Connect with us

Fast Switching Relay for High frequency Signals

Discussion in 'General Electronics Discussion' started by naumankalia, Apr 24, 2018.

Scroll to continue with content
  1. naumankalia

    naumankalia

    10
    0
    Feb 11, 2018
    Hi all

    I am in search of some sort of fast switching relay which can stop/pass high frequency (190 - 450 KHz), high voltage (100 Vrms) signals without attenuation.

    Any help in this regard is highly appreciated.

    Thanks
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,449
    2,809
    Jan 21, 2010
    That's not really high frequency. A normal relay rated for sufficient voltage may be sufficient.

    There are also special relays made for RF use, but the may be overkill.
     
  3. davenn

    davenn Moderator

    13,721
    1,913
    Sep 5, 2009
    as Steve say, that isn't high frequency
    as long as you are not expecting the relay to switch/cycle at that frequency
    any normal mechanical relay would suffice



    ALL relays, mechanical or semiconductor, will have some losses

    what is the signal level and what losses can you realistically tolerate



    Dave
     
  4. hevans1944

    hevans1944 Hop - AC8NS

    4,547
    2,122
    Jun 21, 2012
    As per usual, the OP doesn't tell us what they are trying to DO, instead they inform us of their "solution" and ask where it can be procured. Lossless "high frequency" relay, huh? Where did the OP get the idea that such a relay even existed? I am pretty sure they don't make any in Pakistan, or anywhere else for that matter.

    Hmmm. [BEGIN SPECULATION] Maybe the OP is looking for a relay with room-temperature superconducting contacts. Good luck finding one of those since no one has discovered a room-temperature superconductor yet. OTOH, high-temperature superconductors cooled with liquid nitrogen are available, and one could construct an electro-mechanical relay from such material. In fact, if the relay coil were also superconducting (in addition to the electro-mechanically actuated contacts), it would not be too much trouble to build a latching relay, requiring no power to remain in the latched condition, and which would exhibit no ohmic attenuation through its contacts. [/END SPECULATION]

    Addendum:
    Magnetic Reed relays are the fastest practical mechanical relays, some being capable of switching thousands of times per second, holding off several hundred volts, and having very little contact resistance (attenuation). Google for what you need, but they are plentiful on eBay.
     
    Last edited: Apr 24, 2018
    WHONOES likes this.
  5. Alec_t

    Alec_t

    2,909
    791
    Jul 7, 2015
    Do you mean the change-over time of the relay contacts must be fast, or energising the coil results in almost immediate contact closure, or the relay will be activated repeatedly in a short time?
     
  6. HellasTechn

    HellasTechn

    1,544
    215
    Apr 14, 2013
  7. naumankalia

    naumankalia

    10
    0
    Feb 11, 2018
    Thanks for reply. The signals are sinusoidal around 100 Vrms. By Fast switching, i meant fast ON and OFF time of these relays.
     
  8. naumankalia

    naumankalia

    10
    0
    Feb 11, 2018
    Thanks for reply. The signals are sinusoidal around 100 Vrms. By Fast switching, i meant fast ON and OFF time of these relays.
     
  9. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    You have not defined by fast. Many small relays will switch at 50Hz and you may be able to go faster if you overdrive the relay and use appropriate snubbers.

    If the relay is to be switched often it will soon go out of adjustment or wear out. Consider using solid state such as a fet.
     
  10. naumankalia

    naumankalia

    10
    0
    Feb 11, 2018
    Thanks for help. I need this relay at output of a power amplifier to enable/disable PA output by switching this relay on/off. By fast i meant the time taken to ON and OFF this relay should be in micro seconds (again if practically possible) . By Lossless i meant as much low attenuation as possible practically.
     
  11. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    The obvious way of doing what you want is to switch the amplifier input and dispense with the relay, that should give low attenuation. Rapid switching of input or output will give spurious frequencies. More information of what the signal is to be used for please.

    Incidentaly, I do not see where temperature comes into it. I think you mean 450kHz not 450KHz.
     
  12. hevans1944

    hevans1944 Hop - AC8NS

    4,547
    2,122
    Jun 21, 2012
    So there you have it. It makes almost no sense to switch the high-level output of a PA power amplifier when all you have to do is turn its input on and off. If the PA amplifier is providing high-level audio power to the speakers, and you switch its output on and off with a relay, there is a good chance that the transients that are produced by this action will damage the speakers. If you MUST use a relay, use it to short the low-level audio input signal to common. You might also need to put a series resistance and a shunt capacitance RC filter between the audio source and the input jack of the PA amplifier to "filter out" any "clicks and pops" that occur when the relay contacts switch. Just make sure the low-pass RC filter, if you need it, doesn't eliminate too much of the higher frequency content of the audio signal. You may want to consider using one of the many solid-state analog signal switches, instead of a relay, to disable the audio input.
     
