Buck-boost with common mode choke?

Thread Starter

Tiago Rocha

Joined Jul 12, 2021
21
hello,

I'm trying to make an buck-boost, but i've a doubt about the inductor.
Can i use an inductor in common mode?
Or should the inductor have only one winding?
 

Papabravo

Joined Feb 24, 2006
17,240
hello,

I'm trying to make an buck-boost, but i've a doubt about the inductor.
Can i use an inductor in common mode?
Or should the inductor have only one winding?
I think it should have one winding.
The differential mode and common mode chokes should maybe be considered as part of an input filter to prevent switching noise from polluting the input bus.
Your proposed schematic would be most helpful in assessing the proper answer to your question.
 

Thread Starter

Tiago Rocha

Joined Jul 12, 2021
21
I think it should have one winding.
The differential mode and common mode chokes should maybe be considered as part of an input filter to prevent switching noise from polluting the input bus.
Your proposed schematic would be most helpful in assessing the proper answer to your question.
I think i dont realy need to send the schematic. I'm trying to do a regular inverting buck-boost.

I'm not shure about what inductor value i should use.
In the formula of this document i send bellow L1 depends on I(L1)(pp) and vice-versa. How can i know what values use in one of this to calculate the other? Do you know?

https://www.ti.com.cn/cn/lit/an/slv...91545&ref_url=https%3A%2F%2Fwww.google.com%2F
 

ronsimpson

Joined Oct 7, 2019
1,630
" Inverting Buck-Boost " lol We spent about 40 posts arguing if a inverting PWM is a Buck-Boost pwm.
I think i dont realy need to send the schematic.
A schematic is worth 1000 words. That is a 2000 year old saying.
common mode choke
The current rating and core saturation numbers for a common mode choke are not for the way you are using the part. In a CMC the load current passes through the transformer and then back again through the transformer and the energy cancels out leaving almost no stress on the core. The core will certainly saturate in this application.

Are you certain it is CM choke or is it a choke with two windings? There is a difference.
 

Papabravo

Joined Feb 24, 2006
17,240
I think i dont realy need to send the schematic. I'm trying to do a regular inverting buck-boost.

I'm not shure about what inductor value i should use.
In the formula of this document i send bellow L1 depends on I(L1)(pp) and vice-versa. How can i know what values use in one of this to calculate the other? Do you know?

https://www.ti.com.cn/cn/lit/an/slva721a/slva721a.pdf?ts=1621957891545&ref_url=https%3A%2F%2Fwww.google.com%2F
The schematic is necessary because the term "buck-boost" is not as precise as you might imagine. Your confusion about using a single inductor or a common mode choke is also problematical. I'm invoking the @crutschow policy of no schematic, then no more answers.
 

Thread Starter

Tiago Rocha

Joined Jul 12, 2021
21
The schematic is necessary because the term "buck-boost" is not as precise as you might imagine. Your confusion about using a single inductor or a common mode choke is also problematical. I'm invoking the @crutschow policy of no schematic, then no more answers.
OK, no problem. Here is the schematic. I made some calcullations and i've got an inductor of at least 11.2mH and 10 Amps considering 10%DeltaIL. I am new in this so i don't understand much. All the inductors I found within this parameters had 2 coils like the " 7448051012 ", and should be installed in common or differential mode. I've implemented this but i'm not getting expected results.
 

Attachments

ronsimpson

Joined Oct 7, 2019
1,630
The inductor is not designed to be used like this. But it will work at low current.
What is the input voltage 220VAC?
What is a "achs1" does not come up in google.
MOSFET = 5.6 ohm 100V.
 

Papabravo

Joined Feb 24, 2006
17,240
A couple of questions because I am not quite sure what is going on with this design.
  1. What is an ACHS1? I am not familiar with this part or it's purpose.
  2. FL1 as a square box obscures the important detail of how the inductors are connected. It could be used as 2 inductors in parallel or it could be connected in a nonsense fashion.
  3. What is the AC input voltage?
  4. What is the purpose of the connector labeled Terminal Cap 1?
  5. What is the desired output voltage and current?
  6. What is the Zener voltage and current of Z1?
  7. What is the capacitance of C5?
  8. What is the frequency and duty cycle range of the signal on the MOSFET GATE?
 
Last edited:

Thread Starter

Tiago Rocha

Joined Jul 12, 2021
21
A couple of questions because I am not quite sure what is going on with this design.
  1. What is an ACHS1? I am not familiar with this part or it's purpose.
  2. FL1 as a square box obscures the important detail of how the inductors are connected. It could be used as 2 inductors in parallel or it could be connected in a nonsense fashion.
  3. What is the AC input voltage?
  4. What is the purpose of the connector labeled Terminal Cap 1?
  5. What is the desired output voltage and current?
  6. What is the Zener voltage and current of Z1?
  7. What is the capacitance of C5?
  8. What is the frequency and duty cycle range of the signal on the MOSFET GATE?
The ACHS1 is just a current sensor and the zener diode, resistances and c5 are used to read the input voltage.
The terminal cap is to put a capacitor, (consider the input voltage dc).
Vin: 5v-48v
Vout-5v-45v
Io: 5A
frequency: 20kHz
 

