CN101154885A - Pulse width modulation boosting system and starting method thereof - Google Patents

Abstract

The invention discloses a pulse width modulation boosting system and a starting method thereof. The pulse width modulation boosting system comprises a boosting circuit, a voltage division circuit, a comparator, a pulse width modulation circuit, a front oscillator and a current limiting circuit. The starting method comprises the following steps: (1) providing an error voltage; (2) generating a pulse width modulation signal according to the error voltage; (3) controlling a switch in a boost circuit by the pulse width modulation signal to control an inductive current flowing through a boost inductor in the boost circuit; (4) charging a capacitor in the boost circuit with the inductor current, wherein the stored charge of the capacitor defines a dc output voltage; and (5) providing a feedback voltage to adjust the error voltage according to the direct current output voltage.

Description

Pulse Width Modulation Boost System and Starting Method

technical field

The present invention relates to a pulse width modulation boost system (pulse width modulation boost system) and its starting method, in particular to a pulse width modulation boost system with a current limit soft-start function and its starting method method.

Background technique

1 is a conventional pulse width modulation boost system 1, which includes a boost circuit 10, a pulse width modulation circuit (pulsewidth modulation circuit) 11, a pre-oscillator (pre-oscillator) 12, a comparator 13, A voltage dividing circuit 14 and a stabilizing circuit 15 . 2( a ) and 2 ( b ) are diagrams showing relevant signals when the output voltage V _out of the pulse width modulation boosting system 1 is connected to a light load and a heavy load, respectively. The signals V _out , V _EO1 and I _L1 respectively represent the DC output voltage of the pulse width modulation boosting system 1 , the voltage of the node EO1 connecting the comparator 13 and the pulse width modulation circuit 11 (that is, the error voltage) and An inductor current flowing through a boost inductor L1 in the boost circuit 10 . The stabilization circuit 15 includes a resistor R3 and a capacitor C2 connected in series between the node EO1 and the ground.

Referring to Fig. 2 (a), when the pulse width modulation boost system 1 starts, a reference voltage V _ref is applied to the non-inverting input terminal of the comparator 13, and the inverting input terminal of the comparator 13 is connected from The feedback voltage V _FB of the voltage divider circuit 14 is used to define the magnitude of the DC output voltage V _out . When the DC output voltage V _out is less than a first predetermined voltage V _uvlo (undervoltage lockout voltage) (i.e. the previous oscillation period), the front oscillator 12 outputs a front oscillation signal S _OSC to the pulse width modulation circuit 11 to Generate a pulse width modulation signal S _PWM . Note that in the pre-oscillation period, the comparator 13 does not output a signal (that is, the level of V _EO1 is 0). The pulse width modulation signal S _PWM is used to change the turn-on or turn-off time of the switch SW1, so that the inductor current I L1 generated by the first voltage V _in and flowing through the boost inductor _L1 can charge the capacitor C1 intermittently, And the charges stored in the capacitor C1 generate the DC output voltage V _out . The diode D1 limits the discharge direction of the capacitor C1. After entering the pulse width modulation period, the DC output voltage V _out remains at the first predetermined voltage V _uvlo for a period of time. When the DC output voltage V _out increases upwards, an inrush current (inrush current) will be generated along with the inductor current _IL1 ; when the DC output voltage V _out rises to a second predetermined voltage V _ref ×DIV( Wherein, DIV=(R1+R2)/R2), the inductor current _IL1 drops.

Referring to Figure 2(b), the operation in the pre-oscillation period is the same as that in Figure 2(a). However, after the current oscillation period is over, because the output of the PWM boost system 1 is connected to a heavy load, the signal V _EO1 is continuously switched between the two operation modes of the previous oscillation period and the PWM period, and cannot be used The PWM circuit 11 generates an appropriate PWM signal S _PWM . As a result, the DC output voltage V _out has been oscillating near the first predetermined voltage V _uvlo , but cannot reach the second predetermined voltage V _ref ×DIV (that is, the pulse width modulation boosting system 1 cannot be started smoothly ).

