Patent ID: 7508176

Claim:
A controller for a DC to DC converter capable of switching between a linear mode and a switch mode, comprising: linear mode control circuitry capable of providing a first control signal to a controlled device of said DC to DC converter, said controlled device operating as a variable resistor in response to said first control signal to control an output voltage of said DC to DC converter; switch mode control circuitry capable of providing a second control signal to said controlled device of said DC to DC converter, said controlled device operating as a switch to turn ON and OFF in response to said second control signal to control said output voltage of said DC to DC converter, one of said linear mode control circuitry and said switch mode control circuitry being enabled to control said controlled device in response to a state of an enable signal; and protection circuitry, responsive to said enable signal, and configured to accept a signal representative of said output voltage of said DC to DC converter and compare said signal to an under voltage threshold using an undervoltage hysteresis comparator, said protection circuitry further configured to compensate said first or second control signal provided to said controlled device if said signal representative of said output voltage is less than said under voltage threshold, said protection circuitry further configured to compare said signal representative of said output voltage to an over voltage threshold using an overvoltage hysteresis comparator and to compensate said first or second control signal provided to said controlled device if said signal representative of said output voltage is greater than said over voltage threshold, said undervoltage hysteresis comparator and said overvoltage hysteresis comparator being configured to force said first control signal to a desired voltage level; wherein said switch mode control circuitry comprises pulse width modulation (PWM) circuitry and said second control signal comprises a PWM output signal, wherein said controlled device switches ON and OFF in response to a duty cycle of said PWM output signal if said PWM circuitry is enabled to control said controlled device, and wherein said protection circuitry compensates said PWM output signal by increasing said duty cycle if said signal representative of said output voltage is less than said under voltage threshold, and by decreasing said duty cycle if said signal representative of said output voltage is greater than said over voltage threshold; wherein said PWM circuitry comprises an error amplifier and a driver to provide said PWM output signal, each of said error amplifier and said driver individually responsive to said enable signal to provide said PWM output signal when said enable signal is in a first state and to not provide said second control signal when said enable signal is in a second state.