# Current buck converter weird behavior

#### Samantha Groves

Joined Nov 25, 2023
62
Hello I have designed a current boost converter:

As you can see in the final equation if D<2/3 then the output current has a 180 degrees phase shift from the input current even though I am using DC.I dont understand why this is happening and for D=3/2 we get a 0 which means that the output current is always 0.Why are these weird stuff happening?

#### ronsimpson

Joined Oct 7, 2019
3,137
In the bottom circuit, are you shorting out the input supply? It looks like the switch is across the input.

#### BobTPH

Joined Jun 5, 2013
9,138
Sure does.

#### crutschow

Joined Mar 14, 2008
34,682
That is not a proper boost converter circuit.
Try again.

#### Samantha Groves

Joined Nov 25, 2023
62
In the bottom circuit, are you shorting out the input supply? It looks like the switch is across the input.
Yes im shorting out the input supply.But since a capacitor is a short for current sources current is divided exactly into 2.

#### Samantha Groves

Joined Nov 25, 2023
62
That is not a proper boost converter circuit.
Try again.
It is a current boost converter not a voltage boost converter.We take for granted that the input is a voltage source but what if its a current source?Why is it not proper?Due to the inversion of the I/O?

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#### BobTPH

Joined Jun 5, 2013
9,138
Define a “current boost converter.”

#### Samantha Groves

Joined Nov 25, 2023
62
Define a “current boost converter.”
it boostes current of a current source

#### ronsimpson

Joined Oct 7, 2019
3,137
it boostes current of a current source
I now see the input is a current source.
Where did you get this information? We have never seen this. Does not work.

#### Samantha Groves

Joined Nov 25, 2023
62
I now see the input is a current source.
Where did you get this information? We have never seen this. Does not work.
I havent seen it anywhere.But why should we be limited to voltage sources?I just thought it would be a nice exercise to create a current source boost converter.Also many electronic circuits behave like current sources(MOSFET) because they have almost infinite input resistance.Also in nature there are current sources (the photovoltaic cell)so I was wondering if we could boost up its current somehow.

#### BobTPH

Joined Jun 5, 2013
9,138
I havent seen it anywhere.But why should we be limited to voltage sources?I just thought it would be a nice exercise to create a current source boost converter.Also many electronic circuits behave like current sources(MOSFET) because they have almost infinite input resistance.Also in nature there are current sources (the photovoltaic cell)so I was wondering if we could boost up its current somehow.
So, if I understand you correctly, it should produce higher current at a lower output voltage. Can you explain your theory of operation?

#### Samantha Groves

Joined Nov 25, 2023
62
So, if I understand you correctly, it should produce higher current at a lower output voltage. Can you explain your theory of operation?
Yes if we assume there arent any losses , due to conservation of energy if the output current doubles , the output voltage is halved.In the first picture the switch ( a PWM controlled MOSFET) is open->the diode conducts so the current through the capacitor is Ii-Io.By the equation for the IV relationship of the capacitor we find the dVc.In the second picture the switch is closed so the current through the capacitor is Ii/2.Ahhh here is the mistake guess need to work on it a bit

#### Papabravo

Joined Feb 24, 2006
21,259
This is what a proper boost converter should look like.

#### Samantha Groves

Joined Nov 25, 2023
62
I retract I am correct(I think).

In the first picture the switch ( a PWM controlled MOSFET) is open->the diode conducts so the current through the capacitor is Ii-Io.In the second picture the switched is closed so the current through the capacitor is -Io.From the IV equation of the capacitor and the duty cycle we arrive to the equations already posted.

#### Samantha Groves

Joined Nov 25, 2023
62

#### crutschow

Joined Mar 14, 2008
34,682
How can you boost the current when the constant current is all the current you have?
Where do you think the extra current is going to come from?
Your equations don't prove the circuit works.

It's not the same as boosting the voltage with a reduced current.

#### Samantha Groves

Joined Nov 25, 2023
62
How can you boost the current when the constant current is all the current you have?
Where do you think the extra current is going to come from?
Your equations don't prove the circuit works.

It's not the same as boosting the voltage with a reduced current.
By that reasoning how can we control the output voltage on a "normal" boost converter when in the input we have a fixed voltage reference???We do have fixed current but we dont have fixed voltage thats the trick I believe.

#### Papabravo

Joined Feb 24, 2006
21,259
You are correct 100% if my source was a voltage source but my input is a current source.
IMHO that is a ridiculous proposition. Even a small current source into a small resistance will produce a very large voltage. I'm not sure your understanding of circuits runs very deep.

#### Papabravo

Joined Feb 24, 2006
21,259
By that reasoning how can we control the output voltage on a "normal" boost converter when in the input we have a fixed voltage reference???We do have fixed current but we dont have fixed voltage thats the trick I believe.
The inductor provides the means to accomplish this from a fixed voltage by controlling the derivative of the current through the inductor.

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#### Samantha Groves

Joined Nov 25, 2023
62
This is my final push for today

When the switch is open the diode conducts so the current through the capacitor is Ii-Io and by the IV relationship for a capacitor we end up with a equation.

When the switch is closed the diode doesnt conduct so the current through the capacitor is -Io(the capacitor is discharging through the load) and by the IV relationship for a capacitor we end up with another equation.

We equate them and we end up with our relationship.Note that when D=0.5 the output current is infinite so the output voltage is 0(there is a pole at D=0.5)

Feel free to comment , I want to discuss this because I dont understand it very well either so lets do the first baby steps together.