# Questions tagged [resistors]

A resistor obeys Ohm's law ($\small V=I\cdot R$); the current through it is equal to the voltage across it divided by the resistance (equivalently $I=\frac{V}{R}$).

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### Need help identifying resistor

According to my colour-blindness-free wife, this is: red, orange, yellow, black. Which, according to https://resistorcolorcodecalc.com/ works out at 230 kΩ. However, that's not what the meter shows: ...
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### What would be the value of a fusible resistor that was color coded red, gold, ,gold ,gold? [closed]

There were two of them on a small circuit board at the end of an LED garage light and they preceded a small full wave rectifier.
59 views

### How do I use the given voltage drop across $R_3$

I can't figure out how to solve this circuit if I use mesh I get these 3 equations what is the fourth equation?  24E3*i_1 - 12E3*(i_2+i_3) = 24-v_{52} \\ -12E3*i_1 + 25E3*i_2 - 10E3*...
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### Calculating the resistance after a plunge cut laser trim

How do I calculate the resistance of this example resistor? For this example I have a 100 by 100 units of resistive material that is 100 ohms per square and a perfectly uniform thickness. If I make a ...
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1 vote
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### RC timing circuit

I'm reading AOE 3rd edition, book say below: Here’s how the circuit works: the voltage divider R3R4 holds the (−) input at 37% of the supply voltage, in this case about +1.8 V; let’s call that the “...
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305 views

### Determining the ohmic value of a carbonized resistor in a flashlight circuit [closed]

this circuit is for a rechargeable flashlight. It charges the battery using a 220V power supply, after reducing the voltage. A capacitor and a resistor in this circuit are damaged. The capacity and ...
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1k views

### Can I replace this resistor (in USB adapter that plugs to mains) with this other resistor?

I would just test this instead of asking here, but because this goes to mains, dangerous voltages and all that, I prefer to be safe than sorry. An old USB adapter stopped working, and I finally took ...
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### Variable resistor values for a guitar amplifier circuit

This is a continuation from a previous post. Read here if you have further questions. I have decided to makee a simple guitar amplifier with the circuit seen in the attached figure. What maximum value ...
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### Scale a rheostat range

I have a rheostat that ranges between 61/186 ohm, and I'm looking for a method to make it between 16/160 ohm, how can I achieve that using only passive components if possible please.
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### How to choose correct resistor values when designing a circuit?

I have designed this voltage divider circuit. The idea was to ensure the 5V LED (L1) and the 3.3V LED (L2) receive the correct amount of current so that they do not burn up. So far I figure the ...
1 vote
131 views

### How does this delay circuit work?

Just wondering if there is an explanation to how this "delay circuit" works. (Above screenshot from YouTube video "Fun with Transistors" at timestamp 716s (11m 56s) by HackMeMod) ...
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### Using 48V 25A AC/DC power supply to power multiple components?

I was basically wondering if I may be able to control a NEMA 34 stepper (6.2A rated), Arduino Mega, and a linear actuator with just this single power supply (48V, 25A)? The NEMA 34 stepper would max ...
66 views

### Confusion regarding driving a MOSFET through optoisolator

I am currently developing a circuit board for a control chassis, that will control various light outputs depending on what inputs are active, no fast switching is required. I have the input side ...
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133 views

### RC circuit equation why have negative sign

I'm reading a book named The Art of Electronics. What are some of the features of circuits with capacitors? To answer this question, let’s begin with the simple RC circuit (Figure 1.31). Application ...
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### IR Blaster Resistor Calculation for IR LED (breaking ohm's law?)

We are trying to build IR Blaster based on schematics provided by Tuya. I believe Tuya based IR blasters sells hundred of thousands per month if not millions. So I am quite sure that their schematics ...
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1 vote
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### Why does the reciprocal of sum of reciprocals relationship appear commonly?

The relationship of 1/x = 1/x1 + 1/x2 + ... seems to appear rather commonly within engineering. Off the top of my head, I can think of resistors in parallel, ...
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### Highest Attenuation with Unit Resistors?

What is the most efficient unit resistor arrangement for high ratio attenuation ? For example, if I want to attenuate a (voltage) signal by a large factor (e.g. approximately 1000x), I could use 999 R ...
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### How to design digital rheostat that can handle 100 mA?

Specification: Bidirectional current Output current: 1 uA to 100 mA Terminals common-mode voltage: +/- 12V That would be 24 Meg to 240 Ohm if that is possible. Stability: +/- 1% if possible Bandwidth:...
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### Adding Resistor to Match Power Draw for Fan Replacement

I'm replacing a 12V 0.23A fan with a 12V 0.06A fan and want to keep the power draw the same. I believe there is load-sensing at the power supply side, which detects lower draw and shuts down due ...
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165 views

### How does this simple circuit work if the diodes are replaced by LEDs?

How does the simple circuit in the answer to What is the simplest and best device (or circuit) to stop the flow of current in a line when current in another line is present? work? What I don´t ...
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141 views

I need to add some wirewound resistor in series with a voltmeter to make it high range. I am converting the voltmeter from 300 V FSD to 900 V FSD. As per my calculation the wattage should be 20 W, but ...
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### What happen if both sides of LED connected to positive?

