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Old 14-05-2018, 03:27 PM   #1

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Default Dimming around 20 LED's query

Slight conundrum on dimming LED's. The main part would to be able me to dimm the LED's on a mimic panel & i am not sure which way to do it: IE: Dim the input or output of the 5 volt transformer. The bit that confuses me is will the not change the resistor values that i am using on each LED when i use a dimmer.??
Oh!, its one independent 5v power supply for this mimic panel.
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Old 14-05-2018, 04:19 PM   #2
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Yes it would change the resistor value but that would in effect maintain the brightness level - which is the thing you are trying to change!
Not all LEDs lend themselves to dimming (I think) and if you reduce the voltage too far they will probably just switch off.
You could try fitting a voltage controller into the output of the transformer but the ‘correct’ way to do it would be to experiment with different resistors on a spare LED until you find one that matches the light level you want, then change all the resistors on the mimic board to match.
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Old 14-05-2018, 04:20 PM   #3
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You wont be able to reduce the 5 volts very much before the LEDs go out as their working voltage is going to be around 3 volts depending on their colour and possibly 4 volts if white.

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Old 14-05-2018, 07:10 PM   #4
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You need to reduce the power without reducing the voltage, easiest and very cheap is to drive the LED's via a PWM circuit
They can be had as a remote devices but just set and forget.

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Old 14-05-2018, 07:25 PM   #5
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If you are planning to control the brightness of LEDs with a potentiometer (variable resistor) there are some precautions to observe. As a potentiometer can be turned down to zero resistance that would immediately blow the LEDs, it is important that you have a resistor in series with the potentiometer which will limit the current to the maximum the LED will stand the potentiometer can then be used to increase resistance thus reducing current to dim the LED. LEDs have a switch on threshold round about 0.7V below this value they simply will not switch on. With a voltage range from approx. 2V to about 3.5V for a white LED the voltage range of LEDs is quite small.

The most efficient method of controlling LED brightness is to use PWM (Pulse Width Modulation). There are circuits available that can produce a string of pulses ON and OFF. By varying the length of the on or off period of each pulse the LED will appear to dim.

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Old 14-05-2018, 08:55 PM   #6

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Ah!, well done guys, i have a couple of PWM dimmers i lent to a friend that's i fitted on some LED cabinet lights & will get these back & give this a try.

Last edited by collectors; 14-05-2018 at 08:58 PM.
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