All Questions
Tagged with current-limiting transistors
38
questions
0
votes
1
answer
86
views
How to limit power to LED, efficiently
I am looking to use a 12V, 5 ampere car battery on a small 5V, 2A LED. Typical applications online use a resistor or voltage regulator, but since I am using a battery I would like to conserve power, ...
- 239
2
votes
2
answers
277
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LED Matrix to reduce current consumption
I'm trying to control RGB LEDs via USB. All LEDs have the same color, so I'm controlling them with only 3 PWM signals (generated from a PIC).
The problem I'm facing is to reduce the current needed in ...
- 23
0
votes
1
answer
434
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PNP Darlington pair as a current limiter
I am trying to analyse what is controlling the load current in the below Darlington configuration.
Is it the base current of transistor Q3 which is controlling current through R14 / emitter current ...
- 328
1
vote
5
answers
3k
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Current limit to 500mA (maximum) at 12V
I have a 12V DC output which can output 1A (maximum.)
I want a circuit that limits the current to maximum 500mA, so I don't accidentally draw more than 500mA as that would probably mean I have shorted ...
- 147
-2
votes
2
answers
745
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Current limiter using 2 bipolar junction transistors (BJTs)
I want to know where are the input and the output of this circuit in LTspice. I also need the values I should use for the resistors and the transistors in order to see clear results for current ...
- 1
1
vote
3
answers
312
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Is a base resistor always needed in a single transistor inverter circuit?
For the circuit shown, I'm trying to figure out if I need a base resistor or not.
What I'm looking to accomplish is a simple logic inverter to hold a power amp's active low shutdown at logic low ...
- 520
1
vote
4
answers
151
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Current limiting circuit operation
I cannot understand how this current limiting circuit works.
Image source: UNLV Physics Department, Bill O'Donnell, Current Limiter Circuit
Here is where I get confused:
When Q2 is turned on, the ...
0
votes
1
answer
204
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Constant current limiting circuit
Can someone help me understand the working of this circuit:
My questions :
Please explain me how this circuit will work in its entire operation range.
I am not able to understand the purpose of the ...
user220456
1
vote
1
answer
80
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LED strange behavior
I am analyzing ways to make a current limiting circuit, and here I'm having an unexpected problem. The schematic is as follows:
The problem I am encountering is twofold:
Even when node Vin is ...
- 31
2
votes
2
answers
1k
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Does a BJT optocoupler have an inherently short circuit proof output?
I want to use an NPN optocoupler (ACPL-214) to drive an offboard relay. I know how to size the input resistor to limit the LED current to 20mA. This will cause the output current to be in a certain ...
- 489
6
votes
1
answer
2k
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Using a depletion mode mosfet as a current limiting device
I have recently discovered the exciting world of depletion mode mosfets. Curiously, even in this document, I found nowhere that a depletion mode mosfet could be used as a current limiting/inrush ...
- 1,898
2
votes
2
answers
210
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Transistor Limit Current
I am using a LM395T transistor for an inductive load (a motor). The voltage limit is well within the 36V threshold. But current isn't limited. The specs of the transistor say that 1.5 A is maximum. ...
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1
vote
1
answer
803
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How to limit current while almost keeping voltage same
I am supposed to design a power supply to a project. I have 3 alternative power supply designs for this purpose. However, one of them sucks huge current while giving enough current. My design is given ...
0
votes
1
answer
100
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Why does the high Side Current Shunt monitor fault as soon as power is on
The high side current shunt monitor fault goes high as soon as power is turned on preventing the P-MOSFET from turning on, its not faulting because of over current but as soon as the Enable signal ...
- 45
0
votes
2
answers
515
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NPN Transistor Current Limiting Changes From Collector Load To Emitter Load
as part of an audio project I've been working on, I've been measuring the current consumption of a class A amplifier driving a 4Ohm 5W speaker (square wave signal).
Strangely, I notice that this:
...
- 151
1
vote
2
answers
2k
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Transistor Power Dissipation / Overheating
I am working on an audio project in which a voltage controlled square wave oscillator drives a 5W 4Ohm Speaker. I am using a unipolar 12V supply. In order to limit the current going through the ...
- 151
0
votes
2
answers
4k
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How to calculate this two transistors Constant Current Source circuit?
I came across a constant current source calculator at Electronic Product website:enter link description here
For example, for a 13.5V input, 300mA output, it comes out the following parameters:
<...
- 283
0
votes
2
answers
75
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Analysis in a motor controll amplifier circuit
I've the schematic that is in the picture below:
simulate this circuit – Schematic created using CircuitLab
And I did the following analysis:
the opamp acts as a voltage follower, so when \$...
- 31
0
votes
1
answer
2k
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Parallel current limiters, ballast resistors and transistor matching
Are ballast resistors (R17, R8 and R5) required when using parallel current limiters as show below?
