Capacitor Resistors

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!

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A lie detector is an instrument uses to detect blood pressure, respiration and pulse. This instrument usually uses as a forensic instrument. It is commonly used in police station for investigation but this simple instrument can be use in your house.

This article tries to give you information to make a simple lie detector. Lie detector is also known as a polygraph. This simple detector can be extremely helpful if you want someone to tell you the truth. This simple instrument may be not as high-tech as the expert use but it could help you. This instrument operates by assessing the resistance of the skin that will down when you lie. Your skin will go down when you lie because lying will make you feel uncomfortable and nervous. This reaction will make your skin go down.

The first thing to do before making the detector is preparing all the details. Here is the list:

1. MISC 1 Case, Wire, Electrodes (you can use electrodes with alligator clip but you can also uses wire or strap like in hospital), the simple one is wires and tape.
2. 4.5V batteries (2)
3. electrolytic Capacitor C1 1uF 16V
4. R3 1 1.5K 1/4 W Resistor
5. Q1 1 2N3565 NPN Transistor
6. Analog meter M1 1 0-1 mA
7. R2 1 5K Pot
8. R1 33K 1/4W Resistor

These components can be easily found in electrical shops. You can read on the components part to make sure that you have bought the right things. Then you can put and attach each component with the wire. Connect the batteries separately using wires. Put the analog meter between the batteries, so there will be battery wires battery using the wires between the batteries you put the R3 and analog meter. Then, the R1 and R2 after the analog meter is put there. Q1 is near the electrodes.

You need to adjust the analog meter to 0. Attach the wire using tape to the back of the subject’s hand. If the analog meter changes from 0 it means that the subject is lying to you.

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The SM-1000M is a semi-automatic pick and place machine for prototyping and small lot production. It can work with a wide range of SMT components such as resistors, capacitors, QFP’s, SOIC’s and many others. High productivity is achieved by eliminating the need to refer to a PCB layout diagram as with manual machines. Software quides operator to the correct pick and place positions eliminating placement errors and reducing operator fatique. more detail info at v.vartsov@gmail.com

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In power applications, switches perform function to energize or unenergized an electric load. On the high end of the scale are load-break switches and disconnecting switches in power systems at the highest voltages (several hundred thousand volts).

Load-break switches are required to maintain the capability of interrupting the load current. The load break switch in a circuit with several hundred thousand volts, designed to carry a large amount of current without overheating the open position, having enough insulation to isolate the circuit in closed position, and equipped with arc interrupters to interrupt the load current.

Load break switches of air break are of versatile switch gear for transformer control & protection. They can also be used for Motor feeder in conjunction with Vacuum contactors. They are highly useful for Ring feeders for isolation of faulty section either manually or through remote control if fitted with motor operation. Load break switch in conjunction with HRC fuse can tackle high fault current and offer very good protection against dead short circuit capacity up to 40KA.The fault clearance and isolation through this combination will be achieved in a few milli seconds provided a proper selection of LBS and fuse is done. HRC fuses are manufactured with silver strips/silver coated Cu. Strips wires surrounded by granular quartz. When short-circuit occurs the metal element melts and the molten metal melts the surrounding quartz, making the combination an insulating material, called fulgarite. There will be a number of sections in the element which will create similar insulating media in quick succession and thus the arc will be extinguished in a matter of few milliseconds, say 5 to 8 milli-seconds, ie., less than 1/2 a cycle.

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