Startup for DC/DC converters

• US 20070253229A1
• Filed: 04/27/2007
• Published: 11/01/2007
• Est. Priority Date: 04/27/2006
• Status: Active Grant

• Current Assignee: Ahmad Dowlatabadi
• Original Assignee: Ahmad Dowlatabadi
• Inventors: Dowlatabadi, Ahmad
• Granted Patent: US 8,797,010 B2
• Time in Patent Office: Days
• US Class Current: 363/49
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters

Abstract

A design and method for controlling the initial inductor current in a DC/DC switching regulator. The T_on or T_off time, depending upon implementation, is gradually increased such that power applied to a load is initially constrained until the system reaches a stable state, at which time normal power is connected to the load. In an embodiment, the on or off time is limited by a circuit which controls a pair of complementary transistors. The states of the transistors are controlled by the use of a startup-phase voltage and a reference voltage, which are then compared in an error amplifier. The result of the comparison is compared to a sawtooth signal in a comparator, the output of which controls the state of complementary transistors.

Claims

1. A startup circuit for controlling initial current in a DC/DC switching regulator, comprising

an input for receiving power from a primary power source,

an output adapted to be connected to a load,

a first pair of switches connected together at a first midpoint node, each having a control terminal, and the pair having first and second terminals, wherein the first terminal is receives power from the primary power source and the second terminal is connected to ground, and the load receives power during normal operation via the midpoint node

driver logic connected to each of the control terminals of the pair of switches,

a reference signal generator for controlling the duration of the on or off times of the pair of switches to gradually increase the power applied by the primary power source to the load.

2. The startup circuit of claim 1 wherein the pair of switches are transistors.

3. The startup circuit of claim 1 wherein the reference signal generator includes a voltage divider having a second midpoint node and connected between the first midpoint node and ground, and comparison logic for selectively applying a startup signal to control the operation of the pair of switches.

4. The startup circuit of claim 3 wherein the comparison logic comprises error logic, selected from a group comprising an error amplifier and a comparator, and also includes a second pair of switches for applying the startup signal at startup.

5. The startup circuit of claim 4 wherein the comparison logic further comprises second comparison logic, one input to which is provided by a sawtooth signal and the other input to which is provided by an output of the error logic, the comparison logic having an output which forms an input to the driver logic.

6. The startup circuit of claim 4 wherein the comparison logic comprises comparator, charge pump, filter and controller connected serially.

7. A startup circuit for controlling initial current in a DC/DC switching regulator, comprising

a power input for receiving power from a primary power source,

an output adapted to be connected to a load,

a pair of complementary transistors connected together at a midpoint node, each having a gate, and together having a first terminal and a second terminal, the first terminal connected to the power input and the second terminal is connected to ground,

an inductor connected between the midpoint node and the output,

a capacitance connected between the output and ground,

a resistor divider having a pair or resistors connected serially at a divider node, the resistor divider being connected in parallel with the capacitor,

reference voltage,

error amplifier with negative feedback having connected at one input to the reference voltage and at a second input to the divider node,

switch logic for selectively enabling a preset voltage to be applied to the error amplifier at startup,

comparator connected at one input to an output of the error amplifier and at another input to a sawtooth signal,

driver logic responsive to an output of the comparator for switching the states of the pair of transistors to gradually increase the power applied to the load from the primary source.

8. A startup circuit for controlling initial current in a DC/DC switching regulator, comprising

a power input for receiving power from a primary power source,

an output adapted to be connected to a load,

a pair of complementary transistors connected together at a midpoint node, each having a gate, and together having a first terminal and a second terminal, the first terminal connected to the power input and the second terminal is connected to ground,

an inductor connected between the midpoint node and the output,

a capacitance connected between the output and ground,

a resistor divider having a pair or resistors connected serially at a divider node, the resistor divider being connected in parallel with the capacitor,

comparator connected at one input to the divider node and at another input to a reference signal,

a charge pump responsive to the output of the comparator,

controller responsive to a startup signal in a first mode and responsive to the output of the charge pump in a second mode,

switch means for selecting between first mode and second mode, and

driver logic responsive to an output of the comparator for switching the states of the pair of transistors to gradually increase the power applied to the load from the primary source.

9. The startup circuit of claim 8 wherein the controller is a PWM controller.

10. The startup circuit of claim 8 wherein the controller is a PFM controller.