WEEK 9

TITLE:

Description of the circuit driver

OBJECTIVE:
To give reader an understanding about the function of the components in circuit driver

DISCUSSION/ANALYSIS:

The circuit showing in the Week 8 is the complete driving circuit system with values of each component. This one set of circuit is used for three phase output. The power MOSFET IRF 640 is chosen because it has high Vdss (200 V), high Id (15 A), low Rds (on) and high switching capability. When dealing with the power MOSFET, several things have to pay attention like it is extremely static sensitive and if the Gate is left open, the power MOSFET can be self destruct. The Gate is a very high impedance device and noise can trigger the power MOSFET. Therefore resistor R3, R4, R7, R8, R11 and R12 (10kΩ) are added to stop the power MOSFET from self destructing. The MOSFET become more stable after these resistors are installed. The resistors pull down the Gate and turn off the MOSFETs and add some static protection to them.

The resistor R1, R2, R5, R6, R9 and R10 (22Ω) are connected in series with the Gate. This resistor can help to reduce the ringing of the MOSFET.For instant, a higher value of resistance will reduce the ringing of the MOSFET but the efficiency of the switching will also reduced. The efficiency is affected because the resistance courses the MOSFETs gate voltage to rise slower as opposed to a MOSFET with no Gate resistance.

The IRF 640 consists of built-in diodes, so they are no need to add another one outside it. The motor can make a lot of electrical spikes when starting and stopping especially when changing direction. The capacitor C4 (250 V, 470 uF) was used to suppress the noise spikes and remove the AC components which not needed. The power MOSFET is mounted on the heat sink for dissipating the heats. This will protect the power MOSFET from overheating and destruct. The protections method or components used in this circuit are:

1. MOSFET driver (IR 2110) – This driver consists of a built- in level shifting protection which can isolate the high power side from the low power side. This chip is control a set of high and low side power MOSFET; it will ensure that this six MOSFET will not on together to prevent the short circuit happen. It also has under voltage and overvoltage lockout protection.
2. Resistor – Limit the current flowing through the path
3. Capacitor – Reduce the AC components in the signal which may defect the DC components.