“LED signs are safe due to the low voltage”, a slogan often heard or read in advertisements, might be misleading. Besides high-current hazards, and not just with circuit shorts,  hazardous high voltages may be present in the “low-voltage” LED circuit, depending on the power-supply type and construction.

In some cases of remote control, this hazard can even lead to the destruction of components. This discussion stems from some regulatory rules for the LED power-supply circuit designer. But let’s start from the beginning, because this problem surfaced in the last decade.
Low-voltage sign applications aren‘t new, and LED neon signs have been used in signage for nearly 20 years. With “classic” low-voltage power supplies – those with a bulky core-and-coil transformer at mains frequency to step down the 115V to 12 or 24V – everything was fine.

But then, as modern semiconductors and electronics evolved, “switching type” power supplies debuted, and they’ve become sturdy enough for 24/7 operation in the last 5-10 years. As discussions now include energy savings and wireless-communication safety, several regulations have been implied by authorities, such as:

1. 
Power supplies for lighting fixtures and signs must have a minimum efficiency of 95% or higher.
2. 
Power supplies must not generate high-frequency interference to wireless communication.

Core-and-coil LED power supplies often no longer meet requirement (1), and (2) has never been an issue because no frequencies higher than mains-line frequency are generated in the circuit. The modern, switching types meet (1), but require costly and bulky additional components to meet (2).
The operating principle of “switching” a voltage very quickly (30,000 to 1 million times a second) means the stepdown transformer for the same power rating can be very small and low cost compared to the “classic” types.

However, switching electricity very quickly generates high-frequency/radio-frequency (RF) currents, which must not leave the power-supply box/circuit to meet requirement (2), because the currents cause interference in nearby or remote electronic equipment. To prevent high-frequency currents from leaving the power supply, filter circuits must be used to block the high frequency on the mains and output leads of the power supply.
These filter …

Many of us take a multivitamin on a daily basis.  Although it is in theory possible to get all the nutrients your body needs from your food, most of us like the reassurance of a multivitamin to fill in any deficiencies. But you may have noticed that there are multivitamins available nowadays aimed at different age groups.  So you may wonder if your nutritional needs change as you age or if it is just a marketing gimmick.

Vitamins and Minerals For Children

While children are growing and developing they need a wide range of nutrients to support the changes their bodies are going through.  Ideally they would be getting these from their meals but there are many reasons they might not be getting the full amount they need.  Children on regular medication, such as asthma suffers, may not be absorbing as many nutrients from their food as normal.  Children who are very picky eaters may be missing out on some vital nutrients.

Concern for children’s development has led the Department of Health in the UK to recommend that all children aged 6 months to 5 years are given vitamin supplements containing vitamins A, C and D every day. However caution is needed when giving children supplements as the effects could be adverse instead of beneficial.  Ideally, a food dairy would be kept and research done to work out which vitamins or minerals their diet is missing. Care has to be taken in checking if some of the food they eat has been fortified with nutrients, such as B vitamins, vitamin D, calcium and iron, as then there is a possibility of overdosing.  If possible it would be advisable to consult a professional.

Vitamins and Minerals For Teenagers

Rapid growth is still taking place through the teenage years with the added complications of puberty.  Pressure from the media and friends can lead to restrictive diets and over exercising.  Greater freedom and responsibility for what they eat can result in many teenagers indulging in junk food.  The pressures of taking exams and make major life choices can lead to high levels of …