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How Does Temperature Hysteresis Work?

Key Takeaways

  • Learn what temperature hysteresis is.

  • Gain an understanding of the accuracy of temperature hysteresis.

  • Acquire some design tips for temperature hysteresis controllers.

Cooking is usually a stress reliever for me but my last attempt at pan-searing sea bass was a struggle. I just couldn’t get the temperature right with my erratic, slow-heating electric stove. Instead of being able to focus on the fish—my main priority—I would have to keep adjusting the knob to correct for a burner that was constantly either too cold or too hot. 

If I had a stove that was smart enough to sustain just the right amount of heat, it would probably come with a built-in temperature hysteresis controller. Let’s look at what temperature hysteresis is, another method for precise temperature control, and some design tips for a temperature hysteresis controller. 

What Is Temperature Hysteresis?

temperature hysteresis diagram.

An example of temperature hysteresis with a set point of 80°C.

If you’re using one of the latest computer graphics cards, you’ll probably come across the term “temperature hysteresis” in the settings. Depending on the value that you configure, the graphics card will be cooled to remain within a precise temperature range.

Hysteresis refers to a scenario where changes in a parameter lag behind the force that triggers them. Temperature hysteresis follows the same principle, where a temperature’s rise or fall trails behind the act of supplying or cutting off the heating/cooling supply. It’s a principle that is used for temperature control in various applications.

In a temperature controller, temperature hysteresis is defined by a minimum and maximum temperature value, where the heat will be turned on and off respectively. For example, if the graphics card’s VRM temperature is to be maintained at 80°C with a hysteresis of 5°C, the cooling fan will activate when the temperature reaches 85°C and turn off when the temperature drops to 75°C.

Besides graphics cards, temperature hysteresis can be used to optimize the power efficiency of a room’s temperature control or allow power regulators to reliably function without getting overheated.

How Accurate Is Temperature Hysteresis?

Controlling a thermostat with temperature hysteresis.

Temperature hysteresis is meant for applications that do not require precise control.

Temperature hysteresis is more accurate than having no regulation at all but it isn’t the most accurate form of temperature control that’s available. The result of temperature hysteresis, when plotted on a chart, is a series of oscillations between the hysteresis window. 

With temperature hysteresis, the temperature of the subject is allowed to fluctuate within a specific range. It’s algorithm isn’t meant to keep the temperature at a specific, set value. Therefore, temperature hysteresis is suitable for applications that do not require high-precision regulation.

If a system demands a precisely regulated temperature, using a PID (proportional-integral-derrivative) controller is a better option. A PID controller’s algorithm is based on the proportional, integral, and derivative constants and it automatically tunes temperature regulation depending on the monitored feedback. The result is a precise temperature value that’s unachievable with temperature hysteresis control.  

Designing a Temperature Hysteresis Controller

A temperature hysteresis controller and a microcontroller

A temperature hysteresis controller design starts with a microcontroller.

Due to its simplicity, you’re quite likely to come across a project that requires temperature hysteresis control—perhaps when you place a voltage reference in your PCB layout. Thankfully, building one is reasonably straightforward, but it needs both hardware and firmware to work properly. 

In terms of hardware, you’ll need a microcontroller that’s capable of controlling the heating element and sampling the temperature input. This means a digital output that’s connected to a relay or power MOSFET and an analog input connected to a temperature sensing circuit. 

The microcontroller will need a read/write memory—either an internal EEPROM or battery-backed up RAM—to store the hysteresis values. A user interface must also be built to allow configuration of the minimum and maximum limits. This can be in the form of a keypad, LCD, or connectivity to configuration software. 

The hysteresis controller is then brought to life via the firmware that’s loaded into the microcontroller. The firmware is relatively simple, as it involves sampling temperature input and comparing it against the saved hysteresis limits. It then turns the output on or off based on the measured input.

You shouldn’t have any serious difficulties with hardware design if you’re using the right PCB design and analysis software. Allegro PCB Designer has all the tools needed to design a temperature hysteresis controller with little effort. You can also use InspectAR to accurately assess and improve PCBs using augmented reality and intuitive interaction. Inspecting, debugging, reworking, and assembling PCBs has never been faster or easier.

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