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- The values of all input fields can be changed.
- If an input field is left empty, a default value is chosen. This value is displayed after leaving the input field in question.
- The switch mode power supply operates within a certain input range i.e. between
*V*_{in_min}and*V*_{in_max}. - The program needs the output values
*V*_{out}and*I*_{out}. - The switching frequency
*f*is the operating frequency of the transistor. - If the field "proposal" is activated, the proposed choking coil
*L*is chosen such that Δ*I*_{L}is 40% of the average value of the inductor current*I*_{L}, for*V*_{in_min}as the input voltage. - If you should not be content with the proposed value, you can change
*L*or Δ*I*_{L}. If this is the case, the field "proposal" is deactivated automatically. - The value
*V*_{in}is the value for the calculation of the current and voltage diagrams on the right side of the display.*V*_{in}must lie between*V*_{in_min}and*V*_{in_max}.

Illustration 1: Buck Boost Converter |

During the on-time of the transistor, there is an input voltage *V*_{in} applied across the inductor *L*. The inductor current *I*_{L} increases linearly. Energy is loaded into the inductor.

During the blocking phase of the transistor, the current *I*_{L} continues to flow through the inductor and loads the output capacitor *C*_{out}. The inductor transfers its energy to *C*_{out}.

One can make a distinction between continuous and discontinuous mode depending on whether the inductor current *I*_{L} goes to zero or not.

For continuous mode using Faraday's Law gives:

From this it follows that:

- In continuous mode the output voltage depends only on the duty cycle
*t*_{1}/*T*and the input voltage*V*_{in}, it is independent of the load.

Continuous Mode | Discontinuous Mode |

Illustration 2: Operating modes of the Buck Boost Converter

- The larger the chosen value of the inductor
*L*, the smaller the current ripple Δ*I*_{L}. However this results in a physically larger and heavier inductor. - Choose Δ
*I*_{L}so that it is not too big. The suggestions proposed by us have adequately small current ripple along with physically small inductor size. With a larger current ripple, the voltage ripple of the output voltage*V*_{out}becomes clearly bigger while the physical size of the inductor decreases marginally. - The higher the chosen value of the switching frequency
*f*, the smaller the size of the inductor. However the switching losses of the transistor also become larger as*f*increases.

** V_{in_min}**,

Using these parameters, the program produces a **proposal for L**:

where

From this it follows that:

- For
**Δ**the converter is in continuous mode and it follows that:*I*_{L}< 2*I*_{L}

,

- For
**Δ**the converter is in discontinuous mode and it follows that:*I*_{L}> 2*I*_{L}

,

Main page | | How to use the program | | Function principals | | Mathematics used in the program | | |

Top of page | | Application | | Tips | | Literature Notes | | Help for choking coils |