Contents of the invention

The purpose of the present invention is to provide a pulse width modulation boost system (pulse width modulation boost system), by adding a current limiting circuit and a comparator that cooperates with an enable signal (enable signal) to start in a pre-oscillation period to eliminate Inrush current at light load startup and smooth startup when connected to heavy load.

Another object of the present invention is to provide a start-up method of a pulse-width modulated boost system, by limiting the inductor current flowing through a boost inductor and starting a comparator in the pre-oscillation period to eliminate the inrush current and enables smooth start-up when the connection is heavily loaded.

In order to achieve the above object, the present invention discloses a pulse width modulation boost system, which includes a boost circuit including a boost inductor, a voltage divider circuit, a comparator, a pulse width modulation circuit, a pre-oscillator and a current limiting circuit. The boost circuit boosts 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 for comparing a reference voltage and the feedback voltage to generate an error voltage. The pulse width modulation circuit receives the error voltage to generate a pulse width modulation signal to control the boost circuit. The pre-oscillator generates a pre-oscillation signal to the pulse width modulation circuit during a pre-oscillation period. The current limiting circuit controls an inductor current through the boost inductor. The pre-oscillation period is defined when the DC output voltage is lower than a first predetermined voltage, and a pulse width modulation period is defined when the DC output voltage is greater than the first predetermined voltage.

The present invention further discloses a method for starting a pulse width modulation boosting system, which includes the following steps: (1) providing an error voltage; (2) generating a pulse width modulation signal according to the error voltage; (3) passing the The pulse width modulation signal controls a switch in a boost circuit to control an inductor current passing through a boost inductor in the boost circuit; (4) using the inductor current to control a boost circuit in the boost circuit charging a capacitor, wherein the stored charge of the capacitor defines a DC output voltage; and (5) providing a feedback voltage to adjust the error voltage according to the DC output voltage. The period when the DC output voltage is less than a first predetermined voltage is defined as a pre-oscillation period, and the period when the DC output voltage is greater than the first predetermined voltage is defined as a pulse width modulation period and the error voltage The generation is enabled by an enable signal during the pre-oscillation period.

Description of drawings

Fig. 1 is a conventional pulse width modulation boosting system;

Figures 2(a) and 2(b) are diagrams showing the relevant signals when the output voltage of Figure 1 is connected to a light load and a heavy load respectively;

Fig. 3 is a schematic diagram of the pulse width modulation boosting system of the present invention;

4(a) and 4(b) are diagrams showing relevant signals when the output voltage of FIG. 3 is connected to a light load and a heavy load, respectively; and

FIG. 5 is a flow chart of the starting method of the pulse width modulation boosting system 2 in FIG. 3 .

