CN101154884A - Current mode pulse width modulation booster circuit and feedback signal sensing method thereof - Google Patents

Abstract

The feedback signal sensing method of the present invention comprises the steps of: providing a pulse width modulation signal with a period; (b) charging a capacitor through a current source during the pulse duration of the period to form an equivalent slope compensation ramp signal; (c) in the pulse duration of the period, enabling an inductive current flowing through a boost inductor to flow through an equivalent resistor to form an equivalent inductive current signal; and (d) utilizing the coupling characteristic of the capacitor and matching the equivalent slope compensation ramp signal and the equivalent inductor current signal to form a feedback signal.

Description

Current Mode Pulse Width Modulation Boost Circuit and Its Feedback Signal Sensing Method

technical field

The present invention relates to a current mode pulse width modulation boost circuit (current mode pulse width modulation boost circuit) and its feedback signal sensing method, specifically relates to a direct sensing inductor current (inductor current) and slope compensation ramp signal ( A current mode pulse width modulation boost circuit with slope compensation ramp signal) function and its feedback signal sensing method.

Background technique

1 is a conventional current mode pulse width modulation boost circuit 10, which includes a boost unit 11, a voltage divider circuit 19, an error amplifier 12, a comparator 13, and an inductor current generator (inductor current generator) 14. A slope compensation ramp generator 15, an oscillator 16, a pulse width generator 17 and a buffer 18. A voltage V _IN is boosted by the boost unit 11 to generate a higher DC output voltage V _OUT . The boost unit 11 includes an input capacitor C1, a boost inductor L, a MOS transistor T, a rectifier diode D and an output capacitor C2. The input capacitor C1 is used to filter out the ripple voltage of the voltage V _IN . When the MOS transistor T is in the conduction state and the rectifier diode D is reverse biased, the current will flow forward through the boost inductor L, and the voltage of the boost inductor L will rise; however, the current Instead of flowing through the boost inductor L instantaneously, it increases linearly, thus creating an electromagnetic field. At this time, when the MOS transistor T is in the conduction state, the output current is completely provided by the output capacitor C2. When the MOS transistor T is in the cut-off state, the boost inductor L can no longer store energy, so the electromagnetic field stored in the boost inductor L will be released; at this time, the boost inductor The polarity of the voltage on L will be reversed, so that the boost inductor L releases its stored energy to the output capacitor C2, and at the same time, the rectifier diode D is connected to one end of the boost inductor L (ie node N3) obtains a voltage higher than the voltage V _IN , this energy provides a load current and recharges the output capacitor C2 at the same time. The voltage dividing circuit 19 is composed of two series resistors R1 and R2. A divided voltage V _F1 is obtained from a node N2 connected to the resistors R1 and R2 , sent to the error amplifier 12 for comparison with a reference voltage V _REF to generate an error signal EO. Then, the error signal EO is compared with a feedback signal V _SUM by the comparator 13 . The output of the comparator 13 (ie, V _F2 ) is input to the pulse width generator 17 together with an oscillation signal S1 from the oscillator 16 . A driving signal S _DR generated by the pulse width generator 17 is then passed through a gate control signal S _G generated by the buffer 18 to adjust the conduction time of the MOS transistor T (that is, to adjust the driving signal S _DR pulse duration (pulse duration)), and then control the DC output voltage V _OUT .

The inductor current generator 14 receives a voltage signal V _SEN from the node N3, and generates it through an internal voltage conversion current mechanism (for example, through a resistor or a transconductance amplifier). An inductor current _ISEN passing through the boost inductor L. 2( a ) to 2 ( c ) illustrate different pick-up points N31 , N32 and N33 of the voltage signal VSEN in the conventional technology. Although the acquisition method of the voltage signal V _SEN in FIG. 2( a ) is more accurate than the other two methods, it consumes more power. 2( b ) and 2( c ) have the advantage of being lossless compared to _FIG . 2( a ), but have the problems of low accuracy and matching respectively. And after the voltage signal V _SEN is acted on by the inductor current generator 14 , the inductor current I _SEN will easily cause distortion. In addition, the purpose of the slope compensation ramp generator 15 is to solve the duty cycle of the driving signal S _DR when it operates in the continuous conduction mode (continuous conduction) in the current mode converters (current mode converters). When it is greater than 50%, problems such as open-loop instability, sub-harmonicoscillation, and noise sensitivity are generated. The slope compensation slope generator 15 receives an oscillation signal S2 from the oscillator 16, and generates a slope compensation slope signal I _SLO after an internal voltage conversion current mechanism (such as a transconductance amplifier) acts on it. . Likewise, the slope compensation ramp signal 1 _SLO is easily distorted by the slope compensation ramp generator 15 . Finally, the inductor current I _SEN and the slope compensation ramp signal I _SLO flow through a resistor R _f to generate the feedback signal V _SUM at a node N1 .

