Over on YouTube [Lockdown Electronics] reviews an old bit of kit known as the Silicon Controlled Rectifier (SCR). Invented in the 1950s the SCR is a type of thyristor and they were popular back in the 1970s. They are often replaced these days by the TRIAC and the MOSFET but you might still find some old schematics that call for them and you can still buy them.
The SCR is a three terminal electronic switch which latches on. You apply a signal at the gate which allows the other two pins, the anode and cathode, to conduct; and they continue to do so until power is removed. The silicon inside the device is comprised of three semiconductor junctions, as: PNPN. The P on the left is the anode, the N on the right is the cathode, and the P in the right middle is the gate.
In the video [Lockdown Electronics] runs us through how to use them and compares them with a TRIAC. Unfortunately the lighting is a bit off for the demo of the SCR with AC power. To finish the video [Lockdown Electronics] wraps up with a windshield wiper control circuit from back in 1977 which is based around SCR technology. If you’d like to learn more about the SCR technology we have covered the basics.
Back in the mid-90’s I used SCRs to make a simple fault latch for our mountaintop Microwave sites. We would get a fault sent out but it didn’t narrow it down to a specific unit that was intermittent. It actually worked quite well.
Back in the 80’s I was in high school and I built so many different light effect boxes for clubs and mobile DJs. The heart of these were always the trusty and unbreakable BT151. From high, low and mid frequency filters and of course, the LM3914 (you needed inverters for the outputs). Zapped myself with 220 a few times. Ahhh those were the days…. 😁
Me, too! Though, starting in the 60s. At around 15, I got written up in a local newspaper as a “boy genius” for having done lightshows for college dance events (but really just using ideas that I cribbed from Edmund Scientific :-). Have you stayed with color organs? In my retirement years I’ve been having a blast experimenting with modern tech to make ever-more-sophisticated music visualizers.
SCRs are used today in a variety of power applications including UPS that power the internet. They are definitely not relics.
Well, SCRs and IGBTs.
I remember DC drive systems from 1974-1978 using hockey puck sized SCRs in parallel banks of 6 pulse 3-phase rectifiers. Same cicuitry still used for Turbine-Generator rotor current supply (4kA & 700V).
“They are often replaced these days by the TRIAC and the MOSFET but you might still find some old schematics that call for them and you can still buy them.”
I could argue that 1) the TRIAC is still a SCR, 2) a MOSFET will never replace the thyristor in crowbar circuits and 3) they are still the king in HVDC applications where you cannot beat their multi-kV commutation capability.
You win! :)
I vaguely recall a Light Activated SCR (LASCR) circuit, used to slave camera flash units.