AN-1118 - 5V to 12V DC Converter

This circuit was built in the lab using the components shown in Figure 1. The -12V output varied between -11.99V and -11.97V under a load variation between 50 mA and 100 mA and a line variation between 4.5V and 5.5V. The +12V output varied between 11.15V and 11.45V under the same conditions. The +12V output is lower than the -12V output because of the voltage divider effect of the leakage inductance and a mismatch in the forward voltage drops of D2 and D3.

The efficiency of this circuit varied between 76% and 83% over the line and load variation. The ripple voltage on the +12V and the -12V outputs is less than 1%. A majority of this ripple voltage is due to the ESR (Equivalent Series Resistance) of the output capacitors C2 and C3. The capacitors used in this circuit have an ESR of 0.65O.