Guest Zeppelin Posted April 9, 2006 Report Share Posted April 9, 2006 I was thinking of using digitally selected outputs for the LM317 regulator. IC's Datasheet has the circuit attached which uses discreet transistors; though for a large number of outputs this is not practical :(Is there anyway to get around this without using discreet transistors?Thank youZeppelin Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 9, 2006 Report Share Posted April 9, 2006 Hi Zeppelin, the resistors need something to drive one with 10mA, so a Cmos output won.t be strong enough.Think about driving the transistors with a binary group of signals, the 4 transistors would give 16 voltages, 5 transistors would give 32 and 6 transistors would give 64 voltages etc. Quote Link to comment Share on other sites More sharing options...
gogo2520 Posted April 9, 2006 Report Share Posted April 9, 2006 Hello Zeppelin I built a power supply like that, it uses a logic switch to control the voltage. I got a PDF file of the project. check it out gogopower.pdf Quote Link to comment Share on other sites More sharing options...
windoze killa Posted April 9, 2006 Report Share Posted April 9, 2006 You could use something like a UNL2003 darligton driver chip. It has 7 outputs. Would give you more combinations than you could ever need. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 9, 2006 Report Share Posted April 9, 2006 You could use something like a UNL2003 darligton driver chip. It has 7 outputs.Darlington transistors don't saturate so have a pretty high voltage drop when turned on. A transistor array IC would be better because a transistor can saturate with a very low output voltage. Then the current in the voltage-adjustment resistors is predictable. Quote Link to comment Share on other sites More sharing options...
windoze killa Posted April 9, 2006 Report Share Posted April 9, 2006 We current use ULN2003 chips for a very similar application and they work very well. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 9, 2006 Report Share Posted April 9, 2006 We current use ULN2003 chips for a very similar application and they work very well.What about temperature compensation?The turned-on voltage would drop with increasing temperature, wouldn't it? Quote Link to comment Share on other sites More sharing options...
windoze killa Posted April 10, 2006 Report Share Posted April 10, 2006 To be honest we haven't noticed it or paid much attention to it. Being in R&D we tend to work on the premis that if it works, leave it alone or if it aint broke, don't fix it.We came up with the design and it seems to work well. When we have trouble we will investigate more Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 10, 2006 Report Share Posted April 10, 2006 We came up with the design and it seems to work well.Good. I just didn't want somebody to make it with a darlington array then discover that it has a problem with temperature change when the output voltage is set low. An ordinary saturating transistor array won't have a temperature problem. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 3, 2006 Report Share Posted May 3, 2006 Five binary bits will give you 32 different output levels. A bit's output is a transistor with a voltage-setting resistor in series with its collector. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 4, 2006 Report Share Posted May 4, 2006 You are making your own D to A converter. Look it up in Google. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 8, 2006 Report Share Posted May 8, 2006 The LM317 is the summing amplifier.The D to A converter just gives it some resistors for its ADJ terminal to ground. Quote Link to comment Share on other sites More sharing options...
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