Hi all,
I'm stuck with an engineering mistake and now I don't know how to handle it properly. My circuit is supposed to send singal to a din rail relay (12V / 220V). To make the long story short, only 3 cables leave from the rail and go to the mcu, which is about 10meters away. 2 for dc power and one from the one end of the relay's coil. The other end of the coil is getting +12 from the rail power unit.
On my mcu circuit, i connect the relay wire to the collector of a 2n4401 transistor and the emmiter is connected to gnd. So I am actually sinking. The base is taking signal from my mcu. Everything worked perfectly until I realised I was
getting some back EMF when i switched off the relay.
The problem is that i can't connect anywere a protection diode. I mean that i have no access to the 2 ends of the coil which stand on the rail but only on the one end that is connected on my transistor. So , how am i going to protect my circuit?
Adding a 4th cable must be my last option.
I'm stuck with an engineering mistake and now I don't know how to handle it properly. My circuit is supposed to send singal to a din rail relay (12V / 220V). To make the long story short, only 3 cables leave from the rail and go to the mcu, which is about 10meters away. 2 for dc power and one from the one end of the relay's coil. The other end of the coil is getting +12 from the rail power unit.
On my mcu circuit, i connect the relay wire to the collector of a 2n4401 transistor and the emmiter is connected to gnd. So I am actually sinking. The base is taking signal from my mcu. Everything worked perfectly until I realised I was
getting some back EMF when i switched off the relay.
The problem is that i can't connect anywere a protection diode. I mean that i have no access to the 2 ends of the coil which stand on the rail but only on the one end that is connected on my transistor. So , how am i going to protect my circuit?
Adding a 4th cable must be my last option.
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