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| {{Explanatory Guide | | {{Explanatory Guide |
| |Device=Resistors | | |Device=Diodes |
| |Type=Component | | |Type=Component |
| |Difficulty=1. Easy | | |Difficulty=1. Easy |
| }} | | }} |
| This article aims to provide a comprehensive overview of resistors from a repair perspective, detailing their function, types, common issues, testing methods, and replacement considerations. | | This article aims to provide a comprehensive overview of diodes from a repair perspective, detailing their function, types, common issues, testing methods, and replacement considerations. |
| [[File:Resistor symbols.jpg|thumb|Resistor symbols commonly found in schematics (Figure 1)]]
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| ==What is a resistor?== | | ==What is a Diode?== |
| A resistor is a fundamental electrical component found in every single electronic device and circuit. '''Its role is controlling the flow of electric current within a circuit (limit the current).''' | | A diode is a fundamental semiconductor device commonly found in electronic circuits. '''Its primary function is to allow the flow of electric current in one direction while blocking it in the opposite direction.''' This property makes diodes useful for rectifying alternating current (AC) into direct current (DC), protecting circuits from reverse voltage, and more. |
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| Resistors are measured in "Ohms (Ω)"
| | Diodes have different characteristics found in their datasheets, the most important value when measuring is the forward voltage drop in "Volts" |
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| Resistors in schematics look like in Figure 1 and are usually denoted with the letter R followed by an identifier number. (E.g. R381)
| | Diodes are typically identified by the symbol shown in Figure 1 and are usually denoted with the letter D followed by an identifier number. (E.g., D38) |
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| === Function === | | ===Function=== |
| Even though resistors can only limit the current, they can be used in clever ways -using physical laws- to perform different functions in electrical circuits. Here are a few common ones:
| | Diodes serve various functions in electronic circuits, with the most common being: |
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| ==== Voltage divider ==== | | ====Rectification==== |
| A voltage divider is an electrical circuit that divides a higher input voltage into a lower output voltage using two or more resistors in series. It is commonly used to create reference voltages or reduce voltage levels for specific applications in electronics.
| | Diodes are frequently used to convert AC voltage to DC voltage. They allow the current to flow during the positive half-cycle of the AC signal and block it during the negative half-cycle, effectively converting the signal to a unidirectional flow. |
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| The output voltage is determined by the ratio of the resistance values in the circuit like so:[[File:Voltage divider circuit.png|thumb|234x234px|Voltage divider circuit (Figure 2)]]
| | ====Voltage Regulation==== |
| '''Voltage Divider formula (assuming NO LOAD on Vout):''' <math>V_\mathrm{out} = \frac{R_2}{R_1+R_2} \cdot V_\mathrm{in}</math>
| | Zener diodes, a specific type of diode, are used to regulate voltage. They maintain a constant voltage across their terminals, making them suitable for stabilizing power supplies and protecting sensitive components from voltage spikes. |
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| Uses:
| | ====Switching==== |
| | Diodes are used as switches in various applications, including signal routing, switching power supplies, and protection against reverse voltage. |
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| * Reference Voltage: Voltage dividers are employed to create stable reference voltages for sensor calibration, analog signal processing, and feedback in control systems.
| | ===Types=== |
| * Voltage Scaling: They can be used to scale down high input voltages to levels suitable for analog-to-digital converters (ADCs) or microcontrollers, ensuring safe and accurate measurements.
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| * Biasing Transistors: Voltage dividers set the base voltage of transistors in amplifier and switching circuits, influencing their behavior.
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| * Voltage Monitoring: In battery-powered devices, voltage dividers are used to monitor the battery voltage to determine its state of charge.
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| * Voltage Regulation: In some cases, voltage dividers are used in conjunction with other components to approximate voltage regulation in simple power supply circuits.
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| * And much more
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| ==== Resistor sensors ==== | | ====Regular/Rectifier Diodes==== |
| Resistor sensors, also known as resistive sensors, are a class of sensors that rely on changes in resistance to detect and measure various physical phenomena, such as temperature or light
| | Regular or rectifier diodes are the most common type of diodes. Mainly used for converting AC to DC. They come in various package types and sizes. |
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| ==== Pull-up / Pull-down ====
| | If used to rectify mains AC to DC, you'll typically find 4 didoes in full bridge configuration in one package. |
| Pull-up and pull-down resistors are commonly used in digital electronics to ensure that a digital input signal is in a known state when it's not actively being driven by an external source. They are essential for preventing floating or undefined states
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| A pull-up resistor connects a digital input to a voltage level (usually Vcc, which is the supply voltage). This effectively "pulls up" the input to a logical HIGH state when the switch or sensor is not actively grounding it. Pull-up resistors are often used with switches and sensors that are normally open. When the switch is closed or the sensor is active, it grounds the input, causing it to read as LOW. When the switch is open or the sensor is inactive, the pull-up resistor ensures the input reads as HIGH.
