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Basic Knowledge of trimmer potentiometers

What is Trimer Potentiometer

Trimmer Potentiometers are semifixed potentiometers that it's resistance can be changed freely. They are used in some applications that usually almost have no need to adjust again after first time adjustment. So to avoid be touched easily, they are set inside of products. On the other hand, rotary position sensors are also called variable resistor, but they are the parts that adjusted by turning the knob outside of products.

There is a table about the classification of trimmer potentiometers.
In general classification, there are sealed type products with high regard for environment resistance and open type with high regard for cost. And there is also another way for distinguishing, multi-turn products with high resolution and single - turn products with high cost performance.

Structure/
Adjudtment turns
Sealed type Open type
Single - turn Sealed type/Single - turn Open type/Single - turn
Multi - turn
( ) number of rotation
Sealed type/Multi - turn  

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Applications of Trimmer potentiometers

Example1: Flicker adjustment for LCD (Liquid - crystal display)

To adjust the reference voltage (VCOM) of LCD.
With inappropriate reference voltage, there will be flicker on LCD screen.
Use trimmer Potentiometers to adjust reference voltage for flicker restraining.

LCD has some flickers if the voltage is not suitable for LCD.

LCD has some flickers if the voltage is not suitable for LCD.

You can reduce the flickers when you adjust the voltage by using trimmer potentiometer.

You can reduce the flickers when you adjust the voltage by using trimmer potentiometer.

Adjustment circuit

Example2: Gain adjustment for Blu-ray, DVD, CD disc reading optical pick - up.

As record media Blu-ray, DVD and CD etc. usually be used, and we use optical pick - up for the data reading and writing from disc. In an optical pick - up, there is a light - sensitive element to detect reflected light from disc.
And a trimmer potentiometer is used to adjust the sensitivity of this light - sensitive element.

Circuit example Playback system device (ex, DVD, CD, playback)

Circuit example Playback system device (ex, DVD, CD, playback)

Example3: Sensitivity adjustment for sensor products.

There are all kinds of sensors around our life.

  • Lights turn on automatically when human be detected.
  • Smoke detector for fire preventing.
  • Parking assist system for distance from car to wall.
  • Product detection sensor in factory.

For these sensors, trimmer Potentiometers are used for suitable sensitivity.

For these sensors, trimmer Potentiometers are used for suitable sensitivity.

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Principle of Trimmer Potentiomerets

A fixed resistor with a mechanism to change resistance construct a trimmer potentiometers. The principle is with the changing of resistive element length according a wiper sliding, the resistance will be changed. Use this method, with same sectional area, the resistance can be changed relative to resistive element length, and products can be manufactured in low cost.

Principle of Trimmer Potentiomerets
R = ρ × L/S
R: Resistance [Ω]
ρ: Resistivity [Ω/m]
L: Resistive element length [m]
S: Resistive element sectional area [m2]
  • The position of contact point decide the length of resistive element.
    Resistance between No.1 and No.2 (R12) will become higher if contact point become closer to No.3.
  • For easy introduction, we drew the resistive element like a rectangular solid. Actually, almost resistive element is round shape (U - shaped) .
    So the track of wiper is circle, and resistance is decide by the angle of wiper.

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Change in resistance of Trimmer Potentiometers

There is the relationship between wiper position (angle) and resistance in below figure.

*The output wave is besed on below conditions.
Resistive element is round shape (U - shaped) /Single - turn/No whirl - stop.

Construction
Single - turn, no whirl - stop type

Fig1. Construction Single - turn, no whirl - stop type


The relationship between wiper position (angle) and resistance

Fig2. The relationship between wiper position (angle) and resistance

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Feature of Trimmer Potentiometers

By using trimmer potentiometers, it is no problem to set surrounding circuit constant roughly.

Would you please use trimmer potentiometers if it is difficult to decided on a resistance value in your circuit. You can design your circuit roughly and quickly as the result.

In case of fixed resister, you will need much time to decided on the value.

In case of trimmer potentiometer, you can desing your circuit easily and speedy.

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