A Spike’s Mortal Enemy

MicroCrystal RV-8803 – A Really Accurate RTC June 17, 2019- RTC chips traditionally were the domain of Maxim and NXP. Switzerland-based MicroCrystal recently made quite a buzz with its RV-8803, which offers simple integration, an I2C interface and extreme accuracy. Let us start out by looking at a system overview. Figure one shows how this I2C RTC is made up internally – interested observers note … Continue reading MicroCrystal RV-8803 – A Really Accurate RTC
Analog Devices’ LTM2887 – If a Digital Bus Needs Galvanic Isolation June 15, 2019- In theory, digital buses are intended to connect things to one another. Sadly, one sometimes wants but a logical connection – in many cases, galvanic isolation helps out. Should you ever feel like isolating very fast buses, definitely give the LTM2887 a chance. From a technical point of view, Linear Technologies attempt at entering the … Continue reading Analog Devices’ LTM2887 – If a Digital Bus Needs Galvanic Isolation
AVAGO APDS-9008 or APDS-9005-020 – Keeping an Eye on Ambient Light June 14, 2019- Recent times saw quite a bit of interest for part numbers such as the APDS-9008 or APDS-9005-020 – they are a very interesting type of ambient light sensor. One of the oldest questions in regards to light sensors involves their spectral sensitivity. If a part is to output but one voltage level, the conversion between … Continue reading AVAGO APDS-9008 or APDS-9005-020 – Keeping an Eye on Ambient Light
STMicroelectronics’ LIS2DH12 – Low Power Motion Sensing June 12, 2019- Apple’s iPhone introduced gyroscopic sensors to a wider range – before that, accelerometers were not commonly found in consumer hardware. STM sells excellent parts which, however, get little media attention – time to take a look at the LIS2DH12. Integrating the part into your circuit as an MPU6500 alternative or MPU9500 alternative is not difficult. … Continue reading STMicroelectronics’ LIS2DH12 – Low Power Motion Sensing
Panasonic AMG8833 – FLIR for cheap June 7, 2019- FLIR made infrared thermal sensors cool – sadly, their parts are all but cheap (and suffer from export control problems). Panasonic’s Grid-EYE family is a low-resolution alternative which comes at significantly lower cost. From a technical point of view, Panasonic’s image sensor could not be simpler. We are looking at an 8×8 sensor with an … Continue reading Panasonic AMG8833 – FLIR for cheap
DipTronics DTS-62R-V – Small Switch, Very Big (and Very Cheap) June 5, 2019- When yours truly was but a lowly cadet, various US manufacturers produced (pricey but quite reliable) switches. Chinese vendors recently started to catch up – seeing the DTS-62R-V top our customer interest list shows that the run stage of the crawl-walk-run cycle is reached. DipTronics has been around the Asian switch market for ages, exhibiting … Continue reading DipTronics DTS-62R-V – Small Switch, Very Big (and Very Cheap)

Disturbances of the power supply are common…

Disturbances of the power supply are common – in the automotive space just as much as in classic AC grids. Additional demands imposed by various forms of alternate energy will only make the issue worse, thereby ensuring that surge protection will remain a topic.

Metal Oxide Varistors, also known as MOVs, are a knee-jerk reaction to designs facing line-related problems. In principle, a MOV is a variable resistor: as the supply voltage raises, its resistance falls.

GDT – the term is short for gas discharge tube, but the parts are also known as gas plasma arresters – takes a slightly different approach to the problem. A GDT is a tube filled with a special gas waiting for an opportunity to become conductive.

If only you could drill into the part…

When the voltage across the two terminals reaches a set point, the gas becomes ionized. From that moment onward, current can flow in the gas until it deionizes – a process which takes place when the current falls low enough.

Low capacitance…

Classic MOVs tend to have a high capacity – a problem not known to GDTs. We recently saw a lot of search interest in the Bourns 2049 family of diodes. It consists of 12 different parts able to clamp DC voltages from 75 to a whooping 600V.

In addition to their robustness – a spike of 20000A can be handled once, while the 15000A will be survived for a minimum 10 times – the parts are very low in capacitance. When dealing with a switching frequency of 1 MHz, Bourns promises a capacity of less than 1.5pF. Due to this extremely low capacity, GDTs find frequent use in telecom applications.

…Find out more!

GDTs really comes alone: in many cases, manufacturers combine them with a MOV or a set of zener diodes. This is caused by a physical effect: establishing the gas connection is a process which takes a bit of time. During this span, the spike can travel further down into the circuit, thereby giving all kind of grief to the system.

Given that GDTs are not particularly common, let OEMsecrets take you on a little ride through the world of documentation. First of all, Bourns provides an excellent overview of the technology here. Chinese vendor Bencent has a great introduction into the concept as whole – it can be found here.

…Finally

Littelfuse -a competitor, whose parts we also price-compare for you at OEMsecrets.com – cover combined MOV-GDT applications in a whitepaper available here.