audioguru Posted October 25, 2006 Report Share Posted October 25, 2006 Are the resistor values correct in this nice new project?http://www.electronics-lab.com/projects/games/005/index.htmlThe red LED has a forward voltage much less than the green or blue but it has the lowest current-limiting resistor value. Therefore if the transistor saturates then its current will be 554mA which is way more than its 350mA rating.If its transistor saturates then the current in the green LED is 125mA.The blue LED is the least sensitive and has a high forward voltage. Its current limiting resistor has the highest value so if the transistor saturates then its current will be only 83mA and it won't be very bright.But the 10k base resistors allow a base current of only 430uA. For the transistor to conduct 300mA then its current gain would need to be 700! These transistors can't saturate.The current gain of the BC327 is typically 135 but could be as low as 54.The PIC can output much more than only 430uA so shouldn't the base resistor values be reduced to supply the transistors with enough base current to saturate? A value of 680 ohms would work fine. Quote Link to comment Share on other sites More sharing options...
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