Negative supply from positive supply is needed if the circuit need both positive and negative supply while we have only positive supply. The circuit shown in the schematic diagram below is a negative supply generator, built using a TLC497CN integrated circuit. The TLC497CN is used as the main switching circuit, and it can provide negative supply of up to 150mA. With an input supply of 10V, this circuit has efficiency about 50% but it is decreased under 50% when the input voltage is 5V. This circuit use resistor R1 to protect the IC1 from damage by limiting the current at the input to IC1 because this circuit is often be fed from high current supply. To control the average output voltage, TLC497CN uses a variable clock frequency and a fixed pulse width. The timing component in the oscillator section of the PWM this circuit is capacitor C3. capacitors C2 and C1 are supply-decoupling components on the input supply.