Question 1: If we connect both ends of an LED to the positive terminal of a battery, will it create a short circuit and damage the LED? Question 2: If connecting both ends of an LED to the positive ...
137 views

### Why does a 230V 16A socket supply only the needed current to loads? [duplicate]

If I connect a 150W laptop charger to a socket that supplies at home 16A 230V, it will only draw the necessary amperage needed for the laptop charger at 230V. Why? Why doesn't my charger simply draws ...
64 views

### RC series analysis with H parameters model

I'm writing this just to be sure I understood well the process of analysing a circuit with the $H$ parameters model. In this case, it is a very simple example of application; the circuit I'm ...
124 views

### Identifying a component from an Acer Aspire F15 Laptop

I am currently working on a Laptop for a client, I have identified this part as a potential cause of the failure to boot, yet I have no Idea what it is?, what it does?, how to test it properly, and ...
92 views

### Cant figure this out [closed]

Below circuit pulled from homemade-circuit.com, Practical Voltage Regulator Project with Feedback for Enhancing Output Accuracy, https://www.homemade-circuits.com/simple-voltage-regulator-circuits-...
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### How to find current for Thevenin equivalent circuit

I'm trying to figure out how to calculate the Thevenin equivalent circuit for a voltage divider like the following one: I understand that V_th is obtained by opening the terminals of the output, so ...
564 views

### Can we find the equivalent resistance just by using series and parallel combinations?

Can we calculate the equivalent resistance between $A$ and $B$ by using just the concept of series and parallel combinations$?$ I can solve this by assuming that a battery of voltage $V$ is ...
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### Does the rise time equal the decay time in a DC LR circuit?

The time it takes the voltage to decay from its maximum to zero after the switch is closed is ≈5$\tau$. I was wondering, does the same applies during de-energizing, i.e, when the switch is connected ...
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1 vote
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### Resistor after voltage divider changing the maths?

I would like to get the correct voltage value after a voltage divider. In some way R7 is affecting the estimated voltage output value but I don't know how. My math, (Vout) calculated after R7: Vout = (...
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### Battery draining and resistor question [closed]

Say I have a motor that uses 9v @400ma, but it's powered by a 12v battery. I 'd use the ohm law and get a: 7.5 ohm resistor. But, as soon as the battery is being drained, let's say now the battery is ...
1 vote
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### DigiPot Actual Resistance Range?

I'm currently looking at a the AD8400 digipot: I'm guessing that the minimum resistance is determined by the wiper resistance? But besides that, does it mean that worst case, my digipot will have a ...
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### Find the equivalent resistance between $A$ and $B$ [closed]

In the figure shown below, find the equivalent resistance. I know I should add my attempt but I don't know how to approach these type of problems. This isn't the standard series-parallel combination ...
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### How do you approach problems like these where we have to find the arrangement of resistors?

Is there any specific methodology to approach them or is it just intuition? Because I am finding them really hard.
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### Relay module I/O pins resistor

I'm making a project with a 12v relay module and a AC motor. The circuit is simple and doesn't need any microcontrollers. I want to control the motor using a relay and a float switch. I was hoping can ...
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### What are the values of these resistors?

I have tried looking at various guides but there is nothing to indicate which way round the top resistor is. The brown bars on both ends are too similar. How, in general, can you tell whether they are ...
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### Proof showing thermal noise of 2 resistors in series behave as a single noisy resistor

For the second part of this question, I came up with two slightly different answers? I believe it's the second one however I am not too sure which one would be the correct one. First one: Second one: ...
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### How does this boost converter circuit work?

The circuit appears on this site in Post #45 by Michal Podmanicky. It is posted so that I can understand how the circuit works. It is not explained fully in the posted link. How does this circuit ...
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### Output voltage didn't change after adding capacitors and resistors

I'm building a power supply that consists of a Type-C female to DPI adapter and a LD1117 voltage regulator (on a perfboard/protoboard). I was advised to add capacitors and resistors. Before adding ...
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### Feedback of amplifier

Would just like to know, why on the first picture RE1 is "part" of the feedback and is RE3 not? Then on the second picture is RE part of the feedback as well? Is there any way generally how ...
104 views

### Strange Resistor Situation

I am looking at a schematic for an RF sensing switch, and I notice that there are two resistors that are marked in the schematic as 18 Ω resistors. They are 2512 SMT types and are installed in ...
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### Saving my resistor [closed]

Does it matter if you put 2 different resistors in parallel and how would you keep the lower rated resistor safe if you know the power output is greater than resistor can handle? Edit: I'm using 2 ...
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1 vote
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### Are multiple SMD Chip Resistors in Series as Safe as a Wirewound Resistor for Mains Voltage?

I realize SMD Chip Resistors are not recommended for Mains Voltage and it's no wonder since their maximum voltage rating is lower than 100 V. I also understand that WireWound Resistors are recommended ...
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### BJT circuit questions

I have landscape lights. The load is 3 VDC 100 mA for each filament. I have two of them so the load is 200 mA at 3 VDC. I have solar panel which varies voltage from 0 V to 1.5 VDC. I want the ...
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### Sourcing a resistor

I'm looking to replace a resistor in a 300w + 300w Mosfet amplifier. It's the one in the photo and while I'm happy removing the old component and soldering in a new one, I'm not sure where to start ...
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### Troubleshooting Voltage Sensing Issues in Buck-Boost Chip Simulations

I performed a simulation on a buck-boost chip (LT8390). I understand that the sensing resistor placed between LSP and LSN is supposed to sense the differential voltage. This voltage is then amplified ...
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### Selectively Activated External Circuit for ADC Measurement

I'm looking for efficient yet simple-to-integrate solutions where analog signal outside of microcontroller's range is being measured (e.g. 12V power supply) and measurements are done selectively. This ...
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### Resistor's markings don't match readings

I'm using a component tester to measure a resistor which I have removed from a circuit. The tester gives a reading of around 0.46 - 0.50 Ω. I have 7 other identical resistors (in circuit) and they all ...
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### Selecting resistor value for PWM LED driving

I want to create a circuit to drive some LEDs with PWM. The circuit consists of a PMOS switch at the high-side and the gate driven by the MCU PWM pin that is configured open-drain. The LEDs have ...
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