Construct a circuit diagram of a step-up chopper in Multisim

[Fatima Hasan]

Homework Statement

Attached below.

Relevant Equations

-

Using any Electrical Engineering software:

I tried to simulate using Multisim, but the output voltage remains constant even after varying R1. Also, I only got the voltage from the oscilloscope, but how to find the current ?
Here's my attempt:

Any help would be greatly appreciated!

 

[berkeman]

How can you use the clue that the output voltage is one diode drop below the input 5V?

 

[Fatima Hasan]

How can you use the clue that the output voltage is one diode drop below the input 5V?

Sorry, I didn't understand what you mean.

 

[berkeman]

Sorry, I didn't understand what you mean.

Well, when I looked at your simulation, I expected to see an output voltage that is higher than the input 5V source. That's what the "Boost" chopping action of Q1 does in that circuit when it is running correctly. There's pretty much only one main way that the output voltage could be one diode drop below the input 5V supply in a Boost circuit. Have you put a 'scope probe on the drive for Q1 and on Q1's drain? What do those test points show?

 

[Fatima Hasan]

Well, when I looked at your simulation, I expected to see an output voltage that is higher than the input 5V source. That's what the "Boost" chopping action of Q1 does in that circuit when it is running correctly. There's pretty much only one main way that the output voltage could be one diode drop below the input 5V supply in a Boost circuit. Have you put a 'scope probe on the drive for Q1 and on Q1's drain? What do those test points show?

/

That's what I got :

 

[berkeman]

Looks flatline in the window in time that you are looking at the drive. You need to be sure that your Q1 is being driven by the 555 IC. If there is no drive, there is no Boost...

 

[DaveE]

I'm not seeing any power connection to the 555. Also, don't you have to connect the ground on your scope channels?

 

[Fatima Hasan]

I'm not seeing any power connection to the 555. Also, don't you have to connect the ground on your scope channels?

Xsc1 :

After connecting the other channels to ground on scope 1:

 

[Fatima Hasan]

Looks flatline in the window in time that you are looking at the drive. You need to be sure that your Q1 is being driven by the 555 IC. If there is no drive, there is no Boost...

Q1 is connected to R4 which is connected to the IC555.

 

[berkeman]

Q1 is connected to R4 which is connected to the IC555.

So what waveforms would you expect for the FET gate voltage drive waveform and the current waveforms through the inductor and diode?

https://components101.com/articles/boost-converter-basics-working-design

 

[Fatima Hasan]

So what waveforms would you expect for the FET gate voltage drive waveform and the current waveforms through the inductor and diode?

https://components101.com/articles/boost-converter-basics-working-design

View attachment 262133

I think they should be triangular waveforms , right ?

 

[berkeman]

I think they should be triangular waveforms , right ?

Which "they" waveforms? Not the gate drive voltage...

The overall inductor current does have a triangular shape (why?), but the diode and transistor switch currents are not exactly regular triangle waves (why not?).

https://en.wikipedia.org/wiki/Boost_converter

 

[Fatima Hasan]

The overall inductor current does have a triangular shape (why?),

In the ON-state,diode is off : the current flows through the inductor ( charging) and the inductor stores the energy.
In the OFF-state, (Discharging),diode is ON: the inductor will act as a source and the diode makes the inductor to flow a current from itself and the energy will be dissipated. Since the switch cycled fast , the current won't reach 0 .

 

[Ltfy]

How can you use the clue that the output voltage is one diode drop below the input 5V?

try this

 

[Tom.G]

I suggest that you look at the data sheet for the 555 timer, especially the circuit for Astable operation. Then compare your connections on the 555 to what is in the data sheet.

The datasheet for the LM555 by Texas Instruments is quite informative.

Cheers,
Tom

p.s. Please keep us updated on your progress.

 

[Ltfy]

I suggest that you look at the data sheet for the 555 timer, especially the circuit for Astable operation. Then compare your connections on the 555 to what is in the data sheet.

The datasheet for the LM555 by Texas Instruments is quite informative.

Cheers,
Tom

p.s. Please keep us updated on your progress.

Hello Mr. Tom,
Could you please check attached circuit and I would like to ask if I can step up voltage more and connect it to mobile power bank as volt source (as shown the current 17.3A )
Overloading may damage the battery!
Thanks

 

[TonyStewart]

The problem here is the high Q and low resonant frequency of the series LC tank circuit with 2.3 Henries and requires at least 5 or more cycles to settle. With 2.3H changing to 2.3uH is best.

Then it is becoming lower reactance, over damped but faster response.

Compute timescale / div to 1 cycle at resonant frequency. T= 2pi sqrt(LC)

Although settling time , damping factor changes with duty cycle as switch blocks inductive series impedance.

- reducing L by 6 orders of magnitude to uH also raises the output voltage ratio by only about 6 times not 6 million. due to load regulation and impedance ratios.