10 votes

How to filter out the switching noise from a DC/DC converter

The Measurement Technique As mentioned in the comments by some of the folks, the first thing I would make sure is appropriate is the measurement technique. Measuring power supply noise accurately ...
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  • 5,150
8 votes

Why don't we make negative output voltage like this?

You're on the right track for one fairly common method of generating a negative output voltage. Take a look at the circuit below: simulate this circuit – Schematic created using CircuitLab The ...
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6 votes
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Sizing the DC/DC inductor for only momentary high currents

The inductor should be sized to handle the peak current loads without saturating. Most parts will spec both saturation (usually at 20-30% drop in inductance) and DC/thermal limits (typ. 30 C rise). ...
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5 votes

Why don't we make negative output voltage like this?

Your idea is correct, in that the polarity of the output of a single supply just depends on which one you "call positive". You could connect any component or circuit to the output to get one ...
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5 votes
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For a switching boost regulator, will putting the inductor on the bottom side of the PCB cause issues?

For switching regulators, loop area is usually the prime concern. Loops are not only in the XY plane, but are also in the Z axis as well. So, sometimes, you can get a smaller overall loop by placing ...
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5 votes
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What are the differences between these ferrite cores?

EC and ETD are almost identical. ER is slightly different. EC and ETD (ETD means economic transformer design) have both circular centre leg and circular winding window. ER's winding window is not ...
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5 votes

Using fuse during initial tests?

Why would you ever not use a fuse? It's basic protection. Sometimes a tungsten filament bulb or several in parallel (in series with the fuse) can help during early testing. It has relatively low ...
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5 votes
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Why is an inductor rather than a capacitor used to smooth switch mode regulators

In a switching regulator (buck, boost, buck-boost etc.) the inductor isn’t there to smooth the output. It’s there to store and release energy in a controlled way. The input switch will ‘charge’ the ...
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5 votes

Sizing the DC/DC inductor for only momentary high currents

The inductor current limit is thermal only. RMS current is what matters, and averaged over the thermal time constant, so, some seconds. The regulator however needs nominal inductance, so saturation ...
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  • 3,017
4 votes
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System blocks of switching power supplies

I am aiming for a 12V/10A (120 Watts) DC switching power supply. OK What I think the system block should look like 1- 220V AC to some DC value this will be mainly a transformer, plus usual filter ...
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4 votes
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Synchronous Buck Converter - PWM modulation

My question : Does the equation I used to calculate 5.5us only apply for no load conditions? When you have a synchronous buck regulator (as per your schematic), the duty cycle multiplied by the input ...
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4 votes
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Why does a flyback converter in DCM mode have a different oscillation waveform at start and end of MOSFET turn off?

Why does this primary inductance not participate during turn off or why does the leakage inductance not participate in oscillation before turning on? There is only one coupled inductor, right? Image ...
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4 votes

How to filter out the switching noise from a DC/DC converter

A passive lowpass is the correct way for this >= 100 MHz noise. How to realize it? If you have some voltage to sacrifice after the boost converter, put an RC filter. Inefficient but reliable. It ...
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4 votes

How to filter out the switching noise from a DC/DC converter

I'll try to solve as many problems as I can before going to the first PCB. Except... most of the problems you have are due to the assembly technique. It is entirely inappropriate for the application. ...
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4 votes
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How to check output voltages?

Judging from the bits that are truncated to the right in that service manual you copied, the right hand connector is numbered 1..12 from top to bottom like the other connectors (also notice the three ...
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3 votes

How to filter out the switching noise from a DC/DC converter

To get rid of these HF pulses, you need a filter. A LC filter is a voltage divider: at high frequencies, L attempts to create a high impedance, and C attempts to create a low impedance. The best ...
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3 votes

How to filter out the switching noise from a DC/DC converter

There are two very good answers already which cover measurement technique (to make sure the noise is even really there and as bad as you think it is) and layout (keep those loop areas small!). You ...
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3 votes
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Using fuse during initial tests?

Does the fuse protect the circuit from these failures (...?) Would the fuse protect the switching element? Probably not - this is consistent with my experiences as well. do you recommend continuing ...
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  • 947
3 votes

Why don't inverters use BJTs to easily produce a pure sine wave?

The overarching concern is efficiency. To avoid significant losses you would prefer to have no current with full voltage across the collector and emitter (transistor off), or full current and no ...
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3 votes
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determining the Bmax for inductor design

Generally the limiting factor is the temperature of the core. The heat generated within the volume of the core is just one factor. To this we have to add ... heat generated in the windings ambient ...
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3 votes

Are SMPS (inductor) current limits mostly thermal?

As with all components, an inductor has several limits, and you have to stay within them all. The inductor has a saturation current limit, above which the inductor value quickly drops, to possibly 1/...
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3 votes

Why does a flyback converter in DCM mode have a different oscillation waveform at start and end of MOSFET turn off?

In addition what Tim says in his answer which is absolutely correct, I'd like to remind you that in CCM the primary winding is not allowed to reset (the stored energy will be partially transferred to ...
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2 votes

Synchronous Buck Converter - PWM modulation

The equation applies for no-resistance condition and instantaneous switching. Include Rds(on), inductor ESR, and capacitor or supply impedances, and you will see it needs slightly more under load. ...
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  • 3,017
2 votes
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How critical is the sense resistor?

Besides the fact that your 1/3 Ω ±1% resistance is close enough (within the tolerance of the 0.34 Ω ±5% given), the exact value of the sense resistor is not typically critical in this type of ...
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2 votes

How critical is the sense resistor?

That should be perfectly fine. Your intuition is correct.
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2 votes

Why does a flyback converter in DCM mode have a different oscillation waveform at start and end of MOSFET turn off?

Draw out the circuit and note which components are on and off (transistor and diode) during which phases. Then simplify the equivalent circuit for each phase: While transistor is on, it becomes an ...
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  • 3,017
2 votes

Filter cap between positive rails in multi-rail power supply

FYI, variants 2 and 3 are worse, as the current from the top winding goes through the bottom, requiring thicker wire there (or more strands thereof). Better this way: Which you will notice is just ...
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  • 3,017
2 votes

For a switching boost regulator, will putting the inductor on the bottom side of the PCB cause issues?

Glue is typically unnecessary if you keep the components on the bottom of the board small. The inductor will require extra steps (glue) to keep in on during reflow. Of course if you keep all the large/...
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2 votes

How to check output voltages?

Although brhans is right, you can still find the voltages by simple continuity checks: It should be easy to find the GND/return of DC outputs because it's common for all. Find C881 on the board and ...
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1 vote

Are SMPS (inductor) current limits mostly thermal?

To add to Neil's answer -- Note that some types don't saturate very aggressively at all: most powdered iron (toroid and composite / molded) types roll off gradually, with -20 to -50% inductance being ...
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  • 3,017

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