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Relay coils polarity, why some matter and others dont ?
Relay coils polarity, why some matter and others dont ?
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Old 11th July 2019, 07:32 AM   #11
dhaen is offline dhaen  Europe
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Incidentally, a diode shunt does cause a de-energise delay. Whether this is important depends on the application. In power switching it might shorten the life of the contacts.
The simplest way to avoid this problem is to use a suitable zener in series with the diode.
The details can be found here:
https://www.te.com/commerce/Document...=CS&DocLang=EN
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Old 11th July 2019, 01:50 PM   #12
nigelwright7557 is offline nigelwright7557  United Kingdom
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Thanks for your comprehensive reply.
Regards Nigel
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Old 11th July 2019, 02:49 PM   #13
Mark Johnson is offline Mark Johnson  United States
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Relay coils polarity, why some matter and others dont ?
Quote:
Originally Posted by dhaen View Post
Incidentally, a diode shunt does cause a de-energise delay. ... The simplest way to avoid this problem is to use a suitable zener in series with the diode. ...
It might be even simpler to specify a 300V transistor; this approach requires zero extra components.

A normal 1N4148 diode in series with a zener diode requires two extra components.

A zener diode to ground requires only one extra component. If the transistor's Absolute Maximum Rating for collector-to-emitter voltage is "V" volts, select a Zener voltage which is less than 80% of V volts. For example if the transistor is a BD139 rated for 80 volts, choose a 1N5264B zener diode rated for 60V ±5%.

This topic is covered in Douglas Self's book Audio Power Amplifier Design, 6th edition, excerpt below

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Old 11th July 2019, 02:52 PM   #14
dhaen is offline dhaen  Europe
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OK, that's simpler
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Old 17th July 2019, 02:56 AM   #15
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Mark Johnson View Post
It might be even simpler to specify a 300V transistor; this approach requires zero extra components.

A normal 1N4148 diode in series with a zener diode requires two extra components.


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I have designed a few model train electronic controllers.
I had noticed the relay is quieter when it drops out compared to when it turns on. I have updated my next version pcb's to use a 1n4004 and a 12 volt Zener.
That should help the relays last a bit longer.
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