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.

In electrical engineering, a switch is an electrical component that can "make" or "break" an electrical circuit, interrupting the current or diverting it from one conductor to another. The mechanism of a switch removes or restores the conducting path in a circuit when it is operated. It may be operated manually, for example, a light switch or a keyboard button, may be operated by a moving object such as a door, or may be operated by some sensing element for pressure, temperature or flow. A switch will have one or more sets of contacts, which may operate simultaneously, sequentially, or alternately.

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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 MOSFETs are a better choice for switches (see here and…
Mark
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What are some ways to improve a voltage multiplier?

I am working on a Nixie power supply, but I would like to improve it. I have 4x9V batteries in series for a total of 36V to be switched across a multiplier. A (TTL) 555 timer is running astable from only the first 9V battery to generate a 8.5-ish…
Yankee
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Ribbon Cable Cross Talk - Is there a fix after the fact?

I'm involved in a project where the customer defined pins in a ribbon cable, without considering possible cross-talk issues. The signals are 1 MHz data signals with no ground wire separating them. I've never had experience with cross-talk and was…
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When does a transistor act as a switch, and when as an amplifier?

I'm a beginner with electronics, anyway I'm experimenting a lot with it. I still don't understand how you can use the same transistor for example to amplify an audio signal, or to act as a switch for turning on and off the current of a motor. Do you…
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Light bulb burns out -- why there is an arc in the switch?

I use light bulbs (common incandescent) in the room and they burn out periodically, ca. one bulb in 4 months burns out. Very often, exactly at the moment when it happens, I see an arc (blueish light flash) in the switch, so the bulb always burns…
Mikhail V
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Why does switching cause power dissipation?

I know that switching logic values causes power dissipation but I could never understand why. Is it because transistors need to be turned on each time we want to charge/pull up a node and discharge/pull down a node? Is this power consumed by the…
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Help me understand this circuit - unexpected LED behaviour

I'm well out of my depth here – please be kind! My kids and I have set up the circuit below and the LED is lighting up unexpectedly. When the switch is off, so is the motor BUT the LED is on. But when the switch is on, the motor is on but the LED is…
MG_
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Why do BLDC motor (1 kW) controllers have so many MOSFETs?

I have a 1 kW three-phase BLDC motor from China, and I was developing the controller myself. At 48 Vdc, the maximum current should be about 25 Amps and a peak current of 50 Amps for short durations. However when I researched BLDC motor controllers,…
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Is it good practice to run large amounts of current through a MOSFET?

I have been looking for a good way to control the flow of a lot of current in my project. This may at some points be 40-50 amperes at 12-15 V. While relays are a good choice, they are mechanical and therefore take time to activate and wear out over…
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Why to disconnect the negative/ground terminal, not positive?

To break off any circuit, the common way is to disconnect the negative and or ground terminal. I rarely see people disconnecting the positive and if so, they're not well educated in electrical engineering most of the times. Well, I've no…
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In which region should a MOSFET be operated as a switch?

I have a question about MOSFET switching operation. According to an article: In order to operate a MOSFET as a switch, it must be operated in cut-off and linear (or triode) region. According to another article: MOSFET in saturation region is…
Rivon
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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 the lowest possible PWM frequency, because switching…
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Connect two different sources with two Digital Ouptuts using an Adam 4055

I would like to operate an Adam 4055 module to control two different applications having their own power supply. Adam 4055 is Digital Input/Output control module over RS-485, I use only the DO part here. Reading the doc, Adam 4055 DO are Open…
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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 want to use it to shift voltage level. The input is…
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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 resistor values and magnitudes of V1, V2…
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