Buck Converter Calculator Excel

[Alayna Rother]

TheExternal Component Calculator for the MAX5072/MAX5073 converters is a simple-to-use design tool to set up a buck or a boost converter. The tool calculates the principal external component values, the compensation network type (II or III), and its associated component values.

The External Component Calculator has two calculator worksheets used to set up a buck converter, and two similar worksheets for a boost converter. The first of each pair of worksheets calculates the principal external component values; the second worksheet calculates the compensation network type (II or III) and the associated component values.

The worksheets are presently configured to calculate component values for channel 1 of the MAX5072 and MAX5073. Because the two converter channels have different RDS(ON) values and internal switch current limits, it is important to update the RDS(ON) value if you are setting up channel 2. You should also double-check the peak currents and average currents to make sure that they are within the limits of channel 2. Consult the MAX5072 and MAX5073 data sheet EC tables and TOC plots for these values.

REMEMBER that once calculated cells are edited to fixed values, the automatic calculations will no longer be able to update these cells. It is a good idea to back up a copy of the spreadsheet before replacing calculated values with actual component values.

When you have set up the basic external component values (CIN, COUT, LOUT), you can unprotect the worksheets by using the password 'maxim.' Enter the actual capacitor ESR and capacitance values into the green cells for Max ESROUT and Min COUT, respectively. This will ensure accurate compensation values on the next worksheet. The capacitor values that are calculated are limits, not actual capacitor specifications.

Within the worksheets, the cells with a blue background are editable, and are for key power-supply design parameters. The green cells show the results that you need to implement your design. Some parameters are checked for validity: if a parameter goes out of specification, the cell value will turn red and the cell that needs adjustment will turn orange.

This tool will allow a user to quickly approximate or easily evaluate a variety of design options. This calculator is obviously not the definitive tool for switch-mode power-supply design. Always make a common-sense check, and verify all component values using standard switching power-supply design techniques.

I am building a simple buck converter to regulate a 5V form my 9.6V battery. The battery is a pack of 3 18650 cells (3S) and the output is supposed to power my MCU (PIC) a couple of sensors and a servo motor.

Initially I thought I could get away with a simple Linear regulator like 7805, but the efficiency of these devices are very bad. Also, since I am running on battries I hae limited juice and have to use a switched power supply like a Buck Converter. I went though the basics of the converter and now I am stuck at a place where I have to decide the value of the inductor for my circuit which is shown below

So far I have decided to use the IRFZ44N MOSFET as a switch and the controller will be an Arduino so make things easy for my first run. Can some one please explain me how to calculate the value Inductor? A direct formulae will be more helpful.

The value of an Inductor in a Buck converter is decided by considering a lot of factors. Before we get into that you should know that the buck converter can operate in 3 different modes based on the value of the Inductor you are using and you have specified nothing about it. The three modes are

Most converters operate in the CCM mode, but to keep calculations simple people normally calculate the Inductor value for BCM. This Inductor value is called the Critical Inductor Value. Once we get this Critical inductor value we can slightly increase it to work in CCM mode ot decrease it to operate in the DCM mode based on the required ripple voltage.

This formula will help you in calculating the value of Inductor in Henry, it gives a rough figure, but it should work fine for your application. Here Vi is the Input Voltage, Vo is the Output Voltage is the average current through your load and DT is the switching frequency of your MOSFET in ton/ton+toff.

The value of Vi and DT are variable as you said, you can calculate the L value for minimum and maximum value of Vi. DT is controlled through program. If you PWM can be from 0% to 100% then you can play with the formulae in such a way that for all values of Vi you should be able to get the desired output voltage Vo for your value of L by simply varying the duty cycle.

Hi, that did clear up my doubts. I roughly approximated my inductor value to be 100uH, with this value of L I should be able to get a constant 5V by varing by duty cycle between 40% to 90% for an input voltage varying from 7V to 13V.

