Diode's function?

[reeferj]

Hi, I am looking at the wiring diagram of carrier supra 722, in each circuit, there must a diode just after each fuse, then connected to the M2 in the Microprocessor, I dont understand what is it function? How does the micro pick up the alarm signal "fuse bad"?

[Gary]

A diode is the electronic equivalent of a check valve, allowing flow in one direction and blocking flow in the other direction.

[cadwaladr]

yes a one way valve ,back emf is stopped from returning the bigger the current the bigger the diode i guess.

[reeferj]

Thanks, Gary. I knew its basic function. In terms of the diode in the carrier unit specifically, i didn't know what is its function in the wiring diagram. Why do we need a diode just after those fuese?

[reeferj]

If there are no these diodes, what will happen?

[DaButcher]

If there are no these diodes, what will happen?

It will burn out the relay over time

[cadwaladr]

ground control to major tom dont flick that switch!are you there major tom hello hello,anyone smell something burning how much is a micro for a 722.

[DaButcher]

A google search and I came up with a pretty good explanation


Protection diodes for relays


Signal diodes are also used to protect transistors and ICs from the brief high voltage produced when a relay coil is switched off. The diagram shows how a protection diode is connected 'backwards' across the relay coil. Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.

http://http://www.refrigeration-engineer.com/forums/attachment.php?attachmentid=6754&d=1308787248

[reeferj]

Thanks a lot DeButcher. I really do agree with what you said on that diode. But in Carrier Supra 722 Diagram, there are two diodes in one circuit. The one you mentioned is the diode just close to the load, which is grounded beside the load coil.

Then there is another diode in the same circuit, which is just after the fuse, before the relay contacts. That is the one that i didn't understand. Do we need two diodes to protect the coil in one circuit?

[reeferj]

thanks, Cadwaladr. If what you said is true, We just need one diode for Micro. Why is not just one diode grounded, rather than every circuit has that diode?

[Gabster]

This is how the diode works 12 volts current limited coming out of micro m2. When the fuse blows voltage passes through the diode and attempts to energise the load.The voltage goes to ground the micro senses this voltage drop and generates the fuse bad alarm.

[Magoo]

diodes are for DC voltage.

[reeferj]

This is how the diode works 12 volts current limited coming out of micro m2. When the fuse blows voltage passes through the diode and attempts to energise the load.The voltage goes to ground the micro senses this voltage drop and generates the fuse bad alarm.

Thanks Gabster. I really agree with what you said. After I talked to some technicians, we all thought this is what the diode's function. But the voltage coming out from M2 is not 12v, it might just 5v or lower.

Thank others help too...