And then it is fed to a step-down transformer which is comparable to the weight and size characteristics of a transformer unit of 50Hz. The output of the step-down transformer is further fed into the rectifier. This filtered and rectified output DC power is used as a source for loads, and a sample of this output power is used as a feedback for controlling the output voltage. With this feedback voltage, the ON time of the oscillator is controlled, and a closed-loop regulator is formed. As shown in the circuit above, the switch is driven by the PWM oscillator, such that the power fed to the step-down transformer is controlled indirectly, and hence, the output is controlled by the PWM, as this pulse width signal and the output voltage are inversely proportional to each other. It is converted into DC by rectification process using a rectifier and filter.
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This article is written as per the request made by Mr. If charge full the green led will glow If charge low the red led will glow But now this charge not working Now the new diode also damaged Pls guide me sir In our area shop..
But my aim is not to buy new one.. Pls help me sir Sorry for bad english. You can try replacing it with a new one, and also make sure to change the adjoining 10 ohm resistor which also looks like it is burnt. Repairing the SMPS Circuit Referring to the images above, the primary side of the unit appears to be the popular 1 amp 12V SMPS adaptor using a mosfet based switching design, and includes an opamp based auto cut off charger section at its secondary section of the board From the first two images we can clearly see that one of the diodes being completely blown apart, and responsible for shutting down the entire circuit board.
This primary side switching causes an equivalent low voltage pulsating DC to be induced at the secondary side of the transformer, which is then smoothed using a large value filter capacitor at the the secondary side for acquiring the final stepped down SMPS DC output. From the image it appears that the entire design is based on a mosfet, inductor switching topology wherein the mosfet becomes the main switching element in the circuit. The diodes in the bridge rectifier appears to be the normal 1N diodes which are capable of handling not more than 1 amp current, therefore if this 1 amp value exceeds the diodes can get ripped through and damaged.
The diode might have burnt due to a high current passage which in turn might have happened due to a stalled mofet inductor operation. Which means that the mosfet might have stopped osculating causing a short circuit through itself, allowing the entire AC to go through the components within the input supply line.
The shown burnt SMPS can be repaired with the following simple steps. Now you can feel free to check the output voltage of the SMPS with a meter and confirm that it is producing the right readings. These may include high value resistors above 50K, or low value wirewound resistors above 1K.
Similarly, capacitors which may be rated above V can be left unchecked unless one of these look somewhat damaged externally. Testing for a Burnt Inductor Transformer Every SMPS circuit will essentially include a small ferrite transformer, which this part can also possibly become the cause of a burnt SMPS circuit, although the chances of a damaged transformer can be too remote.
This is because the wires inside the inductor might require some time to burn, and before this can transpire the other more vulnerable parts such as diodes and transistors would be forced to blow off ,preventing any further damage to the inductor. So basically you can be rest assured that the transformer is the one element which might be the safest and the undamaged part in a given faulty SMPS circuit.
If in a rare event the inductor burns, this would be distinctly visible from the burnt insulation tape which may be also melted and stuck with the winding. An SMPS with a burnt transformer could be virtually irreparable, because a burnt transformer would mean most of the elements burnt out, along with PCB tracks uprooted.
Time to buy a new SMPS unit. The secondary side mostly will not require any checking as it is isolated from the primary and can be expected to be aloof from the dangers. Well, this concludes this article explaining tips to repair an SMPS circuit, if you think I have missed some crucial points, or if you have something important to add in the list, please tell us through your valuable comments.
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