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| A pull-down resistor connects a digital input to ground (GND). This "pulls down" the input to a logical LOW state when the switch or sensor is not actively driving it HIGH. Pull-down resistors are typically employed with switches and sensors that are normally closed. When the switch is open or the sensor is inactive, it keeps the input grounded (LOW). When the switch is closed or the sensor is active, it drives the input HIGH.
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| Usually, pullup or pulldown resistors are 2.2k to 10k ohms.
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| ==== Current measurement ==== | | ====Zener Diodes==== |
| Current measurement using shunt resistors is a widely used method in electronics and electrical engineering to accurately measure the current flowing through a circuit.
| | Zener diodes are designed to maintain a constant voltage across their terminals when operated in the reverse-biased breakdown region. They are used for voltage regulation and are often labeled with their nominal voltage value. |
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| The principle behind this technique is Ohm's Law <math>V = I * R</math>
| | ====Schottky Diodes==== |
| | Schottky diodes are known for their fast switching speed and low forward voltage drop. They are used in high-frequency applications and as rectifiers in power supplies. |
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| A low resistance, precise "Shunt" resistor is used in series with the rest of the circuit "load" to measure the current flowing in said circuit by measuring the voltage drop across the shunt. In some cases, the voltage drop is very tiny and needs to be amplified using [[Repair Basics - Operational Amplifiers (Op-Amps)|Op-Amps]]. In modern electronics, specialized Integrated Circuits "ICs" are used to measure the voltage drop/current draw.
| | ====Light Emitting Diodes (LEDs)==== |
| | LEDs are a specialized type of diode that emits light when forward-biased. They are commonly used in displays, indicators, and lighting applications. |
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| The shunt resistor is specifically designed with a known and well-calibrated resistance value, very close to 0 Ohms, usually 0.002.
| | ====Varactor Diodes==== |
| | Varactor diodes, also known as varicap diodes, are used in tuning and frequency modulation applications due to their ability to change capacitance with a varying reverse bias voltage. |
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| Usually, the shunt resistor is placed where a fuse might be, where all the current passes through it. Sometimes, the shunt resistor itself acts as a fuse if a short circuit happens since it will be the highest resistance point in the circuit.
| | ====Photodiodes==== |
| | Photodiodes are light-sensitive diodes that produce a current in response to incident light. They are used in light detection and optical communication systems. |
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| [https://www.researchgate.net/figure/Current-measurement-with-a-shunt-resistor-and-low-pass-filteradapted-from-14_fig2_221045514 Example and further reading]
| | ===Testing a Diode=== |
| | Testing a diode can help determine if it is functioning correctly. Most diodes can be tested using a digital multimeter in diode test mode. It's best to test the diode '''outside the circuit'''. |
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| === Types ===
| | # Identify the anode and cathode terminals of the diode. The cathode is typically marked with a band or line on the diode's body. |
| | # Set your multimeter to the diode test mode (usually indicated by a diode symbol). |
| | # Place the red probe on the anode and the black probe on the cathode. |
| | # The multimeter should display a voltage drop reading (around 0.2 to 0.7 V for silicon diodes). If it shows "OL" or less than 0.2, the diode is likely faulty. |
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| ==== Fixed value resistors ====
| | You can test the diode in-circuit, but keep in mind that other components in the circuit may affect the measurement '''but only lowering it'''. |
| These are the most common type and come in various packages, sizes, and materials.
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| [[File:Resistor types.png|thumb|192x192px|Different types of resistors (Figure 3)]]
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| ===== SMD Fixed value resistors ===== | | ==Replacement Considerations== |
| SMD (surface mount) resistors are usually black with numbers on top. [https://www.newmatik.com/knowledge-base/KB-EN-00928/resistor-case-sizes They come in different sizes], and there are multiple standards for value marking, most common one is numeric where the last number is the multiplier or "number of zeroes" (for example, 221 on a resistor means 220 ohms).