Contents of the invention

One aspect of the present invention provides a current mode pulse width modulation boost circuit, through a feedback signal generation unit including a current source and a capacitor, directly measure the inductor current and the first class of the current mode pulse width modulation boost circuit An effective slope compensation ramp signal (equivalent slope compensation ramp signal) is used to form a feedback signal and adjust a DC output voltage, thereby reducing the signal distortion caused by measuring the inductor current and generating the slope compensation ramp signal in the conventional technology.

Another aspect of the present invention provides a feedback signal sensing method applied in a current-mode pulse width modulation boost circuit, by directly measuring the inductor current flowing through the boost inductor in the boost circuit and through a current source pair An equivalent slope compensation ramp signal formed by a slope characteristic of capacitor charging is used to generate a feedback signal and adjust a DC output voltage.

The invention discloses a current mode pulse width modulation boost circuit, which includes a boost unit, a voltage divider circuit, an error amplifier, a comparator, a pulse width generator and a feedback signal generation unit. The boost unit includes a boost inductor and a switch, and the boost unit boosts a voltage to generate a DC output voltage. The voltage dividing circuit generates a divided voltage by using the DC output voltage. The error amplifier compares a reference voltage with the divided voltage to generate an error signal. The comparator compares the error signal with a feedback signal to generate a first signal. The pulse width generator receives the first signal and a second signal from an oscillator to generate a third signal, wherein the third signal is used to control the switch. The feedback signal generating unit is coupled to the boost unit to generate the feedback signal, wherein the feedback signal includes an equivalent inductor current signal passing through the boost inductor and an equivalent slope compensation ramp signal.

The present invention further discloses a feedback signal sensing method applied to a current mode pulse width modulation boost circuit, which includes the following steps: (a) providing a pulse width modulation signal with a period (period); (b) in In a pulse duration (pulse duration) of the cycle, charge a capacitor through a current source to form an equivalent slope compensation ramp signal; (c) during the pulse duration, make a current flow through a boost The inductance current of the inductor flows through an equivalent resistance to form an equivalent inductance current signal; and (d) utilizing the coupling characteristics of the capacitance and cooperating with the equivalent slope compensation ramp signal and the equivalent inductance current signal to form a feedback signal. In an embodiment of the present invention, the feedback signal is obtained from a junction between the current source and the capacitor.

The current mode pulse width modulation boost circuit of the present invention directly measures the inductor current and uses the feedback signal generating unit to directly generate the equivalent slope compensation ramp signal, and does not involve a voltage-to-current transfer structure ), so compared with the conventional technique, the present invention has the following advantages: (1) reduces the distortion of the feedback signal; (2) has a preferred reaction rate because of the direct measurement and generation of the signal; (3) can dispense with the conventional technique The problem of open loop stability.

Description of drawings

Fig. 1 conventional current mode pulse width modulation boost circuit;

Figures 2(a)-2(c) illustrate different acquisition points of conventional technology voltage signals; and

FIG. 3 is a current mode PWM boost circuit according to an embodiment of the present invention.

