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simple ltspice help

Discussion in 'CAD' started by chapmjw, Feb 16, 2007.

  1. chapmjw

    chapmjw Guest

    How can I set a voltage source based on a measured voltage?

    For example, take 2 simple loops.
    I'd like to set V3 to 5 times V2
    Loop 1: V1(10 volts) to V2(0 volts) to R1(100ohm) to ground.
    Loop 2: V3(V2 * 5) to R2(100 ohm) to ground.


    * C:\Program Files\LTC\SwCADIII\Draft1.asc
    V1 N002 0 10
    V2 N003 N002 0
    R1 N003 0 100

    V3 N001 0 V2 5 <---tried many different combinations here
    R2 N001 0 100

    ..tran 0 1 0 .01 startup
    ..backanno
    ..end

    thanks
    jim
     
  2. Jim Thompson

    Jim Thompson Guest

    LTspice is reading "V3 N001 0 V2 5" as "V2" is a node. Since you then
    have too many nodes LTspice is probably giving you an error message.

    I think it's the same in LTspice as in PSpice...

    V3 N001 0 {V(N003)*5}

    I don't know if...

    V3 N001 0 {V2*5}

    will work in LTspice or not. PSpice would require a .PARAM statement.

    ...Jim Thompson
     
  3. Hell Jim,

    There are voltage controlled voltage and current sources and current
    controlled voltage and current sources.
    (VCVS=E, VCCS=G, CCVS=H, CCCS=F)

    You can solve your problem with a E-source.
    It has two inputs for the control voltage and two output nodes. You have to
    set the gain to 5 in your case.
    These sources are available for schematic drawings of course.

    Syntax: Exxx n+ n- nc+ nc- <gain>
    The final netlist will look like the following.
    E1 N001 0 N003 N002 5

    All this is pure SPICE. I recommend to read about the devices of SPICE or at
    least the help of LTspice.

    Best regards,
    Helmut
     
  4. john jardine

    john jardine Guest

    I'm not sure what V2 is there for but lose it and label the 10V source to
    resistor wire as (say) Fred. That fred node can be referred to elsewhere
    using the very handy "bv" component.

    V1 Fred 0 10
    R1 Fred 0 100
    R2 N001 0 100
    B1 N001 0 V=v(fred) * 5
    ..tran 1
    ..backanno
    ..end
     
  5. john jardine

    john jardine Guest

    My nodes number up slightly different, so clarify by the diagram ...

    Version 4
    SHEET 1 480 164
    WIRE 48 -304 -96 -304
    WIRE -96 -208 -96 -304
    WIRE 48 -160 48 -304
    WIRE 336 -144 176 -144
    WIRE 336 -96 336 -144
    WIRE 176 -80 176 -144
    WIRE -96 -48 -96 -208
    WIRE 48 32 48 -80
    WIRE 176 32 176 0
    WIRE 336 32 336 -16
    FLAG -96 32 0
    FLAG 48 32 0
    FLAG 176 32 0
    FLAG 336 32 0
    FLAG -96 -208 Fred
    SYMBOL voltage -96 -64 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value 10
    SYMBOL res 32 -176 R0
    SYMATTR InstName R1
    SYMATTR Value 100
    SYMBOL res 320 -112 R0
    SYMATTR InstName R2
    SYMATTR Value 100
    SYMBOL bv 176 -96 R0
    SYMATTR InstName B1
    SYMATTR Value V=v(fred) * 5
    TEXT -210 44 Left 0 !.tran 1
     
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