Friday, December 30, 2011
Sunday, December 25, 2011
Understanding Transistor Data and Replacement
If, for some reason, you can't get an exact replacement for the transistor that you want to replace, you can refer to one of the transistor substitution guides or book, and try to identify a "near replacement". Beware, however. A substitution guide will sometimes list a replacement for your part, even though the two parts are not very similar. The most commonly used transistor substitution guides is the Philips ECG semiconductors Master Replacement Guide. Selecting the right transistor parameters or specifications for the equipment you repair will avoid callbacks from customers. Callbacks or repeated repairs due to wrong transistor substitution will cost you extra money and a waste of time.
Some important transistor parameters are:
Maximum collector-to-base voltage (VCBO) - The replacement part should have a VCBO rating equal to or higher than the original.
Maximum collector-to-emitter voltage (VCEO) - The replacement part should have a VCEO rating equal to or higher than the original.
Maximum emitter-to-base voltage (VEBO) - The replacement part should have a VEBO rating equal to or greater than the original.
Maximum collector current (IC) - The replacement part should be able to handle as much (or more) collector current as the original.
Power dissipation (PD Watts) - The replacement part should be able to dissipate as much (or more) power as the original part.
Gain (hFE) - The replacement should have a gain equal to or better than the original and it should be as close to the original specification as possible.
Gain-bandwidth (fT) - the replacement should have a transition frequency equal to or faster than the original and it should be as close to the original specification as possible.
Below is a table of application requirement and important specification that you can use for guidelines when comes to transistor substitution.
Application Requirement and Important Specifications
1. General purpose low level amplifier and switching transistors. Spec- hFE, IC (max), fT, VCEO
2. Power switching applications. Spec- VCEO, VCBO, hFE, IC (max), PD (max)
3. Low level IF/RF amplification. Spec- IC (max), fT, VCEO
4. Audio amplification. Spec- IC (max), PD (max), hFE, VCEO
5. High voltage transistors. Spec- VCEO, VCBO, IC (max), fT
Remember, the replacement transistor should not run hot and if problem still persist, try another replacement number or get the original number if possible. Do not overlook that the surrounding components also may caused the transistor to run hot even if original number is used.
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Wednesday, December 14, 2011
Discount Light Bulbs
There are several stores that carry all major brands of discount lighting. Prices are fixed very competitively in order to entice prospective customers. Both regular and online stores deal in discount light bulbs. Some stores lure customers with weekly special discount offers on light bulbs. Every week certain light bulbs are tagged with heavily discounted prices. These weekly specials are changed frequently, ensuring that some customers become regulars in order to pick up good discount deals.
Purchasing discount light bulbs can be good for maintaining a reserve supply of spare bulbs. A fair amount of window shopping will ensure that you get quality discounted bulbs easily. Discount light bulb dealers stock all varieties of light bulbs like regular household light bulbs, long-life bulbs, reflector bulbs, decorative bulbs, low-voltage bulbs, pool lamps, heat lamps, etc. Several stores offer quality brands at discount prices. They are able to do this due to arrangements with the manufacturer regarding trade volumes and stock lots.
Specialty light bulbs like Christmas lights, medical lights, fluorescent lighting, automotive lights, and halogen lights-you name it, and most discount light stores will have it.
Online discount light bulb stores enable you to compare brands for the best prices and then make a buying decision.
The most popular manufacturers like Carousel, Kodak, Sylvania, Philips, General Electric, Feit, and Westinghouse have arrangements with discount light bulb stores. So, one does not need to compromise quality for discount prices.
Most online stores contain a lot of information about light bulbs, and you can find out about different kinds of bulbs like halogen, fiber optic, fluorescent, automobile, projector, and black light. Information about how they work, what goes into their making, etc., is made available. You can also become familiar with terms like full spectrum, 12 volt, grow lights, ultraviolet, low-voltage, miniature bulbs, and the like.
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