The Function and Connection Method of Potentiometer

Introduction

A potentiometer is actually a variable resistor. Because it functions in the circuit to obtain an output voltage that is related to the input voltage (applied voltage), it is called a potentiometer.

Article Core	Potentiometer
Purpose	Introduce what the function of potentiometer and the connection method of potentiometer are.
Application	Semiconductor industry.
Keywords	Potentiometer

Catalog

Introduction
Potentiometer Overview	Circuit Graphic Symbol Main Parameters of the Potentiometer
	Resistance Change Characteristics of Potentiometer
	Potentiometer Resolution
	Potentiometer's Maximum Operating Voltage
	Potentiometer Noise
Potentiometer Structure and Type
Potentiometer Application	(1) Dimming Table Lamp Circuit
	(2) DC Stabilized Power Supply Circuit
Potentiometer Connection
Power Amplifier General Fault Repair	1.The whole Machine Doesn’t Work
	2. No Sound Output
	3.Sound Light
	4.Large Noise
	5.Distortion
	6.Howling
	7.Howling	(1). Power and Grounding Point Processing
		(2). Output Stage
		(3). Preamplification Section

Potentiometer Overview

Circuit Graphic Symbol

The unit of the potentiometer resistance is the same as the resistor, and the basic unit is also ohm, which is represented by the symbol Ω. The potentiometer is represented in the circuit by the letter R or RP (old standard W), and Figure 1 is its circuit graphic symbol.

Figure 1 Potentiometer Circuit Graphic Symbol

Main Parameters of the Potentiometer

The main parameters of the potentiometer are nominal resistance, rated power, resolution, sliding noise, resistance change characteristics, wear resistance, zero resistance and temperature coefficient.

1. The nominal resistance and rated power of the potentiometer

2. The resistance value marked on the potentiometer is called the nominal resistance.

3. The rated power of the potentiometer refers to the maximum power that can be consumed by the long-term continuous load at the specified rated temperature in the DC or AC circuit when the atmospheric pressure is 87~107kPa. The rated power series for wirewound and non-wirewound potentiometers are shown in Table 1.

Table 1 Nominal series of potentiometer rated power (unit: power)

Potentiometer	0.025, 0.05, 0.25, 1, 1.6, 2, 3, 5, 10, 16, 25, 40, 63, 100
Wire wound potentiometer	0.25, 0.5, 1, 1.6, 2, 3, 5, 10, 16, 25, 40, 63, 100
Non-wire wound potentiometer	0.025, 0.05, 0.1, 0.25, 0.5, 1, 2, 3

Resistance Change Characteristics of Potentiometer

The resistance change characteristic refers to the relationship between the resistance value of the potentiometer and the change of the length of the movable contact or the rotation angle of the rotating shaft, that is, the resistance output function characteristic. There are three commonly used resistance change characteristics, as shown in the figure.

Figure 2 potentiometer resistance curve

Straight type (X type): As the position of the moving point changes, the change in resistance is close to a straight line.

Exponential (Z type): The change in the resistance of the potentiometer is exponentially related to the change in the position of the moving corner point.

（1）The linear resistance of the linear potentiometer changes linearly with the angle of rotation. When the conductive material on the resistor body is evenly distributed, the resistance per unit length is approximately equal. It is suitable for applications where uniform adjustment is required (eg voltage divider).

（2）The exponential potentiometer is unevenly distributed due to the conductive material on the resistor body. When the potentiometer starts to rotate, the resistance value changes slowly. When the rotation angle increases, the resistance value changes steeply. The exponential potentiometer allows the power to be unequal in unit area, and the end of the resistance change is allowed to withstand a large amount of power. It is commonly used in volume adjustment circuits because the human ear is most sensitive to the sound of the sound. When the volume is loud to a certain extent, the hearing of the human ear becomes dull. Therefore, the volume adjustment generally uses an exponential potentiometer to make the sound change appear smooth and comfortable.

（3）The  logarithmic potentiometer has a non-uniform distribution of the conductive material on the resistor body. When the potentiometer starts to rotate, its resistance value changes rapidly. When the rotation angle increases, when it rotates to the end near the resistance value, the resistance value The change is slow. Logarithmic potentiometers are suitable for use in electronic circuits that are contrary to the requirements of exponential potentiometers, such as contrast control circuits and tone control circuits for televisions.

Potentiometer Resolution

The resolution of the potentiometer is also called the resolution. For the wirewound potentiometer, when the moving contact moves one turn, the output voltage changes discontinuously. The ratio of this change to the output voltage is the resolution. The theoretical resolution of a linear wirewound potentiometer is the reciprocal of the total number of turns of the winding N and is expressed as a percentage. The higher the total number of turns of the potentiometer, the higher the resolution.

