DONOFF iot light dimmer
Placed onMOSFET control circuit
This is the most important part of the DONOFF electronics. D2, D3, R3, R4 and C2 function as a low power 15 Volt voltage source to drive the gate of Q1. The gate of the MOSFET is pulled to GND by R7 at rest (MOSFET switch “open” – LED lamp is Off). To close the MOSFET, the optocoupler must pull the gate to 15 Volts (MOSFET switch “closed” – LED lamp is ON). The Optocoupler (U1), R6 and R7 use about 2.2mA (15v/(150+6800)). C2 serves as an energy buffer and D2 ensures that the energy does not leak away when the rectified voltage (MAINS-DC) falls below 15 Volt. Together with the Zener Diode D3, the control voltage for the gate of Q1 remains between 12.5 – 15 Volt (Q1 is fully closed when the gate voltage Vgs > 10 Volt).
Gate Fall Time
Gate Fall time Max.
The voltage is normally 15 Volts but drops to 13 Volts at 100% PWM (the MOSFET is then constantly closed)
The current flowing through R4 is also about 2.2mA, which means that R4 has to convert about 0.7 Watt (I2 * R = 4.8 * 150) into heat. The temperature of R4 becomes a maximum of 15°C higher than the ambient temperature. It is therefore necessary that a 400 Volt 2 Watt resistor is used for R4 (a bit over dimensioned).
Resistor R6 limits the current through the optocoupler and the gate of Q1.
C1 filters the “MAINS” DC voltage.
The current flowing through R4 is also about 2.2mA, which means that R4 has to convert about 0.7 Watt (I2 * R = 4.8 * 150) into heat. The temperature of R4 becomes a maximum of 15°C higher than the ambient temperature. It is therefore necessary that a 400 Volt 2 Watt resistor is used for R4 (a bit over dimensioned).
Resistor R6 limits the current through the optocoupler and the gate of Q1.
C1 filters the “MAINS” DC voltage.