Papabravo

Joined Feb 24, 2006
17,240
The ACHS1 is just a current sensor and the zener diode, resistances and c5 are used to read the input voltage.
The terminal cap is to put a capacitor, (consider the input voltage dc).
Vin: 5v-48v
Vout-5v-45v
Io: 5A
frequency: 20kHz
The Zener diode has a Zener breakdown voltage and a Zener current.
I don't think the part you are intending to use for the inductor will be suitable for a 5A output current.
I'm asking for component values because I was going to put together a simulation file to see if the basic concept works. If you don't want me to do that then 'vaya con dios'
 

Thread Starter

Tiago Rocha

Joined Jul 12, 2021
21
The Zener diode has a Zener breakdown voltage and a Zener current.
I don't think the part you are intending to use for the inductor will be suitable for a 5A output current.
I'm asking for component values because I was going to put together a simulation file to see if the basic concept works. If you don't want me to do that then 'vaya con dios'
Of course i want you to do that. I didnt implement the zener diode in the board.
Didn't i tell all the values you should know to simulate?
can you please tell me whats missing?
 

Papabravo

Joined Feb 24, 2006
17,240
Of course i want you to do that. I didnt implement the zener diode in the board.
Didn't i tell all the values you should know to simulate?
can you please tell me whats missing?
The resistors you have chosen will give a V_in of just over 20 Volts. If the Zener voltage is larger, then it will have no effect. If the Zener voltage is smaller, then V_in should be a bit lower than the knee voltage of the Zener. I thought you said you wanted the input to be up to 45 volts.

If the ACHS1 provides a current path from the Bridge Rectifier and Terminal Cap 1, the voltage at the MOSFET drain will be about 310 volts. Was this your intention?

I have the datasheet for the 7448051012, but I don't have a specific spice model for it. You appear to have it connected as two parallel inductors. This means that you will see the parallel combination of 12 mH and 12 mH which is 6 mH. Is this what you intended. The inductance in the datasheet is characterized at a single frequency of 10 kHz. Your operating frequency will be 20 kHz so you may want to verify that the part will have approximately the same inductance at 20 kHz.

You did not answer my question about the proposed duty cycle of the gate signal.
 

Papabravo

Joined Feb 24, 2006
17,240
This is what I have so far. The schematic is clearly incomplete since the feedback loop has not been closed and thus the output is completely unregulated. Notice that the current in each leg of the inductor exceeds the rated current of 10 A by 30%. This does not appear to be a feasible design at this point base on a preliminary simulation and analysis.

1634236525228.png
 

Thread Starter

Tiago Rocha

Joined Jul 12, 2021
21
I think he said -5 to -45 volts. It is apparently an inverting buck-boost.
I mean Vout of -5 and -45 in fact.
The resistors are there to get 3.3V max on the adc reading of microcontroller.
the inductor is the following:
https://pt.mouser.com/ProductDetail...GAEpiMZZMv126LJFLh8y18kcQkXZy1gX%2BvrnnuLXfY=

For know i want to implement an buck-boost to control output voltage in a resistive load. In the future, i will use supercapacitors as load and try to charge them with constant current, thats why i need the current sensor. The control is being made with a microcontroller.
 

Thread Starter

Tiago Rocha

Joined Jul 12, 2021
21
This is what I have so far. The schematic is clearly incomplete since the feedback loop has not been closed and thus the output is completely unregulated. Notice that the current in each leg of the inductor exceeds the rated current of 10 A by 30%. This does not appear to be a feasible design at this point base on a preliminary simulation and analysis.

View attachment 250242
In the simulation i made, I just used one winding inductor 13mH and got the values i expected. I did it in PSIM. I tried also with high capacitive loads and i was getting nice results. I used diferent values to test it out
 

Attachments

Ian0

Joined Aug 7, 2020
3,754
A common-mode choke won't work in this circuit, with either one winding or two windings in parallel. You need a choke with an iron powder core or a ferrite core with a GAP. Common mode chokes don't have a gap. They will saturate almost immediately. as @ronsimpson said back in post #5
In order to work they must have an equal and opposite current in the second winding.
Your simulation will work perfectly, because SPICE doesn't simulate inductor saturation. If you make it with a common mode choke it will blow up (rapidly). A 11.2mH inductor that works at 10A will be huge.
Micrometals' software predicts a toroidal inductor 132mm diameter x 40mm high.
You can download the design software here
http://www.iec-international.com/micrometals/micrometals/software.html
 

Papabravo

Joined Feb 24, 2006
17,240
At least we can see that it is an inverting buck-boost as opposed to the buck-boost where the input can be below, equal to or above the output voltage. Still doesn't help the the TS's need for a component engineer.
 

ronsimpson

Joined Oct 7, 2019
1,630
Vin: 5v-48v
Vout-5v-45v
Io: 5A
Vout 5V 5A = 25W
Vout 45V 5A =225 watts. ???
----------------------------
Vin = 48V @ 5A, Vout=45V @ 5A That seems good.
-------------------------------------
Vin -= 5V @ 45A, Vout=45V @ 5A The input current is very large.
-------------------------------------
What I am trying to point out is, a 45W switcher is moderately easy but a 225 watt is much harder.
If you really need to burn 45A in the input side, that is hard.
-------------------
Is this just a way of learning, or do you have a real application? Can we choose numbers that are easy?
What you have started to make is not easy. A 10:1 input range is hard. A 9:1 output voltage and power range is hard.
 
Top