- #1
Automatic electrical switch to between two paths
- Thread starter radaballer
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- Automatic Electrical Switch
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Discussion Overview
The discussion centers around the design of an automatic electrical switch that alternates current flow between two diverging wires at a specified rate. Participants explore various switching mechanisms, including relays, transistors, and MOSFETs, while considering the technical requirements for the application.
Discussion Character
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- Some participants suggest using a relay connected to a square wave oscillator as a straightforward solution.
- Others propose using two MOSFETs or transistor switches, emphasizing the need for additional information about the load and control circuit.
- One participant mentions the term "demultiplexer" as a potential relevant concept.
- It is noted that the switching frequency of 167 Hz may be too fast for mechanical relays, indicating a preference for pass transistors.
- Participants discuss the importance of ensuring no overlap during switching and the need for precise duty cycle control.
- One participant recommends using PMOS power MOSFETs for lower voltage drop, while also highlighting the challenges of driving gate capacitance.
- Another participant suggests low side switching as a simpler alternative, allowing direct interfacing with logic circuits.
Areas of Agreement / Disagreement
Participants generally agree on the need for transistors over mechanical relays due to the high switching frequency. However, there are multiple competing views regarding the best type of transistor and switching method to use, and the discussion remains unresolved on several technical details.
Contextual Notes
Participants express the need for more specific information regarding load characteristics, control circuit design, and operational requirements, indicating that the discussion is contingent on these factors.
Who May Find This Useful
Individuals interested in electrical engineering, circuit design, and those looking for solutions to switching mechanisms in high-frequency applications may find this discussion relevant.
- #2
davenn
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you could use a relay connected to a square wave oscillator would probably be the easiest
could be done with transistor switching as well using the same square wave oscillator
could be done with transistor switching as well using the same square wave oscillator
- #3
meBigGuy
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The function you need is a single pole double throw switch. As dave said, that could be a relay, or it could be two MOSFET or transistor switches.
But, you need to provide more info if you want help:
What sorts of loads are you switching (voltage and current).
What sort of control circuit are you using to produce the "decided rate" .
What is the frequency range and duty cycle of the decided rate?
How accurate does the duty cycle need to be?
Does there also need to be an OFF position?
Does there need to be a guaranteed off time when switching (time between loads being powered)?
Can there be overlap when switching load? Or is guaranteed non overlap required?
Does the circuit really need to operate upside down :)
We will probably think of a few more things that need to be decided as we continue.
But, you need to provide more info if you want help:
What sorts of loads are you switching (voltage and current).
What sort of control circuit are you using to produce the "decided rate" .
What is the frequency range and duty cycle of the decided rate?
How accurate does the duty cycle need to be?
Does there also need to be an OFF position?
Does there need to be a guaranteed off time when switching (time between loads being powered)?
Can there be overlap when switching load? Or is guaranteed non overlap required?
Does the circuit really need to operate upside down :)
We will probably think of a few more things that need to be decided as we continue.
- #4
sophiecentaur
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Yes. A bit of (quantitative) context would help. In engineering, it's the numbers that count,
- #5
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The word demultiplexer also comes to mind.
- #6
sophiecentaur
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Perhaps . . . . from kW to mW.anorlunda said:
- #7
radaballer
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meBigGuy said:
What I know:
The power source is a 12 v car battery, so the amplitude is unknown until I can test it , it needs to oscillate every .006 seconds (167 hz)so the switch needs accuracy to the thousandth of a second , duty cycle .5, duty cycle Should be as accurate as possible, there should be no time between the current changing directions, guaranteed non overlap is required, thanks for the help
- #8
berkeman
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radaballer said:
That's too fast for a mechanical relay, so you need to use pass transistors. Can you say more about the application? What is the load current? Are the two load currents equal? What is the nature of the load -- is it inductive?
- #9
radaballer
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The load current is 1.25 amps on both sides, the load is purely resistiveberkeman said:
- #10
berkeman
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So you need to use 2 power transistors (probably power Darlingtons based on the current), with the base drive circuits based off of a square wave oscillator at your frequency. You will want to tune the drive circuits to make the current switchover smooth, with little glitching of the total current out of the battery. Are you comfortable taking it from here?
- #11
meBigGuy
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I'd recommend PMOS power mosfets. Lower voltage drop, but driving power MOSFET gate capacitance can be tricky. The non overlap part can be tricky in either case (BJT or PMOSFET)
Look at circuits on google (2 phase clock generator) to create non-overlapping waveforms.
On the other hand, It would be a lot easier to use low side switching. then you can interface logic directly to NMOS or NPN transistors (Connect both loads to +12 and ground one or the other to turn it on).
http://reibot.org/2011/09/06/a-beginners-guide-to-the-mosfet/ show PMOS and NMOS switches.
Look at circuits on google (2 phase clock generator) to create non-overlapping waveforms.
On the other hand, It would be a lot easier to use low side switching. then you can interface logic directly to NMOS or NPN transistors (Connect both loads to +12 and ground one or the other to turn it on).
http://reibot.org/2011/09/06/a-beginners-guide-to-the-mosfet/ show PMOS and NMOS switches.
- #12
radaballer
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yes thank youberkeman said:So you need to use 2 power transistors (probably power Darlingtons based on the current), with the base drive circuits based off of a square wave oscillator at your frequency. You will want to tune the drive circuits to make the current switchover smooth, with little glitching of the total current out of the battery. Are you comfortable taking it from here?