JP2006033958A - Switching regulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To overcome the problem that the quantity of a slope compensation is not correct since the quantity of the slope compensation outputted from a slope compensating circuit is fixed although an increase rate and a decrease rate of a coil current changes in accordance with changes in an input voltage and an output voltage in a conventional current mode switching regulator requiring the correct quantity of the slope compensation for preventing a subharmonic oscillation. <P>SOLUTION: The current mode switching regulator variably changes the quantity of the slope compensation outputted from the slope compensating circuit in response to the input/output voltages VIN/VOUT, calculates the correct slope compensation from the input/output voltage VIN/VOUT, and always maintains the correct quantity of the slope compensation by changing the quantity of the slope compensation outputted from the slope compensating circuit in proportion to a calculated result even if the input voltage VIN and the output voltage VOUT change. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a current mode switching regulator that changes the amount of slope compensation in accordance with an input voltage and an output voltage.

  As a conventional current mode step-up switching regulator, a circuit as shown in the block diagram of FIG. 4 is known.

  When the switch 107 is turned on, the input voltage VIN is accumulated in the coil 108, and when the switch 107 is turned off, the energy accumulated in the coil 108 is transferred to the output capacitor 112 via the diode 109.

  The error amplifier 101 amplifies the difference between the voltage obtained by dividing the output voltage VOUT by the resistors 110 and 111 as feedback resistors and the reference voltage VREF supplied from the reference voltage source 100. The slope compensation circuit 102 generates a sawtooth compensation ramp wave that is synchronized with the output signal of the oscillator 104, and is input to one input terminal of the adder 103.

  Information on the current flowing through the switch 107 or information obtained by converting the information on the current flowing through the coil 108 into a voltage is input to the other input terminal of the adder 103. Normally, a current flowing through each element is detected using a sense resistor connected in series with the switch 107 or the coil 108, and a value proportional to the current flowing through the switch 107 or the coil 108 is input to the input terminal of the adder 103 as voltage information. Is done.

  The output signal of the error amplifier 101 is input to the inverting input terminal of the comparator 105, and the output signal of the adder 103 is input to the non-inverting input terminal. When the output voltage VOUT is low, the output of the error amplifier 101 rises. Therefore, in order for the state of the comparator 105 to transition from L to H, a larger value needs to be applied to the non-inverting input terminal of the comparator 105. That is, when the output voltage VOUT is low, the output of the comparator 105 is inverted by passing a large amount of current through the switch 107 or the coil 108. The output of the comparator 105 is input to the reset terminal R of the SR-latch 106.

An oscillator 104 is connected to the set terminal S of the SR-latch 106, and a pulse having a constant period is output from the oscillator 104 as shown in the figure. The output terminal Q of the SR-latch 106 is connected to the switch 107. When the output terminal Q of the SR-latch 106 is H, the switch 107 is turned on (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-41924

  In the current mode switching regulator, “Characteristics of DC-DC Converter with Peak Current Control”, IEICE Transactions '86 / 4 Vol. J69-C No. As indicated by Kosuke Harada et al. In 4 pp 487-494, the ratio of the period during which the inductor current rises with respect to the clock cycle, that is, when the duty exceeds 50%, the duty of the current mode switching regulator changes periodically. It becomes unstable (sub harmonic oscillation state).

  Furthermore, Harada et al. Point out that in order to prevent subharmonic oscillation, it is necessary to perform an appropriate amount of slope compensation for the rate of increase and decrease of the coil current. In the current mode step-up switching regulator of FIG. 3, a slope compensation value necessary for preventing subharmonic oscillation is obtained.

That is, when the switch 107 is ON, the current increase rate m1 of the coil 108 is as follows: m1 = VIN / L (1) where the inductance of the coil 108 is L and the input voltage of the switching regulator is VIN.
When the switch 107 is OFF, the current reduction rate m2 of the coil 108 is approximately m2 = (VOUT−VIN) / L (2) when the voltage drop due to the diode 109 is ignored.
It becomes.

