Voltage-Exposure Testing

A project log for Edgerton, A High-Speed LED Flash

Affordable photography tool used to capture images of bullets with no apparent motion blur

tyler-gerritsenTyler Gerritsen 05/25/2019 at 19:330 Comments

Shortly after assembling the device, I tested a bank (3x LED's) by increasing the voltage until the LED's were damaged.  The test began at 45 V and incremented by 10 V following a single flash.  Major damage occurred at 125 V.

More recently, I started a series of longevity tests with a single LED.  It was strobed over 100,000 times at various voltages.  Surprisingly, the LED reached 125 V and survived a battery of cycles at that voltage.

Some head-scratching later and I realized that the FET driver was changed since the original destructive testing (TC4420 to TC4452).  The new driver could ground the MOSFET gates faster, shortening the pulse and probably preventing the LED from premature death.

The results of these tests will be posted shortly, but in the meantime I wanted to check whether the LED's output continued to increase at higher voltages.  Testing consisted of about 4x strobes at 1 microsecond, starting at 70 V and incrementing by 5 V until it reach 125 V.  The LED was positioned 20 cm from an 18% grey card and a DSLR photographed the card during the flash.  Each image was cropped to 1000 x 1000 px and the average pixel brightness of that crop was calculated using ImageJ.

As you can see, the LED's output continues to increase with voltage.  The control board could not exceed 125 V, so higher voltages need to be tested on a different board.

I'm currently building an integrating sphere for better measurements.  When it's complete, I will repeat this test using the sphere.  The current draw will also be measured using an oscilloscope.