Low-voltage start up circuit and method for DC-DC boost converter
AssigneeTexas Instruments Incorporated
InventorVadim V. Ivanov
Life of this patent
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Abstract
A start up circuit (4-1) for a boost circuit (10) includes an adjustable-duty-cycle oscillator (1-2) that turns on a switch transistor (MSW) connected to an inductor (L) receiving an input voltage (VIN). If a voltage (V9) of a junction between the transistor and the inductor exceeds a predetermined value corresponding to a maximum inductor current (IL), an amplifier (A1) immediately terminates a first phase of an oscillator cycle, which turns off the transistor. Built-up inductor current is steered into a load. Duty-cycle-adjustment circuitry (R1,R2,C1) causes the oscillator to complete a normal second phase of the cycle before a new cycle begins.
Claims20
A start up circuit for assisting start up of an inductive boost circuit including a switch transistor coupled to the inductor rises to a predetermined input voltage level, the boost circuit generating a first voltage indicative of a current flowing in the inductor, the start up circuit comprising:
- (a) oscillator circuitry including
- 1) delay circuitry having an input coupled to a first conductor and an output coupled to a second conductor,
- 2) the second conductor being coupled to a first terminal of a first capacitor, a second terminal of the first capacitor being coupled by the second conductor to a first terminal of a first resistor, a first terminal of a second resistor, and a first terminal of a second capacitor, the first resistor having a second terminal coupled to a drain of a first transistor, the second resistor having a second terminal coupled to a drain of a second transistor, the first transistor having a source coupled to a first supply voltage and a gate coupled to the first terminal of the first capacitor, values of the first and second resistors and values of the first and second capacitors being determinative of a duty cycle of the oscillator circuitry, the second transistor having a source coupled to a second supply voltage and a gate coupled to the gate of the first transistor;
- and
- (b) amplifier circuitry having a first input coupled to receive the first voltage and also having an output coupled to turn off the switch transistor if the first voltage exceeds a predetermined level to prevent the inductor current from exceeding a predetermined inductor current level.
A method for assisting start up of an inductive boost circuit including a switch transistor having a drain coupled to a first terminal of an inductor having a second terminal coupled to receive an input voltage, the method comprising:
- (a) turning on the switch transistor in response to a first phase of a cycle of oscillator circuitry having an adjustable duty cycle, to cause a build-up of the inductor current;
- (b) coupling a drain voltage of the switch transistor to a first input of amplifier circuitry to cause a first change in an output of the amplifier circuitry if the drain voltage exceeds a predetermined value corresponding to a maximum desired build-up of the inductor current;
- (c) immediately turning off the switch transistor in response to the first change in the output of amplifier circuitry by immediately terminating the first phase of the oscillator circuitry;
- (d) steering the built-up inductor current into a load;
- (e) operating the oscillator circuitry to complete a normal second phase of the cycle immediately after the terminating of the first phase;
- and
- (f) repeating steps (a) through (e).
A start up circuit for assisting start up of an inductive boost circuit including a switch transistor having a drain coupled to a first terminal of an inductor having a second terminal coupled to receive an input voltage, comprising:
- (a) means for turning on the switch transistor in response to a first phase of a cycle of oscillator circuitry having an adjustable duty cycle, to cause a build-up of the inductor current;
- (b) means for coupling a drain voltage of the switch transistor to an input of amplifier circuitry to cause a first change in an output of the amplifier circuitry if the drain voltage exceeds a predetermined value corresponding to a maximum desired build-up of the inductor current;
- (c) means for immediately turning off the switch transistor in response to the first change in the output of amplifier circuitry by immediately terminating the first phase;
- (d) means for steering the built-up inductor current into a load;
- and
- (e) means for operating the oscillator circuitry to complete a normal second phase of the cycle immediately after the terminating of the first phase.
Dependencies are inferred from the claim text.