ec Posted May 30, 2011 Report Share Posted May 30, 2011 HiI am building a single ended MOSFET output stage and the circuit is attached. I am using Wideband transformer WB4-6.Its datasheet is attached. I need to drive a a transducer which can be assumed to be a 20 ohm load. The problem I am facing is the max. input current rating of the transformer is 250mA. My current is exceeding this limit. How can I make sure that current is lowered without changing the power supply. I have fix power supply of 5V, 15V and 8V.Thanks :)WB4-6.PDF Quote Link to comment Share on other sites More sharing options...
Hero999 Posted May 31, 2011 Report Share Posted May 31, 2011 How are you using the transformer?That topology is only any good for a flyback which produces high voltage negative spikes, not a sine wave or even a very good square wave.The only solution is to drop the single ended approach, use a push-pull driver and reduce the turns ratio of the transformer.This is confirmed by my calculations below:Turns ratio:Np:Ns = sqrt(Lp/Ls) = sqrt(50/200) = sqrt(0.25) = 0.5:1 = 1:2Reflected impedance of the 20R transducer:Zp = Zs *(Np/Ns)2 = 20*(1/2)2 = 20*0.52 = 20*0.25 = 5RSo at 5V, the current will be 1A, Ohm's law.I = V/R = 5/5 = 1A.Why are you using the transformer? Is it for isolation? Do you need to boost the voltage? If it's the latter, you need a transformer with a higher power rating. If it's just isolation the same size transformer will do but it needs to be 1:1. Quote Link to comment Share on other sites More sharing options...
ec Posted June 1, 2011 Author Report Share Posted June 1, 2011 ThanksI need the transformer to boost the voltage. Can you suggest me any transformer with small size and with higher power rating? I tried but was not able to fine one Quote Link to comment Share on other sites More sharing options...
Hero999 Posted June 1, 2011 Report Share Posted June 1, 2011 What are your size constraints? Quote Link to comment Share on other sites More sharing options...
ec Posted June 1, 2011 Author Report Share Posted June 1, 2011 whole output stage is going to be put on a PCB. So transformer similar in size to the one I used before will do. No specific size constraint is there Quote Link to comment Share on other sites More sharing options...
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