How can I add soft on/off functionality in simple lamp
How can I add soft on/off functionality in simple lamp
(OP)
I have a small LED lamp and I would like it to slowly ramp up when turned on and slowly fade out (the reverse) when turned off.
The input power will be removed at power off
The LEDs take 6.6VDC, 50mA at full on
The input voltage is on a vehicle so it is 9-16 VDC
The solution must be very "cost effective"
I have explored thermistors and different voltage regulators, LED drivers, etc but have not found a suitable solution to the design problem.
The input power will be removed at power off
The LEDs take 6.6VDC, 50mA at full on
The input voltage is on a vehicle so it is 9-16 VDC
The solution must be very "cost effective"
I have explored thermistors and different voltage regulators, LED drivers, etc but have not found a suitable solution to the design problem.





RE: How can I add soft on/off functionality in simple lamp
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RE: How can I add soft on/off functionality in simple lamp
LEDs typically have a series resistor. Add a capacitor across the LEDs after the resistor. It might have to be a large capacitance value, but large value supercaps are getting cheaper. It's certainly the simplest solution, but it might not be the cheapest in large quantities. But for a one-off it's a no brainer.
PS - resistor power rating might have to be increased with some combinations of circumstances. Worth double checking.
RE: How can I add soft on/off functionality in simple lamp
But a capacitor will still give you a ramp as you have described.
But if this is for production, a swItcher would be better. But you have to think how it knows the power has been cut while it still has power to ramp down on power off.
RE: How can I add soft on/off functionality in simple lamp
The capacitor for the slow off is perfect and is in fact in
my current design, but then I am stuck on the ramp on.
I am afraid a switcher is both $$ and an EMI/EMC concern.
RE: How can I add soft on/off functionality in simple lamp
If the 'slow off' is perfect, and the 'ramp on' isn't (too fast?) then I suspect you're talking about a normal power supply capacitor somewhere else in the circuit.
RE: How can I add soft on/off functionality in simple lamp
I also ran across this (another helpful person sent it my way). I would welcome any comments if you see potential issues.
http://w
Thanks again.
RE: How can I add soft on/off functionality in simple lamp
RE: How can I add soft on/off functionality in simple lamp
Dan - Owner

http://www.Hi-TecDesigns.com
RE: How can I add soft on/off functionality in simple lamp
I am just getting back to the design this morning.
RE: How can I add soft on/off functionality in simple lamp
Dan - Owner

http://www.Hi-TecDesigns.com
RE: How can I add soft on/off functionality in simple lamp
How fixed is this requirement? Decaying the light with no external power is possible but considerable added expense if always on power is not available. How long a decay for the lamp?
RE: How can I add soft on/off functionality in simple lamp
RE: How can I add soft on/off functionality in simple lamp
OperaHouse's suggestion certainly limits the size of the capacitor and controls the ramp up. However, there's always the LM393, which is a dual output rather than a quad. Here's the datasheet: http://www.national.com/ds/LM/LM393.pdf
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RE: How can I add soft on/off functionality in simple lamp
If this device has a microprocessor in it with a spare output pin, a bit of s/w to PWM the LED might be the simplest solution.