Input front-end circuit for switching power supply control integrated circuit and switching power supply controller having the same

Abstract

An inverting amplifier creates a voltage C using a reference voltage (voltage B) as a reference point. An adder composed of two input inverting amplifier circuits ultimately creates a voltage D by carrying out weighted addition of the voltage A and the voltage C. By using the voltage D created by an input front-end circuit, the internal functions of the control IC can prevent the operating points and control amounts for each function from being different relative to the input voltage and make it possible to distinguish voltage within the control IC from zero voltage when the lowest input voltage is received.

Claims

1. An input front-end circuit for a switching power supply control integrated circuit, comprising: a first inverting amplifier that receives a first voltage originating from an input voltage at an input and that receives a first reference voltage at a reference input so as to generate an inverted and amplified voltage as a second voltage; an adder comprising a second inverting amplifier that receives the first voltage at a first input, the second voltage at a second input, and a second reference voltage at a reference input so as to output a resulting added, inverted, and amplified signal to one or more components within the switching power-supply control integrated circuit.

2. The input front-end circuit for the switching power supply control integrated circuit according to claim 1, further comprising an input terminal that receives the input voltage and forwards the received input voltage to the first inverting amplifier as the first voltage.

3. The input front-end circuit for the switching power supply control integrated circuit according to claim 1, further comprising: an input terminal that receives the input voltage; and a resistive divider that divides the input voltage received by the input front-end circuit and forwards the divided input voltage to the first inverting amplifier and the second inverting amplifier as the first voltage.

4. The input front-end circuit for the switching power supply control integrated circuit according to claim 1, wherein the first reference voltage is greater than the second reference voltage.

5. A switching power supply controller, comprising: the input front-end circuit for the switching power supply control integrated circuit according to claim 1; and the switching power supply control integrated circuit.

6. The switching power supply controller according to claim 5, wherein said input front-end circuit is integrally formed within the switching power supply control integrated circuit.

7. An input front-end circuit for a switching power supply control integrated circuit, comprising: a first inverting amplifier that receives a first voltage originating from an input voltage at an input and that receives a first fixed reference voltage at a reference input so as to output an inverted and amplified voltage as a second voltage, the input voltage being a rectified alternating-current commercial power supply; a second inverting amplifier that receives the second voltage at an input and that receives a second fixed reference voltage at a reference input so as to output a resulting inverted and amplified voltage to one or more components within the switching power-supply control integrated circuit.

8. The input front-end circuit for the switching power supply control integrated circuit according to claim 7, further comprising an input power supply terminal that receives the input voltage and forwards the received input voltage to the first inverting amplifier as the first voltage.

9. The input front-end circuit for the switching power supply control integrated circuit according to claim 7, further comprising: an input power supply terminal that receives the input voltage; and a resistive divider that divides the input voltage received by the input front-end circuit and forwards the divided input voltage to the first inverting amplifier unit as the first voltage.

10. The input front-end circuit for the switching power supply control integrated circuit according to claim 7, wherein the first fixed reference voltage is greater than the second fixed reference voltage.

11. A switching power supply controller, comprising: the input front-end circuit for the switching power supply control integrated circuit according to claim 7; and the switching power supply control integrated circuit.

12. The switching power supply controller according to claim 11, wherein said input front-end circuit is integrally formed within the switching power supply control integrated circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the configuration of an input front-end circuit for a switching power supply control IC according to Embodiment 1 of the present invention.

(2) FIG. 2 is a graph showing changes for voltages A to D calculated using the configuration shown in FIG. 1.

(3) FIG. 3 shows the configuration of an input front-end circuit for a switching power supply control IC according to Embodiment 2 of the present invention.

(4) FIG. 4 shows the configuration of an input front-end circuit for a switching power supply control IC according to Embodiment 3 of the present invention.

(5) FIG. 5 shows the first out of two example configurations of a conventional input front-end circuit for a switching power supply control IC.

(6) FIG. 6 shows an example configuration of a general switching power supply device configured to include a switching power supply control IC.

(7) FIG. 7 shows the second out of two example configurations of a conventional input front-end circuit for a switching power supply control IC.

DETAILED DESCRIPTION OF EMBODIMENTS

(8) Embodiments of the present invention are described in detail below.

Embodiment 1

(9) FIG. 1 shows the configuration of an input front-end circuit for a switching power supply control IC according to Embodiment 1 of the present invention. The operations of the input front-end circuit 40 according to Embodiment 1 of the present invention are described using FIG. 1.

(10) The input front-end circuit 40 shown in FIG. 1 divides input voltage from a wide input voltage range (voltage VAC from a rectified alternating-current commercial power supply, for example) using a resistive divider unit, sends the input voltage into a control IC unit, and then carries out signal processing.

(11) Specifically, (1) a voltage A is created by dividing the input voltage (VAC, for example) using resistors R1 (41) a R2 (42).

(12) (2) A voltage C is created by inverting and amplifying the voltage A using an inverting amplifier (inverting amplifier 1; first inverting amplifier) with a reference point, voltage B (43), which is configured to be lower than the internal voltage of the control IC unit. Here, using voltage B as a reference point means having voltage C, which is the output voltage of the inverting amplifier, be represented by the expression below using the input voltage A and the voltage B.
Voltage C=Voltage BK0(Voltage AVoltage B)

(13) Here, K0 represents a constant.