(1) From equation (2), the slope compensation value m required to prevent subharmonic oscillation at the input voltage VIN and output voltage VOUT is m ≧ (m2−m1) / 2 = (VOUT−2VIN) / (2L (3)
It becomes.

  However, in the conventional current mode step-up switching regulator shown in FIG. 3, since the rate of increase of the compensation ramp wave, which is the amount of slope compensation output from the slope compensation circuit, is constant, the input voltage VIN and the output voltage VOUT are generally considered. It is necessary to set the maximum slope compensation value in the range. However, in this case, the slope compensation value is usually a large value, and there is a problem that the characteristics of the switching regulator in the current mode are impaired by the large slope compensation value.

  In order to solve the above problem, in the present invention, the slope compensation amount output from the slope compensation circuit is changed according to the input voltage and the output voltage.

By changing the increasing rate of the compensation ramp wave, which is the amount of slope compensation output from the slope compensation circuit, to be proportional to the function of the input voltage VIN and the output voltage VOUT, the input voltage VIN and the output voltage VOUT change. However, it is possible to construct a current mode switching regulator that always maintains an appropriate amount of slope compensation.

  Embodiments of the present invention will be described below with reference to the drawings of the embodiments.

FIG. 1 is a block diagram of a current mode step-up switching regulator according to a first embodiment of the present invention. By adding a slope compensation value calculation circuit 130 that outputs an appropriate slope compensation value from the input voltage VIN and the output voltage VOUT to the conventional current mode step-up switching regulator shown in FIG. 3, the slope compensation circuit 102 is made slope compensation. The increase rate of the compensation ramp wave according to the output of the value calculation circuit 130 is set. The slope compensation value calculation circuit 130 includes an addition / subtraction circuit including resistors 120, 121, 123, and 124 and an amplifier 122.
Hereinafter, a case where the slope compensation value calculation circuit 130 outputs a slope compensation value corresponding to the input voltage VIN and the output voltage VOUT will be described in detail.
When the resistance values of the resistors 120, 121, 123, and 124 are R120, R121, R123, and R124, respectively, the output voltage VC of the amplifier 122 is VC = {(R123) / (R123 + R124)} × {(R120 + R121) /
(R120)} (VOUT)-{(R124 / R120)} (VIN)
... (4)
It becomes. Regarding the resistance values of the resistors 120, 121, 123, and 124, R123 + R124 = R120 + R121 (5)
R123 = R121 / 2 (6)
(5) If it sets so that Formula (6) may be satisfy | filled, Formula (4) will be VC = {(R121) / (2 * R120)} (VOUT) -2 (VIN).
Thus, the output of the slope compensation value calculation circuit 130 is an output proportional to (VOUT−2VIN).

On the other hand, the minimum slope compensation value m required to prevent subharmonic oscillation of the current mode boost switching regulator is
m = (VOUT−2VIN) / (2L) (7)
And is proportional to (VOUT-2VIN). Therefore, the slope compensation value calculation circuit 130 is configured so that the slope compensation value m is proportional to (VOUT−2VIN), thereby maintaining the minimum slope compensation that does not cause subharmonic oscillation for any input voltage VIN and output voltage VOUT. A current mode step-up switching regulator can be configured.

  FIG. 2 is a block diagram of a current mode step-up switching regulator according to the second embodiment of the present invention. The present embodiment is the same as the first embodiment except that the number of resistance elements is reduced by sharing the voltage dividing resistors, resistors 123 and 124 and the feedback resistor resistors 110 and 111 of the slope compensation value calculation circuit 130.

In the above, the case where the current mode step-up switching regulator is applied has been described. However, when the current mode step-down switching regulator is applied, the current increase rate m1 and the current decrease rate m2 of the coil are m1 = (VIN−VOUT) / L, respectively. ... (8)
m2 = VOUT / L (9)
Therefore, the appropriate slope compensation value m is m = (m2−m1) / 2 = (2VOUT−VIN) / (2L) (10)
It becomes.

Similarly, when applied to a current mode inversion switching regulator, m1, m2 and m are: m1 = VIN / L (11)
m2 = VOUT / L (12)
m = (m2-m1) / 2 = (VOUT-VIN) / (2L) (13)
Given in.

