Correct LED illuminated push button switch voltage
« on: February 12, 2021, 03:49:37 AM »
I am building a pair of 500 series EQs and want to use an illuminated push button switch for the EQ in/bypass in place of a toggle switch and separate LED. As I understand it, there is already a resistor installed in the LEDs of these switches.
I measured 15VDC at the pads on the PCB going to the LED. According to the specs of the switch, there is an option for the illumination voltage of  "base voltage" (which I assume is no resistor), 6V,12V and 24V. Is this spec the voltage needed to power the LED and if so, would the 12V be the best option in this case? I have one of the base voltage versions I received as a sample from a distributor and it is marked 2.8V on the part. I tried it just for kicks and it seemed to work fine with no issues. What problems would arise from using it with 15VDC powering it?



abbey road d enfer

Re: Correct LED illuminated push button switch voltage
« Reply #1 on: February 12, 2021, 04:11:06 AM »
I am building a pair of 500 series EQs and want to use an illuminated push button switch for the EQ in/bypass in place of a toggle switch and separate LED. As I understand it, there is already a resistor installed in the LEDs of these switches.
I measured 15VDC at the pads on the PCB going to the LED. According to the specs of the switch, there is an option for the illumination voltage of  "base voltage" (which I assume is no resistor), 6V,12V and 24V. Is this spec the voltage needed to power the LED and if so, would the 12V be the best option in this case? I have one of the base voltage versions I received as a sample from a distributor and it is marked 2.8V on the part. I tried it just for kicks and it seemed to work fine with no issues. What problems would arise from using it with 15VDC powering it?
This "base voltage" is almost certainly an LED without series resistor. An LED is a current device.
The resistor in series can be calculated with the formula R= (V-Vb)/I.
For example, if you want to operate the LED at 15mA from a 15V source, the resistor is (15-2.8)/0.015 = 813 ohms. The closest value is 820.
However, there is not much luminosity difference between 10 and 15mA, and you may find a correct operating current with a resistor of 1-2 kohms. Actually, most users prefer a dimmed illumination, operating LD's at 1mA or less. That would be a resistor of 10 to 20 kiloohms.
This is extremely variable, since the efficiency of LED's can vary over a range of 1 to 20.
However, when LED's are incorporated in a pushbutton, there could be a significant loss of luminosity.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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