AC motor controller

This is a standard circuit which can be used to adjust the brightness of mains lights and the speed of AC motors. It uses a triac, diac and has a radio-frequency interference (RFI) noise suppression circuit built into it as well.The circuit here controls the average power to a load through the triac by phase control. The ac supply is applied to the load for only a controlled fraction of each cycle. The triac is held in an OFF condition for a portion of its cycle then is triggered ON at a time determined by the circuit.

The main problem with this circuit is radio frequency interference (RFI.). Each time the triac is turned on the load current changes very quickly – a few micro seconds – from zero to a value determined by the lamp resistance and the value of the mains voltage at that instant in time. This transition generates RFI. Since there may be long lengths of mains wire between
the triac and the lamp load which will radiate this RFI an L-C RFI suppression network is usually built into these types of circuits. You may detect this RFI by bringing an FM radio close to the dimmer circuit. Short out the choke coil and notice that the RFI increases. The wire-wound coil and C1 provide the RFI suppression network.

AC motor control


2 thoughts on “AC motor controller

  1. do you have part numbers for the inductor and cap C1 that you could recommend?
    does the inductor need to be a common mode choke coil?

    since i am building a ac dimmer for dimmable ac light bulbs i was wondering if the inductor/choke could be smaller maybe even SMD? if so any specific part number you can recommend?

    thanks a bunch.

    1. Hello ,choke and cap is not critical ,as for capacitor i am using a Polyester Capacitor buuut for choke it absolutely deepens on the amperage you are going to control .Smd inductor is not proper for this use. You have to mind the thickness of the inductor. For example if you want to control 200W load , inductor must be at least 1 A ,it means arounf 0.5mm wire. If inductor is a problem ,try to leave out and the capacitor

      i am using this

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