Hi,
I am trying to simulate cable losses into a DCDC converter connected to a load. In particular I am trying to make the DCDC part ideal or behavioral. The idea is attached. The idea is as follows:
1. The load is fixed
2. Input to the DCDC can be anywhere from 100 to 200V

Am trying to simulate at different cables (resistance vs length).
I use LTspice occasionally, and for the life of me, I cannot find what I am looking for on-line
Thanks
ph

 

Can't you just model it as a bit of inductance with series resistance? Plenty of on-line sources have cable resistance tables for various wire gauges.
If you want to use cable length as a variable, are you aware that in LTspice a resistor can be behavioural, so you can use a formula to specify resistance in terms of the cable properties, by setting R=<formula>, e.g. R=resistance per unit length x length.

 

Hi Alec_t
The cable part is fine. The part I am struggling with is the ideal DCDC step down.

 

Being thinking about this a bit more, to clarify better... I am looking for a way to
1. transform: DCDC Vin and Iin to Vout Iout, where Iout is fixed at say 1A, 5V.
2. So 1A 5V is 5W out
3. Set DCDC input to say 100V
4. Model will then adjust input current to 50mA
5. Cable current is now 50mA
6. Calculate PSU voltage overhead for cable resistance
i.e. what additional PSU Voltage is needed to ensure 100V at DCDC i.e. at the end of the cable

 

Hi Alec_t
The cable part is fine. The part I am struggling with is the ideal DCDC step down.

In his book, Basso defines a behavioral DC-DC transformer. It is not a complicated subcircuit.

 

How “ideal” is your DC to DC converter? If it were perfect, wouldn’t it just be a DC source?
Could you simulate it as repeating pulse waveform followed by an LC filter?

 

I solved it (inspiried by ideal DC transformer posted earlier). I knew the solution would be somewhat easy, I just couldnt see the correct way to model it behaviorally. After a coffee I realised an ideal DCDC can be modeled using a constant power source (and I didnt realise there was such a model in LTspice

 

Ok, not quite solved, but this is heading towards a solution