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Zerofossilfuel's PWM

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by tblo163, May 3, 2009.

  1. tblo163

    tblo163 New Member

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    NOTTINGHAM ENGLAND
    I've built dozens of PWMs,for various applications,usually operated remotely by a "Pot" and monitored by a digital ammeter (with shunt).Zoro indicates that his PWM,(once set up) requires no further adjustment,as the current limiting will remain the same regardless of load.This obviously is an improvement on the basic PWM. After studying the circuit I can see that it looks quite feasable,& will certainly build one.However,there are 2 things that I'm not sure of,1st.,R12,the value of this resistor is very low,& I don't think it is available. 2nd.,the 12000µF-25V Cap (C7).what purpose does this serve? is it intended as a stiffening capacitor? & considering the cost of a cap of this value,it would make the project expensive.(unless I can salvage one from a redundant circuit board).I also understand that the case of the IRFP064N Mosfet,is insulated from the Drain pin,which makes it possible to mount it onto a heat-sink that is grounded.Does anyone have an opinion of this PWM?
    Regards Terry.
     

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  2. chemelec

    chemelec Well-Known Member

    Joined:
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    Location:
    Hedley, B.C. Canada
    R12 is Made from a piece of 16 AWG Wire.

    This circuit has a Number of Problems, But the Biggest Problem is Over Heating of the Mosfet.
    When this circuit goes in Current Limit Mode, It is putting the Mosfet into a Variable Resistive Mode.

    So the Greater the Current Foldback, The Greater the Resistance, Between Source to Drain, So the GREATER the HEAT Dissipation. So, USE A BIG HEATSINK.

    Also to Avoid using that 12000uf Cap, Wire the PCB's Positive and ground, Seperately and Directly Back to the Battery Terminals.
    And use SEPERATE Wires for the Load and Mosfet, Also Back to the Battery Terminals.

    Gary
     
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