Buck converter calc

bucks.c

/*  Compile with $ gcc -Wall -o bucks bucks.c
 * For Watcom: $ wcl -bcl=$(DEST_OS) -wx -fe=$(EXE_file) bucks.c
 * or use make
 * Buck converter Power State calculator
 * Formuli from SLVA477B by TI, Rev. 8/2015
 * C adaptation by Project Crew 2024
 */

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

int
main(int argc, char ** argv) {

    char strg[40];
    double
        freq,           // frequency
        vin,            // input voltage
        vout,           // output voltage
        ioutmax,        // max output current
        voutripple,     // desired output voltage ripple
        D,              // duty cycle
        iripple,        // ripple current
        L,              // inductor value
        mincap,         // minimum output capacitance
        idiode;         // avg. forward diode current

    if (argc == 1) {
        if (fgets(strg, 40, stdin) == NULL) // process input
            goto usage; // NO_VALUE
        else if ((isdigit(strg[0]) == 0) && (strg[0] != '.'))
            goto usage;
        freq = atof(strg);
        fgets(strg, 40, stdin);
        vin = atof(strg);
        fgets(strg, 40, stdin);
        vout = atof(strg);
        fgets(strg, 40, stdin);
        ioutmax = atof(strg);
        fgets(strg, 40, stdin);
        voutripple = atof(strg);

        // begin calc section
        D = vout * 0.85 / vin;  // equation 1
        iripple = 0.3 * ioutmax;  // equation 6
        L = vout * (vin - vout) / (iripple * freq * vin);  // equation 5
        mincap = iripple / (8.0 * freq * voutripple);  // equation 12
        idiode = ioutmax * (1 - D);  // equation 7

        // spacer
        fputs("-\n", stderr);

        // send formatted output
        printf("%.3f\n%.3f\n%.3f\n%.3f\n%.3f\n",
               D * 100,
               iripple,
               L * 1e6,
               mincap * 1e6,
               idiode
               );
        exit(EXIT_SUCCESS);
    } else {
usage:
        puts("   bucks is a buck converter power state calculator.");
        puts("   5 output paramaters including inductor value\n");
        puts("   5 position dependent input paramaters from stdin, 1 per line");
        puts("   scriptable and designed to be used with formvar");
        puts("   Input: frequency, Vin, Vout, Ioutmax, Voutripple");
#if defined (__DOS__)
        puts("   Output: dutyCycle, Iripple, L(\xe6\H), "
            "minimumOutputCapacitance(\xe6\F), Idiode");
#else
        puts("   Output: dutyCycle, Iripple, L(µH), "
            "minimumOutputCapacitance(µF), Idiode\n");
#endif

        exit(EXIT_FAILURE);
    }
    return(EXIT_SUCCESS);
} /* main */