Pspice Etable produces wrong duty ratio signal

[Brandon Yau]

Hi everyone,

I have no idea what happens. The Etable source (E2) cannot produce a normal square wave duty ratio, but a sawtooth wave instead. Does anyone know what is the problem?

 

[mvaseem]

What are your table entries for E2 ?

 

[Brandon Yau]

(-15,-15)(15,15)

I did not change the parameters inside, cuz the result is correct using the same parameters in E1.

 

[mvaseem]

A table is actually a transfer function in forms of value pairs.
The first value of each pair is input (which is difference between IN+ and IN-) and second value is output.
Linear interpolation is performed between entries.
The difference between your blue and green inputs never reaches till -15V and 15v, so output would not be affected.
Try different table values.

 

[Brandon Yau]

A table is actually a transfer function in forms of value pairs.
The first value of each pair is input (which is difference between IN+ and IN-) and second value is output.
Linear interpolation is performed between entries.
The difference between your blue and green inputs never reaches till -15V and 15v, so output would not be affected.
Try different table values.

Hi mvaseem,

Can you make an example of this? I find that it would be useful!

 

[Brandon Yau]

A table is actually a transfer function in forms of value pairs.
The first value of each pair is input (which is difference between IN+ and IN-) and second value is output.
Linear interpolation is performed between entries.
The difference between your blue and green inputs never reaches till -15V and 15v, so output would not be affected.
Try different table values.

How can I modify the table values to produce a effective duty ratio output?

 

[FvM]

You'll want a table like

(-1m,-15)(1m,15)

 

[Brandon Yau]

You'll want a table like

(-1m,-15)(1m,15)

Hi everyone, this is my new version


1. The output needed to be regulated is 1.8V (From 3.3V to 1.8V), and it is tested and run correctly without the feedback circuit.
2. As it is 1.8V, the reference value in the error amplifier should be 1.8V.

Now the question comes,
1. What should be the setting of the etable (error amplifier)?
2. What should be the setting of V1 and V2 of the Sawtooth wave pulse?
3. What should be the setting of the etable2 (PWM modulator)?

PS: The components value of the feedback circuit are the same as the specification, so there should be no mistakes of them.

I have been so confused in these issues for days!

Im happy to see that you guys are helping!!

 

[Brandon Yau]

You'll want a table like

(-1m,-15)(1m,15)

Well, now I set Etable1=(-1m,0.3)(1m,0.7),
It means when the subtraction result is positive, =0.7.
when the subtraction result is negative, =0.3.

I set Vpulse V1=0, and V2=1, such that the error amplifier output is always within the sawtooth wave.

While Etable2 is set (-1m,0)(1m,1), to give a 0101 waveform to drive the switch

However, it fails to converge.

Any ideas?

 

[Brandon Yau]

Well, now I set Etable1=(-1m,0.3)(1m,0.7),
It means when the subtraction result is positive, =0.7.
when the subtraction result is negative, =0.3.

I set Vpulse V1=0, and V2=1, such that the error amplifier output is always within the sawtooth wave.

While Etable2 is set (-1m,0)(1m,1), to give a 0101 waveform to drive the switch

However, it fails to converge.

Any ideas?

Is my concept about Etable correct?
The +ve supply voltage of the Etable must be greater than the output, and the positive input, and the -ve supply voltage of the Etable must be smaller than the negative input.