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Hi run,
Here is the latest version of the LED constant current driver circuit
(1) The LED constant current is defined by 0.6V/R15.
(2) The fuse in the power line and the Zener across the LED protect the LED to a degree in case of component failure/other malfunctions
(3) The 2N2905A transistor has been specified because it is particularly reliable and has excellent, fully specified, parameters. As it is a critical component only buy it from main-line sources: Mouser, RS, Farnell etc. On no account buy it from Ebay, for example. Also, only buy main-line manufacturers's versions of the 2N2905A: Texas Instruments, ON (Motorola), Fairchild: Vishay (Siliconix), Aglient (hp), STM, International Rectifier, Linear Technology.
(4) In view of the high cost of the LED, to prove the circuit, I would advise that the LED be replace by a 47 Ohm resistor. Only when you have established that the circuit is functioning correctly should the LED be fitted.
(5) R19 may need to be adjusted to suit the characteristics of your signal generator.
(6) This is not a current steering circuit so it will not be as fast as my previous two circuits. It should be fairly fast though.
Make sure it has a heat sink. The hottest part will have the largest voltage drop to size ratio.
The UV chip is only a few mm Wide in a small can and thus high 'C /W without a sink. Follow the supplier advice.
The UV is optimized and working as I want it to. Thanks for great help, especially spec! Made a heat sink myself.
Next and last issue is to get the detector working as it should.
The UV is optimized and working as I want it to. Thanks for great help, especially spec! Made a heat sink myself.
Next and last issue is to get the detector working as it should.
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