Hi all,
I have several 3W & 5W white LED star mounted pieces. There is no drive circuit on the star, just the LED. I have been playing around with these using PWM to change the brightness, etc. I am using lab equipment so all is very tightly controlled. I had run one of the 3W for 30+ hours on my heat sink at about 2.0W. I had the voltage into the circuit around 4.1 volts to mimic Li-ion battery I will eventually use. I wanted to see if the Li-ion would cause any noticable (measurable) changes, due to internal resistance etc. So I removed the lab supply and used one 18650 cell. In moving some things around the PWM sig driving the gate of the HEXFET got loose and the LED got zapped with the full voltage for a short period of time.
Here is where I get confused. The module has been running at around 3.6v 600ma; but it seems after the zap this particular LED now has much higher voltage drive requirements @ 600ma it now requires 7.00v to drive.
I could understand if it had burned out; or if some of the individual cells in the module stopped working and the current requirements were reduced at a lower light output, but how does the voltage requirement go up? The band gap should not have changed - could it? I'm just wondering if anyone has an explanation?
I have several 3W & 5W white LED star mounted pieces. There is no drive circuit on the star, just the LED. I have been playing around with these using PWM to change the brightness, etc. I am using lab equipment so all is very tightly controlled. I had run one of the 3W for 30+ hours on my heat sink at about 2.0W. I had the voltage into the circuit around 4.1 volts to mimic Li-ion battery I will eventually use. I wanted to see if the Li-ion would cause any noticable (measurable) changes, due to internal resistance etc. So I removed the lab supply and used one 18650 cell. In moving some things around the PWM sig driving the gate of the HEXFET got loose and the LED got zapped with the full voltage for a short period of time.
Here is where I get confused. The module has been running at around 3.6v 600ma; but it seems after the zap this particular LED now has much higher voltage drive requirements @ 600ma it now requires 7.00v to drive.
I could understand if it had burned out; or if some of the individual cells in the module stopped working and the current requirements were reduced at a lower light output, but how does the voltage requirement go up? The band gap should not have changed - could it? I'm just wondering if anyone has an explanation?