Detailed ways

3 is a current mode pulse width modulation boost circuit 20 according to an embodiment of the present invention, which includes a boost unit 21, a voltage divider circuit 29, an error amplifier 22, a comparator 23, a pulse width generator 27, A buffer 28 and a feedback signal generation unit 24 . The boost unit 21 includes a boost inductor L', a MOS transistor T', a rectifier diode D' connected to the junction P1 of the boost inductor L' and the MOS transistor T', and a filter An input capacitor C3 that drops the ripple voltage of the voltage V _IN and an output capacitor C5 connected between the rectifier diode D' and a ground terminal, wherein the output capacitor C5 is used to generate a DC output voltage V _OUT . The voltage dividing circuit 29 utilizes the DC output voltage V _OUT to generate a divided voltage V _F3 . The voltage divider circuit 29 includes a first resistor R3 connected to the rectifier diode D' and a second resistor R4 connected between the first resistor R3 and the ground terminal, wherein the divided voltage V _F3 is obtained from a node P3 connecting the first resistor R3 and the second resistor R4. The error amplifier 22 compares a reference voltage V _REF with the divided voltage V _F3 to generate an error signal E′O. The comparator 23 compares the error signal E′O with a feedback signal V′ _SUM to generate a signal V _F4 . The pulse width generator 27 receives the signal V _F4 and a signal S _OSC from an oscillator 26 to generate a signal S′ _DR , wherein the signal S′ _DR is used to control the MOS transistor T′. The buffer 28' is optional, and it increases the driving capability of the signal _S'DR to form a gate control signal _S'G to control the MOS transistor T'. The feedback signal generation unit 24 is coupled to the boost unit 21 to generate the feedback signal V' _SUM , wherein the feedback signal V' _SUM includes an equivalent inductor current signal ( not shown) and an equivalent slope compensation ramp signal (not shown). The feedback signal generating unit 24 includes a capacitor C4 and a current source I _s connected in series with the capacitor C4 . One end of the capacitor C4 is coupled to the junction P1 of the boost inductor L′ and the MOS transistor T′. The current source Is is coupled to the other end of the capacitor C4.

The method of generating the feedback signal V' _SUM of the current mode pulse width modulation boost circuit 20 of the embodiment of FIG. 3 is different from that of the current mode pulse width modulation boost circuit 10 of FIG. 1 , and the present invention will be described in detail below. The sensing method of the feedback signal V′ _SUM is described above.

When the MOS transistor T' is turned on, the inductor current IL' generated by the voltage V _IN and flowing through the boost inductor L' will flow to the ground through the turned-on MOS transistor T'. A potential V' _SEN formed by the inductor current IL' at the node P1 can be obtained by the following formula (1):

V′ _SEN ＝V _IN ×DTs×Rds/L (1)

Where DTs represents the pulse duration of the fourth signal S' _DR (that is, the time when the MOS transistor T' is turned on), Rds represents the resistance when the MOS transistor T' is turned on and L represents the boost The inductance value of the inductor L'. Because the potential V' _SEN contains information about the inductor current IL', it is also called an equivalent inductor current signal, which is connected to the voltage V _IN , the boost inductor L', and the MOS transistor T'. The on-time resistance Rds is related to a duty cycle of the pulse width generator. In addition, the current source I _s charges the capacitor C4 when the MOS transistor T' is turned on, so a potential difference V _SLO will be established between the nodes P1 and P2, which can be obtained by the following equation (2): ,

V _SLO =I _s ×DTs/C (2)

Wherein DTs represents the pulse duration of the fourth signal S′ _DR (ie, the time when the MOS transistor T′ is turned on), and C represents the capacitance value of the capacitor C4 . Because the potential difference V _SLO contains information related to the slope compensation ramp signal (ie, the slope characteristic exhibited by the capacitor C4 is similar to the third signal S _OSC generated by the oscillator 26 when charging the capacitor C4 ), Therefore, it is also called an equivalent slope compensation ramp signal, which is related to the duty cycle of the current source I _s , the capacitor C4 and the pulse width generator 27 . Therefore, by utilizing the coupling characteristics of the capacitor C4, the feedback signal V′ _SUM obtained from the node P2 is the sum of the equivalent inductor current signal and the equivalent slope compensation ramp signal. That is to say,

V' _SUM ＝V' _SEN +V _SLO ＝V _IN ×DTs×Rds/L+I _s ×DTs/C

＝(V _tN ×Rds/L+I _s /C)×DTs (3)

(V _IN ×Rds/L+I _s /C) in the formula (3) has a characteristic of a fixed slope.

It can be seen from the above description that the current mode PWM boost circuit and its feedback signal sensing method of the present invention directly measure the current mode PWM boost circuit through a feedback signal generation unit including a current source and a capacitor. The inductance current inside the voltage circuit is directly converted into an equivalent inductance current signal; at the same time, an equivalent slope compensation ramp signal with slope characteristics is directly generated by using the current source to charge the capacitor, and directly in the current source The connection point with the capacitor forms a feedback signal. Therefore, the present invention has the advantages of (1) reducing the distortion of the feedback signal; (2) having a better reaction rate; and (3) avoiding the open loop stability problem compared with the conventional technology.

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 substitutions and modifications that do not depart from the present invention, and should be covered by the appended claims.

