Can someone please point me to a PSU that will illuminate the fixtures instantaneously (or darn near) when I flip the wall switch?
Thanks!
edit: I need units in the 3-5 amp range
Probably the only type where you're highly likely to get "instant-on" would be old-school supplies using 60 Hz transformers and linear regulators. A 12V, 5A supply like that is going to weigh probably north of 5 pounds, and it'll get at least very warm in use, if not hot. There's a good reason they started making high-frequency switching supplies. Greater efficiency, much smaller transformers, less waste heat.
The delays you're experiencing are a product of design. A lot of these supplies slow start to limit the inrush currents into the filter capacitors and rectifier diodes. Another reason might be power factor correction.
I've mostly designed/built drivers for automotive uses, with a few other similar applications thrown in. In all cases these were DC/DC converters where I had a raw source of DC power available. Yes, they come on instantly, probably within milliseconds, but they wouldn't be much help to you here since I assume you want a 120VAC to 12VDC supply. I never designed or made those, although I understand the principles involved. The reason why was the market is already saturated with such supplies selling for far lower cost than I could make them for, and there are a bunch of liability and product certification issues for anything using 120VAC.
There are two ways I'd move forward on this if it were my project. Obviously, one way is to keep trying supplies until you hit on one that works. That Competition Electronics supply sounds like it fits the bill but is overkill for what you want.
The other way is a hack which frankly I think would be more trouble than it's worth. I'm thinking something along the lines of a small 12V battery which charges from the power supply. A small lead-acid battery would do fine on a 13.8VDC supply. From the battery you have a 120VAC relay to connect to the LED strip. The relay coil is connected to the same 120VAC as the power supply. When you turn the switch on, the relay goes on almost instantly, connects the strip to the battery, and the strip goes on instantly. You don't need a huge capacity battery since it's only carrying the load for a few seconds, until the power supply kicks on. Once the supply is on, it powers the strip, and float charges the battery. You would need to put a diode between the supply and battery so that the supply doesn't see the battery voltage when it's off. The diode would need to be rated for at least as many amps as the LED strip.
If supercaps didn't self-discharge so fast, this would be a perfect application for them. To carry 5A for maybe 5 seconds with a 1V drop, you would need a supercap of at least 25F, and rated for at least maybe 15V. But due to the self-discharge, this isn't a good application for a supercap.
EDIT: Not exactly what you're looking for but here's a 24V, 72W supply:
Buy ROAL 24V LED Power Supply 120-277V 50/60HZ 72WATTS MAX RSLP070-24: Internal Power Supplies - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
Now the reason I linked to this was I converted a circline fluorescent fixture in the bathroom to LEDs using the same brand driver, but in my case I used their constant current (350 mA) driver. It comes on within maybe 1/2 second maximum. I figure the one I linked to might function similarly since it's the same brand.
They do have a 12V, 4A version according to the
datasheet. If it turns on quickly, it might be just what you're looking for. I couldn't find the 12V version on either Amazon or Future Electronics but someone must sell it.