PWM BOOST SYSTEM AND START-UP METHOD THEREOF
A PWM (pulse width modulation) boost system includes a boost circuit, a voltage dividing circuit, a comparator, a PWM circuit, a pre-oscillator, and a current limit circuit. A start-up method of the PWM boost system includes (1) providing an error voltage; (2) generating a PWM signal according to the error voltage; (3) controlling a switch in a boost circuit with the PWM signal, so as to control an inductor current flowing through a boost inductor in the boost circuit; (4) charging a capacitor in the boost circuit with the inductor current, wherein charges stored in the capacitor define a DC output voltage; and (5) providing a feedback voltage according to the DC output voltage to adjust the error voltage.
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BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to a pulse width modulation (PWM) boost system and a start-up method thereof. More particularly, the present invention relates to a PWM boost system with a function of current limit soft-start and a start-up method thereof.
2. Description of Related Art
Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Referring to
Referring to
One aspect of the present invention is to provide a PWM boost system, which adds a current limit circuit and a comparator enabled in a pre-oscillation period according to an enable signal, so as to eliminate an inrush current when the PWM boost system is started up with a light load, and to ensure a successful start-up when the PWM boost system is connected to a heavy load.
Another aspect of the present invention is to provide a start-up method of a PWM boost system, which limits an inductor current flowing through a boost inductor and enables a comparator during a pre-oscillation period, so as to eliminate an inrush current when the PWM boost system is started up with a light load, and to ensure a successful start-up when the PWM boost system is connected to a heavy load.
The present invention discloses a PWM boost system, which includes a boost circuit including a boost inductor, a voltage dividing circuit, a comparator, a PWM circuit, a pre-oscillator, and a current limit circuit. The boost circuit increases a first voltage to generate a DC output voltage. The voltage dividing circuit uses the DC output voltage to generate a feedback voltage. The comparator is used to compare a reference voltage and the feedback voltage to generate an error voltage. The PWM circuit receives the error voltage to generate a PWM signal to control the boost circuit. The pre-oscillator generates a pre-oscillation signal to the PWM circuit in a pre-oscillation period. The current limit circuit controls an inductor current flowing through the boost inductor. Here, the pre-oscillation period is as the period when the DC output voltage is lower than a first predetermined voltage, and the PWM period is as the period when the DC output voltage is higher than the first predetermined voltage.
The present invention further discloses a start-up method of a PWM boost system, which includes (1) providing an error voltage; (2) generating a PWM signal according to the error voltage; (3) controlling a switch in a boost circuit with the PWM signal, so as to control an inductor current flowing through a boost inductor in the boost circuit; (4) charging a capacitor in the boost circuit with the inductor current, wherein charges stored in the capacitor define a DC output voltage; and (5) providing a feedback voltage according to the DC output voltage to adjust the error voltage. A pre-oscillation period is as the period when the DC output voltage is lower than a first predetermined voltage, a PWM period is the period when the DC output voltage is higher than the first predetermined voltage, and the error voltage is generated during pre-oscillation period by actuation of an enable signal.
The invention will be described according to the appended drawings.
Comparing
The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.
Claims
1. A pulse width modulation (PWM) boost system, comprising:
- a boost circuit comprising a boost inductor, wherein said boost circuit increases a first voltage to generate a DC output voltage;
- a voltage dividing circuit configured to generate a feedback voltage with said DC output voltage;
- a comparator configured to compare a reference voltage with said feedback voltage in a PWM period to generate an error voltage;
- a PWM circuit configured to receive said error voltage to generate a PWM signal to control said boost circuit;
- a pre-oscillator configured to generate a pre-oscillation signal to said PWM circuit in a pre-oscillation period; and
- a current limit circuit configured to control an inductor current flowing through said boost inductor;
- wherein a pre-oscillation period is a period when said DC output voltage is lower than a first predetermined voltage, and wherein a PWM period is a period when said DC output voltage is higher than said first predetermined voltage.
2. The PWM boost system of claim 1, wherein said boost circuit further comprises:
- a switch connected in series with said boost inductor, wherein a turn-on time of said switch is controlled by a PWM signal;
- a diode connected to a connection point of said boost inductor and said switch; and
- a capacitor connected between said diode and a ground terminal to generate the said DC output voltage.
3. The PWM boost system of claim 2, wherein said voltage dividing circuit comprises:
- a first resistor connected to said diode; and
- a second resistor connected between said first resistor and said ground terminal, wherein said feedback voltage is acquired at a connection point of said first resistor and said second resistor.
4. The PWM boost system of claim 1, wherein said DC output voltage has a level increasing with time to a second predetermined voltage in said PWM period following said pre-oscillation period.
5. A start-up method of a PWM boost system, comprising the steps of:
- providing an error voltage;
- generating a PWM signal according to said error voltage;
- controlling a switch in a boost circuit with said PWM signal, so as to control an inductor current flowing through a boost inductor in said boost circuit;
- charging a capacitor in said boost circuit with inductor current, wherein charges stored in the said capacitor define a DC output voltage; and
- providing a feedback voltage according to said DC output voltage to adjust said error voltage;
- wherein a pre-oscillation period is a period when said DC output voltage is lower than a first predetermined voltage, and wherein a PWM period is a period when said DC output voltage is higher than said first predetermined voltage.
6. The start-up method of the PWM boost system of claim 5, wherein the step of adjusting the error voltage comprises the step of comparing the feedback voltage with a reference voltage.
7. The start-up method of the PWM boost system of claim 5, wherein the error voltage is generated by a comparator.
8. The start-up method of the PWM boost system of claim 7, wherein the comparator is enabled by an enable signal in the pre-oscillation period.
9. The start-up method of the PWM boost system of claim 5, wherein the error voltage increases with time during the pre-oscillation period.
10. The start-up method of the PWM boost system of claim 5, wherein the PWM signal is generated according to a pre-oscillation signal during the pre-oscillation period.
11. The start-up method of the PWM boost system of claim 5, wherein the PWM signal is generated according to the error voltage together with a carrier signal inside a PWM circuit during the PWM period.
12. The start-up method of the PWM boost system of claim 5, wherein the DC output voltage increases with time to a second predetermined voltage during the PWM period.
13. The start-up method of the PWM boost system of claim 5, wherein the step of controlling said inductor current comprises:
- sensing said inductor current;
- limiting said inductor current with a current upper limit value; and
- adjusting said PWM signal according to a result of limiting said inductor current.
14. The start-up method of the PWM boost system of claim 13, wherein the current upper limit value is adjusted with time.
Type: Application
Filed: Jan 9, 2007
Publication Date: Mar 20, 2008
Applicant: ADVANCED ANALOG TECHNOLOGY, Inc. (Hsinchu)
Inventors: Yung Ching Chang (Hsinchu), Yen Kuo Lo (Hsinchu), Wen Chia Pi (Hsinchu)
Application Number: 11/621,519
International Classification: G05F 1/00 (20060101);