DONOFF iot light dimmer

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MOSFET 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
Gate Fall time Max. 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.
Current Page 5. MOSFET control circuit 1. Introduction 2. Project Objectives 3. The Electronics 4. Mains AC to DC 5. MOSFET control circuit 6. optocoupler circuit 7. ESP8266 Microprocessor 8. 3v3 DC power supply 9. The firmware 10. Upload Firmware 11. First time startup 12. telnet server 13. build DONOFF Posted by Website Willem Aandewiel (1955) has a background in electronics and digital techniques. However, most of his working life he has worked in automation where he has worked in just about all disciplines from programmer to project leader and project manager. Willem was one of the first Dutchmen with a micro-computer (KIM-1, 1976) at a time when the PC had yet to be invented. Nowadays he is mainly concerned with the design and production of small electronic circuits with microprocessors. His 'mission in life' is to make people enthusiastic about making their own electronic circuits, microcomputers and programming.

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