Claims (18)

1. A feedback signal sensing method, which is applied to a current mode pulse width modulation boost circuit, is characterized in that it comprises the following steps: (a) providing a pulse width modulated signal having a period; (b) charging a capacitor through a current source during a pulse duration of the cycle to form an equivalent slope compensation ramp signal; (c) causing an inductor current passing through a boost inductor to flow through an equivalent resistance for the duration of said pulse to form an equivalent inductor current signal; and (d) Utilizing the coupling characteristic of the capacitor and cooperating with the equivalent slope compensation ramp signal and the equivalent inductor current signal to form a feedback signal. 2. The feedback signal sensing method according to claim 1, wherein the pulse width modulation signal is used to turn on a switch inside the current mode pulse width modulation boost circuit during the pulse duration . 3. The feedback signal sensing method according to claim 2, wherein the switch is a MOS transistor. 4. The feedback signal sensing method according to claim 1, wherein the equivalent slope compensation ramp signal is a voltage signal and is defined by the following formula: I _s ×DT _s /C Wherein I _s represents the current of the current source, DT _s represents the duration of the pulse, and C represents the capacitance of the capacitor. 5. The feedback signal sensing method according to claim 1, wherein the equivalent slope compensation ramp signal is a potential difference across the capacitor. 6. The feedback signal sensing method according to claim 1, wherein the equivalent resistor is a MOS transistor in an on state. 7. The feedback signal sensing method according to claim 1, wherein the equivalent inductor current signal is a voltage signal and is defined by the following formula: V _IN ×DT _s ×Rds/L Where V _IN is a voltage of a voltage source that generates the inductor current, DT _s represents the pulse duration, Rds represents the equivalent resistance, and L represents the inductance of the boost inductor. 8. The feedback signal sensing method according to claim 1, wherein the feedback signal is the sum of the equivalent slope compensation ramp signal and the equivalent inductor current signal. 9. The feedback signal sensing method according to claim 1, wherein the feedback signal is obtained from a junction between the current source and the capacitor. 10. A current mode pulse width modulation boost circuit, characterized in that it comprises: A boost unit, including a boost inductor and a switch, the boost circuit boosts a voltage to generate a DC output voltage; A voltage divider circuit, which generates a divided voltage using the DC output voltage; an error amplifier, which compares a reference voltage with the divided voltage to generate an error signal; a comparator, which compares the error signal with a feedback signal to generate a first signal; a pulse width generator receiving the first signal and a second signal from an oscillator to generate a third signal, wherein the third signal is used to control the switch; and A feedback signal generating unit coupled with the boost unit to generate the feedback signal, wherein the feedback signal includes an equivalent inductor current signal passing through the boost inductor and an equivalent slope compensation ramp signal. 11. The current mode pulse width modulation boost circuit according to claim 10, characterized in that the boost unit further comprises: a rectifier diode connected to the junction of the boost inductor and the switch; and An output capacitor is connected between the diode and a ground terminal to generate the DC output voltage. 12. The current mode pulse width modulation boost circuit according to claim 11, characterized in that the voltage divider circuit comprises: a first resistor connected to the rectifier diode; and A second resistor connected between the first resistor and the ground terminal, wherein the divided voltage is obtained from the junction of the first resistor and the second resistor. 13. The current mode pulse width modulation boost circuit according to claim 10, further comprising a buffer connected to the output terminal of the pulse width generator for boosting the third signal drive capability to control the switch. 14. The current mode pulse width modulation boost circuit according to claim 10, characterized in that the feedback signal generating unit comprises: a capacitor having one end coupled to the junction of the boost inductor and the switch; and A current source is coupled to the other terminal of the capacitor. 15. The current-mode PWM boost circuit according to claim 14, wherein the equivalent slope compensation ramp signal is generated by charging the capacitor when the switch is turned on by the current source. 16. The current mode pulse width modulation boost circuit according to claim 14, characterized in that the equivalent slope compensation ramp signal is related to a duty cycle of the current source, the capacitor and the pulse width generator . 17. The current mode pulse width modulation boost circuit according to claim 10, wherein the equivalent inductor current signal is a voltage signal and is related to the resistance value when the switch is turned on. 18. The current mode pulse width modulation boost circuit according to claim 10, characterized in that the equivalent inductor current signal is a voltage signal, which is connected to the voltage, the boost inductor, and the switch When the resistance value is related to the duty cycle of the pulse width generator.

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