(14) Specifically, if the resistance values of the resistors R3 (45), R4 (46) are represented by R3 and R4, then K0=R4/R3.

(15) Note that the inverting amplifier (inverting amplifier 1) is composed of an inverting amplifier circuit (second inverting amplifier). The inverting amplifier circuit is composed of an operational amplifier (44), a reference voltage (43), and resistors R3 (45), R4 (46).

(16) (3) Finally, a voltage D is created by adding the voltage A and the voltage C together using an adder. In other words, the adder has two inputs (the voltage A and the voltage C) and is composed of an inverting amplifier circuit that uses, as a reference point, a voltage E that is a reference voltage E (48). The adder adds together signals having an inversion amplified voltage A and voltage C. The voltage A and the voltage C have been inverted and amplified at respectively different amplification rates. The adder outputs the product of that addition. (The inverting amplifier circuit in the adder is composed of an operational amplifier (49), the reference voltage (48), and resistors R5 (47), R6 (50), R7 (51). Note that how the formula representing the voltage D was derived will be described hereafter.

(17) By using the voltage D created by the input front-end circuit 40, it becomes possible to prevent the operating points and control amounts for each function from being different relative to the input voltage (VAC, for example) and at the same time makes it possible to distinguish voltage within the control IC from zero voltage when the lowest input voltage is received, thus making it possible to avoid mistaking the voltage for noise as well as making it possible to prevent malfunctions during signal processing within the control IC. The input front-end circuit can be integrally or separately provided with the switching power supply control integrated circuit.

(18) FIG. 2 is a graph showing changes for the voltages A to D calculated using the configuration shown in FIG. 1.

(19) Voltage A is the value for the input voltages (VAC, for example) after being divided using resistors R1 (41), R2 (42). Note that the input voltages correspond to a scale different from the scale represented by the vertical axis of FIG. 2 (this scale is not shown and is larger than the scale of FIG. 2). Voltage B is a fixed value configured to be lower than the internal power supply of the control IC. Voltage C is an output value created using the inverting amplifier (the direction that the voltage of the output value C changes is the inverse of the direction that voltage A changes). Voltage D is the output voltage created using the adder (and is the result of carrying out weighted addition on voltage A and voltage C). Voltage D is the target signal created by equipping the input front-end circuit 40.

(20) As can be seen from the waveforms shown in FIG. 2, the output signal (target signal) (voltage D) of the input front-end circuit is higher than zero voltage when a low input voltage is received, thus making it is easy to distinguish the signal from noise, and making it possible to prevent malfunctions during signal processing within the control IC.

Embodiment 2

(21) FIG. 3 shows the configuration of an input front-end circuit for a switching power supply control IC according to Embodiment 2 of the present invention. The configuration of an input front-end circuit 60 according to Embodiment 2 of the present invention shown in FIG. 3 is the same as the configuration of the input front-end circuit 40 according to Embodiment 1 of the present invention shown in FIG. 1, except that the feedback resistor R5 of the adder has been removed and that the adder has been substituted with a single input inverting amplifier 2.

(22) In the configuration shown in FIG. 3, the inverting amplifier 2 is provided instead of the adder shown in FIG. 1, and the voltage C, which is the output of the inverting amplifier 1, is level shifted using the inverting amplifier 2 to obtain the voltage D. Note that the inverting amplifier 2 is composed of an inverting amplifier circuit. The inverting amplifier circuit is composed of an operational amplifier (68), a reference voltage (67), and resistors R6 (69), R7 (70). In addition, the inverting amplifier (inverting amplifier 1) is composed of an inverting amplifier circuit. The inverting amplifier circuit is composed of an operational amplifier (64), a reference voltage (63), and resistors R3 (65), R4 (66). Thus, even when the resistor R5 shown in FIG. 1 is removed, it is possible for the configuration shown in FIG. 3 to carry out roughly the same operations as the configuration shown in FIG. 1, because the configuration shown in FIG. 3 is set to obtain the output voltage C of the inverting amplifier 1, which is related to the voltage A, and furthermore to obtain the output voltage D by level shifting the voltage C using the inverting amplifier 2.

(23) However, when the input front-end circuit 60 is configured to have the resistor R5 of Embodiment 1 shown in FIG. 1 removed, a constant term (voltage Vd when Vin=0) determined using formula 4 described hereafter may have a tendency to be negative when voltage V.sub.B>voltage V.sub.E.

(24) In this case, it is desirable that the resistor R5 be not removed (because the output of the input front-end circuit 60, or in other words, the target voltage D, is close to zero voltage (see FIG. 2). This is described in detail later.