Potentiometer's Maximum Operating Voltage

The maximum working voltage of the potentiometer refers to the highest operating voltage that the potentiometer can work under long-term reliable operation under the specified conditions, which is also called the rated working voltage.

The actual operating voltage of the potentiometer is less than the rated operating voltage. If the actual working voltage is higher than the rated working voltage, the potentiometer's power exceeds the rated power, which will cause the potentiometer to overheat and damage.

Potentiometer Noise

When the potentiometer slides on the resistor under the action of applied voltage, the electric noise generated is called the dynamic noise of the potentiometer. Dynamic noise is one of the main parameters of sliding noise. The magnitude of dynamic noise is related to the speed of rotating shaft, the contact resistance between contact point and resistor body, the non-uniform change of resistivity of resistor body, the number of dynamic contact points and the magnitude of applied voltage.

Potentiometer Structure and Type

The potentiometer consists of a housing, a sliding shaft, a resistor body and three terminals, as shown. There are many types of potentiometers. According to the adjustment method, they can be divided into rotary (or rotary handle) and straight slide potentiometers. According to the number of joints, they can be divided into single-connected and multi-connected potentiometers. There are two kinds of switches and switches; according to the resistance output function characteristics, it can be divided into three types: linear potentiometer, exponential potentiometer and logarithmic potentiometer. Such as solid potentiometers, chip potentiometers, carbon film potentiometers, glass glaze potentiometers, precision conductive plastic potentiometers and other potentiometers.

Potentiometer Application

(1) Dimming Table Lamp Circuit

Figure 4 shows a simple and practical dimming table lamp circuit. Adjusting the resistance of RP can change the charging time of capacitor C to reach the UG worth time, that is, adjust the conduction angle of the thyristor, so that the thyristor triggers conduction earlier or later, thereby adjusting the output voltage of the thyristor so that the voltage across the lamp can be 0. Change between ~220V. The voltage is high, the light is bright; the voltage is low, and the light is dark.

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Resistance Classification and Its Parameters

Introduction

Resistor is generally called resistance directly in daily life. It is a current-limiting component. After the resistor is connected to the circuit, the resistance of the resistor is fixed. Generally, it is two pins, which can limit the current through the branch connected to it. A resistor cannot be changed and is called a fixed resistor. A variable resistance is called a potentiometer or a variable resistor. The ideal resistor is linear, ie the instantaneous current through the resistor is proportional to the applied instantaneous voltage. Variable resistor for voltage division. On the exposed resistor body, one or two movable metal contacts are pressed. The contact position determines the resistance between either end of the resistor body and the contact.

Article Core	Resistance classification and its Parameters
Purpose	Introduce what the resistance classification and its parameters are.
Application	Semiconductor industry.
Keywords	Resistor.

Catalog

Introduction
Resistance Overview	1.Classification
	2. Main Performance Indicators
	3. Naming Methods
	4. Use Common Sense
Model Name of the Resistor
Main Characteristic Parameters
Chip Resistor Brief	Chip Resistor Classification
	Chip Resistor Package And Size
	Chip Resistor Package And Power Relationship
	Chip Resistor Characteristics
	Name Method of Chip Resistor
	Chip Resistor Purchase
	Chip Resistance Value Recognition

Resistance Overview

The basic knowledge resistor is the most widely used one of the circuit components. It accounts for more than 30% of the total number of components in electronic equipment. The quality of the circuit has a great influence on the stability of the circuit. Its main purpose is to stabilize and regulate the current and voltage in the circuit, and secondly as a shunt divider and load.

1.Classification

Resistors commonly used in electronic circuits have fixed resistors and potentiometers. According to different materials and processes, fixed resistors can be divided into: film resistors (carbon film RT, metal film RJ, synthetic film RH and oxide film). RY), solid core resistance (organic RS and inorganic RN), metal wirewound resistor (RX), special resistor (MG type photoresistor, MF type thermistor).

