Modifying IR LED array for brighter light

[Dannyx]

Good day folks. I'm going to install a camera for my door and to make it less obtrusive and prone to vandalism, I got myself an intercom outdoor unit which already had a camera in it and 6 white LEDs. I replaced the camera module with a better one and now I wanted to replace those highly obvious white LEDs with some IR ones. I salvaged some from some old CCTV cameras and installed them. They DO come on, but they're very dim and not useful at all. I drew the schematic of the LED section hoping to somehow be able to give them more oomph without frying them of course.

One thing I find strange is that the original white LEDs when tested individually with my bench supply came on at 3v. Anything lower and they wouldn't light up at all. These IR ones come on VERY brightly at 3v and draw a not inconsiderable 50mA (from what I could briefly spot on my supply's display), so I was afraid they'd actually burn out, but on the contrary: they're dim.

I was thinking of dropping the value of either R9 or R8. What do you guys think ? Have you seen a similar circuit before ?

[eccerr0r]

Re: Modifying IR LED array for brighter light

IR LEDs use a different chemistry than white/blue/violet LEDs and have a much lower characteristic forward drop, typically around 1.5V. Getting them to 3V will likely kill them.

Most consumer cameras have IR filters that make IR LEDs appear dimmer than they really are. You will need to remove the IR filter or get a camera that will respond to IR if you want full brightness.

[Dannyx]

Re: Modifying IR LED array for brighter light

Right, forgot to mention the test conditions: I used my phone to do it. Not only to check the polarity when installing them, but also to get an idea of brightness. As expected, it showed up as a purple light. It was fairly bright at 3v, but not so bright in-circuit, obviously.
Yes, you're right: they may not help the camera out in the dark. This is actually a camera module I picked up from Ali. It's got a joystick and some menus you can mess with and this IR filter you're mentioning could be part of the lens or something, because I see two thin wires running to the base of the lens (where it meets the board). Messing with some options in this menu, I could hear something clicking there, so there's some sort of aperture or filter moving in and out of the way, probably related to those wires...could have an effect on how effectively IR works.

[redwire]

Re: Modifying IR LED array for brighter light

Q3 is supposed to be constant-current source- but missing a zener (constant voltage) from the base to gnd, so Q3 ends up being a switch like Q9. Unless R8 goes to +5V instead, that would make more sense.
Right now R9 ends up limiting current to the LED strings, about 60mA total or 30mA per string by my guess. Lowering R3 to 47R 1W would give double current ~120mA or 60mA per string.

I don't think 5mm IR LED's can take 50mA or more without getting damaged? They also have a very low forward voltage 1.25-1.6VDC compared to red, blue etc.
Don't look at them with the eye or you can damage it, you don't "see" IR but the light still gets in to the retina.

[Dannyx]

Re: Modifying IR LED array for brighter light

First order of business is to figure out if the camera can work with IR light, otherwise it's all for nothing. I'll check the circuit again, but I believe it's correct.

Can you explain some of your calculations ? I'd like to know how you got those numbers.

[budm]

Re: Modifying IR LED array for brighter light

https://www.radio-electronics.com/in...ent-source.php
Q3 is the low side CI source.

[Dannyx]

Re: Modifying IR LED array for brighter light

Oops, I missed something indeed: there's two diodes on the base of Q3 arranged in series like so. 1n4148 judging by their looks, as I can just about make out 1n on there, since they're flat on the board and can't really see them.

Are they using the Vf of the diodes as a "zener" reference voltage ? The Vf of a 1n4148 is around 1v from what I remember, so would this mean the "zener voltage" is 2v ?