| | When replacing a diode, always read the datasheets and pay attention to the following parameters: |
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| "R" on SMD resistors means a dot "." (for example 5R60 means 5.60 Ohms)
| | # '''Type:''' Ensure the replacement diode is of the same type and has similar electrical characteristics as the faulty diode. |
| | # '''Forward Voltage:''' Match the forward voltage rating closely to the original diode. Using a diode with a significantly different forward voltage may affect circuit performance. |
| | # '''Reverse Voltage (Zener):''' Pay attention to the reverse voltage rating. That's the most important parameter for Zener diodes. |
| | # '''Power Rating:''' Match or exceed the power rating of the replacement diode with the original diode. |
| | # '''Package Type:''' Choose a replacement diode with a compatible package type and size. Different packages have different mounting and pin configurations. If space is not a concern, you can use any size as it won't affect the circuit behavior. |
| | # '''Reverse Recovery Time:''' In high-frequency applications, the reverse recovery time of the diode is crucial. Ensure the replacement diode has a similar or faster reverse recovery time. |
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| [https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-smd-resistor-code Here is an online calculator] for the 3 widely used standards.
| | Replacing a diode with the wrong specifications can lead to circuit malfunctions or failure, so it's essential to choose a replacement carefully. |
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| ===== THT Fixed value resistors =====
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| THT (Through Hole) resistors are varied in colors and [https://www.electricalengineering.xyz/sheet/resistor-power-rating-chart/ sizes], they usually have [https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code colored bands on them to indicate their value]. On ceramic type, the value is written.
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| ==== Variable resistors ====
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| ===== Potentiometers =====
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| These can be adjusted to change the resistance value, usually with a knob or a screw.
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| They find applications in volume controls, dimmer switches, and tuning circuits.
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| ===== Thermistors =====
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| Thermistors are designed to exhibit a predictable change in resistance in response to changes in temperature, which makes them useful in a wide range of applications, especially in temperature-sensing and temperature-compensation circuits.
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| There are two common types of thermistors:
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| ====== Negative Temperature Coefficient (NTC) ======
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| * NTC thermistors are the most common type. As the temperature increases, their resistance decreases, hence the term "negative temperature coefficient."
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| * The resistance-temperature relationship of NTC thermistors is nonlinear, meaning that the change in resistance is more significant at some temperature ranges than others.
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| * NTC thermistors are often used in temperature sensors and temperature compensation circuits or protection circuits. For example, they are found in thermostats, thermometers, and devices that require temperature control.
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| ====== Positive Temperature Coefficient (PTC) ======
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| * PTC thermistors exhibit an increase in resistance as the temperature rises, hence the term "positive temperature coefficient."
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| * The resistance-temperature relationship for PTC thermistors is also nonlinear.
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| * '''PTC thermistors can be used as self-resetting fuses or current limiters. When they heat up due to excessive current, their resistance increases, reducing the current flow.'''
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| ===== Varistors =====
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| A varistor is an electronic component that is used to protect electrical circuits and devices from voltage spikes or transient overvoltage conditions. Varistors are also known as voltage-dependent resistors (VDRs) because their electrical resistance changes with the applied voltage. They are commonly used in various electronic and electrical systems to absorb and dissipate excess voltage, preventing damage to sensitive components.
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| ===== Photoresistors (LDRs) =====
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| Also known as Light Dependent Resistors, these exhibit changes in resistance based on the intensity of light falling on them. They are used in light-sensitive applications.
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| [[File:Resistor measurement.png|thumb|181x181px|Testing a resistor (Figure 4)]]
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| == Testing a resistor ==
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| Once you have identified the resistor and its specified resistance, you can accurately measure its resistance using a multimeter, as depicted in Figure 4.
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| * '''It's important to note that when measuring a resistor, polarity is not a concern.'''
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| * Ideally, you should measure the resistor outside of the circuit.
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| ** When measuring a resistor within a circuit, the measured value will always be either equal to the ideal resistance or lower. If you happen to measure a resistance higher than the ideal value, this indicates a faulty resistor.
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| *** The reason the resistance of a resistor within a circuit is lower than its ideal value is because you are effectively measuring not only that specific resistor but also everything else connected to it in parallel. '''When resistors are connected in parallel, they collectively reduce the overall resistance.'''
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| * Resistors typically fail in an "open" state, which means they will exhibit a significantly higher resistance than normal or even an open circuit.
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| ** This is often a result of excessive current causing them to overheat.
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| * Rarely, resistors might exhibit a '''Value Drift'''
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| ** Over time, a resistor's resistance value might change due to environmental factors or aging.
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| == Replacement considerations ==
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| The most important things to keep in mind when replacing a faulty resistor are as follows:
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| # '''Resistance:''' Choose a replacement resistor with the same resistance value as the faulty one. Keep in mind that there are different tolerances (1,5,10, or 20 percent). Try to stick to 1% if possible.
