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

• Engineering

Attached below.

## Relevant Equations:

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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!

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

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
Mentor
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?

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

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:

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
Mentor
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

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 .

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