Hi. I'm trying to find out if I am using this diode device correctly as a protection device against high voltage.
I'm trying to use the diode as in the first attachment schematic. I want to use an arduino pin to send a voltage to the base of a transistor in order to complete a circuit that will close the switch in a relay that is controlling wall voltage (120V) powering other mechanics.
I've read that the diode is necessary to protect the arduino when the relay switch closes.
The second attachment image shows my breadboard. The diode is in the middle of four wires.
Upper left and lower right wires (larger red) go to the switch on the relay.
Upper right(smaller red with black cap) is 12V.
Lower left(smaller yellow with black cap) goes to leg of transistor(collector).
Is this diode connected properly to protect the arduino?
thanks
Yes connected ok, you can simply deduct it, if you place it the other way round you put Vrelay-0,6V on the collector and short it if you operate the transistor
Now the diode only conducts if the voltage on the collector goes over the Vrelay+0,6V and the conducts it to Vrelay safely. Place it as close to the relay as possible.
Lots of relays come with the protection diode built in (or some cheaper ones use a parallel resistor). It's worth checking the datasheet. Certainly all the automotive "plug and play" relays I've encountered have some form of protection in them.
Your diode is correctly placed. The reason you need it is that the back EMF from the relay coil when it de-energises can be as much as 40 TIMES the applied voltage, in your case 480v with a 12v relay. It is always good practice to put a diode across a relay coil as you have done.
Your diode is correctly placed. The reason you need it is that the back EMF from the relay coil when it de-energises can be as much as 40 TIMES the applied voltage, in your case 480v with a 12v relay. It is always good practice to put a diode across a relay coil as you have done.
+1 to that. I got my hand bit pretty hard once by a relay in a 24V vehicle that had been miswired and was oscillating. I heard the buzzing, and was feeling around in the confined space to find the buzzing thing. Turned it it was the relay, and my hand found the back of it, and it felt on par with grabbing 120V mains with one hand. But it was un-expected so it was quite startling.