Electronic circuit design, especially power design is an iterative calculative process that needs several assumptions to be made at the time of calculations and may need iterative adjustments of such assumptions depending on acceptability of the result. A computer worksheet becomes an indispensable tool for such calculations, wherein it allows designer to change assumed values giving results instantly. A very simple and effective scheme of doing such calculations has evolved at Ascenten and is demonstrated by this example: Click Here
The calculations are those of a Boost DC-DC converter converting an input voltage range of 7V to 17V into an output at 18V. The worksheet has been divided into five columns:
Column 1:
The first white column lists the parameters being described, along with their symbol.
Column 2, 3, 4:
The next three columns: green, yellow and orange contain values. The green and orange columns are extreme values. For example the sheet shows that the input voltage Vin is ranged from 7V to 17V, with green showing the minimum and the orange showing the maximum. As calculation proceeds in the next few lines, the green may contain a maximum, while the orange may contain a minimum. In short remember that the green and orange are extreme values of a parameter, with green not necessarily being the minimum and the orange not necessarily being the maximum. This fact is illustrated while calculating the duty cycle D that hides Vin in its formula. The yellow column shows typical or exact values.
Column 5:
This column contains unit of the corresponding value.
Column 6:
This column contains comments that may include any necessary additional information or formula used in calculation.
Column 7:
This column contains legend description. All fixed values beyond the control of the designer or as required by specification are bold faced (it is easy to remember in terms that bold things are fixed and not changeable). For example, the input voltage Vin and the diode drop is fixed.
Values that are chosen or assumed by the designer are italic, as in the case of switching frequency f being chosen to 100,000 Hz. Next, all values evaluated by formula are underlined (remember underlining results in your homework?). And finally, holy values that required to be tested at the time of production are honored by a box.
Corrections can be made at times by striking out values while furnishing an appropriate comment, rather than deleting a value altogether.
This scheme of calculations offers many advantages. Firstly it is very simple, just like the best things in life. Next, it is very easy to iteratively move back and forth and observe effect of a parameter on other parameters. Next, with a single glance at the sheet one can tell apart parameters that are fixed, the ones that have been chosen and the ones that have popped out of a calculation. At the same time extreme and typical values are clearly distinguished. And test points are instantly identified too. It is very convenient and quick to make values underlined, bold or italic by Ctrl-U, Ctrl-B and Ctrl-I respectively. This format is monochrome printer friendly and the three value bands (green, yellow and orange) appear as three light shades. At Ascenten, we supplement every circuit diagram with such a worksheet and it acts as a convenient medium to preserve and exchange detail among engineers.
At this point we believe that this scheme has a good enough balance between simplicity and objectivity to be easily acceptable. Of course, more rules can be added but they come with a possibility of being mistakenly twisted.
Well, this information is not free. We’d like to have your comments in return.
Download Excel Calculation template for your use. (23 KB)
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