Questions tagged [switching]

Switching can be defined as the change in state whether it be an analog, digital, or mechanical device. For digital devices, switching can be defined as a transition from HIGH to LOW or vice versa. For analog devices, switching can be defined as a change of operation within a transistor. Mechanical device examples include physical light switches or button switches. Ultimately, switching interrupts current from going into another conductor path.

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73
votes
8answers
68k views

When is a MOSFET more appropriate as a switch than a BJT?

In my experimentation, I've used only BJTs as switches (for turning on and off things like LEDs and such) for my MCU outputs. I've been repeatedly told, however, that N-channel enhancement-mode ...
3
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2answers
2k views

Automatic switching between external 5V and USB bus power supplies

I'm designing a USB device which can either be powered by USB or an external 5V power supply. When an external 5V power supply is present, the device should be powered solely by this external supply. ...
3
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2answers
12k views

How to create automatic dual battery changeover/switching circuit for uninterruptible power?

I've search for a solution to my problem both on this site and on Google but I did not find a complete and adequate response. I need a circuit that switches two 12v sources (one that comes from a ...
0
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1answer
423 views

Switching between 2 power supplies upon dropping below cutoff voltage efficiently

I am making a circuit which is powered by a lipo battery of 11.1V(3.7V*3). I need to check for the lipo's under-voltage so that the circuit automatically switches to a second lipo when the first one ...
9
votes
3answers
10k views

Use BJT transistor as a switch without inverting the signal

I know I can use a transistor as a switch like this: simulate this circuit – Schematic created using CircuitLab Can I use only one transistor that will output the same signal (not inverted)? I ...
7
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4answers
12k views

Switching between battery and USB using diode OR logic

I have a Raspberry Pi that is powered by a USB cable from a Samsung charger. Now since my college has frequent power cuts, I designed a basic switch to automatically switch between a portable mobile ...
2
votes
2answers
426 views

Detecting state of LED to control another circuit

I need to add functions to equipment I am not allowed to modify in any way. To do this I need to monitor the status of a Yellow/Amber LED and translate its status into a signal that can be used to ...
2
votes
2answers
4k views

Electronic pendulum

I am building an electronic pendulum. I want to use a 2N2222 to power the drive coil when the pendulum bob interrupts an IR beam. The pendulum bob is magnetic and moves in reaction to the drive coil. ...
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2answers
7k views

Automatic Power Selection Circuit

I am trying to build a circuit with 2 inputs and 1 output using Mosfets. I will try to explain what I want.. The circuit should accepts 2 input DC voltages , the first input voltage called "...
7
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2answers
7k views

Under what conditions does an optocoupler work fastest?

I want to use the optocoupler FODM452R2 in my design. I want this optocoupler to run as fast as it can (i.e.; work with minimum propagation delay and least rise/fall times). What is the optimum R1, R2 ...
4
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2answers
6k views

How to Use Diode Oring to Switch between Two Power Sources? [duplicate]

I want to switch Power Between a AC/DC adapter which is supplying power to the circuit when AC power is On and when power loss power the circuit using 12V 7Ah Battery. AC/DC adapter is rated 12V 1Ah. ...
4
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5answers
2k views

Pressing a physical button, but digitally using an Arduino in an existing circuit

I have a pair of speakers that by default select their input as bluetooth and I have to press a physical button (every time I power them up) to switch their input to auxiliary. So I'm thinking of a ...
8
votes
1answer
2k views

How does a “speed up capacitor” work in Schmitt trigger?

Hello I'm trying to understand how adding a capacitor across R2 in below circuit increases the switching speed. I don't see how C2 supplies charge to C1. With the additional capacitor C2, it seems ...
3
votes
1answer
5k views

Normally ON Switch using N-CH MOSFET and pull-up resistor

I am learning about electronics and am having a hard time finding a normally closed (i.e. on) switch using transistors and FETs. Am I violating any rules with the circuit below which is using an ...
4
votes
1answer
315 views

Is it possible to use a NPN BJT as switch, from single power source?

