I realize a kind of late response but you’re post here was for me (initial) a reason to register on this website. I’m very interested in LED lighting/dimming. I have build a T5 compact dim (PIC) in my current tank (a modified Red Sea Max) and I want to use this circuit to generate a reference power that will regulate the brightness (is this understandable English? ;-)
The timer/dimmer circuit that I use now is a commercial product: Flora-mate. It is used to dim Tube Lights by analog 10v. However the device is not sending a voltage but is – and I hope you understand my English – is used to pull down the controllers dimsignal to 0. As you probably know this type of electronic controllers generate their own 10 volt. Actually the timer/dimmer is working as manual putting a shortcut wire on the 0-10v connection or a trimmer (potentiometer). Anyway the owner has given me the opportunity to use the original schematics to build my own model. I needed a much smaller model of the circuit to build it the hood of my tank. Look at the modificaties on my website. Since many people in The Netherlands are using this timer/dimmer I want to build for this timer/dimmer (under TAPR open-source license) an ‘add-on’ led dimming driver. A module that can be attached to the original model without the need to modify the original. So as much as possible people who do own the Flora-mate can use this module by simply connecting it.
As soon I am allowed to post URL's I will do! (goto 3w eliveld.nl - select 12 maart 2008 in Sitemap to read more about the Flora-mate) For now I just have a few questions:
I noticed that in you’re model a 900 hz is used to generate a ramp. Is this frequency not a problem in your household? Most ramp generators I know off generate between 100 and 300 hz. Any idea’s what effects could be on fish or plants? And any idea’s what kind of colour leds are best?
About the picture you published: as you mentioned is the eagle board not the same as the one on the photo. On the board many more capacitors are placed while on the photo a transitor is visible. In the schematic the capacitors are drawn. However its not clear why they are there. (just for flattening the power?) On the photo I see a blue trimmer (dont know name in English). Where is it in the schematic? And what is it for?
Hope to hear from you soon!
Kind regards, Erwin
Goodness, Erwin, I'm so sorry to have missed your post!
If I'm understanding you correctly, you can in fact drive this dimmer straight from a Floramate if it outputs a variable analog voltage -- in fact that's the entire purpose of this circuit! It will require no modifications to do so. Use 10v as VCC, and feed the variable output into the input.
I chose 900hz just because it seemed like a useful number. It was completely arbitrary. Change C5 to change the frequency.
As for errata, the photos and the Eagle board are NOT identical, they just do the same thing. The photos are of the first version. I did make a few hardware changes since then. I removed a trimmer and replaced it with fixed resistors. I did add more filtering capacitors -- large electrolytics to help with sags when the driving op-amps change state, and small electrolytics (or large ceramics) to help control ringing. They're just for stability. The transistor in the original was to fire the MOSFET -- turns out its better to just let the op-amps do that for as low of a frequency as I'm using, since they both push and pull at a few milliamps (enough to switch the FETs on in a few microseconds).
Incidentally, I used a larger version of this circuit (at a 50khz frequency) to power a flyback transformer. By feeding music into the voltage input, I can make musical arcs
I actually made my own MOSFET driver for that, with a 4011 quad-NAND gate driving two 2N2222 transistors to slam the MOSFET gate open and shut. But I'm also using an 800V 10A FET...