Table 1 Structure and characteristics of several commonly used resistors

Type of resistance	Resistor structure and characteristics
Carbon film resistor	Gaseous hydrocarbons decompose at high temperatures and in vacuum, and carbon deposits on porcelain rods or porcelain tubes to form a crystalline carbon film. Different resistance values can be obtained by changing the thickness of the carbon film and changing the length of the carbon film by the method of notching. Carbon film resistors have lower cost and performance.
Metal film resistor	The alloy is heated in a vacuum and the alloy is evaporated to form a conductive metal film on the surface of the ceramic rod. The groove can be changed by changing the thickness of the metal film. Compared with the carbon film resistor, this resistor has a small volume, low noise, and good stability, but the cost is high.
Carbon resistor	The mixture of carbon black, resin, clay and the like is pressed and then heat-treated. The resistance is represented by a color circle on the resistor. This kind of resistor has low cost and wide resistance range, but its performance is poor and it is rarely used.
Wirewound resistor	It is made of a copper or nickel-chromium alloy resistance wire wound on a ceramic skeleton. This type of resistance is fixed and variable. It is characterized by stable operation, good heat resistance and small error range. It is suitable for high power applications, and the rated power is generally above 1 watt.
Carbon film potentiometer	Its resistor body is made of a carbon film coated on a horseshoe-shaped paper board. Its resistance change and the position of the intermediate contact are linear, logarithmic and exponential. There are several types of carbon film potentiometers, large and small, and some are combined with switches to form a switch potentiometer.There is also a straight-slip carbon film potentiometer that slides on the carbon film to change the resistance. This potentiometer is easy to adjust.
Wirewound potentiometer	It is wound on a ring skeleton with a resistance wire. It is characterized by a small resistance range and a large power.

2. Main Performance Indicators

Rated power: The maximum power allowed to be dissipated on a resistor under the specified ambient temperature and humidity, assuming that ambient air is not circulated, in the case of long-term continuous load without damage or substantially no change in performance. To ensure safe use, the rated power is generally 1-2 times higher than the power it consumes in the circuit. The rated power is divided into 19 grades. Commonly used are 0.05W, 0.125W, 0.25 W, 0.5 W, 1 W, 2 W, 3 W, 5 W, 7 W, 10 W. The rated power of the non-wire wound resistor in the circuit diagram. The symbol is represented as follows:

Resistor resistance indication method

(1). Straight-mark method: The resistance value is marked on the surface of the resistor by the number and unit symbol. The allowable error is directly expressed as a percentage. If the resistance is not biased, it is ±20%.

(2). Text notation: A regular combination of Arabic numerals and literal symbols is used to represent the nominal resistance, and the allowable deviation is also indicated by a text symbol. The number before the symbol indicates the integer resistance, and the following numbers represent the first decimal resistance and the second decimal resistance.

a literal symbol indicating the tolerance

Text symbol D F G J K M

Allowable deviation ±0.5% ±1% ±2% ±5% ±10% ±20%

(3). Digital method: A three-digit digital representation of the nominal value on a resistor. From left to right, the first and second digits are valid values, and the third digit is the index, which is the number of zeros. The unit is Europe. Deviations are usually indicated by text symbols.

(4). Color scale method: Mark the nominal resistance and allowable deviation on the surface of the resistor with different colored bands or points. Most of the foreign resistors use the color standard method.

Black-0, Brown-1, Red-2, Orange-3, Yellow-4, Green-5, Blue-6, Purple-7, Gray-8, White-9, Gold-±5%, Silver-±10 %, colorless - ± 20%

When the resistance is four-ring, the last ring must be gold or silver, the first two digits are significant digits, the third digit is the power square, and the fourth digit is the deviation. When the resistance is five rings, the distance between the last ring and the front four rings is larger. The first three digits are significant digits, the fourth digit is the power square, and the fifth digit is the deviation.

Example:

1) A color ring is marked on one end of the resistor body, and the color code of the resistor is arranged from left to right. The resistance of Fig. 1 is 27000 Ω ± 0.5%.

2) The color ring mark of the precision resistor is represented by five color rings. The first to third color circles represent effective figures of the resistance, the fourth color ring represents a multiplier, and the fifth color ring represents a tolerance, and the resistance of FIG. 2 is 17.5 Ω ± 1%.

Represents 27000 Ω ± 5% Represents 27000 Ω ± 5%

Represents 17.5 Ω ± 1% Represents 17.5 Ω ± 1%

Unit labeling rules for resistors and potentiometers in the circuit diagram.

The resistance is above megaohms and the unit is marked M. For example, 1 megohm, marked 1M; 2.7 megohms, marked 2.7M.

The resistance is between 1 kohm and 100 kohm, and the unit is marked k. For example, 5.1 kilo ohms, marked 5.1k; 68 kilo ohms, marked 68k.

The resistance is between 100 kohm and 1 megohm, and the unit k can be marked or the unit M can be marked. For example, 360 kohms can be labeled 360k or 0.36M.

