| E-Math Pro is the essential formula tool for Engineers, Technicians and Students. E-Math contains over 300 useful formulas in 19 categories.  A simple example of using E-Math is to calculate resistor values for a resistor divider. You have a reference voltage of 1.2 VDC and you know you have plenty of 10K resistors in stock. What value do you need to get a reference voltage of 0.75 volts? Select the Fundamental DC Equations Voltage Divider Equation, select Ro as the value to solve for, enter the values you know, and let EMATH calculate the required resistor value.  A more interesting example might be something like calculating the maximum duty cycle of a buck regulator. Select the Buck and Boost Topologies Section and Buck, Dmax, with Parasitics category, enter the values for the Input and Output voltages, enter the output current and the L and C parasitic resistance. Need some help with the Buck power supply configuration or the definition of the formula values? Press F1 and pull up the help screen for the formula. Buck Regulator Maximum Duty Cycle Help Screen | Dmax | = | Maximum duty cycle | | Vo | = | Regulated output voltage, in volts | | Vf | = | Forward voltage drop of freewheeling diode, DF, in volts | | Io | = | Regulated output current, in amperes | | Rl | = | Coil resistance of inductor, in ohms | | Vin | = | Input voltage in, volts DC | | Vson | = | Voltage drop across switch, when on, in volts. For BJT's this is the saturation voltage, Vsat. For FET's use an average value of the current pulse through the FET times the on resistance, RDSon, of the FET. |
Because of parasitic losses in the circuit, the maximum duty cycle required to regulate the full load output is going to be greater than that calculated from the transfer function of Buck, Vo, Transfer function equation. The above equation includes most of the parasitics encountered in the real world. The following is the basic schematic for Buck topology illustrating these losses.  The coil resistance loss is due mainly to the DC current through RL, and IL(dc) = Io(dc), thus, IoRL can be used. There are hundreds more formulas to explore, including other power supply topologies, filters and op amp equations, thermal calculations. |