Now I where to buy this 100uH, is it a good idea to find my own inductor I have a toroid core with me. My local electronics shop only has color ring type inductors which I thin is not suitable for this circuit.

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where RT is the top feedback resistor in the enable-resistor network, RB is the bottom feedback resistor in the enable-resistor network, VON is the desired input voltage for turn-on, VOFF is the desired input voltage for turn-off, RHYS is the hysteresis resistor, IDRAW is the current drawn by the enable-resistor network, and VEN is the enable-threshold voltage (a datasheet specification).

An example shows how the analysis translates into actual values. Here, the converter will be enabled once the input voltage reaches 10 V. Once on, the input voltage will decrease down to 7.5 V before the converter becomes disabled. This means designing a system hysteresis of 2.5 V into the enable signal. The specific design parameters are:

The Excel design calculator can calculate the resistor values corresponding to your desired design parameters. In the yellow boxes (see table), enter the preferred turn-on voltage, the amount of added hysteresis, the VEN threshold, the total desired current draw, and the output voltage. Use the enable-resistor network-current draw entry to select how much current, in microamperes, you will budget for the enable network. Selecting a smaller value will increase the resistor magnitudes.

You can use the TINA-TI SPICE-Based Analog Simulation Program to simulate turn-on and turn-off performance with the calculated resistor values. Adjust RT, RB, RHYS, VEN, and VOUT amplitude to match your design calculations. Figure 2 shows the TINA-TI Simulation schematic that can be adjusted to test out different values.

The Excel calculator quickly recommends the appropriate component values for the desired VON and VOFF (see bottom of table), where the RT, RB, and RHYS values that have been calculated to meet the input criteria are shown.

Actual wiring of the hysteresis resistor to the available EVM allows for testing in the lab. For this example, the TI LM73605 EVM was used with a small resistive load and a signal generator to provide the input ramp waveform. Figure 4 demonstrates the physical implementation of the hysteresis example with results measured on an oscilloscope.

The Excel calculator allows for quick design of a hysteresis network. The simulation files prove the mathematical validity, showing the same turn-on and turn-off threshold values as the calculator. Finally, testing in the lab proves that at the applications level, the turn-on and turn-off thresholds are very close to the ideal, corresponding to the calculator. The Excel calculator, simulation tools, and EVM testing provide a quick and accurate method to add hysteresis to your dc-dc converter.

The Inductor Design software allows engineers to choose from several topologies like Power Factor Correction or AC inductor, collects all the pertinent electrical, thermal and mechanical inputs, and returns a wide range of solutions that can be sorted based upon key criteria. The results can also be downloaded for closer analysis. Our inductor calculator is an easy-to-use yet powerful design tool for experienced or early career engineers or designers.

Micrometals Inductor Analyzer allows engineers to quickly analyze wound core designs using any of our cores by providing electrical and thermal parameters. Solutions developed by our Inductor Design software can be transferred to the Inductor Analyzer for optimization. Engineers can also launch the Inductor Analyzer through our product search by clicking the icon next to the desired core. This inductor calculator lets users compare 1-3 different inductor designs side-by-side. It is especially useful when comparing windings, differtent permeabilities or material types for a specific inductor design.

Additionally, Micrometals offered a downloadable Excel File with magnetic characteristic curve fit formula and coefficients for Permeability vs. DC Magnetizing Force, Core Loss vs. Bpk and Frequency, Permeability vs. Bpk, Permeability vs. Frequency and Initial BH Curves.

PowerEsim is a free web-based power supply design tool which is sponsored by component manufacturers and active members. It provides a virtual environment that users can build hundreds of "real" power supply with real constructed transformer and see all loss, stress, life, temperature in a fraction of a second.

The circuit simulator is a combination of iteration, equation based approach and time step integration. The circuit is defined by non-linear equations and the simulator will first solving the switching condition solution for t=infinity by bracketed iteration, then fine step of point by point results will be generated by those equations for V, I and loss analysis.

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