Here we are discussing a pretty affordable yet surprisingly effective way to protect our power supply circuits from short circuits. This is super useful for anyone who loves tinkering with electronics, whether you're an enthusiast or a professional engineer.
Now we all know that power supply units are essential for our electronic projects. Even though most of us are using fancy power supplies these days that come with built-in protection features, there are still plenty of people out there who stick with the good old basic power supplies that don’t have any protective measures at all.
The biggest threat to any power supply unit is definitely the risk of a short circuit. This can happen at the output terminals, usually because of an accidental connection or maybe a problem with whatever load we’ve got connected.
There are quite a few electronic circuits out there that we could use to tackle this issue. However, the tricky part is that some of these circuits can end up being vulnerable themselves due to various electrical limitations.
But don’t worry. We’ve come up with a really clever solution to this problem. The best part is that we can use just a single relay to both sense when something goes wrong and trip the output to protect us from any malfunction.
How the Circuit Works
If we take a look at the circuit diagram we’ll see that there’s a relay connected directly to the DC output of our power supply. But this connection is made through what we call the N/O contacts of the relay.
Just so you know, N/O stands for "normally open" which means that these contacts are open at first. This keeps our output disconnected from the positive side of the power supply.
Now when we press the push button for just a moment it allows current to flow through and bypasses those N/O contacts. This energizes the relay coil, which then closes those contacts and latches them in place. The best part, It stays latched even after we let go of the push button!
As long as everything is running smoothly and under normal conditions the relay stays latched. But if there happens to be a short circuit at the output terminals we’ll see a sudden drop in voltage. The moment this voltage dips below what’s needed to keep the relay coil energized, it loses its holding strength.
This causes it to immediately release its contacts and trip, effectively cutting off the supply to the output. In doing so it also switches off the latch which helps prevent any hazardous short circuit conditions.
After this happens our relay goes back to its original state but we’ll need to reset it if we want to restore power to the output.
Power Supply Short Circuit Prevention using SCR and Triac Circuit
Lets talk about another cool circuit we can use for protecting our power supply from overcurrent situations. This one uses an SCR (Silicon Controlled Rectifier) along with a relay to give us the protection and cut-off we need. It’s pretty straightforward but super effective and it can handle up to 24 VDC.
Just keep in mind that the maximum output voltage will depend on the secondary voltage of the transformer we’re using.
Now whats really neat is that we can adjust the output voltage thanks to a 500-ohm potentiometer. This gives us some flexibility to get just the right voltage we want.
So here’s how it works: as soon as our protective circuit senses that there’s a spike in current like when something goes wrong the SCR kicks in and activates the relay coil.
This action cuts off power to the load putting the whole circuit into idle mode. If we ever run into that overcurrent issue, all we have to do is press S1 to turn off the SCR once we’ve sorted out the problem.
In this setup, we also have a 2N3055 transistor acting as our voltage regulator pass transistor. But if we want we can swap this part out for any standard voltage regulator IC like the LM317 and it’ll still work just fine!
To make things even better theres a 1-megohm variable resistor included in the circuit. We can use this to tweak how sensitive our SCR protection circuit is. This way we can fine-tune it to respond just right for our specific needs.