I'm attempting to build the following circuit to better understand how to use a NPN BJT as a switch. What I've Tried I'm calculating the current across the LED (in order to light it up) as: ...
3
votes
3answers
3k views

Reduce MOSFET switch off time

I am using this switching circuit to switch a lamp. I am controlling a rising slew rate at Vout (from 0-Vcc) that is adjustable by setting R2 with a poteniometer. It's not necessary for my project, ...
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0answers
40 views

How to implement a switch in spice? [duplicate]

I have designed a circuit where I want to give a pulse of very short duration using a switch. How can I implement it in spice.
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2answers
2k views

Triac Switching circuit with Optocoupler

I am trying to control home devices using a microcontroller and a TRIAC. For switching, I intend to use an optocoupler and triac-based circuit. The circuit is given below (also plenty are available on ...
1
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1answer
3k views

MOSFET Always On despite of Pull-Down

I'm currently trying to get the hang of using a MOSFET as a switch. My schematic looks something like this (it's the first schematic I've ever drawn, so please don't be too hard on me). simulate ...
7
votes
3answers
22k views

How fast can a transistor switch?

An NPN transistor can be made a switch by applying some power to the base. Is there a limit to how fast I can switch the transistor on and off, or I can switch it on and off as fast as I can turn the ...
2
votes
1answer
240 views

Using transistor as switch with low voltage

Basically, I need to monitor a circuit's output so I can activate another system. The output voltage of active stage is 140mV. If I am not wrong (from what I read about transistors) 140mV is not ...
8
votes
4answers
8k views

How to increase mosfet switching speed, and decrease switching losses?

I hope this is not a too broad question, but what are the best practices to achieve fast switching on a MOSFET driven by a PWM signal? My current knowledge tells me I can do two things: 1 - To use ...
6
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2answers
3k views

P CHANNEL MOSFET gate directly GPIO

I'm currently using this circuit to control my load from MCU logic HIGH why just not do like this ? circuit ? It's safe for my MCU ? I use NDP6020P is a Vgs(th) max -1V my VCC is 3.7V. I know in ...
5
votes
2answers
11k views

Is it possible to turn an audio signal ON/OFF using a solid state relay?

I'm thinking about controlling an audio signal (turning it ON/OFF) using a solid state relay switch? Is that even possible? If not, is there a different or easier way to do this? I'm a noob in the ...
5
votes
5answers
1k views

Device to power either a red LED or a green LED

I have a green LED and a red LED. I want a sort of switch to turn either the red LED or the green LED on. For example: Where if the switch is off, the red LED is on but if the switch is on, the green ...
2
votes
2answers
693 views

Switching a current source through a MUX

I have a current source of square pulses (0-20 uA) generated by a NI 9265 device. I am trying to build a fast switching circuit using TI CD4051 multiplexer to switch the current signal between ...
1
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2answers
599 views

What are the different ways to switch power using a microcontroller (Arduino, Raspberry Pi, BeagleBone, etc.) and what are the pros/cons for each?

I'm using an Arduino to control a 12v water pump for a self-watering plant wall. I'd also like to use the same power supply for both, and probably need surge protection of some kind to avoid spikes. I ...
6
votes
2answers
3k views

Why is my power MOSFET heating up when on?

I'm switching a 12V 500mA resistive load (LED strip) with a IRF540 MOSFET and it's getting very hot when it's on and conducting. This confuses me as MOSFETs are ...
3
votes
2answers
169 views

Understanding semiconductor failure mode

Why after serving well for years, a smps controller ic fails without apparent reason? My Sharp TV (LC46LE835X) worked well for 37 months but suddenly while being watched in the middle of calm night, ...
3
votes
3answers
7k views

MOSFET overheating in pwm control

I'm using a MOSFET to switch a 24V, 15A load, with the gate input being a 500Hz PWM signal. However, this is causing the MOSFET to overheat and blow. Any suggestions would be appreciated. R1 = 100 ...
2
votes
1answer
76 views

Will replacing MOSFET with a MOSFET with lower rds(on) reduce the thermal characteristics?

