Two LM2670-ADJ regulator ICs are used to architect two Buck-Boost inverter circuits: one (U1) that inverts the input voltage to create a negative output voltage, and the other (U2) that also inverts the input voltage yet re-inverts the signal through a coupled inductor arrangement to create a re-inverted positive version of the same voltage. The inverter circuits charge their inductors, L1 and L2. During the off-time of the switch the discharge of the inductor pulls current in the negative direction to ground. The U1 based inverter is able to program its output voltage between -5V and -13V by adjusting the voltage divider resistors R6 and R3. With the component values in this design the output voltage is set to -7.44V. The U2 based inverter uses the L2 secondary winding to invert the inverted signal so that the positive voltage tracks the negative voltage. The second output is programmed through the current sensed across R7 by the current source circuit formed by Q1. Capacitors C3 & C7 and C8 & C5 are used for inverter stabilization. Output capacitors, C10 & C11 and C14 & C16 respectively, charge to the required output voltage and serve to shunt ripple currents to ground. The LM2670 is a PWM regulator with internal FET switch and compensation circuitry. These two features minimize the number of external components, thus making the design inexpensive.
Schematic
Example Schematic Showing Connection for all Components.
Example Schematic Showing Connection for all Components.