Detailed ways

FIG. 3 is a schematic diagram of the pulse width modulation boosting system 2 of the present invention. 4( a ) and 4 ( b ) are diagrams showing relevant signals when the output voltage V _out of the pulse width modulation boosting system 2 of the present invention is connected to a light load and a heavy load, respectively. The pulse width modulation boost system 2 includes a boost circuit 20 comprising a boost inductor L2, a voltage divider circuit 24, a comparator 23, a pulse width modulation circuit 21, a pre-oscillator 22, a current limiting circuit 26 and a stabilization circuit 27. The boost circuit 20 includes a boost inductor L2 connected to a first voltage V _in , a switch SW2 connected in series with the boost inductor L2, and a diode connected to the boost inductor L2 and the switch SW2 D2 and a capacitor C3 connected between the diode D2 and a ground terminal. The charge stored in the capacitor C3 is used to generate the DC output voltage V _out . The boost circuit 20 intermittently charges the capacitor C3 by controlling the conduction time of the switch SW2 to boost the first voltage V _in to generate a DC output voltage V _out . In this embodiment, the voltage dividing circuit 24 includes a first resistor R4 connected to the diode D2 and a second resistor R5 connected between the first resistor R4 and the ground. The voltage dividing circuit 24 utilizes the DC output voltage V _out to generate a feedback voltage V _FB . When the DC output voltage V _out is less than a first predetermined voltage (that is, in the previous oscillation period), an enabling signal ENABLE activates the comparator 23 to compare a reference voltage V _ref and the feedback voltage V _FB to generate An error voltage V _EO2 (that is, the voltage of the node EO2 ). The pulse width modulation circuit 21 receives the error voltage V _EO2 to generate a pulse width modulation signal S _PWM to control the boost circuit 20 . The pre-oscillator 22 generates a pre-oscillation signal S _OSC to the PWM circuit 21 during a pre-oscillation period. The current limiting circuit 26 controls an inductor current I _L2 flowing through the boost inductor L2 . The stabilization circuit 27 includes a resistor R6 and a capacitor C4 connected in series between the node EO2 and the ground. The period when the DC output voltage V _out is less than the first predetermined voltage (undervoltage lockout voltage, V _uvlo in this example) is defined as the pre-oscillation period, and when the DC output voltage V _out is greater than the The period of the first predetermined voltage is defined as a pulse width modulation period.

FIG. 5 is a flow chart of the starting method of the pulse width modulation boosting system 2 in FIG. 3 . Firstly, an error voltage V _EO2 is provided (step S10 ). 4(a) and 4(b), during the pre-oscillation period, the enable signal ENABLE starts the comparator 23 to generate the error voltage V _EO2 ; meanwhile, the pre-oscillator 22 also generates a pre-oscillation signal S _OSC . The pulse width modulation circuit 21 generates a pulse width modulation signal S _PWM according to the pre-oscillating signal S _OSC (step S20 ). The pulse width modulation signal S _PWM controls the conduction time of the switch SW2 in the boost circuit 20 to control the inductor current I _L2 passing through a boost inductor L2 in the boost circuit 20 (step S30 ). Next, use the inductor current _IL2 to charge a capacitor C3 in the boost circuit 20, wherein the charge stored in the capacitor C3 defines the DC output voltage V _out (step S40). When the DC output voltage V _out is greater than the first predetermined voltage V _uvlo (that is, enters the pulse width modulation period), the inductor current I _L2 also increases accordingly. At this time, the current limiting circuit 26 uses the node S to sense the inductor current I _L2 , then limits the inductor current I _L2 with a current upper limit, and finally transmits a control signal Crt according to the result of limiting the inductor current I _L2 Go back to the pulse width modulation circuit 21 to adjust the pulse width modulation signal S _PWM . Note that during the PWM period, the PWM signal S _PWM is generated according to the error voltage V _EO2 and a carrier signal inside a PWM circuit 21 . Wherein the upper limit of the current can be adjusted with time. In this embodiment, the current upper limit is stepwise increasing until a rated current upper limit. According to the DC output voltage V _out , the voltage dividing circuit 24 provides a feedback voltage V _FB to the comparator 23 for comparison with the reference voltage V _ref to adjust the error voltage V _EO2 (step S50 ).

Comparing Figures 4(a) and 2(a) and Figures 4(b) and 2(b) respectively, the DC output voltage generated by the pulse width modulation boosting system of the present invention, whether it is connected to a light load or a heavy load In the case of , it can be increased to a second predetermined voltage with time in the pre-oscillation period and the pulse width modulation period, and there is no situation in which the DC output voltage stagnates at the first predetermined voltage (see Figure 2(a)) Or the case of oscillation around the first predetermined voltage (refer to FIG. 2(b)) occurs. In addition, through the use of the current limiting circuit, the generation of inrush current can be effectively reduced. Therefore, the pulse width modulation boosting system and its starting method of the present invention can indeed achieve the expected purpose of eliminating the inrush current during light load starting and smooth starting under heavy load.

