A silicon controlled rectifier (SCR) is a four-layer power semiconductor device. The term ‘silicon controlled rectifier’ was coined by General Electric when SCRs were first introduced in 1957. Like rectifiers, SCRs are unidirectional devices. Today, SCRs are recognized as a type of thyristor. Other types of thyristors, such as triacs, are inherently bidirectional. This FAQ […]
FAQ
Bidirectional power supplies support new UPS requirements: Part 1
Bidirectional power supplies dynamically direct power from multiple sources to different loads, some of which are also power sources at other times. We recently had a short-term power failure in the neighborhood due to a storm and a downed tree. As the outage lasted only about eight hours, it was a minor inconvenience in the […]
The humble neon lamp: down, but definitely not out, Part 3
Despite the convenience and availability of LEDs, the neon lamp still has a viable position as a power-on indicator as well as use in some specialty applications. Thus far, we have looked basic neon lamp principles and operation. This part looks at some special issues related to these versatile indicators. Q: Why use a neon […]
The humble neon lamp: down, but definitely not out: Part 2
Despite the convenience and availability of LEDs, the neon lamp still has a viable position as a power-on indicator as well as use in some specialty applications. This part continues the exploration of the neon lamp. Q: Are there more details of the various operational phases? A: Yes, the entire glow process has been studied […]
The humble neon lamp: down, but definitely not out: Part 1
Despite the convenience and availability of LEDs, the neon lamp still has a viable position as a power-on indicator as well as use in some specialty applications. The classic neon indicator lamp with its reddish-orange glow has been used since the early 1890s. Now, the availability, convenience, longevity, and other attributes of LED-based indicators have […]
How does current sensing work?
Current sensing and measurement are important in applications such as power conversion, battery charging, and industrial processes. Different current sensing technologies are used, depending on whether the measurement is for alternating current (AC) or direct current (DC) and how much current needs to be measured. This FAQ reviews Hall effect, and induction sensing and resistive […]
Measuring power choke inductances
The inductance of power chokes changes with current level. Conventional small-signal-measuring bridges are out of their depth here! Hubert Kreis, ed-k • Alan Lowne, Saelig Co. Inc. With the exception of air-core coils, all power inductances show a saturation behavior; their inductance drops with rising current. The core materials can lose permeability and then behave […]
Why I still like electromechanical relays – and you should, too (maybe)
The solid-state relay may be the first choice, but the venerable electromagnetic relay offers attributes the SSR cannot provide and so may be the best solution. Everything is solid-state these days, right? Even that one holdover, the vacuum-tube magnetron at the heart of the home microwave oven, is seeing some early signs of competition from […]
How to gauge LED flicker
A few years ago, back when ordinary LED bulbs still sold for north of $10 a piece, there was a great brouhaha about LED light flicker. Light flicker can certainly be dangerous. Sufficiently intense flicker at between 3 and 70 Hz can cause epileptic seizure in a small percentage of the population. And flicker that […]
Long-life batteries harness the passivation effect
A little known chemical reaction helps extend battery life. Sol Jacobs, Tadiran Batteries As remote wireless devices become increasingly essential to the Industrial Internet of Things (IIoT), there is a growing need to understand the principles behind extended battery life. Many IIoT nodes require a battery-driven energy source. These off-grid low-power applications fall into two […]