I need help creating a transistor circuit for delay

Thread Starter

*synonymous*

Joined Nov 29, 2013
35
Hello and thank you!

I am looking to create a transistor delay circuit to replace a relay delay device. Hopefully the attached image gives all the necessary information for the idea. I am looking for an approximate 1 second delay, 2 seconds is fine also. A quick reset condition is appreciated also. This "delay switch" will power a bank of relays consuming up to approx 2W in some circumstances and a low of about 1.2W in others. Basically I hope to have it start it's cycle when the mains power is on and have it "turn off" when the mains power is switched off. In the attached image as an option I would like to possibly operate the "delay switch" by some means, showing a ground signal controlled operation. If it is easier or better, controlling this "switch" using either the positive or negative rail is fine as well. Word on the street is that a JFET circuit is the way to go in this instance. Hopefully I haven't missed anything

Thank you in advance for all the help!!
Scott
 

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inwo

Joined Nov 7, 2013
2,416
Is that 2 watts each?

You should really tighten the specs. Either initiated with a switch or with application of power.
 

inwo

Joined Nov 7, 2013
2,416
Sorry, I remembered the other thread. Didn't want to steal his thunder.

Also I thought the spec was transistor timer which seems a simple step for #12.

A darlington might work and still be in the spirit of a single device.

A parallel load on relay coil, but to ground, like a pilot light might help circuit recover faster.
 

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iimagine

Joined Dec 20, 2010
388
A darlington might work and still be in the spirit of a single device.
I think the OP wants to keep the switch on until shuts off. The circuit that you post would turns off the transistor after the cap discharged.

Edit: Nevermind, I read your circuit wrong, my bad
 
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Thread Starter

*synonymous*

Joined Nov 29, 2013
35
Thanks for the replies!

I've only got the 2 12v rails to work with and at a minimum be using 3 relays rated at 400mW a piece. In a future incarnation i may be using up to 5 relays, hence the 2,000mW power requirement. I also know that there are many more good circuits out there that could be made to work in this project and was curious if just a slight modification to the previous circuit would work. The response was that a jfet is the best way. I certainly appreciate the ideas offered! Looking for the best fit

Thanks again
Scott
 

#12

Joined Nov 30, 2010
18,076
One of the reasons I bugged out was that I had to go to work. Look at the time! 7 am and I'm just getting home. I probably won't feel too peppy on Sunday, either.

Edit:
I just wanted to say all of you are welcome to out think, out design, and out deliver me on this site. Being bested does not insult me. Giving the original poster a wrong or misleading answer because you weren't paying attention does seem to irritate me. Try to keep it sharp. This site has a reputation for being pretty good at electronics.
 
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inwo

Joined Nov 7, 2013
2,416
They must be really tiny relays.
<100 ma total seems low. That's why I asked about total.

The circuit I've shown is a small step from the transistor switch that I copied.

An scr makes a good timer also.

I'm sure others will post fet circuits if that's the way you'd like.

I'm a transistor/ scr guy.

Alternate to pilot lite is led or double pole switch for C1 discharge.
 

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inwo

Joined Nov 7, 2013
2,416
"Basically I hope to have it start it's cycle when the mains power is on and have it "turn off" when the mains power is switched off."

The first circuit will work rail to rail delaying power to relay.
The second uses grounded switch.
 

#12

Joined Nov 30, 2010
18,076
The link in post#3...I have been using those for 30 years and didn't know they came (retail) in a DC version! I got most of my fet timing education from taking those apart. If and when I get up to speed today, I'll show you how they work.

Other comments: post #2, it's hard to tell how to attach that circuit to a relay. Could you please add some labels? and maybe a relay symbol? (I am just as guilty of posting concepts instead of the finished application.)

post #5, you have a ground label wrong.
Post#10, you fixed it and showed me yet another way to do this. Thank you.

Edit: These relays use twice as much power as the relay in the first thread. Please double check to see if there has been a mistake.
 
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iimagine

Joined Dec 20, 2010
388
Other comments: post #2, it's hard to tell how to attach that circuit to a relay. Could you please add some labels? and maybe a relay symbol? (I am just as guilty of posting concepts instead of the finished application.)
Here, I'm using an LED as an example :D. This method of switching is very efficient by the way. No power consumption to keep the FET on or off. Hope this helps
 

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Alec_t

Joined Sep 17, 2013
10,267
I may be missing something, but why do you need 5 FETs to switch 1 LED? You could do it with 1 FET.
 

#12

Joined Nov 30, 2010
18,076
iimagine is thinking in terms of cmos digital logic gates. Not my preference, but if *synonymous* can see how to make it work for him, that's why we all contribute.
 

Thread Starter

*synonymous*

Joined Nov 29, 2013
35
Hello and thank you again!

Those Versa-Timers I cannot seem to find a price for one. 2" square seems a bit large?

inwo, would you have any idea on the reset time for those darlington circuits? Thank you!

Yes, 3 and possibly 5 coils at 16.7mA each

iimagine, I like the prospect of very low power consumption for the circuit to activate. What kind of FET's or device is that do you propose I look for? Quick reset time? Thank you!

Alec_t, Very well displayed! I like the low part count and release time on that, it appears less than half a second.

I am enjoying all these proposals! Keep it fun for yourselves also, no losing sleep or family time here! Simple, functional and some versatility is my thoughts

Scott
 
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