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FAQ - Trimpot® Trimming Potentiometers

Using Trimmers in Digital Electronic Applications

Q: I work with digital electronics, why would I use an analog component in the first place?
A: An important resource in helping to fine-tune digital elements includes using trimming potentiometers (trimmers) that adjust, regulate, or control circuit drift. Trimmers can enhance an application’s functionality by ensuring it is calibrated as precisely as possible. Fine-tuning of the output of a circuit with a trimmer is a perfect example of how analog technology is needed in a digital design.

trimmer_cutaway
Cutaway view of a trimmer

Q: Can you explain, in more detail, what a trimmer does?
A: Trimmers "trim" the value of a resistance, managing the adjustment, tuning, and calibration of the circuitry. They are part of the circuit design used to allow "tweaks" or adjustments to be made to offset and correct the variation of the other components. Trimmers allow this adjustment of a circuit so each of the components’ attributes are fully utilized. This is done without replacement of product on the board, which reduces costs and the risk of board damage.

Q: Will the use of trimmers complicate my design in a way that may affect my users?
A: Trimmer technology is used when a product must be calibrated before being shipped to an end-user. This set and forget function ensures that the product meets specifications from the start, plus allows for adjustments that may be required later to compensate for component variations over time. New designs can benefit from more exact tuning of board components, helping to achieve optimal performance with little or no customer interaction. Trimmers can also be set by the end-user for their specific performance.

Q: Please explain how a trimmer works.
A: A trimmer is an electromechanical device that acts as a variable resistor. It has three terminals that are connected to a resistive element and a movable wiper. As the position of the wiper is changed mechanically, the resistance value between the wiper and either one of the terminals connected to the element changes in a defined ratio.

Q: What is a trimmer’s most common usage?
A: Trimmers can be used as a rheostat to control current or as a voltage divider for adjusting voltage. More than half of all trimmer applications are used in rheostat mode (using the wiper terminal and either one of the elements terminals), which enables the device to be a variable resistor used to adjust the flow of current in a circuit. Using it in this manner, there is no basic input-output relationship, except as defined by the associated circuitry in which the trimmer is being used. The voltage divider mode is most commonly used in a control device. Control devices are used in applications in which frequent manual adjustment is anticipated and convenient adjustment is desired. Many of these applications involve man-machine interfaces including controls for audio/visual equipment. The voltage divider mode uses an input voltage connected to one of the element terminals, connecting the other element terminal to ground, and monitoring the wiper output. In the voltage divider mode, the trimmer adjusts power voltages as needed, ensuring an adjustable output voltage that is a fractional value of some input voltage.

 

Q: What can I expect from such an application?
A: For power supply-based applications, a trimmer, such as the Bourns® Model 3296 Trimpot® Trimming Potentiometer provides a high degree of accuracy, lifetime of 200 rotation cycles, and temperature rating from ‑55 °C to +125 °C. It also features a miniature package that requires a mere 3/8 inch × 3/8 inch. of board space.

Q: Once the trimmer is set, how often does it have to be adjusted?
A: Many applications with pre-calibrated electronics employ a trimmer for subsequent adjustments in response to component variations, as mentioned above. During routine recalibration of services, some trimmers are used in power supplies for accurate output voltage adjustments, ensuring consistent delivery of voltage levels, and to provide a minimal load at the output.

Q: What characteristics should be considered before choosing a trimmer?
A: A good place to start is to review the specifications of each model for absolute minimum resistance, adjustability, temperature coefficient, shock and vibration, load life, and resistance tolerance (see Frequently Used Terminology below). It is also important to select a quality and experienced trimmer supplier, one known for delivering a proven range of products.

Q: In which applications are trimmers most often used?
A: Communications, signal processing, image processing, and audio processing are just a few of the technologies that digitize data and information for processing, and require a high level of analog precision to interact with real-world phenomenon. In fact, applications that can benefit from trimmers are nearly limitless, and also include automotive; amplifiers; timer/oscillators; voltage regulators; power supplies; consumer electronics; musical instruments; and professional audio and lighting controls, as well as optical, pressure, liquid, and temperature sensors; printers; battery management devices; military products; gaming devices; scanners; and factory automation.

trimmer_applications
Typical applications for trimmers

Frequently Used Terminology
Absolute minimum resistance - Resistance between the wiper terminal (at center) and each end terminal—to provide a minimum value.
Adjustability - Design for the lowest value— for a more precise resistance adjustment.
Temperature coefficient - The resistance change factor per degree Celsius of temperature change— a lower value means a more stable trimmer operation.
Shock and vibration - The device’s ability to effectively operate in and withstand extreme environments.
Load life - The number of hours at which the device will dissipate a specified level of rated power under operating conditions within a noted variation.
Resistance tolerance - In addition to selecting the resistance value, consider selecting a trimmer with a tighter tolerance, which may require a higher-performing trimmer to match the requirements of certain applications, which place a high priority on accuracy.

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