I want to replace a MOSFET in a legacy product. The MOSFET is a P-channel Power MOSFET that is used for PWM switching purposes (VGS @ -12V, PWM is 20% @ 200us). The FET is switching in to a 200uH, ...
2
votes
3answers
273 views

Mystery issue driving load through NFET with microcontroller

U1 is a microcontroller driving M1 to drive a load. I am running into some bizarre behavior and I'll try to include all the relevant information. Hope it's not too much. M1 is a logic-level FET. ...
2
votes
1answer
168 views

High side switching bizarre side effects

I'm not quite sure how to title this question. In essence, I have a high-side power switch circuit that is not switching off all the way under circumstances I cannot explain. First, here's the entire ...
1
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1answer
137 views

LM2678 PCB Layout question / review

After my initial question about switching regulators I had decided on trying to use an LM2678 for an adjustable/variable voltage form 5-24V and 5A max with an input of ~30VDC. The application will be ...
1
vote
1answer
200 views

How to switch 7 wires with a single on/off slide switch

I am working on a project, where I want to build a raspberry pi into a nintendo 64 console, and be able to switch between with a single switch. By that I mean, I want to be able to use a single slide ...
1
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6answers
308 views

Why does a spark occur when an SMPS is connected to the load circuit?

I am using a 36VDc SMPS as a power supply. A spark is generated when I connect 36V with my load circuit. Specification: Voltage source: 36VDc Current consumption: more than 3A I want to know why a ...
0
votes
2answers
351 views

How do I `chain` transistors so that the first transistor `switches` on the second

I am trying to get more hands-on experience with transistors. I have a simple switch working: I wanted to find out how to change the circuit so that a second transistor would be switched on by the ...
0
votes
1answer
737 views

switching between two outputs

I would really appreciate if someone could give me advice on how to build circuit for this case. On my circuit input I have slowly arising voltage from 0V to 10V, and on my circuit I have 2 outputs. ...
5
votes
2answers
475 views

Switch from one battery to another when one is discharged/disconnected?

I'm trying to figure out how to switch source power from one battery to another when one is dead or disconnected. the circuit needs to be able detect the loss of power on the jettisoned battery and ...
5
votes
1answer
901 views

Noise problems in current sensing

I have the following circuit: simulate this circuit – Schematic created using CircuitLab I am using a motor from an electric bike, as a generator and I am rotating it using a drill, to test ...
3
votes
1answer
236 views

500v generation with 24V, request for current limitation

I am generating 500V from a 24V source. Attaching schematics. This circuit is generating stable 500V. I am attaching a load of 7 kohm. In the schematics the buck regulator is supplying 19V to the ...
3
votes
2answers
205 views

Using a transformer with 400 volt rated primary side with a 120 volt line

Is it possible to use a transformer rated for 360 to 400 volts on its primary side on a 120 volt line? Will it still perform adequately? And I would assume the turns ratios still apply? This is the ...
3
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2answers
4k views

How to protect a P-channel MOSFET when driving a motor?

I want to switch a 12 V DC automotive fuel pump in a bench test rig using a P-channel MOSFET, as follows: simulate this circuit – Schematic created using CircuitLab This is a simple on/off ...
3
votes
1answer
8k views

Calculation of diode switching losses

I am an Electrical Engineering student. I'm in my final year and doing a thesis about soft switching. I am trying to grasp the calculation of diode switching losses. I'm having the impression that ...
3
votes
1answer
1k views

How to switch a MOSFET to drive a 5v relay from Raspberry pi?

I've been trying to power my 5v relay through a MOSFET but I can't seem to get it to work. I'm using a IRLI540N with the gate to GPIO 24 that goes high when I click the pushbutton (that much does work,...
2
votes
4answers
448 views

ultrafast catch diode for relay

Is there any reason to not use a UF2008 as catch diode on a DC relay, solenoid, or electromagnet? IN4001 costs $0.07 and UF2008 costs $0.03 and seems to be better suited in all ways simulate this ...
2
votes
3answers
3k views

Multiple MOSFET based AC switching circuits on the same supply

I am trying to build a MOSFET based AC switching circuit, with multiple switching circuits running on the same DC power supply. Each switching circuit is basically an expanded solid state relay. The ...
1
vote
2answers
494 views

Optocoupler to switch 24V using Arduino

I am currently redesigning a circuit to switch a spring applied brake using an Arduino Micro. The current circuit looks like this (please excuse if I'm using wrong symbols, I'm learning by myself): ...
1
vote
2answers
4k views

USB OTG with occasional charging

I'd like to use a mobile phone together with a barcode scanner as a poor-man's version of a computerised barcode scanner, something like this: http://www.thebarcodewarehouse.co.uk/pdas-and-handheld-...
1
vote
2answers
2k views

mosfet switching voltage spikes

I was experimenting with a simple voltage level shifter to convert a signal from 5v to 3.3v. Then i went to simulate my circuit in orcad pspice, and i need help understanding what is causing the ...