Applicable to All Gate Drive Optocouplers. This application note covers the topic of calculating gate driver power and thermal dissipation of the gate drive optocoupler IC. Gate drive optocouplers are used to drive, turning-on and off, power semiconductor switches, MOSFETs / IGBTs. Using a driver transistor worked, but then it became inverted: port low was the on, so effectively default on, and that's not safe for my project. It allows me to pull the gate of the MOSFET to the 12V level using just 3.3V. It sinks the current for the LED in the optocoupler, the gate is pulled high, and the MOSFET switches on.
![Driver Driver](https://i.stack.imgur.com/RsYxA.png)
A MOSFET Q1 is taken which is connected as a high side switch with reference to the load RL. For driving the MOSFET, a bootstrap circuit is connected at the load of the MOSFET. The bootstrap circuit is a capacitor connected at the gate of the MOSFET. Bhai log pakistani movie full. This capacitor is represented as C1 in the circuit diagram. The bootstrap capacitor requires a PWM signal to turn on the MOSFET.
The PWM signal is generated from an Arduino board. For proving PWM signal, bootstrap capacitor is connected to the output of an optocoupler (Shown as opt1 in the circuit diagram) which receives PWM by connecting its input pin to the pin 2 of the Arduino. Another PWM signal is required at the gate of the gate of the MOSFET. The signal is received through the output of another optocoupler (Shown as opt2 in the circuit diagram) which receives PWM by connecting its input pin to the pin 3 of the Arduino. The MOSFET (Shown as MOSFET Q1 in the circuit diagram) is connected in high side configuration as the load (Shown as resistance RL) is connected between the source and the ground. This MOSFET cannot be driven by applying a voltage at its gate and drain. It needs an external circuit to turn ON.
![Using Using](https://i.stack.imgur.com/jYZSf.png)
The MOSFET used in the circuit is IRF840 which requires a gate to source voltage (Vgs) or threshold voltage (Vth) in range from 10 to 12V to fully turn ON. The Bootstrap circuit built using the capacitor C1 and Diode D1 is used to drive this MOSFET. The bootstrap circuit is explicitly shown in the circuit diagram below.
For isolating the input and output, two optocouplers are used. The isolation is optical as in an optocoupler, the input is a LED (Emitter) and the output is a photo transistor(Detector). The pins 2 and 3 of the optocoupler are the input pins of the LED. The forward voltage of the LED is in between 1.23V to 1.5V. The forward current of the LED must be less than 60 mA. For providing the input logic to the optocoupler a microcontroller is used which generates the PWM signal for this purpose. The microcontroller board used in the circuit is Arduino.
The PWM signal is of 5V and the 100E resistance at the input of optocoupler provide a current of 50mA. This resistance saves the optocoupler from high current. Manmathan tamil movie mob ring tone. The microcontroller generates two PWM signals with a phase difference of 180 degree. So at a time only one of the optocoupler is ON and another one is OFF. The ON time and off time of the optocouplers decides the ON and OFF time of the MOSFET.
This time is also used for calculating the value of capacitor used in bootstrap circuit. When the circuit is powered on and PWM signal is applied at the input of both the optocouplers, then initially the first optocoupler Opt1 is OFF for 1s and second one is ON for 1s as per the time period of the PWM signal. The ON and OFF time period of the PWM signal is set in program code of the Arduino board.