audioguru Posted October 24, 2005 Report Share Posted October 24, 2005 Yeah, it might be better to use an LM311 comparator in that circuit but it might oscillate at the zero crossings.A TL071 opamp would also work pretty well, wouldn't oscillate, wouldn't need a pull-up resistor on its output, is a little cheaper and slews almost the speed of an LM311 comparator. Its 13V/us slew-rate is very quick. A TLC071 audio opamp is even quicker. ;D Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 24, 2005 Report Share Posted October 24, 2005 Thanks Ante, that book has made me realize that some maths revision is in order. ;DAudioguru,Oscillation can be eliminated with comparators by using a feedback resistor to give positive feedback and the LM311 is cheaper than the TL072 where I live. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 24, 2005 Report Share Posted October 24, 2005 The best way to add some positive feedback in that circuit would be to swap the comparator's inputs and turn upside-down the pot and its resistors. ;D Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 24, 2005 Report Share Posted October 24, 2005 I've just noticed another thing, Tr3 is an IRF9510 which is a p-channel MOSFET. The motor would run at full power all the time, unless it was connected as a source follower in which case it'd drop a voltage equal to the gate threashold so it'd heat up and the motor would never run at full speed. :o Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 25, 2005 Report Share Posted October 25, 2005 The original circuit has an IRF510 N-channel Mosfet. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 25, 2005 Report Share Posted October 25, 2005 Sorry my mistake I don't know where I got that 9 from. Quote Link to comment Share on other sites More sharing options...
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