Switchers

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These things are everywhere. Sometimes called the unfortunate name of wall warts, but better called a DC Power Brick, or AC/DC adapter.

List

Basic Operation

A good (practical) introduction is in Learn Electronics Repair 16, LED Disco Lights. https://www.youtube.com/watch?v=XgPZ1XpVppE But of course, you can refer to Art of Electronics or Practical Electronics for Beginners. Of course, the problem is that the latter two will tell you the schematic view of operation, whereas LER will show you it on an actual circuit board...

This comes down to: Knowing the schematic view and the circuit board view are different disciplines, and they both must be understood. I.e. drawing a schematic is different from layout, but you must have ability in both fields.

Inductorless Switching / Charge Pump converters

AoE3 9.6.3. Useful for <100mA of current. These are integrated into other ICs at times (covered in AoE).

Calculators

Some manufacturers will have calculators in addition to the app notes that you can use. These are often based on excel/spreadsheet software. Reference: https://www.eevblog.com/forum/projects/buck-loop-stability-tuning/msg5453216/?topicseen#msg5453216 As with any spreadsheet per B. Pease (For reference, see his columns https://archive.org/details/Bob_Pease_Lab_Notes), you can only trust it if, and only if, it doesn't have any mistakes in the formulas it's built with...

TI Power Stage Designer

A useful tool to have in your toolbox. A free Windows Download. I had a set of notes on this software, let me see if I can find it...

Tips/Techniques

Stock 5V and 12V

These are the most common voltages. Always try to standardize on the most common barrel plug (which is 2.1mm, and 5.5mm).

Diode Gone Wild

He has a number of videos that breakdown poorly made / falsely marketed switching power supplies and is of advanced knowledge about them. I will link some of his videos here that I found to be especially useful w.r.t. switchers.

  • https://www.youtube.com/watch?v=GICw2HpsInU - 12V 0.6A flyback power supply (with schematic & waveforms). This video shows a bog standard switcher with a control chip, a TL431, an opto coupler, a couple of snubber networks, and so on. He walks through the complete functionality of the adapter. Also uses an isolation transformer to probe certain waveforms, and shows for example, how all waveforms on the transformer are identical (but at different potentials depending on the turns for a given winding). He shows clearly how the control chip is powered from a separate winding, but also first by a capacitor and connection to the main rail via the startup resistors. He shows the current sensing resistors on the source of the control chip's internal mosfet. Additionally, he shows how the TL431 is powered by a resistor, even when the opto coupler is off, but still being on the same rail/trace. The voltage divider for the TL431 can also be spotted (that is used to signal the chip to power on the opto coupler when at, I think 2.5V). The adapter in this video is used for a AA/AAA battery charger.
  • https://www.youtube.com/watch?v=919KTlZKLcY - 12V 1A wifi router adapter test and analysis. Another good switcher diagnosis. This particular switcher omits some components, but may still pass EMI due to some other component choices, and it runs to 1A without failure.

Example of 5V 8-pin DIP Regulator

https://www.eevblog.com/forum/repair/need-help-to-identify-a-blown-chip-in-skynet-for-z12c-switching-power-supply/msg5445107/ It's always easy to spot the capacitor and diode.

Sync Pin on DC to DC converters

To get better power rail stability, and to reduce EMI, it's possible to either sync multiple DC - DC converters up, or have a power governor that controls when each one draws current. The sync pin requires a clock (pulse) input. The laurent article also goes into how the capacitors impact the power rail stability, proposing using a NOT gate to get a 180 phase shift on the clock from one converter to another. It also discusses ESR and its effect on limiting capacitance response.

http://betadynepower.com/wp-content/uploads/2017/11/Synchronization.pdf

https://www.ti.com/lit/an/sbaa035b/sbaa035b.pdf

https://www.analog.com/en/resources/technical-articles/reducing-noise-by-synchronizing-switching-regulators.html

https://www.laurtec.it/english/EMC_Testing/EMC%20Testing%20-%20009%20-%20DC-DC%20Converter%20-%20SYNC%20pin%20from%20EMC%20perspective.pdf