WHAT ARE THE GUIDELINES OF SMPS PCB DESIGN AND HOW SMPS REPAIRED?

In this article we are going to discuss about WHAT ARE THE GUIDELINES OF SMPS PCB DESIGN AND HOW SMPS REPARIED?

 

SIGNAL LINE CONSIDERATIONS

·         Place low pass filters on signal lines to reduce bandwidth to signal minimum.

·         Put feed and return loops close on wide bandwidth signal lines.

·         Terminate lines carrying HF/RF signals correctly(this minimizes reflection, ringing & overshoot).

·         Reduce lines carrying signals external to a board at the board edge, avoid lead terminations within the PCB and loose leads crossing the board .

·         Avoid cabling/tracking which is close to the quarter wavelength of the signal frequency, this can produce resonance within the signal conductor.

·         Track all signals on the upper layer.

·         Minimize rise & fall times on signal & clock edges (sharp edges produce wide hf spectra), slew rate limiting also reduces crosstalk. Power Supply Considerations

·         Eliminate loops in the supply lines.

·         Decouple power lines at local boundaries (use RCL filters with low Q).

·         Place high speed circuits close to Power Supply Unit(PSU) & slowest sections furthest away to reduce power plane transients.

·         Isolate individual systems where possible (especially analog & digital systems) on both PWR supply and signal lines.

 

PCB CONSIDERATIONS

·         Reduce slit apertures in PCB layout, particularly in ground planes or near current paths.

·         Areas of hi-z give rise to high EMI, use wide tracks for power lines on the trace side.

·         Make signal tracks strip line & include a ground plane & power plane whenever possible.

·         Keep High and radio frequency tracks as short as possible, lay out the HF tracks first.

·         Reduce track stubs, these cause reflection and harmonics.

·         On sensitive components & terminations use surrounding guardring & GND fill wherever possible.

·         A guard ring around trace layers reduces emission out of the board, only connect to GND at single point & make no other use of the guardring (i.e. don’t use to carry GND return from a ckt).

·         Avoid overlapping PWR planes, keep separate over common GND (reduces system noise and power coupling.

·         PWR plane conductivity should be high, therefore avoid localised concentrations of via & through hole pads

·         Try to make tracking run orthogonally between adjacent layers.

·         · Don’t loop tracks, even between layers, this forms a receiving or radiating antennae.

·         Don’t leave any floating conductor areas , these act as EMI radiators, if possible connect to GND .

 

HOW SMPS REPARIED?

When we Repair of SMPS PCB then we get different type of fault in this tutorial we are going to learn how to fault find in SMPS when we repair.

As per below picture see the all section of SMPS, first we have to every section work.

 

WHAT ARE THE GUIDELINES OF SMPS PCB DESIGN AND HOW SMPS REPARIED

 

If we did not get any output power then we will check one by one all step as per section.

First we check I/P connector of AC voltage.

Check fuse by Multi Meter when we check fuse it should be short showing in Multi Meter if it not showing shorting its means its fuse is faulty , if fuse found okay then check filter section it should be open capacitor , if found all capacitor, MOV are open its means this section is okay,

Then check bridge I/P voltage is getting 220VAC and output of Bridge should be more than 310 means VRMS , if we are getting 310VDC its means bridge is okay if we are not getting this voltage then bridge is faulty .

Then check VCC voltage at IC PIN of VCC as per datasheet of IC’s have different pin of VCC so please first read datasheet of IC which one is using in SMPS, then check VCC pin if not getting proper VCC then

 


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