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Old 30th April 2012, 08:06 PM   #1
akis is offline akis  United Kingdom
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Default high frequency relays

Hello

I am looking for a way to switch the output of my amplifier into 2, 3 or possibly 4 channels. The switching will be electronic and done once a second. I was thinking of using a 555 for timing and CMOS chips for the actual switching. The output that needs to be switched, I think also called "load" is AC, sinusoidal, 200 KHz and 50V peak.

I was thinking of using solid state relays so they are 100% quiet. But the ones I looked at only work at very low frequencies - I think they are designed to switch mains voltages and not higher frequency signals.

Can anyone please advise me what to do?

Many thanks
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Old 30th April 2012, 08:26 PM   #2
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Normal mechanically switched relays will be more than fast enough to switch at 1Hz. What kind of current will your load draw through the relay(s)?
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Old 30th April 2012, 08:41 PM   #3
akis is offline akis  United Kingdom
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The current will be trivial, 20mA to maybe 100 mA.

But will mechanical relays not make lots of clicking noises?
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Old 30th April 2012, 09:00 PM   #4
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Hi,
You can use the Avago solid state relay ASSR-1511. It is a 60volts 1.0 or 2.0 amps. Right now I am using one for the mute in an LM3886. You can use it in AC/DC voltage.
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Old 30th April 2012, 09:49 PM   #5
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Small relays to carry 100mA will be fairly quiet. Why is the noise a problem? Mounted in an insulated box they would be really quiet.

he price of solid state relays and their possible distortion of an audio signal would be concerns to me.
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Old 1st May 2012, 11:48 AM   #6
akis is offline akis  United Kingdom
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Hi again, I am looking at a range of relays now, V23105A5001A201 - TE CONNECTIVITY / AXICOM - PCB RELAY, CONTACTS DPDT | Farnell United Kingdom

but they have them in multiple coil powers, from 150mW to 500mW - why is that?

If the relay can switch with 150mW coil, why would I want to get a 500mW coil and spend more energy on it?

Are there other differences I am not aware of ?
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Old 1st May 2012, 03:27 PM   #7
cliffyk is offline cliffyk  United States
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The higher the coil resistance (lower coil power), the lower the operating current and generated heat--and the higher the sensitivity of the relay. However high sensitivity can be a disadvantage as it also makes the relay more sensitive to electrical and magnetic interference.

Lower coil resistance (higher coil power) decreases the inductance of the coil, increasing response time and reducing back-EMF--at the expense of increased heat.

Shielding, allowable back-EMF in the coil drive circuits, duty cycle, enclosure type, etc should all be considered when selecting coil power.
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Old 2nd May 2012, 07:01 AM   #8
akis is offline akis  United Kingdom
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I have looked at dozens of "signal" relays of similar switching capacity and the manufacturers do not agree on the definitions of "standard" for their coils - so it appears there are versions from 50 mW to 500 mW. Some manufacturers call the 500 mW "standard" whereas others call the 140 mW "standard".

I am looking at current consumption and even the "standard" 140 mW draws 28 mA (at 5 V) - and I believe 28 mA is too much current to have constantly flowing through one of my relays. I am looking for something like 1 mA to 5 mA for activation of a switch, similar to the current drawn by an LED.

So I am looking at solid-state relays rather than mechanical ones.
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Old 2nd May 2012, 08:27 AM   #9
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If normal relay is too "noisy" why not use reed relay? It's alos mechanical relay and also make "click", but you can't hear it unless insert it into ear.
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Old 2nd May 2012, 12:52 PM   #10
cliffyk is offline cliffyk  United States
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What they are referring to is their "standard" production unit, the others being special production available on request--as opposed to being a reference to any universal standard.

Here is an interesting article describing design considerations and design of an SSR for speaker switching. Protecting the amplifier is a more complex issue than switching the speaker.

Quote:
Originally Posted by akis View Post
I have looked at dozens of "signal" relays of similar switching capacity and the manufacturers do not agree on the definitions of "standard" for their coils - so it appears there are versions from 50 mW to 500 mW. Some manufacturers call the 500 mW "standard" whereas others call the 140 mW "standard".

I am looking at current consumption and even the "standard" 140 mW draws 28 mA (at 5 V) - and I believe 28 mA is too much current to have constantly flowing through one of my relays. I am looking for something like 1 mA to 5 mA for activation of a switch, similar to the current drawn by an LED.

So I am looking at solid-state relays rather than mechanical ones.
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