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  1.   Basic Calculation of a Boost Converter's Power Stage
  2. 1 Basic Configuration of a Boost Converter
    1. 1.1 Necessary Parameters of the Power Stage
  3. 2 Calculate the Maximum Switch Current
  4. 3 Inductor Selection
  5. 4 Rectifier Diode Selection
  6. 5 Output Voltage Setting
  7. 6 Input Capacitor Selection
  8. 7 Output Capacitor Selection
  9. 8 Equations to Calculate the Power Stage of a Boost Converter
  10. 9 References
  11. 10Revision History

5 Output Voltage Setting

Almost all converters set the output voltage with a resistive divider network (which is integrated if they are fixed output voltage converters).

With the given feedback voltage, VFB, and feedback bias current, IFB, the voltage divider can be calculated.

GUID-E4AAD15F-9424-40D1-B9D5-1A3C36F5A859-low.gif Figure 5-1 Resistive Divider for Setting the Output Voltage

The current through the resistive divider shall be at least 100 times as big as the feedback bias current:

Equation 9. GUID-FBF81594-D05A-4DA9-904E-D10DA28992EB-low.gif

IR1/2 = current through the resistive divider to GND
IFB = feedback bias current from data sheet

This adds less than 1% inaccuracy to the voltage measurement. The current can also be a lot higher. The only disadvantage of smaller resistor values is a higher power loss in the resistive divider, but the accuracy will be a little increased.

With the above assumption, the resistors are calculated as follows:

Equation 10. GUID-F03BC30B-B7F2-4683-BFC6-76C645F4C612-low.gif
Equation 11. GUID-941B6841-629B-4348-B1F3-2B6B724442F4-low.gif

R1,R2 = resistive divider, see Figure 5-1.
VFB = feedback voltage from the data sheet
IR1/2 = current through the resistive divider to GND, calculated in Equation 9
VOUT = desired output voltage