I would like to create a generic constant power load to mimic a SMPS effect on a network with diodes, capacitors, supercaps, and such.  It would really be cool if limiting behavior of the load could be included (typically current limit) but I can survive without it  I am really after macro-scale behavior (like what a capacitor discharge curve looks like with constant power load or what happens to full-wave rectifier ripple levels with constant power loads). If it makes any difference, I am working at milliWatt levels.  Any suggestions?

Greetings -

 

I would like to create a generic constant power load to mimic a SMPS effect on a network with diodes, capacitors, supercaps, and such.  It would really be cool if limiting behavior of the load could be included (typically current limit) but I can survive without it  I am really after macro-scale behavior (like what a capacitor discharge curve looks like with constant power load or what happens to full-wave rectifier ripple levels with constant power loads). If it makes any difference, I am working at milliWatt levels.  Any suggestions?

 

Many thanks

Jim Wagner, 

Oregon Research Electronics

On 11/13/2024 12:28 AM PST Mathias Born via groups.io <mathias.born@...> wrote:

 

 

Such a device is already provided by LTspice as behavioral source. The help that comes with the new version 24.1 even documents this properly. Have a look there.

For current limit I suggest the ideal voltage controlled switch. For details please see LTspice help.

 

Best Regards,
Mathias

 

On Wed, Nov 13, 2024 at 07:31 AM, Jim Wagner wrote:

Greetings -

 

I would like to create a generic constant power load to mimic a SMPS effect on a network with diodes, capacitors, supercaps, and such.  It would really be cool if limiting behavior of the load could be included (typically current limit) but I can survive without it  I am really after macro-scale behavior (like what a capacitor discharge curve looks like with constant power load or what happens to full-wave rectifier ripple levels with constant power loads). If it makes any difference, I am working at milliWatt levels.  Any suggestions?

 

Many thanks

Jim Wagner, 

Oregon Research Electronics

On 11/13/2024 12:28 AM PST Tony Casey <tony@...> wrote:

 

 

You don't have to create a constant power load. It exists already.

1. Place a B-source on your schematic.
2. Enter a value: P=<PowerValue>

It has already built-in features to handle the zero volts condition that should be fine for most applications, but can be altered, if  necessary.

More information: https://www.analog.com/en/resources/technical-articles/ltspice-modeling-constant-power-loads.html

--
Regards,
Tony

On 13/11/2024 07:31, Jim Wagner via groups.io wrote:

I would like to create a generic constant power load to mimic a SMPS effect on a network with diodes, capacitors, supercaps, and such.  It would really be cool if limiting behavior of the load could be included (typically current limit) but I can survive without it  I am really after macro-scale behavior (like what a capacitor discharge curve looks like with constant power load or what happens to full-wave rectifier ripple levels with constant power loads). If it makes any difference, I am working at milliWatt levels.  Any suggestions?

Thanks, Tony

 

Jim

On 11/13/2024 12:28 AM PST Tony Casey <tony@...> wrote:

 

 

You don't have to create a constant power load. It exists already.

1. Place a B-source on your schematic.
2. Enter a value: P=<PowerValue>

It has already built-in features to handle the zero volts condition that should be fine for most applications, but can be altered, if  necessary.

More information: https://www.analog.com/en/resources/technical-articles/ltspice-modeling-constant-power-loads.html

--
Regards,
Tony

On 13/11/2024 07:31, Jim Wagner via groups.io wrote:

I would like to create a generic constant power load to mimic a SMPS effect on a network with diodes, capacitors, supercaps, and such.  It would really be cool if limiting behavior of the load could be included (typically current limit) but I can survive without it  I am really after macro-scale behavior (like what a capacitor discharge curve looks like with constant power load or what happens to full-wave rectifier ripple levels with constant power loads). If it makes any difference, I am working at milliWatt levels.  Any suggestions?

On 11/13/2024 1:04 PM PST Andy I via groups.io <ai.egrps+io@...> wrote:

 

 

Jim Wagner wrote:

I thought behavioral sources did not allow instantaneous feedback.

If I remember correctly, instantaneous feedback is OK from some things, but not from every arbitrary element.  IIRC, feedback of node voltages, or of currents through voltage sources, is OK.  Feedback of other currents (through resistors or into semiconductors) was maybe not allowed or could be problematic if used.

 

Tony's 2010 circuit used feedback of a node voltage, so it's OK.  LTspice's newer (and only recently documented in LTspice's Help) constant current load is effectively a new self-contained component, without external current paths; it does the calculations internally so the restriction does not apply.

 

Andy