Active dropout optimization for current mode LDOs

• US 20060033481A1
• Filed: 08/08/2005
• Published: 02/16/2006
• Est. Priority Date: 08/06/2004
• Status: Active Grant

• Current Assignee: Erich Bayer, Gerhard Thiele
• Original Assignee: Erich Bayer, Gerhard Thiele
• Inventors: Bayer, Erich, Thiele, Gerhard
• Granted Patent: US 7,282,895 B2
• Time in Patent Office: Days
• US Class Current: 323/266
• CPC Class Codes: G05F 3/262 using field-effect transistors only
• CPC Class Codes: H02M 1/0045 Converters combining the concepts of switch-mode regulation and linear regulation, e.g. linear pre-regulator to switching converter, linear and switching converter in parallel, same converter or same transistor operating either in linear or switching mode

Abstract

A DC/DC converter has a linear voltage regulator for reducing or eliminating the output ripple of the converter with a minimum loss of efficiency. The converter comprises a converter stage with a supply voltage input, a converted voltage output and a control input, a regulator stage having an input connected to the converted voltage output of the converter stage and an output connected to a load, and a tracking circuit with inputs for a voltage at the converted voltage output of the converter stage, a voltage at the output of the regulator stage and a load sense current, and an output connected to the control input of the converter stage. The tracking circuit controls the converter stage so as to increase the converted voltage with an increasing load sense current and vice versa. The output voltage of the converter is always just sufficient to eliminate the ripple without having to operate the regulator'"'"'s pass transistor in its linear range.

Claims

1. A DC/DC converter with a linear regulator for reducing the output ripple of the converter, comprising:

a converter stage having a supply voltage input, a converted voltage output and a control input;

a regulator stage having an input connected to the converted voltage output of the converter stage and an output connected to a load, and

a tracking circuit with input for a voltage at the converted voltage output of the converter stage, input for a voltage at the output of the regulator stage and a load sense current, and an output connected to the control input of the converter stage;

wherein the tracking circuit controls the converter stage so as to increase the converted voltage with an increasing load sense current, and vice versa.

2. The DC/DC converter of claim 1, wherein the linear regulator includes a load current pass transistor in MOS technology, and the tracking circuit controls the converter stage such that the voltage at the converted voltage output of the converter stage is sufficient to avoid operation of the load current pass transistor in an unsaturated state.

3. The DC/DC converter of claim 2, wherein the linear regulator includes a feedback loop with a comparator that compares a feedback voltage derived from the output of the regulator with a reference voltage and an output that controls the pass transistor.

4. The DC/DC converter according to claim 3, wherein the linear regulator includes a current mirror associated with the pass transistor and providing the load sense current.

5. The DC/DC converter according to claim 2, wherein the linear regulator includes a current mirror associated with the pass transistor and providing the load sense current.