The resistance is below 1 kohm, and the unit Ω can be marked or not. For example, 5.1 ohms can be labeled 5.1 Ω or 5.1; 680 ohms, which can be labeled 680 Ω or 680.

Maximum working voltage: It refers to the voltage when the resistor works for a long time without overheating or electric breakdown damage. If the voltage exceeds the specified value, a spark is generated inside the resistor, causing noise or even damage. The table below shows the maximum operating voltage of the carbon film resistor.

Table 5 Maximum operating voltage of carbon film resistor

Nominal power ( W)	1/16	1/8	1/4	1/2	1	2
Maximum working voltage (V)	100	150	350	500	750	1000

Stability: Stability is a measure of the degree of resistance change of a resistor under external conditions (temperature, humidity, voltage, time, load properties, etc.)

(1) The temperature coefficient a indicates the relative change in resistance of the resistor for every 1 degree change in temperature, which is:

In the formula: R1 and R2 are the resistance values at temperatures t1 and t2, respectively.

(2) The voltage coefficient av indicates the relative change in the resistance of the resistor for every 1 volt change, which is:

In the formula: R1, R2 are the resistance values when the voltage is U1 and U2, respectively.

Noise Electromotive Force: The noise electromotive force of a resistor can be ignored in a general circuit, but it cannot be ignored in a weak signal system.

The noise of the wirewound resistor is only expected to be related to thermal noise (caused by molecular perturbations) only related to the resistance, temperature and frequency band of the external voltage. In addition to thermal noise, thin film resistors also have current noise, which is approximately proportional to the applied voltage.

High-frequency characteristics: Resistors are used under high-frequency conditions, taking into account the effects of their fixed inductance and inherent capacitance. At this time, the resistor becomes a DC resistance (R0) in series with the distributed inductance, and then the equivalent circuit in parallel with the distributed capacitance. LR=0.01-0.05 microhenry of the non-wire wound resistor, CR=0.1-5 picofarad The LR of the wirewound resistor is up to several tens of microhenries, and the CR is up to tens of picofarads. Even if it is a wirewound resistor without a sense winding, the LR still has a few microseconds.

3. Naming Method

According to the ministerial standard (SJ-73), the name of the resistor and potentiometer consists of the following four parts: the first part (main name); the second part: (material); the third part (classification feature); the fourth part (Serial number). Their models and meanings are shown in the table below:

Table 6 Model Nomenclature of Resistors

First part		Second part		Third part		Fourth part
Use letters to indicate the main name		Use letters to indicate material		Representing features by numbers or letters		Serial number
symbol	significance	symbol	significance	symbol	significance
R RP	Resistor Potentiometer	T P U C H I J Y S N X R G M	Carbon film Metal film Synthetic film Deposited film Synthetic film Glass glaze film Metal film Oxide film Organic core Inorganic solid core Wire winding Thermal Photosensitive Pressure sensitive	1，2 3 4 5 6 7 8 9 G T X L W D	Ordinary Ultra high frequency High resistance high temperature Precision Resistor - High Voltage Potentiometer - special function Special High power Adjustable Small Measuring Fine tuning Multiple circles	include: rated power Resistance Allowable error

Part 1: Main name		Part 2: Materials		Part 3: Feature Classification			Part 4: Serial Number
symbol	significance	symbol	significance	symbol	significance
					Resistor	Potentiometer
R	Resistor	T	Carbon film	1	ordinary	ordinary	For the main name and material, only the performance index and size are different, but the products that are used interchangeably are not affected, and the same serial number is given; if the performance index and size obviously affect the interchangeability, the capital letters are used after the serial number. As a difference code.
W	Potentiometer	H	Synthetic film	2	ordinary	ordinary
		S	Organic core	3	Ultra high frequency	――
		N	Inorganic solid core	4	High resistance	――
		J	Metal film	5	high temperature	――
		Y	Oxide film	6	――	――
		C	Deposited film	7	Precision	Precision
		I	Glass glaze film	8	high pressure	Special function
		P	Boron carbon film	9	special	special
		U	Silicon carbon film	G	High power	――
		X	Wire winding	T	Adjustable	――
		M	Pressure sensitive	W	――	Fine tuning
		G	Photosensitive	D	――	Multiple circles
		R	Thermal	B	Temperature compensation	――
				C	Temperature measurement	――
				P	Side heat	――
				W	Regulated	――
				Z	Positive temperature coefficient	――

Example: Name of RJ71-0.125-5.1kI: R resistor - J metal film - 7 precision - 1 - 0.125 rated power - 5.1k nominal resistance - I error 5%.

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