I found it hard to find working examples on the internet with values already present to tweek ...
- 103
1
vote
3
answers
274
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Is it possible to overcome a transistor's current limit by running it at lower voltage?
Let's say I have a transistor which is rated for maximum 800mA current at 50V. Is it possible to have it running at 1000mA & 5V for example?
Edit : please provide me some details in your answer ...
- 133
3
votes
3
answers
2k
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How to reduce current in this circuit?
I have the following circuit and I want to reduce the current consumption to the lowest possible.
Basically, I have a series voltage regulator whose output is connected to a transistor to switch on ...
- 79
0
votes
1
answer
301
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negative voltage current limit circuit to control LDO enable
I am looking at the best method to control an LDO enable pin using a negative voltage current limit circuit. The LDO is disabled when the enable pin is 0 to 0.4V. The LDO is enabled when the enable ...
- 1
1
vote
1
answer
750
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"General purpose" current limiter?
I have been trying for a few weeks to create a current limiter that fills my needs but I have failed. Idon't even know if it's possible. Basically I want to make a current limiter that can work with ...
- 483
0
votes
2
answers
134
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Limiting resistor for zener voltage regulator driven by transistor
I have this circuit:
simulate this circuit – Schematic created using CircuitLab
And I would like to understand why I need a limiting resistor for the current flowing through D1. I know the ...
- 561
-2
votes
1
answer
1k
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Transistor - Control current flow
simulate this circuit – Schematic created using CircuitLab
I am having trouble finding how to limit the current flow from the collector to the emitter of a transistor. (Is it possible? I know ...
- 3
0
votes
2
answers
304
views
Help using transistor in active mode as a current limiter
Brief context:
I have a small solar panel, nominal properties are 0.6W, 6V, 100mA. In given conditions I want to measure the maximum power it can produce - I do not want to do anything with this ...
- 23
5
votes
1
answer
7k
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BJT Current limiter for linear power supply
I am trying to design a current limiter or my LM317 based power supply using this schema.
The power supply must be able to provide a maximum of 1.5A@30V.
I made some calculations and I would like to ...
- 561
7
votes
2
answers
6k
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How does this power supply circuit work?
This is the circuit of a power supply with adjustable output voltage and current, and I wish to understand how it works:
What I did understand:
R1 T1 VD5 - they form a voltage divider which provides ...
- 173
1
vote
3
answers
379
views
Current Limiter, can someone troubleshoot this circuit?
so I am trying to limit the current output with x2 3904 transistors and a sensing resistor. This is currently what I have, but am not sure why it doesn't work.
That current supply is going to be a ...
- 13
1
vote
2
answers
597
views
Current limiter its not working as it should?
I have created a voltage regulation circuit using op amp and feedback resistors, now I am trying to add a current limiter to the circuit. have read how to create this using two transistors and a ...
- 113
0
votes
1
answer
1k
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Current limitation of a power supply by using transistors
DALI standard limits the maximum current as 250mA. I have a 12V source that is capable of supplying more current. I implemented from one of Motorola reference design the below schematics that limits ...
- 3,305
3
votes
1
answer
4k
views
Designing a current limiting circuit for my project
I've got a small DC brushless motor for which I would like to set a current limiting circuit as a protection against over-current.
I thought I could pull it off with a simple fuse (or those current ...
- 31
4
votes
1
answer
7k
views
Need help calculating resistor values for IR LED Driver
I'm wiring an IR LED driver for an Arduino project I'm prototyping.
The Arduino will be run at 5V, and I'm planning on using it's 5V output to drive the transistor that runs the LED
The circuit I've ...
- 1,418
4
votes
1
answer
1k
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Does this circuit regulate current?
I am being told that the circuit below will regulate current, I am wondering how true that is and how exactly does it do it if so. As far as I can tell: two NPN transistor with their bases biased by ...
- 58
1
vote
2
answers
3k
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How to limit base current in transistor when collector current is unknown?
In the followig circuit I am trying to replace a push button with a transistor:
simulate this circuit – Schematic created using CircuitLab
In the schematic SW1 is the push button that opens ...
- 323
2
votes
2
answers
2k
views
Transistor current limit circuit - power handling?
I am designing a simple current limiter, which charges a large (4.7mF) capacitor with a charge current of (roughly) 500mA from a supply voltage from about 10-20V - see the below circuit.
My dilemma ...
- 1,504
5
votes
1
answer
14k
views
Current limiters using transistors and diodes
I have been experimenting with simulating current limiting circuits. I am trying to limit current to ~500mA given a fixed 4.8V source. I started a question based on a conventional 2-transistor current ...
- 1,341
8
votes
3
answers
13k
views
Help needed optimising simple current limiting circuit
I have been experimenting with simulating current limiting circuits. I am trying to limit current to ~500mA given a fixed 4.8V source. I have started using a circuit like the one found on this ...
- 1,341