How to Identify and Evaluate Voltage Hysteresis

December 16, 2020 Cadence PCB Solutions

Key Takeaways

  • Voltage hysteresis is a common problem in both electrical and magnetic systems.

  • The main impacts of voltage hysteresis are in designing batteries and complex circuits.

  • Voltage hysteresis is an ongoing problem because it can’t be completely engineered away, despite advances in technology.

How to Identify and Evaluate Voltage Hysteresis

Integrated circuits

Voltage hysteresis can greatly impact integrated circuits, among other things.

When applying or removing current from an electrical system, designers can usually assume a negligible delay between the current change and the effect it has on components. Some delays are expected in certain contexts, such as propagation delays, and designers can plan for them by having updated references for the components they use. 

When the desired effect of applying or removing voltage happens after a delay, this phenomenon is referred to as voltage hysteresis. Voltage hysteresis can happen in many electronic components and constructs, including batteries, comparators, circuits, and transformers.

What is Voltage Hysteresis?

Hysteresis is broadly defined as a phenomenon where the state of a system changes significantly between the time it receives input and the time that input produces an effect. Voltage hysteresis is a specific type of hysteresis that occurs in electrical systems when current or voltage changes, but the effects of the changes are delayed past obvious intervals like propagation delays. 

Voltage Hysteresis and Magnetic Hysteresis

Voltage hysteresis is connected to magnetic hysteresis. Magnetic hysteresis occurs when an electrical current causes persistent magnetism, as can happen inside transformers and inductors. Since electric currents can create magnetic fields, it is possible to reverse some instances of magnetic hysteresis by applying a sufficiently strong current. Like voltage hysteresis, magnetic hysteresis can result in a loss of efficiency and has the added drawback of causing distortion in magnetized substances. 

Fortunately, magnetic hysteresis is not inevitable when voltage hysteresis is present; minimizing voltage hysteresis prevents magnetic hysteresis in many cases. Engineers may not want to prevent all magnetic hysteresis, however, since it also has some helpful uses in engineering.

Is Voltage Hysteresis Considered a Problem?

Voltage hysteresis is more predictable than some other types of hysteresis. Although it is an ongoing problem in many contexts, it also has some helpful uses in engineering, particularly in smoothing out noisy signals or input. 

Whether voltage hysteresis is beneficial or problematic depends on its application, and the level of hysteresis within an electrical system can also determine whether it is helpful or harmful. In general, the lower the level of voltage hysteresis in a circuit, the more efficient that circuit will be.

How Does Voltage Hysteresis Affect Engineering?

Voltage hysteresis is proven to be detrimental in maintaining charge within lithium ion batteries. Overcharging lithium ion batteries increases the possibility of voltage hysteresis, which negatively impacts the battery’s future ability to hold a charge. Voltage hysteresis can also come from many changes within a battery that can affect current flow during normal operation, including structural defects or magnetic distortion. Repeated battery charges increase the likelihood of these changes, which in turn increases voltage hysteresis risk. The process of charging a battery repeatedly, called cycling, increases overvoltage in more than half of cases, but not all of them. This is why some lithium ion batteries last for a long time, while others become useless quickly. The more overvoltage and voltage hysteresis occurs, the more battery life is reduced.

By contrast, voltage hysteresis is a stabilizing force in comparators. Voltage hysteresis smooths out current and voltage fluctuations inside a comparator. Maintaining consistent current and voltage in this way keeps components further down the circuit supplied with steady power and prevents failures. 

Voltage hysteresis is also critical to the concept of a memristor, or a resistor with memory. A memristor relies on a hysteresis loop to create a capacitance effect that allows it to have a variable resistance. The capacitance effect can be triggered by changes in voltage, temperature, or moisture. The changing of resistance can also be demonstrated in other components, and is known as the memristive effect.

How Should Designers Evaluate Voltage Hysteresis?

Designers should evaluate the effects of voltage hysteresis by the effect hysteresis will have on the system. While there is always an unpredictable element to hysteresis, designers can use known information about hysteresis effects to make educated assumptions about how voltage hysteresis will affect a new system they are building.

If a designer were building a project powered by lithium ion batteries, their knowledge of voltage hysteresis potential might lead them to modify their design to carefully manage current around the batteries. While a designer cannot prevent degradation within a battery, they can plan their project to reduce the chances of external forces causing increased degradation over time. A designer using a comparator with a logic circuit, on the other hand, may want to build some voltage hysteresis into their model. Adding the right amount of voltage hysteresis to a logic circuit can stabilize it so it doesn’t switch unexpectedly between states.

Voltage hysteresis can be a headache for designers, but it can be mitigated with the right tools. The PCB Design and Analysis overview page provides tools ideal for minimizing voltage hysteresis, including the Allegro PCB Editor

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

 

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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