  Therefore, the same applies to the current mode step-down switching regulator and the current mode inversion switching regulator by appropriately setting the resistance values of the voltage dividing resistor, resistors 123 and 124 and the feedback resistor resistors 110 and 111 of the slope compensation value calculation circuit 130. It is clear that can be adapted to.

  In FIG. 1, a signal obtained by adding a voltage ramp wave whose slope is proportional to the coil current signal or switch current signal converted into a voltage signal by the slope compensation circuit 102 and the adder 103 and the input voltage VC of the slope compensation circuit is not applied to the comparator 105. It is necessary to input to the inverted voltage input terminal.

  FIG. 3 shows an example of a circuit for generating a signal obtained by adding a coil ramp signal or a switch current signal converted into a voltage signal and a voltage ramp wave having a slope proportional to the input voltage VC of the slope compensation circuit.

  A voltage-current conversion circuit comprising a pnp bipolar transistor 150, an npn bipolar transistor 152, a constant current source 151 and a resistor 153 generates a current proportional to the input signal VC, and this output current is converted into a P-channel enhancement type MOS. By injecting into the capacitor 157 through a current mirror composed of the transistors 154 and 155, voltage ramp waves whose slopes are proportional to the input signal VC are generated at both ends of the capacitor 157. The N channel enhancement type MOS transistor 156 resets the voltage ramp wave according to the oscillation period of the oscillator. The voltage ramp wave is converted into a current by a voltage-current conversion circuit including a pnp bipolar transistor 158, an npn bipolar transistor 160, a constant current source 159 and a resistor 161, and this current is converted into a P channel enhancement type MOS transistor. The voltage is converted again by injection into the resistor 165 through a current mirror composed of 162 and 163. On the other hand, the coil current signal or the switch current signal converted into a voltage signal by a current sense resistor or the like is added to the resistor 165 via the resistor 164. Therefore, it is apparent that a signal obtained by adding the coil current signal or the switch current signal converted into the voltage signal by the circuit of FIG. 2 and the voltage ramp wave whose slope is proportional to the input signal VC is obtained. It is possible to obtain results equivalent to the circuit configuration of FIG. 3 of the present invention with other circuit configurations, and the present invention does not refer to the circuit configuration of FIG.

1 is a block diagram of a first embodiment of a current mode step-up switching regulator according to the present invention. FIG. It is a block diagram of 2nd Example of the current mode step-up type switching regulator of this invention. This is a circuit for generating a signal obtained by adding a coil ramp signal or a switch current signal and a voltage ramp wave whose slope is proportional to the input voltage of the slope compensation circuit. It is a block diagram of the conventional current mode step-up switching regulator.

Explanation of symbols

100 Reference voltage source 101 Error amplifier 102 Slope compensation circuit 103 Adder 104 Oscillator 105 Comparator 106 SR-latch 107 Switch 108 Coil 109 Diode 110, 111, 120, 121, 123, 124 Resistor 122 Operational amplifier 130 Slope compensation value calculation circuit 150, 158 pnp type bipolar transistor 152, 160 npn type bipolar transistor 156 N channel enhancement type MOS transistor 154, 155 P channel enhancement type MOS transistor 162, 163 P channel enhancement type MOS transistor 151, 159 constant current source 157 capacitor 153, 161, 164, 165 resistance

Claims (4)

  A current mode switching regulator characterized by varying the amount of slope compensation in accordance with an input voltage and an output voltage.   A current mode step-up switching regulator which operates with an input voltage VIN and an output voltage VOUT, wherein the amount of slope compensation is varied in proportion to (VOUT-2VIN).   A current mode step-down switching regulator that operates with an input voltage VIN and an output voltage VOUT, wherein the amount of slope compensation is varied in proportion to (2VOUT−VIN).   A current mode inversion switching regulator that operates with an input voltage VIN and an output voltage VOUT, wherein the amount of slope compensation is varied in proportion to (VOUT−VIN).

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