I have a 12VDC 2A power source to light a white LED strip (16 foot long). It came with a dimmer. Apparently it's a current control device. When I check for resistance through the fade control neg to neg I get about 10 meg ohms with a constant descending resistance regardless of where I set the slider. Measuring pos to pos I get 4.6Ω again, regardless of where I set the slider. Input side of the slider - I get an open reading between pos and neg. Same is true when checked at the output side of the slider. So this is not a simple variable resistance.
Checking with scope: At full dim (no light) I get a mostly square wave. As I increase the intensity (no load) I get nearly full 12 volts with some icicles dropping about a volt or two from the 12 volt rail.
Checking amperage: At full bright the lights are drawing 240mA (I'm only using two feet of the strips for lighting during Zoom meetings). At about half brightness the draw is 100mA. LED's light up with as little as 7mA. So I'm concluding that the slider is a current source control.
Here's what I want: Set the brightness to a suitable level (adjusted according to preference) and have a switch that simply switches it on or off. But I don't want sudden on and sudden off - I want to fade between OFF and whatever set brightness. So I'm looking for a circuit to replace the VCC (Variable Current Controller). Fade to ON can be 1 to 2 seconds, there's no need for precise control, and 2 to 4 seconds to fade to OFF when switched off.
Anyone point me in the right direction? Maybe a MOSFET used in the resistance region, since I'm not going to be drawing more than around 100mA? Alternative approaches are also welcome.
Thanks. TR
[edit] with load I clearly get PWM.
Checking with scope: At full dim (no light) I get a mostly square wave. As I increase the intensity (no load) I get nearly full 12 volts with some icicles dropping about a volt or two from the 12 volt rail.
Checking amperage: At full bright the lights are drawing 240mA (I'm only using two feet of the strips for lighting during Zoom meetings). At about half brightness the draw is 100mA. LED's light up with as little as 7mA. So I'm concluding that the slider is a current source control.
Here's what I want: Set the brightness to a suitable level (adjusted according to preference) and have a switch that simply switches it on or off. But I don't want sudden on and sudden off - I want to fade between OFF and whatever set brightness. So I'm looking for a circuit to replace the VCC (Variable Current Controller). Fade to ON can be 1 to 2 seconds, there's no need for precise control, and 2 to 4 seconds to fade to OFF when switched off.
Anyone point me in the right direction? Maybe a MOSFET used in the resistance region, since I'm not going to be drawing more than around 100mA? Alternative approaches are also welcome.
Thanks. TR
[edit] with load I clearly get PWM.
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