The technical content and technical features of the present invention have been disclosed above, but those skilled in the art may still make various substitutions and modifications based on the teaching and disclosure of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to the contents disclosed in the embodiments, but should include various replacements and modifications that do not depart from the present invention, and should be covered by the appended claims.

Claims (14)

1. A pulse width modulation boosting system, characterized in that it comprises: A boost circuit, including a boost inductor, the boost circuit boosts a first voltage to generate a DC output voltage; A voltage divider circuit, using the DC output voltage to generate a feedback voltage; a comparator for comparing a reference voltage and said feedback voltage during a pulse width modulation period to generate an error voltage; a pulse width modulation circuit, receiving the error voltage to generate a pulse width modulation signal to control the boost circuit; a pre-oscillator for generating a pre-oscillation signal to the pulse width modulation circuit during a pre-oscillation period; and a current limiting circuit, controlling an inductor current passing through the boost inductor; The period when the DC output voltage is lower than a first predetermined voltage is defined as the pre-oscillation period, and the period when the DC output voltage is greater than the first predetermined voltage is defined as the pulse width modulation period. 2. The pulse width modulation boosting system according to claim 1, wherein the boosting circuit further comprises: a switch connected in series with the boost inductor, the conduction time of the switch is controlled by the pulse width modulation signal; a diode connected to the junction of the boost inductor and the switch; and A capacitor is connected between the diode and a ground terminal to generate the DC output voltage. 3. The pulse width modulation boosting system according to claim 2, wherein the voltage divider circuit comprises: a first resistor connected to the diode; and A second resistor connected between the first resistor and the ground terminal, wherein the feedback voltage is obtained from a junction of the first resistor and the second resistor. 4. The pulse width modulated boost system of claim 1, wherein the level of the DC output voltage increases over time to a first Two predetermined voltages. 5. A starting method of a pulse width modulation boosting system, characterized in that it comprises the following steps: providing an error voltage; generating a pulse width modulation signal according to the error voltage; controlling a switch in a boost circuit by the pulse width modulation signal to control an inductor current flowing through a boost inductor in the boost circuit; using the inductor current to charge a capacitor in the boost circuit, wherein the stored charge of the capacitor defines a DC output voltage; and providing a feedback voltage to adjust the error voltage according to the DC output voltage; The period when the DC output voltage is lower than a first predetermined voltage is defined as a pre-oscillation period, and the period when the DC output voltage is greater than the first predetermined voltage is defined as a pulse width modulation period. 6. The start-up method of the PWM boost system as claimed in claim 5, wherein the step of adjusting the error voltage is to compare the feedback voltage with a reference voltage. 7. The start-up method of the PWM boost system according to claim 5, wherein the error voltage is generated by a comparator. 8 . The start-up method of the PWM boost system as claimed in claim 7 , wherein the comparator is started by an enable signal during the pre-oscillation period. 9 . 9. The start-up method of a PWM boost system according to claim 5, wherein the error voltage rises with time during the pre-oscillation period. 10. The start-up method of a PWM boost system as claimed in claim 5, wherein the PWM signal is generated according to a pre-oscillation signal in the pre-oscillation period. 11. The start-up method of the pulse width modulation boosting system according to claim 5, characterized in that the pulse width modulation signal is based on the error voltage in the pulse width modulation period and cooperates with a pulse width modulation circuit internal generated by a carrier signal. 12 . The start-up method of a PWM boost system according to claim 5 , wherein the DC output voltage rises to a second predetermined voltage with time during the PWM period. 13 . 13. The starting method of the pulse width modulation boosting system according to claim 5, wherein the step of controlling the inductor current comprises the following steps: sensing the inductor current; limiting the inductor current with an upper current limit; and The pulse width modulation signal is adjusted according to the result of limiting the inductor current. 14. The start-up method of the PWM boost system according to claim 13, characterized in that the upper limit of the current can be adjusted with time.

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