A project with only 2 parts, but is great for addressing an everyday situation that is irritating at best and dangerous at worst. This circuit protects the bulb in flashlights from high switch-on current to make the bulb last longer.
For a standard incandescent flashlight, this is a easy little modification make your flashlight bulbs last longer. High powered flashlights typically run their bulbs hot to get a brighter light from them. They also have a much lower on-resistance when cold, so that when you turn them on, the bulb passes a much higher current than it was designed for. This is why the most common time for a bulb failure is when turning it on.
The transistor and resistor limit the current while turning on the circuit and protect the bulb from an initial high current turn on. A simple resistor in series with the bulb might be a tempting option, but there are a couple problems with that approach. Just adding a resistor would reduce the voltage available to the bulb, and aid longevity, but that would reduce the brightness. The resistor would also be wasting energy getting hot instead of using that energy for light. This solution is better in that it limits current at startup and wastes very little energy when in use and when off.
In this application, it might be easier to insert the batteries in the flashlight “backwards” so the circuit connections and parts have the best fit in the body of the flashlight. Flashlight design was stagnant for decades, but now there are many new technologies available, and in some cases, it can even be easy to bring some of them to an older one you already have. In addition to this circuit, you could also take advantage of newer LED and battery technology to really increase the brightness, “on” time, and lamp life of your old flashlight.
Soft Start For Flashlights - [Link]
Richard Comerford writes:
The first LED replacements for 60 W incandescent bulbs are now appearing on shelves in local stores across the United States. Although current U.S. law will phase out only 100 W incandescent bulbs in 2012, one can easily find replacements for incandescent bulbs of other wattages – 15, 25, 40, 60, and 75. The initial cost of the LED bulbs is relatively high, but they more than pay for themselves over time with their longevity and energy savings.
The LED bulb that has received the most attention so far is the AmbientLED Model 12E26A60, a 12.5 W, 800-lm replacement for 60 W incandescent bulbs made by Philips Lighting (Figure 1). It is similar in configuration to the bulb that won the U.S. Department of Energy’s first Bright Tomorrow Lighting competition, or L Prize. It was also declared a standout among the CFL and LED bulbs in lamp and ceiling fixture tests conducted by Consumer Reports magazine.
Inside the New LED Retrofit Bulbs - [Link]
Step by step instructions for how to build and implement the replacement surgical lamp bulb system using an LED circuit developed by Mohammed Shafir and Zoe Englander as part of the course BME 262-Design for the Developing World at the Pratt School of Engineering, Duke University.
Replacement for surgical lamp bulbs using LED circuit – [Link]
John Graham-Cumming has posted an answer on the question “Why do Christmas lights all go out when one bulb blows?”. He also show us how to quick find the broken one. Check it out. [via]
Why do Christmas lights all go out when one bulb blows? – [Link]
This project is a flasher circuit able to turn on and off a bulb instead of a LED. It is based on the 555 timer IC is connected for astable multivibrator operation. It will create a flashing condition on the brake lights while the brake is pressed.
Automotive Brake Lights Flasher Project - [Link]