y Custom Research Paper Assistance

Introduction Motors require a switch to be able to operate efficiently. The most suitable switches for this kind of operations are silicon MOSFETs. MOSFETs are devices that are voltage driven switches because of capacitance behavior of their insulated gate. In order for the MOSFET switches to carry out the ON/OFF operations at suitable frequencies, they will require a gate driver (Pelly, 2005, pg.78). In cases where high frequencies are needed, then MOSFETs will be driven by gate driver circuits that convert the ON/OFF digital or analog signals from controllers into power signals that would necessitate the control of a MOSFET. The main aim of this report is to show the systematic approach in design and implementation of gate drives for the purpose of motor controls. MOSFET gate drivers Gate drivers are electronic circuits that supply the required levels of power to MOSFETs as well as IGBTs. Gate drivers for MOSFETs can be designed and implemented either as transformers, dedicated integrated circuits or as discrete transistors. When it comes to design of the gate drivers, there are important attributes that are considered (Spaziani, 2009, pg.24). One such example of an attribute is the ability of the gate driver to supply drive current that would be sufficient to go through the Miller Plateau region of the switching transition of the MOSFET fast enough. This transition takes place when the MOSFET is being driven ON/OFF and at the same time the gate driver is charging or discharging the voltage across the MOSFET s gate-to-drain parasitic capacitor (CGD). In order to achieve a full turn ON to the MOSFET gate, a total gate charge (CQ) given in nanocoulombs (nC) must be supplied. In addition to this, it should also be ensured that the capability of the output voltage driver should match the turn voltage of the MOSFET. Figure 1shows an example of a typical three phase inverter. Figure 1: Three phase inverter motor drive (Andrey, 2004). The above three phase inverter operates in such a manner that three switches must be on at the same time while the other three switches are off. From the diagram, it can be seen that the circuit requires 6 gate drives, i.e. two MOSFET gate drives for every phase. The three phase inverter in figure 1 can be interfaced with drive ICs and a microcontroller in order to achieve a full functionality of controlling motor speeds. The gate drive will help in switching the MOSFETs. Low power from the microcontroller is fed to the drive, which then amplifies the power to a required value. The amplified power is fed into the gate of the transistors. The input value to gate transistor is a high voltage which is able to switch on the MOSFET since MOSFETs are voltage driven switches. An interface circuit for the drive, microcontroller and the switching device is as shown on figure 2. Figure 2: motor drive interfaces the microcontroller and switching devices (Gillooly, 2010). Gate drives can either be used as low side switch driver or high side switch driver. A low side driver is a case where the used MOSFET sinks the current and therefore, it acts as a low side switch. In the same case, the load lies between the +V supply and the drain (Pelly, 2005, pg.67). Additionally, the gate is driven with respect to the ground since the source connected to the ground. An example diagram of low side driver is shown on figure 3. Figure 3: side driver switch (Dierberger, 2002, pg.89). High side driver is a case where the load is taken through the source to the ground while the drain is connected to the +V supply. This will mean that the source will not have any connection to the ground. Other than hard wired MOSFET drivers electronic circuits, the drives that are fused integrated ICs exist. IC drivers provide suitable features and also offer convenience to designers. For example, there compactness and low propagation delays impress the designers. Examples of MOSFET gate driver ICs are shown on table 1 together with their manufacturers. Table 1: Some of the available driver ICs Driver IC Manufacturer Cost Cost TC4420CPA Microchip Corporation $ 1.5 $ 1.5 MC33153PG ON Semiconductor $ 1.82 $ 1.82 FAN7382N Fairchild Semiconductor Fairchild Semiconductor $ 1.30 Gate drives need the appropriate power supply in order to power without damaging the electronic component. Since the output voltage for most ICs range between 3.5 V to 5 V, and this voltage is not sufficient to turn on the ON the gate of the switching device. Therefore, this low voltage will be fed into the driver which later on gives an output of approximately 8 to 12 V, which is sufficient to switch the MOSFET. Similarly, the output drivers can sink or source a current of approximately 350 to 630 mA (Dierberger, 2002, pg.88). Silicon MOSFETs drives are designed as easy to drive devices that can operate at higher frequencies that their counterparts IGBTs. Some of the aspects that determine its switching frequencies are: Current requirements for the gate drive Turn on energy (Eon) which is depended on Rg Turn off energy Eoff which is dependent on VGS-off and Rg Applications Other than switching applications, MOSFET gate drivers are used in electric bikes, power supplies, motion control and displays. References Andrey W., 2004. Practical Considerations In High Performance MOSFET, IGBT and MCT Gate Drive Circuits , Unitrode Corporation, Application Note U-137 Dierberger K., 2002. Gate Drive Design For Large Die MOSFETs , PCIM 93, reprinted as Advanced Power Technology, Application Note APT9302 Gillooly D., 2010. TC4426/27/28 System Design Practice , TelCom Semiconductor, Application Note 25 Pelly B. R., 2005. A New Gate Charge Factor Leads to Easy Drive Design for Power MOSFET Circuits , International Rectifier, Application Note 944A Spaziani L., 2009. A Study of MOSFET Performance in Processor Targeted Buck and Synchronous Buck Converters , HFPC Power Conversion Conference, 1996, pp 123-137


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