Dc-dc converters

Abstract

A voltage reducing circuit 102 comprises a power switch circuit portion 10 comprising a high-side 128 and low-side 130 field-effect-transistors connected at a switch node 138. The power switch circuitportion has an on-state wherein the high-side transistor is enabled and the low-side transistor is disabled and, vice versa, an off-state. An energy storage circuit portion 106 comprising an inductor32 connected to the switch node is arranged to provide an output voltage 136. A drive circuit portion 104 receives a pulse width modulated control signal and outputs pulse width modulated (PWM) drivesignals. A pre-biasing circuit portion 150 10 applies bias voltages to the gate terminals of the high-side and low-side transistors in response to the PWM drive signals, wherein the pre-biasing circuit portion is arranged such that the bias voltage applied to the gate terminal of the currently disabled transistor is set to an intermediate voltage before switching between the on-state and the off-state.

Description

technical field [0001] The present invention relates to DC-DC (Direct Current to Direct Current) converters, especially but not limited to DC-DC step-down converters, such as synchronous DC-DC step-down converters. Background technique [0002] Modern portable electronic devices are often provided with a power source, such as a battery, which acts as a direct current (DC) power source for the various electronic components within the device. Typically, however, these components will have different voltage requirements, and so such devices typically employ one or more DC-DC converters that step down the nominal voltage associated with the power supply to a level suitable for the different electronic components. Voltage. While this could be achieved using a voltage divider network (e.g. a series of resistors) to create multiple "taps" with different voltages, this is very inefficient as energy is simply wasted being dissipated across the resistors of heat. [0003] An altern...

AI Technical Summary

Problems solved by technology

While the non-overlapping topology ensures that shoot-through is prevented, such converters require drivers that turn the high-side and low-side transistors on and off relatively quickly in order to limit the amount of "dead time" between voltage states at the switch nodes

However, using a sufficiently fast driver requires relatively large peak currents that introduce unwanted noise into the output voltage, reducing the efficiency of the converter

[0008] Also, with the positive current flowing through the buck converter, the body diode (sometimes called the body effect diode) inside the low-side transistor is usually turned on during high-low and low-high transitions, introducing more noise and reducing transition device efficiency

Such conventional buck converters also suffer from a relatively large "undershoot", where the voltage at the switch node temporarily exceeds the body diode threshold voltage of one of the transistors (typically about 0.7V) causing the body diode within the transistor to conduct , which causes body effect diode and substrate current to flow through it - another source of noise and inefficiency within conventional converters

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