12V PSU Remote Power-On Circuit With RC Delay, NPN (TIP31), LCC120 SSR Review

Guys,
Working on a personal project here, not an EE (though give me huge distributions and i'm all good as an electrician) and its been a long while since I've screwed with IC's. I have a 12V power supply im trying to turn on outside of its typical server installation. This requires connecting two pins on the PSU after a short time delay following applying mains power to the unit.  A simple RC circuit should take care of the delay requirement and an NPN transistor makes the switching easy (I've got a few TIP31's laying around) however i'm also looking to have the unit power up automatically when a remote voltage source is present.
I scrounged a maker buddy's junk drawer and came up with a LCC120 SPDT Solid state relay which should work to provide this functionality while keeping the circuits isolated from each other. I sketched it up quickly, hoping someone could take a look and let me know if i'm on the right track?!Thanks!!Patrick

Hi Pat-Close, but not quite there.  Here are the issues with your circuit:The transistor should be PNP, not NPN.The Emitter should be connected to the +3 volt connection and the Collector to the "ON" pin.The capacitor should not be in series with the base of the transistor.If you connect the 470 ohm resistor directly between the relay output and the base of the transistor, and then connect the positive side of the capacitor to the +3 volts and the negative side to the base, then it would "sort of" work.  The reason I say "sort of" is that the voltage will gradually increase during the delay period rather than having a clean off-on transition.I think you'd be better off with a "one-shot" (astable multivibrator) circuit or a comparator plus a RC circuit.  If you're just looking for a few milliseconds of delay, you could even use a mechanical relay with a resistor in series with the coil and a capacitor in parallel. What could be simpler?I don't have any time right now, but I'll try to sketch something up tonight if you're interested.-Rick 

Hey Rick! Appreciate the help! After a little more research I see what I’ve screwed up here.
this linked circuit (https://imgur.com/gallery/9H8gY) does in fact work to power the supply on with enough time delay to make it work, now I just need to add the control circuitry.My thinking is that I need to add the relay between pin 32 (+5vdc) and my 470ohm resistor any it should all work how I want...Input?

Hey Rick! Appreciate the help! After a little more research I see what I’ve screwed up here.
this linked circuit (https://imgur.com/gallery/9H8gY) does in fact work to power the supply on with enough time delay to make it work, now I just need to add the control circuitry.My thinking is that I need to add the relay between pin 32 (+5vdc) and my 470ohm resistor any it should all work how I want...Input?

Patrick, I was going to reply earlier but left it till (my) morning, and Rick beat me to it.  Even if you use a PNP instead of an NPN, you'll get an immediate short on the pins which will go open circuit after the RC delay, whereas I gather that you want to short the pins after a delay?  Do you need the pins shorted continuously to keep the PSU switched on, or just a momentary contact?  If continuous, then I'd second Rick's solution with a cap across the relay coil.  You might be able to use the LCC120 directly for this but you might get variable resistance on the output for a gradually increasing input current - the datasheet is not specific on this.  Try it - if you do get problems use a mechanical relay as Rick suggests.Lastly, your dropping resistor for the LCC120 input you've put as 1.07 K - you don't need to be this precise.  The LCC120 can take an input current up to 50mA, so a 1K should be fine, if you get problems go down to 820 or 680 ohms.   Let us know how you go.

i screwed up the original diagram and have posted an update but the post have not been moderated and approved yet I guess... 
you're correct to assume i want to short the pins after a short time delay, I believe the way i've rewired this now works. Using the LCC120 with a cap directly is an idea but I lose out on the functionality of being able to manually start the power supply without an external voltage input.Hopefully someone can approve my previous post with the updated schematic link.Thanks for your help!

Hi Pat- Sorry to be so long responding.  I can see how the second circuit you posted MAY work, but there are some downsides.That is called an "emitter Follower" circuit. It doesn't make a rapid transition from "off" to "on", so the PSU input may "chatter" as the voltage passes the threshold.The bigger problem is that once the PSU switches on, the voltage on the enable input will continue to rise above 3 volts because the emitter-base junction of the transistor will be forward biased.If you want to try the mechanical relay approach, connect the normally open contact to the enable pin. Connect the common contact to the +3 volt pin.  Connect one side of the coil to ground, along with the negative side of an electrolytic capacitor. Connect the positive side of the electrolytic capacitor to the other side of the coil. Connect a resistor between the positive side of the capacitor and the +5VDC terminal. Here's a quick schematicI recommend using a relay with a 3 volt coil.  Calculate your resistor value so that it will drop about 2 volts when connected in series between the coil and the 5 volt source.Let us know how it works out!-Rick