  13. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    I am still trying to figure out why there is 190 to 450 kHz coming out of a PA amplifier.

    Bob
     
    davenn likes this.
  14. davenn

    davenn Moderator

    13,721
    1,913
    Sep 5, 2009
    indeed


    there's so many unanswered questions with this topic
    here 's some of them......

    1) what is this power amp ?
    2) why is it operating at 190 - 450 kHz ?
    3) what wattage is this power amp rated at ?
    4) you still never really confirmed if you want the relay to be able to operate ay the 190 - 450kHz ??
     
  15. Alec_t

    Alec_t

    2,909
    791
    Jul 7, 2015
    What application requires you to switch a power amp on or off in 'a few uS' ?
     
  16. hevans1944

    hevans1944 Hop - AC8NS

    4,547
    2,122
    Jun 21, 2012
    We may again be experiencing a language translation problem. The OP uses "output of a power amplifier" followed by reference to "PA output" which may be the same thing. If that is indeed the case, then PA output does not mean Public Address output but is the OP's way of abbreviating Power Amplifier output.

    Then, given the OP wants to switch 100 Vrms sinusoidal waveforms in the range of 190 kHz to 450 kHz, and do this with micro-second switching times, it may now begin (or maybe not) to make more sense of what the OP is trying to DO.


    Ahem... clearly (now) this must be an ultrasonic thingamubob putting out hundreds, maybe thousands, of watts of ultrasonic pulses by switching the power amplifier output on and off with micro-second precision. To what end, we can only speculate because the OP has still not informed us of what they are trying to DO.

    [BEGIN SPECULATION] This is most likely some form of advanced ultrasonic death-ray weapon, designed for underwater immersion to kill whales or Navy SEALS invading the southern border of Pakistan from the Arabian Sea.[/END SPECULATION]


    However, since this forum does not allow discussions of weapons, if the speculation is true then this thread must be closed. It should probably be closed anyway, because the OP has contributed NOTHING towards explaining what they are trying to DO. What a FWOT this thread has been.
     
  17. naumankalia

    naumankalia

    10
    0
    Feb 11, 2018
    The power amplifier is connected with acoustic transducer for echo sounder (depth finding) and side scan sonar application. The main purpose of this relay is to isolate the power amplifier output from receiver electronics during reception.time. Although, T/R switch has been placed but i think this relay will provide additional isolation so that output noise of power amplifier (during off state) does not leak into receiver electronics
     
  18. globecollector

    globecollector

    27
    9
    Jun 27, 2011
    There is not really anything that will do the job you require at the OUTPUT of the amplifier....and another question, what is the POWER being fed to the transducer?

    At that frequency and power the most likely transducer is a Piezo type device which is capacitive, so there will be impedance matching issues between it and the output stage of the amplifier particularly if the transducer is suddenly disconected.

    IF the amplifier is a wide-bandwith sort of amplifier....so not some tuned thing like used in radio tramsmitters, I am assuming something more akin to a class-A or class AB, not class C, then as has been said above, the most logical option for a transmit-receive switch for a Sonar application will be at the INPUT of the amplifier where the power level, voltage and current will be small. At that point in the signal chain CMOS analog transmittance switch chips, like the 4066 or more modern equivalent, could be used and zero crossing switching could be achieved without all the nasty transients and switching edges messing up the output.

    HOWEVER, if the amplifier IS a tuned sort of thing pumped by a class-C or switchmode type of stage, with a resonant circuit on the output that involves the transducer capacitance as part of the output filter...then FORGET IT, you will need to put on your engineer's hat and completely redesign the whole output stage from scratch.

    Are you a PhD. student and doing this as part of your thesis?


    If the amplifier is producing "noise" when there is no signal applied to the input, then it is either under designed or there is something wrong with it....maybe a noisy transistor in the front end, so you will need to put on your service technician's hat and fix it. At any rate, it sounds like you need to draw out the whole circuit of this side scan sonar, or get its manual and study it VERY CAREFULLY until you can work out what went through the head of the guy who designed it and you glean a similar insight into the nuances of its operation as he had.
     
    Last edited: May 5, 2018
  19. Petkan

    Petkan

    19
    2
    Feb 9, 2011
    Petkan:
    Let us clear some basics. Normal relays take tens of ms to energize. Magnetically driven contacts can be below 10ms. Forget about mechanical relays when it comes to half of MHz. High voltage MOSFETs are capable of switching at these frequencies. They will require a gate driver (possibly with a charge pump if the MOSFET is at the high side)
     
  20. naumankalia

    naumankalia

    10
    0
    Feb 11, 2018
    Thanks very much for help. I am using Apex MP108 Power Operational Amplifier with its evaluation board and its output is directly coupled with 50 ohm piezo transducer.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-