Power supply unit
High-accuracy overcurrent detection is performed, while a loss resulting from the current detection is significantly reduced. A switch section outputs the voltage between the both terminals of a current detection resistor using an AND signal between an output signal from a hysteresis comparator and an output signal from a pre-driver. The voltage is filtered by an electrostatic capacitor element and a resistor, and inputted to a comparator. The comparator makes a comparison between the signals inputted to the two input terminals thereof, and outputs the result of the comparison to a digital filter. When an overcurrent begins to flow in a power supply unit, the levels of the voltages inputted to the two input terminals of the comparator are inverted so that the comparator outputs an inversion signal to the digital filter. The digital filter outputs a detection signal to an overcurrent detection circuit when an arbitrary time has elapsed.
1. A power supply unit comprising:
a stabilized power supply section for generating a stabilized power supply; and
a current detection section for detecting an average load current in the stabilized power supply generated by the stabilized power supply section,
wherein the current detection section comprises:
a current detection resistor for performing current detection;
a control section for outputting a control signal in each cycle of an arbitrary period;
a sample/hold section for holding a voltage between both terminals of the current detection resistor at arbitrary time intervals based on the control signal from the control section; and
a filter section for attenuating ripple in a PWM cycle which is included in a signal sampled by the sample/hold section.
2. A power supply unit according to claim 1 , wherein the stabilized power supply section has first and second switching elements each for performing voltage conversion,
wherein the current detection resistor has one coupling portion coupled to an input power supply voltage, and
wherein the first and second switching elements are coupled in series between the other coupling portion of the current detection resistor and a reference potential.
3. A power supply unit according to claim 2 , wherein the control section generates the control signal so as to cause the sample/hold section to sample the voltage between both terminals of the current detection section during a time interval in which the first switching element is ON.
4. A power supply unit according to claim 1 , wherein the stabilized power supply section is a DC-DC converter.