Netduino tutorial – Replacing Relay with SCR


(visit  the second or third post in this series)

Now I am writing down next chapter of my Netduino tutorial and come up with the idea to present to you sort of a brainteaser 🙂

A bit of a prehistory: When powering on or resetting Netduino MCU, ports are going in Hi state, thus causing any connected schematics that uses this state to switch on stuff, become active. This can cause many problems. One example is having a motor control, which we do not want to power up until we do that pragmatically.

In last published chapter of the tutorial, I demonstrated how a PNP transistor switch could be used to control Relay and successfully solve this problem. The schema is:

Relay with PNP switch

You can read the tutorial for details how this schematic works. Calculations and actual values of the elements are also specified in the tutorial. Source code contains example application.

In following chapter, I will demonstrate how the Relay can be replaced with SCR thus making the schematics and mounted PCB more elegant 🙂 Have a look:

SCR with NPN switch

For SCR I am using C106D and as you can see yourself, it is much better now but there are few tricky bits (there are always :P). Like how to switch off the SCR or even more interesting one is why it is switching off the load, when one should expect it to stay switched on until there is no current flowing through Anode-Cathode.

Well, think about it and please do post your thoughts why this may be.

Cheers

(to the follow up post)

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11 comments on “Netduino tutorial – Replacing Relay with SCR

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