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Update 8\/13\/2013<\/strong><\/p>\n
We’ve received the prototype PCBs and soldered up a Storm 10V for testing purposes. As you can see, at its core it is still a Storm LED Controller, but its outputs are boosted up to 10V PWM levels. The boost chip we are using is the ULN2003A Darlington Transistor Array, which is designed to handle enough power\/current to drive small stepper motors. What we discovered is that the voltage drop across the ULN2003A is a little higher than we want. What it means is that instead of outputting a solid 10V signal, the signal is reduced by the voltage drop which can be up to 1.6V! <\/p>\n
![\"ULN2003A\"](\"http:\/\/coralux.net\/wp-content\/uploads\/2013\/07\/ULN2003A.png\")
<\/a><\/p>\nThe 1.6V figure is from the ULN2003A Datasheet<\/a> at a max current of 350mA which is far higher than you’d need to drive PWM drivers (you could run motors at that current). More realistically we’d expect to see a voltage drop up to 0.5V, which would result in a PWM amplitude of 9.5V. This should be good enough to run any PWM driver that requires 10V PWM signals, as the threshold voltage for the driver is usually set back from the actual stated voltage.<\/p>\n
![\"storm_10v_01\"](\"http:\/\/coralux.net\/wp-content\/uploads\/2013\/07\/storm_10v_01-1024x682.png\")
<\/a><\/p>\n![\"storm_10v_02\"](\"http:\/\/coralux.net\/wp-content\/uploads\/2013\/07\/storm_10v_02-1024x682.png\")
<\/a><\/p>\nBecause of the voltage drop problems associated with Darlington Transistor Arrays, we decided to go another route – the add-on board. On this add-on board we’ll use discrete NPN transistors that have a much lower saturation voltage. The NPN transistor we are using is the KST2222A from Fairchild Semiconductor, and the saturation voltage behavior as given in the datasheet<\/a> are below.<\/p>\n
![\"2N2222\"](\"http:\/\/coralux.net\/wp-content\/uploads\/2013\/07\/2N2222.png\")
<\/a><\/p>\nAs you can see from the figure, the Vce voltage drop that we are concerned about is about 0.05V for low-current applications. This will allow us to get extremely close to the 10V PWM signal that we seek. With that we’ve designed the PWM add-on board as well as a 0-10V analog add-on board. The analog portion follows easily from the PWM design by simply adding a resistor-capacitor low pass circuit that converts the digital signal to analog.<\/p>\n
![\"10V_PWM\"](\"http:\/\/coralux.net\/wp-content\/uploads\/2013\/07\/10V_PWM-1024x682.png\")
<\/a><\/p>\n![\"10V_Analog\"](\"http:\/\/coralux.net\/wp-content\/uploads\/2013\/07\/10V_Analog-1024x682.png\")
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