This brief tech blog is one of three that will be appearing on Planet Analog leading up to our “Ask the experts” chat session on Wednesday, September 24, 2014 at 10:00 a.m. PT (1:00 p.m. ET).
If you want to be a successful design engineer, you need to know your enemy. Who is one of the biggest enemies of your circuit design success? Over-current conditions.
Over-current conditions result when the current in the circuit exceeds the rated amperage capacity of the circuit or of the equipment connected to the circuit. Whether you’re designing automotive, LED lighting, or consumer electronics, over-current conditions are a threat to the reliability and durability of the technology you’re developing. When are these situations most likely to occur? When there’s a loose connection, ground fault, short circuit or surge power draw.
Now that you know your enemy, how do you protect your design against it? Over-current circuit protection can be accomplished with the use of either a traditional fuse or positive temperature coefficient (PTC) device.
Fuses are current-sensitive devices purposely designed to serve as the weak link in an electrical circuit. They provide reliable protection for discrete components or complete circuits by melting under current overload conditions. PTCs
PTC devices are passive electronic components used in a wide variety of telecom, computer, consumer electronics, battery, and medical electronics product applications. In these particular applications, over-current events are common and automatic resettability is desired.
Fuse vs. PTC selection
Fuses and PTCs offer their own unique operating characteristics and benefits. Understanding the differences between the two technologies will simplify the selection process — depending on the application.
The most obvious difference is that PTCs are automatically resettable whereas traditional fuses need to be replaced after they are tripped. After most over-current events, a fuse will completely stop the flow of current — a result that may be very beneficial in critical applications. In contrast, PTCs significantly increase in resistance thereby creating the over-current protection, but still allow a trickle current to flow.
Because they reset automatically, many circuit designers choose PTCs in instances where over-current events are expected to occur by user created faults. Also, PTCs are useful when trying to maintain low warranty and service costs, constant system uptime and user transparency. They are often selected for use in circuits that are difficult to access or in remote locations, were fuse replacement would be challenging.
There are several other operating characteristics that should be considered when choosing between a PTC device and a fuse. For optimal safety and reliability, we recommend that you test and verify device performance before use within the end application.
Do you want to learn more about the importance of circuit protection (CP)? Have a question or two about choosing the right CP solutions that combat against over-current conditions in your design?
Join us for the Planet Analog Chat Session on Circuit Protection, September 24, at 1:00 p.m. ET (10:00 a.m. PT).
You can leave some early questions and observations on the chat board, which is now live. You will need to register on Planet Analog in order to ask questions and comment on the chat session.
Sign up now by clicking here to join or to leave an early message. Just click “Reply” or “Post Message” when you get to the site.