Boost Design Example


Simplified Circuit



Boost Design Formulas

The internal reference voltage is 1.245 volts.
= peak inductor current. = maximum output load current.
The value for the current sensing resistor is a given, not derived, formula.
ton and toff > 10 ms and ton + toff < 50 ms
Timing Capacitor
Minimum output filter capacitor
Driver collector resistor , assume

Boost Design Example (AN711)

Vin = 5 volts Vout = 15 volts

Iout (max) = 150 ma Vripple < 1%

Step 1 Calculate the peak current

Step 2 Calculate the current sense resistance

= 33

Step 3 Calculate the ton/toff ratio

Step 4 Calculate the values for ton and toff

Since and

Let then

Step 5 Calculate the timing capacitor CT

Step 6 Determine the minimum inductor size

Step 7 Determine the minimum storage capacitor size

Step 8 Determine the feedback resistor size

Let

(select 1.3k)

(use a 25k potentiometer)

Step 9 Determine the base drive resistor size (if desired)

and assume

Final Circuit

Note: the above schematic is missing the reference and input bypass capacitors.

Basic Waveforms