Embodiment 3

(25) FIG. 4 shows the configuration of an input front-end circuit for a switching power supply control IC according to Embodiment 3 of the present invention. For Embodiment 3, the voltage-dividing resistors R1 (41), R2 (42) from Embodiment 1 shown in FIG. 1 are removed, and the resistor R3 (45) is directly connected to the input voltage going through the input terminal. This configuration corresponds to when the input voltage (VAC, for example) is divided using an external element outside of the control IC, for example. Note that the inverting amplifier is composed of an inverting amplifier circuit. The inverting amplifier circuit is composed of an operational amplifier (82), a reference voltage (81), and resistors R3 (83), R4 (84). The adder is composed of an inverting amplifier circuit. The inverting amplifier circuit is composed of an operational amplifier (87), a reference voltage (86), and resistors R5 (85), R6 (88), R7 (89).

(26) The operations of an input front-end circuit 80 in a switching power supply control IC according to Embodiment 3 of the present invention are described using FIG. 4.

(27) The IC input terminal shown in FIG. 4 receives a voltage V.sub.in that corresponds to the voltage A shown in FIG. 1 from the input voltage (VAC, for example) shown.

(28) Similar to the configuration shown in FIG. 1 described above, the input voltage V.sub.in enters the inverting amplifier via the resistor R3 (83) to obtain the voltage C (V.sub.C).

(29) The resulting voltage C (V.sub.C) enters the inverting amplifier circuit that constitutes the adder via the resistor R6 (88) as one of the inputs. In addition, the input voltage V.sub.in enters, as another input, the inverting amplifier circuit, which constitutes the adder, via the resistor R5 (85). The adder carries out weighted addition on both of the inputs, or in other words, adds signals together that have been inverted and amplified using different amplification factors, to create an output voltage D (V.sub.D).

(30) The resulting voltage D (V.sub.D) enters the next stage function block, as a target voltage that can be obtained by equipping the input front-end circuit 80, and is used by the function block for a desired signal processing.

(31) Even in FIG. 4, it is possible to have a configuration in which the resistor R5 (85) has been removed similar to Embodiment 2 shown in FIG. 3, thus there has been an attempt to calculate and determine the voltage D (V.sub.D) when the resistor R5 (85) has not been removed in FIG. 4 and the voltage D (V.sub.D) when the resistor R5 (85) has been removed as is shown below.

(32) Note that in FIG. 4, the reference voltage B is represented V.sub.B. The voltage C is represented by V.sub.C. The reference voltage E is represented by V.sub.E, and the resistance values for resistors R3, R4, R5, R6, R7 are respectively represented by R3, R4, R5, R6, R7.

(33) (a) In FIG. 4, the formula for calculating the voltage D when the resistor R5 (85) has not been removed is below.
V.sub.C=V.sub.B(V.sub.inV.sub.B)R4/R3
V.sub.D=V.sub.E((V.sub.CV.sub.E)/R6+(V.sub.inV.sub.E)/R5)R7
V.sub.D=((R4R7)/(R3R6)R7/R5)V.sub.in((R4R7)/(R3R6)+R7/R6)V.sub.B+(1+R7/R5+R7/R6)V.sub.EFormula 1:

(34) (b) In FIG. 4, the formula for calculating the voltage D when the resistor R5 (85) has been removed is below.
V.sub.D=((R4R7)/(R3R6))V.sub.in((R4R7)/(R3R6)+R7/R6)V.sub.B+(1+R7/R6)V.sub.EFormula 2:
If K1=(R4R7)/(R3R6), K2=R7/R5, and K3=R7/R6, then Formula 1 becomes Formula 3, which is V.sub.D=(K1K2)V.sub.in(K1+K3)V.sub.B+(1+K2+K3)V.sub.E, and Formula 2 becomes Formula 4, which is V.sub.D=K1V.sub.in(K1+K3)V.sub.B+(1+K3)V.sub.E. Here, when considering the constant term (voltage V.sub.D when V.sub.in=0V) in Formula 4,

(35) $\begin{array}{c}\mathrm{Constant}\mathrm{term}=-\left(K1V_B\right)-K3\left(V_B-V_E\right)+V_E\\ =-K1\left(V_B-V_E\right)-K3\left(V_B-V_E\right)+\left(1-K1\right)V_E\\ =-\left(K1+K3\right)\left(V_B-V_E\right)+\left(1-K1\right)V_E.\end{array}$
Thus, the constant term tends to be negative when V.sub.B>V.sub.E.

(36) In other words, the first item in the constant term, (K1+K3)(V.sub.BV.sub.E), is negative, and the second item, (1K1)V.sub.E, is not a large value, thus the constant term tends not to be a large value, and the constant term tends to be negative.

(37) In comparison, when the resistor R5 is present, as can be understood in Formula 3, K2V.sub.E is added to the second clause of the constant term, thus allowing the second clause of the constant term to increase in value.

(38) In other words, when voltage B>voltage E, it is desirable to add the resistor R5 in order to ensure that the constant term does not become negative.

(39) By doing this, the output signal (voltage D) of the input front-end circuit 80 is higher than zero voltage when a low input voltage is received, thus making it is easy to distinguish between noise and the signals and making it possible to prevent malfunctions during signal processing within the control IC.

(40) It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents. In particular, it is explicitly contemplated that any part or whole of any two or more of the embodiments and their modifications described above can be combined and regarded within the scope of the present invention.