DC-DC Buck Boost Converter Power Losses

Joined Oct 1, 2016
31
I have designed DC-DC buck boost converter, and i want to find the power loss in each item such as resistor, inductor, capacitor, diode, mosfet.
Can someone give me the needed equations to find the power losses for the resistor, inductor, capacitor, diode, mosfet? In order to find the actual efficiency of the buck boost.

ronv

Joined Nov 12, 2008
3,770
I have designed DC-DC buck boost converter, and i want to find the power loss in each item such as resistor, inductor, capacitor, diode, mosfet.
Can someone give me the needed equations to find the power losses for the resistor, inductor, capacitor, diode, mosfet? In order to find the actual efficiency of the buck boost.
The easiest way may be to put the design into LtSpice. Then it is easy to measure the power in each part.
http://www.linear.com/designtools/software/

Joined Oct 1, 2016
31
The easiest way may be to put the design into LtSpice. Then it is easy to measure the power in each part.
http://www.linear.com/designtools/software/
I think the buck-boost is already available in LTspice but how can i find it. I do not want the IC(Chip) I want to see the power stage and control stage. In order to change the needed parameters.

Thank U,

ronv

Joined Nov 12, 2008
3,770
I think the buck-boost is already available in LTspice but how can i find it. I do not want the IC(Chip) I want to see the power stage and control stage. In order to change the needed parameters.

Thank U,

Joined Oct 1, 2016
31
You mean i have to draw my design or what?

RichardO

Joined May 4, 2013
2,268
I think the buck-boost is already available in LTspice but how can i find it. I do not want the IC(Chip) I want to see the power stage and control stage. In order to change the needed parameters.
Look in the Linear Technology selection guide.

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Papabravo

Joined Feb 24, 2006
12,685
You have to draw it anyway so we can help you. An LTSpice schematic would make it so much more helpful than a paper design which we would have to have in order to give you correct and meaningful answers. Of course we could just give you random answers if you prefer, or if the design is too secret to reveal. Most of us have worked with proprietary before.

Joined Oct 1, 2016
31
You have to draw it anyway so we can help you. An LTSpice schematic would make it so much more helpful than a paper design which we would have to have in order to give you correct and meaningful answers. Of course we could just give you random answers if you prefer, or if the design is too secret to reveal. Most of us have worked with proprietary before.

Joined Oct 1, 2016
31
This is it.

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Joined Oct 1, 2016
31
You have to draw it anyway so we can help you. An LTSpice schematic would make it so much more helpful than a paper design which we would have to have in order to give you correct and meaningful answers. Of course we could just give you random answers if you prefer, or if the design is too secret to reveal. Most of us have worked with proprietary before.
This is it.

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Papabravo

Joined Feb 24, 2006
12,685
This is it.
I don't think it will work the way you have it configured. There is no path for the input voltage to get to the output to charge up the output capacitor.

EDIT: Never mind I forgot about the polarity inversion.

When the switch is on, the DC load on the input voltage is the rDS(on) of the switch and the DC resistance of the coil. The dissipation in the switch is:

$$P_{d(SW)}=i^2 \times r_{\small DS(ON)}$$

The DC dissipation in the inductor is:

$$P_{d(L)}=i^2 \times r_{\small L}$$

Is that the kind of stuff you were looking for?

Last edited:

Joined Oct 1, 2016
31
I don't think it will work the way you have it configured. There is no path for the input voltage to get to the output to charge up the output capacitor.

EDIT: Never mind I forgot about the polarity inversion.
What should i correct or add to make it works?
Also I want to make a control stage?

Papabravo

Joined Feb 24, 2006
12,685
What should i correct or add to make it works?
Also I want to make a control stage?
The topology is correct and you can use the pulse generator on the switch to collect some data. What you need to add is a variable duty cycle oscillator. There are a number of ways to implement this part. Checkout this article for information on parameters:

https://en.wikipedia.org/wiki/Buck–boost_converter

Joined Oct 1, 2016
31
I don't think it will work the way you have it configured. There is no path for the input voltage to get to the output to charge up the output capacitor.

EDIT: Never mind I forgot about the polarity inversion.

When the switch is on, the DC load on the input voltage is the rDS(on) of the switch and the DC resistance of the coil. The dissipation in the switch is:

$$P_{d(SW)}=i^2 \times r_{\small DS(ON)}$$

The DC dissipation in the inductor is:

$$P_{d(L)}=i^2 \times r_{\small L}$$

Is that the kind of stuff you were looking for?
May i show you my design in PSIM and you will understand what i want?

Papabravo

Joined Feb 24, 2006
12,685
May i show you my design in PSIM and you will understand what i want?
I wouldn't know what to do with PSIM. Maybe someone else can help with that one. The LTSpice simulation looks good. The output settles to -12V in about 5 milliseconds. The power in the resistor looks like about 6.5 Watts once you get to steady state. The current in the load approaches 600 mA. I think you can get everything you need.

Joined Oct 1, 2016
31
I wouldn't know what to do with PSIM. The LTSpice simulation looks good. The output settles to -12V in about 5 milliseconds. The power in the resistor looks like about 6.5 Watts once you get to steady state. I think you can get everything you need.
So, i will complete my connection in Ltspice then i will show it to you. So you can understand what i want to make. The remaining is just the control stage. Since I want to control my output current.Therefore, I am going to make current control voltage controller.

ronv

Joined Nov 12, 2008
3,770
What should i correct or add to make it works?
Also I want to make a control stage?
So you have it in LtSpice.
You can now place the cursor over the component you want to measure, hold down Alt and click. This will show you the power in the component. Then hold down Ctrl and click the box above the waveform for that part and click. This will give you average power for the component.

Joined Oct 1, 2016
31
I wouldn't know what to do with PSIM. Maybe someone else can help with that one. The LTSpice simulation looks good. The output settles to -12V in about 5 milliseconds. The power in the resistor looks like about 6.5 Watts once you get to steady state. The current in the load approaches 600 mA. I think you can get everything you need.
This is my connection of buck-boost with controller. I want my output current to stay at 0.667 A if the input voltage changes. How can i control this buck-boost. please fill the needed parameter (R,C, voltage) of control stage in order to control the output current.
Vin=15-5V
Vout=12v
Iout=0.667 A
F= 20KHz
Voltage and current ripple Ripple is 5%.
Other parameters of power stage are already filled.

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Papabravo

Joined Feb 24, 2006
12,685
This is your design -- why are you asking me what to do? I'm not sure that I clearly understand the requirements, which you have failed to articulate in detail.