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Troubleshooting linear power supply was rather easy as compare to switch mode power furnishes (SMPS). AC voltage enters to the essential side of linear transformer and then converted the AC into a lower or higher AC voltage depending on the secondary winding. The output AC voltage is then rectified and filtered by a diode and capacitors to construct a clean DC voltage. If there is a problem in the linear transformer circuit, I may say that it is very easy to locate the fault. This is someways dissimilar in the case of a switch mode power supply. The designs were elaborated and a good deal of technicians found it rather hard to to a complete degree perceive how the switch mode power furnishes work. The working principle of switch mode power supply is dissimilar from the linear type. First the AC voltage will flow to a full wave rectifier (bridge rectifier) which formulates an uneven DC output and then filtered by a big capacitor (usually 220 micro farad and up to 450 volts). The clean DC voltage will then flows to get started up resistors and to the input of switch mode power transformer. Once the voltage passed through the high ohms resistor (start up resistors) the voltage would drop to a value where it then flows to the VCC supply pin of Pulse width modulation IC. Once the PWM IC received the voltage it will output a signal to drive the transistor (or FET) and formulates a altering in magnetic field in the transformer essential winding. The altering magnetic field induces voltage in the secondary windings. Each of these AC voltage devised by the secondary windings is then rectified, filtered, and regulated to create a clean DC voltage. One of the main DC output voltage is the B+ that supply to flyback transformer (for TV and Monitor Circuit) The output from the B+ voltage supply is then connected, through a “feedback” loop (which consist of optoisolator ic and an error amplifier TL431 IC), back to the PWM IC. When the voltage from the B+ supply rises or drop a bit, the PWM IC will act to rectify the output. If you still do not comprehend the above explanation, please do not be admonish because you may always buy technical books and schematic diagrams and read it till you get the whole idea of how a SMPS work. You may ask a repair friend or even surf the internet for a better and easy explanation. Here I would like you to download a free SMPS article by Sencore and I found it to be a great support for you who are still struggle on how SMPS work and how to troubleshoot when it fails. You will have to ask your self what is the intention and it is function of the elements in the SMPS circuit and how to check them if they fail. Find out on your own the function of these elements in SMPS circuit: Bridge rectifier, Filter capacitor, Start up resistors Chopper/Power FET Pulse Width Modulation (PWM IC) Current sense resistor Switch mode power transformer Optoisolator/optocoupler Error Amplifier IC (TL431) Secondary diodes Secondary filter capacitors Push yourself further by searching the internet for the datasheet of a PWM IC share number. For example, UC3842 PWM IC is for the most part employed in SMPS. Do you recognise what the function of pin 5 of this IC is? Do you recognise which pin the VCC supply enters? Do you know what the actual voltage that flow to the IC is? Do you recognise which pin that drives the power FET? Can I get a alternate for this IC? And so on……… Let’s take a soldier as an example. Soldiers not only good in handling rifle but likewise knows all the details in regards to it. They recognise how to dismantle and assemble back their rifle fast (imagine in the middle of war the rifle jammed-they may repair it fast). They know how much each bullet cost, how far the shooting distance, how big is the diameter of the bullet, how numerous cm the length of the bullet and so on. Hope you don’t get bored with the soldier’s story, did you get the ideas? Any SMPS that comes throughout my repair bench, I would not without delay fix it, in fact I will take couples of minutes to make an analyzation of the circuit design and see it from all angles before I begin to repair. Troubleshooting SMPS is not fixed to only one procedure in fact a lot of electronic repairers have their own distinctive ways and methods to solve SMPS problems. Some prefer to use light bulb to isolate SMPS faults while others like to use resistors. Troubleshooting SMPS is fun and flexible but in a great deal of cases could make you get very frustrated too. Remember, don’t limit yourself to only one or two origins to get you understand and be competent to fix SMPS. If you have the budget, get the books that have affiliated to SMPS repair-study and begin doing practical with regards to it. Share your difficultnesses with other fellow electronic repairers and the most crucial thing is don’t give up. There’s lot of mountain in the journeying of our live and you yourself have to climb and conquer it. All the best! |
