Universal Regulated Switching Computer Project
Universal Regulated Switching Computer Project @ Amazon.com
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There is two types of transformers in the market- linear transformer and switch mode power transformer. The transformers design is different. Sometimes it is just referred as ac transformer. Linear transformer largely applied in radio, project kits, VCD and etc while switch mode transformer may be found in Monitor, Tv, Fax and so on. A transformer comprises of two or more coils wound on the same core. For power transformers, the core material is normally iron. For a radio-frequency transformer, the core material is normally ferrite or air. The basic property of a transformer is to alter AC voltage. A transformer cannot alter direct current voltage. A step down transformer has a lower AC output voltage at it is secondary winding than the AC input voltage to it is primary winding. Conversely, a step up transformer has a higher secondary than crucial voltage. The transformer laminations or coating of shellac, enamel or varnish is to insulate adjacent turns from shorts amongst winding. I will not go too details when it comes to how transformer work and transformer calculation as you may read more details from most electrical and electronic transformers books. How to test transformers: Transformer failures are comparatively rare in most electronic equipment, equated with other components. If too much current goes through a coil or winding, the winding heats up and may either open up completely, or the insulation amongst turns of wire may break down, causing the coil to be partly or altogether shorted. Just like a coil, you may check continuity of any primary or secondary transformer winding. The actual value of DC resistance you read is rather meaningless, but at least you will recognise whether a winding is open. Checking linear transformer is rather straight forward. Apply the ac voltage to the crucial winding and suppose output voltage at the secondary side. No or low output voltage means the transformer winding has open or shorted winding. Look for any proof of overheating, such as darkened or blackened areas or a burnt smell. About how to test a power transformer-it is a little bit complicated. You can not utilise ac voltage to the instrumentation and suppose the desire output at the secondary side without connect to load other than as supposed or expected over voltage will occur (because you have got rid of all the secondary load) and will blow the power division which consist of power fet, pwm ic and etc. Switch mode power supply are designed to run with load while linear transformer may be test without load. The best way to test a switch mode power transformer is firstborn remove it from the board. Check only the primary winding as secondary winding failures are exceedingly rare. How do we recognise which one is the essential winding? Trace from the big filter cap the positive pin to see where the circuit goes. It will go to one of the pin of the transformer. Then look for the power fet middle pin which is the Drain and it will lead to another pin of the transformer. This two pins is the primary winding of the transformer. Checking the resistance of the primary winding only may disclose whether it is open but it cannot check if it has devised a shorted winding. Only by using a ringer test you will recognise if it shorted or not. A shorted turn in the necessary winding may cause the power division to blow. The most inexpensive ringer tester that i came all over is Dick Smith LOPT METER or flyback tester. Just connect the probes to the important winding and the result are without any delay seen from the Led bar graph. 4-8 bar represent a good winding, 1-2 bar represent partial short and if the led goes off means there is a heavy short in the winding. Besides checking the transformer it may be use to check B+ COIL, horizontal yoke coil and flyback indispensable winding and ballast (choke). The costly ringer tester is from sencore equipment. Sencore LC102 and LC103C besides checking capacitor it also have the capability to check all kind of winding. Whether it is a low voltage transformer, high voltage transformer, current transformer, pulse transformer, electric transformer, habit transformer this instrumentation will be capable to check and test it. If you do not wish to invest on this tester you may use a light bulb to check it. Remove one of the crucial winding pin and connect a 60 watt light bulb. One end to the circuit while the other to the transformer pin. If the bulb light and didn’t goes off suspect a shorted winding and if the light goes off, the winding is ok. Transformer repair is not easy and it require a good skill to do it. Most of the transformer repairer preferent to rewind larger winding such as fan, car alternator and starter. Switch mode power transformer is a little bit difficult to rewind because of the little size and low price. |
