Left Display: Temperature Sensor (in water). Middle display: Voltage drop across a 0.005-ohm current sense resistor. Right display: voltage at the 0.5-ohm load resistor. ~80mV = 16A, at ~9V = (16A * 9V) = ~144W. Not much to see here, you can watch the water boil and the temp rise or just fast forward to the end.
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Operational Amplifier Circuits View the complete course: ocw.mit.edu License: Creative Commons BY-NC-SA More information at ocw.mit.edu More courses at ocw.mit.edu
Troubleshooting linear power supply was quite easy as compare to switch mode power supplies (SMPS). AC voltage enters to the primary 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 produce a clean DC voltage. If there is a problem in the linear transformer circuit, I can say that it is very easy to locate the fault. This is somehow different in the case of a switch mode power supply. The designs were complicated and some technicians found it quite hard to fully understand how the switch mode power supplies work.
The working principle of switch mode power supply is different from the linear type. First the AC voltage will flow to a full wave rectifier (bridge rectifier) which produces an uneven DC output and then filtered by a large capacitor (usually 220 micro farad and up to 450 volts). The clean DC voltage will then flows to start 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 produces a changing in magnetic field in the transformer primary winding. The changing magnetic field induces voltage in the secondary windings. Each of these AC voltage produced by the secondary windings is then rectified, filtered, and regulated to produce 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 correct the output.
If you still do not understand the above explanation, please do not be discourage because you can always buy technical books and schematic diagrams and read it till you get the whole idea of how a SMPS work. You can 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 help for you who are still struggle on how SMPS work and how to troubleshoot when it fails. You must ask your self what is the purpose and its function of the components in the SMPS circuit and how to check them if they fail. Find out on your own the function of these components 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 part number. For example, UC3842 PWM IC is mostly used in SMPS. Do you know what the function of pin 5 of this IC is? Do you know which pin the VCC supply enters? Do you know what the actual voltage that flow to the IC is? Do you know which pin that drives the power FET? Can I get a replacement for this IC? And so on………
Let’s take a soldier as an example. Soldiers not only good in handling rifle but also knows all the details about it. They know how to dismantle and assemble back their rifle fast (imagine in the middle of war the rifle jammed-they can repair it fast). They know how much each bullet cost, how far the shooting distance, how big is the diameter of the bullet, how many 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 across my repair bench, I would not immediately repair it, in fact I will take couples of minutes to analyze the circuit design and see it from all angles before I begin to repair. Troubleshooting SMPS is not limited to only one procedure in fact many electronic repairers have their own unique 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 some cases could make you get very frustrated too.
Remember, don’t limit yourself to only one or two sources to get you understand and be able to repair SMPS. If you have the budget, get the books that have related to SMPS repair-study and start doing practical about it. Share your problems with other fellow electronic repairers and the most important thing is don’t give up. There’s lot of mountain in the journey of our live and you yourself have to climb and conquer it. All the best!
This video demonstrates a forward and reverse bias test of an NPN transistor, care of George Brown College’s Electronics Technician certification program.
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AC# program I made in my spare time to help me with calculating the time constant for an RC circuit. It’s pretty easy to use and very accurate. You just input the capacitor’s capacitance in farads and the resistor’s resistance in ohm and it’ll give you the time constant. Bellow you can input the RC circuits voltage drop and the amount of time passes since the circuit was turned on(assuming the capacitor has no charge) and it will tell you how much voltage will be across the capacitor in that time. I have a nice little demo show it’s functionality.
workshop.search-autoparts.com You can’t measure voltage drop across a resistance unless current is flowing, right? Well, if something is draining the battery, there must be current flowing where there shouldn’t be. SO…let’s measure across easily accessible resistors…the fuses! And see where that current flow is.
Curious about the motor is connected to your microcontroller? In this NerdKits video tutorial, we explore engines from an electrical perspective and see how lead back EMF, resistive and inductive reasoning to build a motor control. Finally, we show two demos, a controlled switch to a motor with a digital output, and the other with a pulse width modulation (PWM) to adjust the speed versus the temperature. For more information, source code, and more, visit:www.nerdkits.com
Background
All batteries comprise two electrodes at which select chemical reactions occur to produce a stream of electrons flowing from one electrode to the other. One reaction is an oxidation, where electrons are liberated, the other is a reduction, where electrons are consumed. The voltage difference between these two reactions and the flow of electrons are the driving forces that enable the battery to provide electrical power. In a lithium Energizer battery, lithium (a light-weight, highly energetic metal) is the negative electrode and a mixture of carbon black, a polymer binder and iron disulfide form the positive electrode. A porous separator and a mixture of a lithium salt dissolved in an organic solvent round out the general composition of this battery such as dell Inspiron 1525 battery, dell Inspiron 1526 battery, Dell HP297 battery. The separator prevents electrical shorting of the two electrodes and the lithium salt in the solvent forms the battery electrolyte. When a load (e.g. a resistor) is placed across the battery terminals, the lithium metal is oxidized forming lithium cations (Li+) which frees electrons from the lithium metal. These electrons flow through the resistor toward the positive terminal of the battery. At the positive electrode, the iron disulfide (FeS2) is oxidized accepting electrons together with the lithium cation to form a new compound, lithium iron disulfide (LiFeS2), which is chemically stable.
However, the reaction sequence is not completed until the LiFeS2 is further oxidized with additional Li+ to eventually form elemental iron (Fe) and lithium sulfide (Li2S).
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