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| # '''Power rating:''' Ensure the replacement resistor can handle the same or higher power as the original. If you're unsure of the original resistor's power rating, opt for the highest-rated resistor available in a similar size.
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| # '''Package size:''' Try to choose a replacement resistor with the same dimensions as the faulty one. If this isn't available and size constraints are not an issue, you can opt for a larger or smaller resistor as long as it matches the power rating, as this will function the exact same way.
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| Diodes - Repair Basics
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| Type
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Component
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| Device(s)
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Diodes
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| Difficulty
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◉◌◌◌ Easy
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This article aims to provide a comprehensive overview of diodes from a repair perspective, detailing their function, types, common issues, testing methods, and replacement considerations.
What is a Diode?
A diode is a fundamental semiconductor device commonly found in electronic circuits. Its primary function is to allow the flow of electric current in one direction while blocking it in the opposite direction. This property makes diodes useful for rectifying alternating current (AC) into direct current (DC), protecting circuits from reverse voltage, and more.
Diodes have different characteristics found in their datasheets, the most important value when measuring is the forward voltage drop in "Volts"
Diodes are typically identified by the symbol shown in Figure 1 and are usually denoted with the letter D followed by an identifier number. (E.g., D38)
Function
Diodes serve various functions in electronic circuits, with the most common being:
Rectification
Diodes are frequently used to convert AC voltage to DC voltage. They allow the current to flow during the positive half-cycle of the AC signal and block it during the negative half-cycle, effectively converting the signal to a unidirectional flow.
Voltage Regulation
Zener diodes, a specific type of diode, are used to regulate voltage. They maintain a constant voltage across their terminals, making them suitable for stabilizing power supplies and protecting sensitive components from voltage spikes.
Switching
Diodes are used as switches in various applications, including signal routing, switching power supplies, and protection against reverse voltage.
Types
Regular/Rectifier Diodes
Regular or rectifier diodes are the most common type of diodes. Mainly used for converting AC to DC. They come in various package types and sizes.
If used to rectify mains AC to DC, you'll typically find 4 didoes in full bridge configuration in one package.
Zener Diodes
Zener diodes are designed to maintain a constant voltage across their terminals when operated in the reverse-biased breakdown region. They are used for voltage regulation and are often labeled with their nominal voltage value.
Schottky Diodes
Schottky diodes are known for their fast switching speed and low forward voltage drop. They are used in high-frequency applications and as rectifiers in power supplies.
Light Emitting Diodes (LEDs)
LEDs are a specialized type of diode that emits light when forward-biased. They are commonly used in displays, indicators, and lighting applications.
Varactor Diodes
Varactor diodes, also known as varicap diodes, are used in tuning and frequency modulation applications due to their ability to change capacitance with a varying reverse bias voltage.
Photodiodes
Photodiodes are light-sensitive diodes that produce a current in response to incident light. They are used in light detection and optical communication systems.
Testing a Diode
Testing a diode can help determine if it is functioning correctly. Most diodes can be tested using a digital multimeter in diode test mode. It's best to test the diode outside the circuit.
- Identify the anode and cathode terminals of the diode. The cathode is typically marked with a band or line on the diode's body.
- Set your multimeter to the diode test mode (usually indicated by a diode symbol).
- Place the red probe on the anode and the black probe on the cathode.
- The multimeter should display a voltage drop reading (around 0.2 to 0.7 V for silicon diodes). If it shows "OL" or less than 0.2, the diode is likely faulty.
You can test the diode in-circuit, but keep in mind that other components in the circuit may affect the measurement but only lowering it.
Replacement Considerations
When replacing a diode, always read the datasheets and pay attention to the following parameters:
- Type: Ensure the replacement diode is of the same type and has similar electrical characteristics as the faulty diode.
- Forward Voltage: Match the forward voltage rating closely to the original diode. Using a diode with a significantly different forward voltage may affect circuit performance.
- Reverse Voltage (Zener): Pay attention to the reverse voltage rating. That's the most important parameter for Zener diodes.
- Power Rating: Match or exceed the power rating of the replacement diode with the original diode.
- Package Type: Choose a replacement diode with a compatible package type and size. Different packages have different mounting and pin configurations. If space is not a concern, you can use any size as it won't affect the circuit behavior.
- Reverse Recovery Time: In high-frequency applications, the reverse recovery time of the diode is crucial. Ensure the replacement diode has a similar or faster reverse recovery time.
Replacing a diode with the wrong specifications can lead to circuit malfunctions or failure, so it's essential to choose a replacement carefully.
