Beside the Mooly amplifier am I trying to experiment and want to make a precise dimmer for one single 3 mm diode.
I think I can use a simple potentumeter for the dimming. It have to be able to dim from off to max on. But how shall the power supply be build? Do I need to make an reference controlled voltage down to i.e. p-p ripple 1uV / 0.1uA or can a less precise power supply do the same?
I hope to be able to dim a single diode and keep the amount of light constant, no matter if the main voltage should change or anything else.
I think I can use a simple potentumeter for the dimming. It have to be able to dim from off to max on. But how shall the power supply be build? Do I need to make an reference controlled voltage down to i.e. p-p ripple 1uV / 0.1uA or can a less precise power supply do the same?
I hope to be able to dim a single diode and keep the amount of light constant, no matter if the main voltage should change or anything else.
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Most LED colors drop roughly 2V, so use a regulated voltage supply several times that.
Connect the LED through the variable resistor and a small series resistor to set the maximum current.
For example, use a 12V three pin regulator, a series 510R, and a 10k pot.
With an LED that drops 2V, this will adjust the current approx. from 20mA to 1mA.
Usually 20mA is the maximum LED current. If 1mA is still too bright, use a larger pot.
Make sure the unregulated voltage applied to the regulator is 15V or more at all times.
Connect the LED through the variable resistor and a small series resistor to set the maximum current.
For example, use a 12V three pin regulator, a series 510R, and a 10k pot.
With an LED that drops 2V, this will adjust the current approx. from 20mA to 1mA.
Usually 20mA is the maximum LED current. If 1mA is still too bright, use a larger pot.
Make sure the unregulated voltage applied to the regulator is 15V or more at all times.
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Thanks lot! But what about ripple, if the psu do have a ripple of 2V the psu would be useless🙂 What are the specification it have to have?
The output of any three pin regulator will be very constant if operated properly.
The input to the three pin regulator should be three volts greater (or more, including
any ripple or sag) at all times than the output voltage, for it to operate well.
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If the mains voltage changes, it tends to change the light output on ALL the lights in the room. Or do you only listen in daytime?
(Yes, this point is getting old, because many new lamps are regulated for 100V-260V.)
Most of your life, lamps had 100% ripple. OK, hot filaments did thermal-filter, but there was more than 20% change of light twice per cycle.
Quit over-thinking. Do you even really need a knob? Generally I guess, try, and change once, and that's fine forever.
the change in voltage do I find can change when a fridge do start up and the light dims for a short while or something like that. The 100V-260V is a SMPS, right?
My idea is exactly to not overthink it, I'd hope to simply have a psu connected to some simple dimmer and if I turn it to half the output, it just gives me half the output, not having to think if the fridge starts or everything else 🙂
My idea is exactly to not overthink it, I'd hope to simply have a psu connected to some simple dimmer and if I turn it to half the output, it just gives me half the output, not having to think if the fridge starts or everything else 🙂
The eye's response to brightness is pretty insensitive, a few percent current ripple and you may never notice. Flicker at the 3 to 20 Hz range is perhaps the most visible.
LEDs output light proportional to current, and you should control the current, not the voltage, either with a constant current circuit (various ways to do this), or with a current limiting resistor and constant voltage supply to feed that (often already available)
LEDs output light proportional to current, and you should control the current, not the voltage, either with a constant current circuit (various ways to do this), or with a current limiting resistor and constant voltage supply to feed that (often already available)
It sounds maybe interesting but would that not make the LED flicker? What I do need is a hopefully way to "just" adjust the lumen from of to full on. Heped it could be done with a transformer, a rectifier, some ripple removal, a current adjustment and finito a flicker free LED with an adjustable rock solid lumen🙂
Arduino Nano setting LED brightness by pwm.
5V redundant phone charger for power.
Set brightness by analogue read of a 10K pot, a pair of tactile switches for brightness up/down or use an IR Receiver TSOP38238 & a redundant TV remote.
5V redundant phone charger for power.
Set brightness by analogue read of a 10K pot, a pair of tactile switches for brightness up/down or use an IR Receiver TSOP38238 & a redundant TV remote.
PWM is far higher frequency than the eye can detect.
If the eyes were so sensitive to flicker we'd have no TV or cinema.
If the eyes were so sensitive to flicker we'd have no TV or cinema.
to bad, I have several small projects where flicker free is important, for filming, black count and other🙂
You can get linear light output if you use a Voltage to current converter. The log characteristic of the LED
will disappear and the current (light output) will be linear with drive Voltage. This is not PWM so there
is no light flickering. I did this about 17 years ago to transmit linear video signals optically. I was
sweeping out to 30 MHz and passing excellent linearity ramps. Back then I was using the no longer available
SHC615 from Burr-Brown but I needed speed and you just need stable no flickering. An opamp should
be adequate for DC. Depending on how much current you need you might require a transistor in the feedback
loop to raise the current capability.
G²
Sounds like a great idea and way to do it. Do I understand it correct that you did chose a frequency that was so high that the LED did never had time to "detect" the short missing current?
If you're responding to me, I didn't explain properly. I got a linear light output up to the current limit
of the LED. It operated from DC to 30 MHz though the response was 3/4 dB down at 30 MHz because
of the turn on/off time of the LED. At the time I was working on an HD telecine (real time film scanner)
and needed to test the photo receiver preamp. The point is that controlling the current will linearly
control the light output. The Burr-Brown chip could go fast but if you don't need speed, an opamp will
do fine.
G²
Okay thanks, it sounds like I did also not understand it correctly🙂
What I do need is, I hope" fairly simple.
1) The LED do go from off to full on by using a single turn 270 deg pot or maybe later by electronic.
2) The LED may not flicker or blink, it has to be rock solid amount of light
I did / do imagine an "analog" power supply that deliver constant power trough a pot to the LED. But can a simple-ish power supply deliver the rock solid power, what specification do it have to perform? Ripple, capacity, amp, voltage and so on?
What I do need is, I hope" fairly simple.
1) The LED do go from off to full on by using a single turn 270 deg pot or maybe later by electronic.
2) The LED may not flicker or blink, it has to be rock solid amount of light
I did / do imagine an "analog" power supply that deliver constant power trough a pot to the LED. But can a simple-ish power supply deliver the rock solid power, what specification do it have to perform? Ripple, capacity, amp, voltage and so on?
WOW!! Thank you a lot for that great work!! 🙂
What about the ripple current / voltage from the power supply?
What about the ripple current / voltage from the power supply?