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Contents

• Prerequisites
• Circuit Protection
  • Introduction
  • Fuses vs Circuit Breakers
  • TVS diodes vs Varistors vs Gas Tubes
  • Other
• Bypass Capacitor

Prerequisites

None

Circuit-Protection

Introduction

Circuit Protection is an essential part of electrical engineering, focusing on keeping your designs safe from a variety of things. Lacking good circuit protection, your design could be unreliable, accidentally fry your most expensive components, or need to be replaced anytime something unfortunate happens. Good circuit protection is not necessarily hard, and it generally takes place near the power source, so it doesn't need to be present in every tiny segment of the wider circuit. Circuit protection generally comes with two choices, fuses vs circuit breakers (which protect against overcurrent), and TVS diodes, varistors and gas discharge tubes (which protect against temporary surges in voltage).

Fuses vs Circuit Breakers

Fuses and Circuit Breakers both fulfill the same essential function, they prevent overcurrent from frying all of your electronics. A short circuit happens somewhere else, and then current surges, which will lead to the fuses and/or circuit breakers from breaking the circuit minimizing damage and power losses. Their comparison can be found below:

Criteria	Fuses	Circuit Breakers	Notes
What is it	Wire that burns when too much current goes through it	System that moves away conductor if too much current goes through it by electromagnetic induction	-
Cost	Dirt Cheap	Varies	-
Reaction time	Very fast	Varies with cost	Some of the more expensive circuit breakers rival fuses in terms of speed
Size	Very small	Medium-Large	This also varies with cost
Reusability	Need a replacement every time it's tripped	Has no need for replacement unless it breaks	-
Applications	Sensitive electronics	3-phase applications	For everything else there is no cut and dry difference

TVS diodes vs Varistors vs Gas Discharge Tubes

TVS diodes, Varistors and Gas Discharge Tubes all perform the same essential function, they act to mitigate damage caused by short term voltage surges (transients). These transients can be caused by a variety of things, from turning a switch to lightning strikes to effectively luck. In all of these cases, these devices will try to effectively short from power to ground, thus absorbing that surge in power. Note that these devices cannot generally handle long term surges in voltage. Their comparison is provided below:

Criteria	TVS Diodes	Varistors	Gas Discharge Tubes	Notes
What is it	Basically a potent zener diode	A variable resistor whose effective resistance changes with applied voltage	A tube with gas that is generally an open circuit but can behave like a short if sufficient voltage is applied across it	-
Cost	Medium	Inexpensive	Varies	-
Reaction time	Very fast	Fast	Relatively slow	-
Size	Very small	Small	Larger	-
Voltage	Small	Large	Very Large	-
Lifespan	Medium	Small	Large	-
Leakage Current	Low	Relatively Large	Very small	GDT have follow current which needs to be mitigated for proper use
Applications	Sensitive electronics	High Energy Systems	Very High Energy Systems (power)	--

Other

There are other a variety of other circuit protection devices out there, but they are far less commonly used. These include PPTC/Resettable Fuses, Thermistors, Transient Blocking Units, Current Limiting Diodes, Thyristors and Ferrite Beads with inductors. I do not suggest using these for Astrobotics purposes (as of Summer 2024), but they may be encountered in industry for specialized purposes.

Bypass Capacitor

I suggest having a 100uF (or more depending on the power source) capacitor going from power to ground near your power source, ideally beyond other circuit protection. This capacitor's job is largely to just absorb many short term fluctuations in the power supply, to smooth it out. While not circuit protection, it is often placed near the other components so it is included here.