Startup for DC/DC converters
First Claim
1. A startup circuit for controlling initial current in a DC/DC switching regulator, comprisingan 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 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 including second switch logic for selectively enabling a single preset voltage to be applied from the time voltage is initially applied to the regulator until the voltage at the output reaches substantially the intended regulated voltage to one of a group comprising a comparator, a pulse width modulator, and a pulse frequency modulator for controlling the duration of the on or off times of the first pair of switches to gradually increase the power applied by the primary power source to the load without the use of an external capacitor to control the increase.
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Abstract
A design and method for controlling the initial inductor current in a DC/DC switching regulator. The Ton or Toff 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.
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Citations
13 Claims
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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 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 including second switch logic for selectively enabling a single preset voltage to be applied from the time voltage is initially applied to the regulator until the voltage at the output reaches substantially the intended regulated voltage to one of a group comprising a comparator, a pulse width modulator, and a pulse frequency modulator for controlling the duration of the on or off times of the first pair of switches to gradually increase the power applied by the primary power source to the load without the use of an external capacitor to control the increase.
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3. 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 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, and a reference signal generator for controlling the duration of the on or off times of the first pair of switches to gradually increase the power applied by the primary power source to the load, wherein the reference signal generator includes a voltage divider having a second midpoint node and connected between the first midpoint node and ground and second switch logic for selectively enabling a single preset voltage to be applied from the time voltage is initially applied to the regulator until the voltage at the output reaches substantially the intended regulated voltage to comparison logic to control the operation of the first pair of switches.
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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, 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.
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9. 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.
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12. 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 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 including second switch logic comprising a second pair of switches for selectively enabling a single preset voltage to be applied from the time voltage is initially applied to the regulator until the voltage at the output reaches substantially the intended regulated voltage to comparison logic for controlling the duration of the on or off times of the first pair of switches to gradually increase the power applied by the primary power source to the load.
Specification