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.

t_on and t_off > 10 ms and t_on + t_off < 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 t_on/t_off ratio

Step 4 Calculate the values for t_on and t_off

Since and

Let then

Step 5 Calculate the timing capacitor C_T

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