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Easy Way To Understand The 11 Circuits Functions of SMPS With The Help Of Schematic Diagrams There are many types of SMPS in the market and it is impossible for me to explain all of them. The main point here is to guide you with the help of a SMPS schematic diagram, so that once you have understood how each circuit functions in the SMPS then there will be no problem in repairing all types of SMPS. Many SMPS in the market are quite the same, except that some use more components while others use fewer components. Some SMPS designs are larger while some are smaller. Some use a single power IC to drive switch mode transformer while others use either power FET or bipolar transistor to drive the switch mode transformer and so on. Let me put it in a simple explanation “Once you know the principle you will know the rest”. That means it is not necessary for you to understand all SMPS designs in the market in order for you to troubleshoot and repair them. Generally SMPS consists of about 11 main circuits in order to form the complete set (circuit). Either one of the circuits malfunction could cause problems in SMPS. The 11 main circuits are: 1. Input Protection and EMI Filtering Circuit 2. Bridge circuit 3. Start up and Run DC circuit 4. Oscillator circuit 5. Secondary Output Voltage circuit 6. Sampling circuit 7. Error Detection 8. Feedback circuit 9. Protection circuit and 10. Standby circuit 11. Power Factor Correction (PFC) Circuit In this topic, I have used the LCD Monitor SMPS and some other equipment schematic diagrams as a guide to easily explain how each of these circuits function and possible causes if they break down.

This is the first circuit where AC supply enters the SMPS. The Varistor R802 protects the power supply from transient voltages resulting from lightning strikes or power surge. The fuse F801 provides protection against circuit faults and effectively isolates the circuit from the AC supply source. Capacitor C801 and C824 are X capacitors and help to reduce the differential mode EMI. Resistor R801 discharges C801 and C824 on AC removal, preventing potential user shock. Inductor L805 is a common mode inductor and helps in filtering common mode EMI from coupling back to the AC source. C802 and C803 are Y capacitors connected from the Line/Neutral to Earth to reduce common mode EMI. Thermistor R840 limits the initial peak inrush current drawn by the circuit at start up

If you have seen all the photos, you will notice that almost all of the power supplies (although the power supplies use different electronic equipment) use common electronic components like Fuse, Bridge Rectifier, Filter Capacitor, Power IC, Power FET, Switch mode transformer, Optoisolator IC, Secondary output diodes, Secondary filter capacitors and etc. Due to this configuration, if you carefully study how power supply works (with the help of block and schematic diagrams) and know how to test electronic components in the power section, I don’t see any reason why you can’t successfully repair any power supply.

EMI/RFI filter section (board location marked as “L” and “C”) - EMI (Electromagnetic Interference), also known as RFI (Radio Frequency Interference), is unwanted electromagnetic energy polluting the environment. Its propagation via radiation and power conduction over system signal and power lines can affect the operating of electrical equipment around the source. This circuit consist of one or two coils and usually one or two non polarity capacitor depending on the design. Sometimes these components are integrated into a module as seen in figure The function of this circuit is to attenuate leaking magnetic field to avoid Radio Frequency Interference. This circuit is quite robust unless if a lightning strikes that could easily destroy the coils. You can test the coil with a normal multimeter set to ohms range and the non polarity capacitor with a digital capacitance meter.

The bridge circuit consists of a bridge rectifier (either 4 individual diodes or a single package rectifier) and a filter capacitor. The function of the bridge rectifier is to convert the incoming AC voltage into DC voltage and the filter capacitor (usually have the value of 220uf 400Volt) to remove the ripples and this will provide a nice DC voltage source to the primary winding of switch mode power transformer. For countries that use the 220 to 240 VAC, the DC voltage that you will get is about 300VDC and for countries that use 110-120VAC, the DC voltage that you will get is about 150 to 160 VDC. The DC voltage that you get is measured across the two pins of the filter capacitor using a multimeter. In some power supply design, you could see that there are capacitors connected across each diode in the bridge rectifier.

In Linear Power Supply AC voltage enters to the primary side of linear transformer and then converts 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.

SMPS የት ጥቅም ላይ ይውላል? ወጪን፣ መጠንን እና ክብደትን ለመቀነስ፣ monitors ፣ ቲቪዎች፣ የሞባይል ባትሪ መሙያ፣ ፒሲዎች፣ላፕቶፕ እና ካምኮርደር ሃይል ጥቅሎች፣ አታሚዎች፣ ፋክስ ማሽኖች፣ ቪሲአርዎች፣ ተንቀሳቃሽ ሲዲ ማጫወቻዎች፣ ዲቪዲ ማጫወቻዎች፣ ማይክሮኤሌክትሮኒክስ ላይ የተመሰረቱ መሳሪያዎች ,አውቶሞቲቭ፣ ኮምፒውተር፣ ኮሙኒኬሽን፣ የሸማች ኤሌክትሮኒክስ፣ እና የኢንዱስትሪ መተግበሪያዎች SMPS ይጠቀማሉ።

መስመራዊ የኃይል አቅርቦቱ ከአንድ በላይ የዲሲ ወጪ ሊኖረው ይችላል ግን አንደ SMPS ወጪ አይበዛም። በመስመራዊ ትራንስፎርመር ዑደት ውስጥ ችግር ካለ, ችግሩን ማግኘት በጣም ቀላል ነው ማለት እችላለሁ, ምክንያቱም በጣም ቀጥተኛ ነው. ስህተቱን በፍጥነት ለማወቅ የሊነየር ትራንስፎርመር (ኤሲ ቮልቴጅ) ወይም የዲሲ outputs (ከዲዲዮው በኋላ) ላይ ለመፈተሽ በቀላሉ መለየት ይቻላል

The linear power supply could have more than one DC output. If there is a problem in the linear transformer circuit, I can say that it is very easy to locate the fault because it is quite direct. Simply use a multimeter to test on the output of the linear transformer (AC voltage) or the DC output (after the diode) to determine the fault fast.

በ መስመራዊ የኃይል አቅርቦት(linear power supply) ውስጥ የ AC ቮልቴጅ ወደ መስመራዊ ትራንስፎርመር( linear transformer) primary side ከገባ በኋላ ይህ ትራንስፎርመር AC voltage ወደ ዝቅተኛ ወይም ከፍተኛ AC ቮልቴጅ ይቀይረዋ ከዛ በ diode እና capacitors አማካኝነት ወደ ንፁህ DC voltage ይቀየራል ከዛ ለሚንፈልገው የኤሌክትሮኒክስ እቃወች እንጠቀመዋለን