National Semiconductor Corporation

Micrel, Incorporated

Harry J Bittner

James Copland Moyer

Tamas S Szepesi

Daniel D Culmer

Walter R Davis

A switching voltage regulator achieves high efficiency by automatically switching between a pulse frequency modulation (PFM) mode and a pulse-width modulation (PWM) mode. Switching between the modes of voltage regulation is accomplished by monitoring the output voltage and the output current, wherein the regulator operates in PFM mode at small output currents and in PWM mode at moderate to large output currents. PFM mode maintains a constant output voltage by forcing the switching device to skip cycles when the output voltage exceeds its nominal value. In PWM mode, a PWM signal having a variable duty cycle controls the switching device. A constant output voltage is maintained by feedback circuitry which alters the duty cycle of the PWM signal according to fluctuations in the output voltage.

Voltage regulator that operates in either PWM or PFM mode

To avoid forward biasing the diodes within an N-channel transistor, the body and source of the N-channel transistor are switchably connected via a high-voltage FET. The gates of the N-channel transistor and high-voltage transistor are connected together so that both transistors are on or off simultaneously. When both transistors are on, the high-voltage transistor shorts the body and source of the N-channel transistor. When both transistors are off, the body and source of the N-channel transistor are disconnected and a third transistor couples the body to a reference potential. The N-channel transistor and high voltage transistor share a common body in a semiconductor substrate. The source of the N-channel transistor provides an output terminal for the circuit. A number of these devices, each connected to a different supply voltage, can be connected to the same output terminal and selectively energized to form a voltage multiplexer.

Field effect transistor with switchable body to source connection

One embodiment of this invention provides an improved version of an existing current source circuit. A reduction in die size of the current source is achieved by modifying the circuit to enable a reduction in the capacitance of its feedback capacitor while improving the frequency compensation of its feedback loop. The modification changes the location of the dominant pole in the circuit and utilizes Miller multiplication to increase the effect of the feedback capacitor. The modification also uses pole splitting to further ensure that the feedback loop will not oscillate.

Capacitor and resistor connection in low voltage current source for

A current sense/limit circuit senses a current of a power switch and turns off the switch when a peak current of the power switch surpasses a preprogrammed value. To prevent the circuit from reacting to a leading edge current spike resulting from the reverse recovery of a clamp or diode which is a part of most power processing circuits, the current sense/limit circuit monitors the voltage on the power switch and disables the current sense circuitry as long as this voltage does not drop below a predetermined threshold value. The predetermined threshold value is higher than the worst case voltage on the power switch during its on-time under normal operating conditions, and much lower than the switch voltage during off-time. As a result, this method adaptively blocks the current sense mechanism during most of the reverse recovery current spike period. The circuit also includes a timer that turns the switch off if the current sense/limit circuit remains disabled longer than a predetermined time to prevent switch damage resulting from a short circuit of the switch's drain-collector to the supply voltage.

Apparatus and method for eliminating false current limit triggering in a

A soft start circuit for a switching regulator is disclosed. The circuit does not require any off-chip parts and, therefore, a five-pin package can be employed. The operation of a soft start circuit in conjunction with a switching regulator operating in the voltage boost mode is set forth in detail.

Soft start for five pin switching regulators

An output stage suitable for monolithic semiconductor IC uses is disclosed. The stage employs a pair conventional NPN output transistors biased and driven with conventional bipolar IC elements. The pull up device, which sources output current for positive or rising inputs, is maintained on for negative signal swings so that it can be used to bias the pull down device which is cut off for positive signal swings.

Integrated circuit output driver stage

A linear amplifier output stage is provided with unity gain buffer means having an input coupled to the output terminal and an output coupled to the stage input. The unity gain buffer means is normally turned off by a control signal. When the amplifier is disabled by switching its bias current off, the buffers are turned on so that the output stage input capacitance is charged or discharged via the buffer means in accordance with the output terminal signal. When a plurality of such amplifiers are commonly coupled to a signal line the off amplifiers cannot be driven into conduction by the operating amplifier's output signal.

Growing community of inventors

Santa Clara, CA, United States of America

Harry J Bittner