Simplified Circuit

Inverter Design Formulas

    The internal voltage reference is 1.245 volts

    is the peak inductor current, is the maximum output load current

    t_on and t_off > 10 ms    and    t_on + t_off < 50 ms

    Timing capacitor

    Minimum output filter capacitor

    Converter efficiency

    Input current

Inverter Design Example (AN711)

V_in = 12 volts V_out = -15 volts

I_{out (max)} = 500 ma V_ripple < 1%

 

Step 1 Calculate the peak current

Step 2 Calculate the current sense resistor

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 inductor size

Step 7 Determine the minimum storage capacitor size

Step 8 Determine the feedback resistor sizes

Step 9 Determine the switching transistor bias resistors

Select

where ( current sense threshold voltage)

(of the external transistor)

 

Final Circuit

Waveforms