Switching-Mode Power Supply Design Problem List

Annotated list of switching-mode power supply design problems and solutions.

| Stability | Controllability | Reliability | Efficiency | Power Management | Components | EMC | Radiation | Layout | Skills |


Power Supply Instability
Why switching-mode power supplies are so difficult to stabilize and how to keep them from oscillating in factory and field.
Ancient god of the shapeless void that preceded the creation of the earth -- who sometimes brings grief to power supply designers.
Input Filter Interaction
The EMI specialists once said adding an EMI filter could not cause a power supply to go unstable. They were wrong, it can, and quite frequently does.
Power Supply Entrainment
Switching frequency latching onto a variable load or noise frequency, often with detrimental results.
Emitter and Source Follower Oscillations
High frequency oscillations of power bipolar and power MOSFET transistors in follower circuits. You want to get rid of them before stabilizing the main loops.


Current-Limit Latchup
Powering a switching-mode power supply from a current-limited source can cause problems. This one catches many new power supply designers.
Solar-Array Latchup
Current-limit latchup problems can get quite subtle.
Controllability in Power Supplies
Discussion of ways power supplies get into modes they can't get out of, such as the start-up problem with no external supplies, latchup in overcurrent protection circuits, SCR type latchup, etc.


Underestimating Complexity of Power Supply Design
The sure path to schedule slips, cost overruns, and poor field reliability.
Low-Line Overstress
Why you never want to bring the input voltage up slowly on a new breadboard. Or conversely, why you want cycle-by-cycle current limit from the start.
Output Filter Overshoot
How you too can blow out every circuit in the system. Explaining how you allowed this to happen to your management or customer is not fun.
Junction-Path Shorts
Unless you have some old design manuals, you will only learn about this here. Unless you understand it, field reliability of your circuits will mostly be luck.
MOSFET Runaway
Everyone knows bipolar junction transistors can exhibit thermal runaway, but they once said power MOSFETs could not. Wrong again.
Design Review
You need it. Here is a cost-effective approach.


Capacitor Energy Loss
Since everyone knows this, how come it catches design engineers unaware time after time.

Power Management

Power Supply Sequencing
OK in a perfect world, but what happens when different circuits need different sequencing, the turn-on is non-monotonic, a fuse blows, etc.?


Transformer Saturation
Excessive volt-seconds or volt-second unbalance can cause transformers to saturate causing transistor failure and other effects.

Electromagnetic Compatibility

Several subjects.

Radiation Environment

Power MOSFET Single Event Burnout
Most know that power MOSFETs can be destroyed by single event burnout (SEB) and single event gate rupture (SEGR) induced by cosmic rays in space. But they may not know that cosmic rays are also a concern in avionics and sea level applications. And other devices are also susceptible -- including bipolar junction transistors (BJT), insulated gate bipolar transistors (IGBT), thyristors, high voltage diodes, small signal epitaxial npn BJTs, and CMOS PWM controllers and drivers.


Electromigration Depletions
Heavy currents can erode printed circuit traces.
Power Device Solder Joints
Large leads on devices such as magnetics and power resistors can "walk" out of solder joints and cause open circuits.
Ground Planes
Use ground planes in power supply layout with caution.


Problem Solving
The theoretical basis of the problem, relevance, solvability, solution approach used in this website.

The unlinked topics above are works in progress. If you have a particular interest in one the unlinked topics and want me to put it at the head of the list, send me an email or phone me. Contact Information

Original: February 1, 1998, revised November 25, 2007

Webmaster and editor: Jerrold Foutz