audioguru Posted October 21, 2005 Report Share Posted October 21, 2005 Hi Kain,Be careful with your transformer because it is rated for only (!) 210VA. Its peak current is normally about 50A into the rectifier bridge to replenish the charge lost in the main filter cap during high loading but its average power rating is still 210W. The rectifier conducts only near the transformer's voltage peaks of 42.4V, so the max average DC current from your supply is limited by the transformer's power rating to 210/42.4= 4.95A.I think you are over here with a 60Hz mains. Your 20,000uF for C1 will discharge about 2.8V each half-cycle with a 5A load. The 2.8V ripple should be reduced by the opamps to only about 0.5mV of ripple at the project's output but yours is 800mV when the output transistors aren't saturated. I think that using a proper "star grounding" technique will solve your ripple problem:1) The 0V wire of R4, R6, U1, the voltage adjust pot P1 and R11 must be connected directly to the output without any of the current that goes into R7. Therefore R7 should have a separate wire connecting it to the output 0V terminal. Voltage regulation will be improved.2) C1 and the rectifier bridge should be connected together with very heavy short wires to carry 50A current peaks.3) The positive voltage feed to the circuit must connect directly to C1, not to a terminal strip.None of the 50A current peaks must reach the circuit.With an output voltage less than 2.5V, I aren't sure why it doesn't give max current. Check that its negative 5.6V supply is OK.I couldn't find a schematic of an OPA445 opamp, but its datasheet shows a different connection to its offset voltage adjustment from the one on U2 in our circuit. Try connecting R10 to negative 5.6V instead of the existing output 0V. Then try removing R10 and connect the slider of RV1 to the negative 5.6V. ;D Quote Link to comment Share on other sites More sharing options...
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