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LTSpice

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codan

New Member
Hi,

In LTSpice in the Component selection you can select a "Load" to add to the schematic.
My question is, in the real world what type of load is it, resistive, inductive etc?

Can i simulate this load with other component selections somehow?

Thanks
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi,

In LTSpice in the Component selection you can select a "Load" to add to the schematic.
My question is, in the real world what type of load is it, resistive, inductive etc?

Can i simulate this load with other component selections somehow?

Thanks
hi,
It can be a passive or reactive load or a combination of both.
You set the parameters of the 'load'.

Do you have an example of a *.asc you are working on, post it.:)
 
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Hero999

Banned
It's normally constant current.

You can set the current and whether it's DC, puled, sine etc.

It has the advantage being able to use LTSpice's efficiency report feature.
 

codan

New Member
Gday Eric & Hero 999,

Eric, i have attached a small timer circuit that it appears i need some help with including how to setup the load as mentioned, so now is my chance hahaha!.

The pulse from the timer OUT seems ok & also the Amperage out of the Mosfet but the Voltage out of the Mosfet is a bit how ya goin, could you suggest what to do to sort it out.

The circuit will be used to drive another circuit so i need a good rectangular wave out of the Mosfet with good voltage & amps, as many volts as i can get & also amps from this circuit. My power supply is not an issue!

I have a feeling the choice of Mosfets i have in LTSpice may not be correct for this circuit but i am unsure how to load more into the program?

If i have no idea as usual i'm sure you'll wack me over the head!

Opps i forgot, this has nothing to to with the stupid HHO PWM, i need the circuit to trigger another circuit that pulses an Inductor--Coil.

Thanks
 

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Hero999

Banned
The circuit is operating correctly.

The MOSFET has an on resistance of 3.5Ω and the load current is 2A so the voltage across it when the MOSFET is on will be 7V.

Selecting a MOSFET with a lower on resistance, i.e. PH6325L, solves the problem.

Also beware, D3 is an 1N4148 which is only rated to 200mA. I don't know why it's there anyway, if it's for back EMF protection it should be in reverse parallel with the load.
 

ericgibbs

Well-Known Member
Most Helpful Member
hi codan,
As hero points out it works, but I've changed the MOSFET and the clamp diode.
 

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codan

New Member
Thanks Guys,

Eric, that's a nice signal from the circuit, thanks for that.

I noticed on the 12v power supply for the circuit, mine had tran 500u & yours has tran 0 20u 0 1u.
I am not sure what the difference is or how to set it differently?

Also the Load component, i had mine for a constant current draw 2A, the circuit that this circuit will trigger only draws power when triggered obviously, so how do i set the load characteristics to simulate this?



Thanks Again
 

MikeMl

Well-Known Member
Most Helpful Member
Since the LTSpice LOAD is just a synonym for a current source, it is not very useful as a simulated "load" when connected in series with a switch that is dynamically turning on and off. If you want to put a 2A load on your NFET, why not just use a 12V/2A=6Ω resistor in its place.
 

Sceadwian

Banned
The "Load" symbol can be used for resistor if you want.
 

MikeMl

Well-Known Member
Most Helpful Member

ericgibbs

Well-Known Member
Most Helpful Member
Thanks Guys,

Eric, that's a nice signal from the circuit, thanks for that.

I noticed on the 12v power supply for the circuit, mine had tran 500u & yours has tran 0 20u 0 1u.
I am not sure what the difference is or how to set it differently?

Also the Load component, i had mine for a constant current draw 2A, the circuit that this circuit will trigger only draws power when triggered obviously, so how do i set the load characteristics to simulate this?

Thanks Again
hi codan,
The tran is shorter so that the plot is going to be less cramped, easier to read.:)

As Mike says use a 'fixed' 6R resistor as a load.
[NB: for an exercise, you can right click on the 6R and set the tolerance and wattage]
 

codan

New Member
Thanks guys,

I was just unsure of what type of load i needed & if there was any difference between load types for the program--resistive, inductive etc!

Another question, from the circuit above if you read the Amps out of the Mosfet & then read the Voltage out of it also they are out of step with each other?
I thought the voltage & amps would have to be in time with each other, out of phase a little maybe if i have this right but out of step?

Could someone explain this, just can't get it!
 

ericgibbs

Well-Known Member
Most Helpful Member
Thanks guys,

I was just unsure of what type of load i needed & if there was any difference between load types for the program--resistive, inductive etc!

Another question, from the circuit above if you read the Amps out of the Mosfet & then read the Voltage out of it also they are out of step with each other?
I thought the voltage & amps would have to be in time with each other, out of phase a little maybe if i have this right but out of step?

Could someone explain this, just can't get it!
hi,
The 'load' can be any of the ones you have listed.

When you say out of step, do you mean the phase.?

If yes, when the MOSFET is ON, conducting, the Drain voltage will be close to zero and the current thru the load will be at a maximum.
So Vds=0 Ids=max [ 12V/6R] =2A
 

ericgibbs

Well-Known Member
Most Helpful Member
hi codan

Run this draft1.asc in Spice.

On L1 the coil reistance is 'external' 100R and L2 is 'internal', right click on L2 to see the setup window.

So L3, as L2 but with some coil capacitance.

Personally I put the resistance external, so its obvious.
 

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Sceadwian

Banned
Mike, all you have to do is drop a load symbol on the schematic and hold down control and right click on it, You can change the prefix there to R and bam it's a resistor with the symbol for load. I have to do this with some of the mosfet models I have as they're not LTspice compatible models they're subcircuits. The symbol you use on the schmatic can be totally independant of the device model. The pin mapping on the symbol just has to be right for a two terminal device you really can't get it wrong =)
 
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