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Simple 2N2222A Switching Relay

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JoseMR
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Simple 2N2222A Switching Relay

#1

Post by JoseMR » 11 Apr 2017 20:50

Hi, I've recently bough an Emotiva audio preamplifier to replace some older audio equipment, this new preamp also have a 12v trigger output to power ON other audio equipment with such similar feature, however since most Pro audio gear/amplifiers does not support this features I had to made a custom circuit to trigger a small SPDT 12v relay for such purpose, so my goal was to use the 12v trigger from the Emotiva PT-100 preamp to activate the small SPDT relay without putting any load on the preamp trigger output.

This small remote circuit can handle up to 120V 10A, however I have 2 old school Samson S2000 amplifiers who need a much higher in-rush and running current, so this small relay will activate a second 120V 30A contactor which will take care of switching up the pro gear/amplifiers.

Note: You can Google: "2N2222A as a Switch" and you will see a bast amount of similar project in this regards.

I will include the circuit schematic and some pictures of the assembled project below:

EDIT: Diagram and pictures are the latest version.
Simple_Remote_PCB-1.jpg
Simple_Remote_PCB-2.jpg
Simple_Remote_Sch.png

Final project will be enclosed in a wall mounted electrical panel with additional Surge suppressors, 30A EMI filter module and fuse/breakers for protection.

Regards
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Last edited by JoseMR on 07 Jul 2018 08:48, edited 7 times in total.
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alexey123
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Re: Simple 2N2222A Switching Relay

#2

Post by alexey123 » 12 Apr 2017 18:12

Hi
Please use my diagram
It work better - transistor will guaranteed close when input voltage will logic low
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Re: Simple 2N2222A Switching Relay

#3

Post by JoseMR » 12 Apr 2017 18:38

Hi, nice diagram draw, I used paint :lol: , I will test that circuit, indeed I will need the shunt resistor to ensure open state wen no input voltage, also I will add a forward diode to the Base input as well for equipment reverse voltage protection just in case of transistor failure. :)

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Re: Simple 2N2222A Switching Relay

#4

Post by alexey123 » 12 Apr 2017 19:06

JoseMR wrote:
12 Apr 2017 18:38
Hi, nice diagram draw, I used paint
I use https://www.expresspcb.com/expresssch
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Re: Simple 2N2222A Switching Relay

#5

Post by JoseMR » 12 Apr 2017 19:32

That's a really nice software for schematics, I can't believe I did miss, I will try it, thanks. :)

P.S I improved circuit and updated forum pictures.

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Re: Simple 2N2222A Switching Relay

#6

Post by pokeyboy » 01 May 2017 19:11

Hey JoseMr,

A little bit of trivia for you. At the company where I worked, back in 70’s or early 80’s, we used a circuit nearly identical to yours. We were designing and building a new industrial machine that used numerous pneumatic solenoid valves. The valves were computer controlled and interfaced with TTL IC’s to a switching circuit like yours.

When we first tried out the new design, there was a serious problem. You could only activate the solenoid valve one time and that was it. It turned out the designer had neglected to include the diode (D2) in his design. The Q1 transistor would turn on just fine and close the valve. However, when turning off the valve, the collapsing field of the solenoid coil would discharge through the transistor and burn it out.
We did burn through a few transistors before we solved that one. The diode was all it took. I don’t recall that we used or needed the C1 Cap.

Thanks for your posting; it brought back some old memories!

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Re: Simple 2N2222A Switching Relay

#7

Post by alexey123 » 01 May 2017 22:16

pokeyboy wrote:
01 May 2017 19:11
I don’t recall that we used or needed the C1 Cap.
Hi, pokeyboy
Capacitor on power line, between plus and minus, must be in ALL projects.
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Re: Simple 2N2222A Switching Relay

#8

Post by was-armandh » 17 Jan 2019 02:05

yep every project builder quickly learns about damper diodes
by using this free advise, you, your heirs, etc
absolve, save, and hold harmless the advisor.
CAVEAT EMPTOR
YMMV

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