Micro Linear Corporation

North American Philips Corporation

Linear Technology Corporation

Bing F Ma

John P Tero

Shaoan Chin

W Richard Davis

A boost DC-DC converter with a synchronous composite rectifier is presented. The boost DC-DC converter limits inductive in-rush current, includes a shutdown mode, operates also in step-down mode, and can be fabricated using conventional bipolar processes. The composite rectifier includes a power NPN transistor and a lateral PNP transistor. During converter start-up and in step-down mode (when the output voltage is less than the input voltage), the lateral PNP transistor drives the power NPN transistor. The lateral PNP transistor is biased such that inductive volt-second balance can be maintained, limiting in-rush current. In boost mode (when the output voltage is higher than the input voltage), the lateral PNP transistor is disabled and the power transistor is driven into saturation. Again, inductive volt-second balance can be maintained.

Synchronous rectifier for boost converters

An R-C relaxation oscillator having two comparators and a silicon controlled rectifier dissipates very low average power without resulting in frequency instabilities due to circuit propagation delays. A timing capacitor C.sub.T is charged through a timing resistor R.sub.T. The first comparator compares the voltage across the timing capacitor with an upper threshold voltage V.sub.TH. When the voltage across the timing capacitor crosses the upper threshold voltage, the comparator turns on the silicon controlled rectifier, which causes the capacitor to discharge the voltage that it has stored. The second comparator turns off the silicon controlled rectifier when the voltage across the timing capacitor falls below a lower threshold voltage V.sub.TL. The silicon controlled rectifier also provides boosted comparator bias current during the discharge phase, enabling the second comparator to respond quickly to the lower threshold voltage crossing and allowing fast capacitor discharge (therefore narrow clock pulses) and increasing frequency stability.

Micro power R-C relaxation oscillator

An output circuit includes a totem-pole output circuit for driving a power MOSFET. A pull-up circuit and a pull-down circuit drive the output node low or high as required. The circuit prevents the pull-up and pull-down circuits from simultaneously conducting current. The pull-up circuit has a pull-up threshold voltage and the pull-down circuit has a pull-down threshold voltage such that the pull-up circuit is turned off before the pull-down circuit is activated when the output node is switched from a high state to a low state and further wherein the pull-down circuit is turned off before the pull-up circuit is activated when the output node switches from a low state to a high state. The pull-up circuit is held off when the output node is switched from a high state to a low state by two diodes from the output node to an input of the pull-up circuit. The diodes are connected in series, one diode having its anode coupled to the output node and the cathode of the other diode coupled to the input of pull-up circuit. The pull-down circuit is cut off before the pull-up Darlington drives the output from low to high by having the pull-down threshold higher than the pull-up threshold. A resistor connected between the base of the controlling transistor for the pull-up Darlington and the ground shortens the output low-to-high propagation delay time and the output rise time by shunting transient parasitic capacitance current of the pull-up controlling transistor to the ground.

Power MOSFET driver with cross-conduction current reduction

An output circuit having the output taken between a pull-up output transistor and a pull-down output transistor connected in series for conducting current alternatively. Separate pull-up and pull-down driver circuits are controlled by a common input signal. The pull-down driver circuit is supplied by a pull-down current source, and a diode is connected from the point between the pull-down driver transistor and pull-down current source to the output node. The effect of a large node capacitance is reduced by the diode, which conducts current from the pull-down current source to any output load capacitance to raise the output voltage more rapidly when the pull-down driver circuit is cut off.

Growing community of inventors

Sunnyvale, CA, United States of America

Bing F Ma