TWI440291B - Average inductor current control using variable reference voltage - Google Patents

Description

Average inductor current type voltage control method and variable reference voltage generating device therefor

The invention relates to an average inductor current voltage control technology which should be used in a DC to DC converter, in particular to a constant off time DC/DC converter which can be applied to a fixed off time. Inductor current type voltage control method and variable reference voltage generating device therefor.

According to the electrical equipment used in daily use or the electronic equipment used in various industries, the input voltage range is between AC 100 and 240 volts, but the load status of each electronic product or equipment is not the same. The drive voltage is also different, so the power supply is adjusted according to the needs of various applications. This is called a voltage converter.

Voltage converters can be roughly divided into several types according to different types, AC to AC converters, AC to DC converters, DC to DC converters, and DC to AC (DC). /AC); Among them, in the case of direct current to direct current (DC/DC) converters, in many electronic circuits, there are often some electronic components that require power supplies other than dual power supplies, such as LCD displays, voltage comparators, operational amplifiers, etc. Or because multiple sets of electronic components have different operating voltages and multiple sets of different potentials, a DC to DC converter is needed to obtain the desired voltage.

Figure 1 is a schematic circuit diagram of a conventional step-down DC-to-DC converter. As shown in the figure, when the transistor switch S is turned ON, the input power Vin has a current flowing through the inductor L, so that the energy is stored in When the transistor switch S is turned off (OFF), the induced current on the inductor L is discharged to the resistor RL to maintain the output of the voltage; wherein, the output voltage of the induced current is converted by the feedback circuit 10 The control circuit 12 is fed back to compare with the reference voltage, and then the size of the duty cycle of the transistor switch S is controlled to achieve the purpose of stable output. Please also refer to Fig. 2, in the transistor (ON) phase, the inductor L is connected to the input voltage Vin, and the other end is connected to the output voltage Vo. At this time, the input voltage must be higher than the output voltage. A forward voltage drop is formed on the inductor L; in the OFF state of the transistor switch S, one end of the inductor L originally connected to the input voltage Vin is connected to the ground GND, and the output voltage Vo is necessarily the positive terminal. A negative voltage drop is formed across the inductor L.

However, in the above architecture, the peak inductor current generated by the peak current mode is used to compare the fixed reference voltage to control the transistor switch. This mode is only adjusted by the peak induced current, and it is easy to generate a peak-to-average error. (peak to average error), and therefore there is poor adjustment accuracy. As shown in Figure 2(a), when the inductance L is large, there is a higher average induced current, and the peak-to-average error is smaller. Conversely, as shown in the second (b), the inductance L is small. When there is a lower average induced current, the peak-to-average error is relatively large; the average inductor current has a considerable relationship with the induced current value, and is susceptible to the inductance, resulting in voltage regulation of the entire converter. The accuracy is quite poor.

In view of the above, the present invention provides an average inductor current voltage control method with a variable reference voltage and a variable reference voltage generating device therefor, which does not require any loop compensation or load that is only used to adjust the average current by the inductor current. Current sensing, with a fixed inductor current controlled by a fixed inductor current, the DC/DC converter operates in continuous conduction mode.

The main object of the present invention is to provide an average inductor current type voltage control method, which is a design for adding a variable reference voltage in a DC to DC converter, and the reference voltage will vary with the inductor current of the inductor current ripple. Combined with the effect of the average inductor current, the reference voltage is dynamically adjusted, and in this way, the conventional technique using the peak current and the independent inductance value is replaced, and the induced current of the high side is not required.

Another object of the present invention is to provide an average inductor current voltage control method and a variable reference voltage generating apparatus therefor, which use an average inductor current as a reference voltage to control a fixed off time DC/ with an average inductor current. The DC converter operates in continuous conduction mode, so it is not directly affected by the inductance used in the converter, and the accuracy of voltage adjustment can be improved.

The average inductor current type voltage control method proposed by the invention can be applied to a DC to DC converter, which first converts the external reference preset twice the reference current into a double reference voltage, and is located in the converter. The valley inductor current generated by one of the inductors is converted into a valley voltage; then, the double reference voltage is subtracted from the valley voltage to generate a reference voltage, which is used as a transistor switch in the control converter. The basis.

Of course, after obtaining the reference voltage, the reference voltage and the inductor voltage of the inductor can be compared, and a comparison result is output, and when the reference voltage is equal to the inductor voltage, the comparison result is a cutoff signal, which can make the transistor The switch is turned off.

Furthermore, in order to generate a reference voltage, the present invention further provides a variable reference voltage generating device for a DC-to-DC converter, which includes a sample-and-hold valley inductor current bill and a reference voltage generating unit electrically connected thereto. The sampling keeps the valley inductor current unit receives the valley inductor current generated by an inductor and converts it into a valley voltage, and the reference voltage generating unit converts the external preset second reference current received into Double the reference voltage, and then subtract this double reference voltage from the valley voltage to obtain the reference voltage. Of course, this reference voltage will change dynamically with twice the reference voltage and the valley voltage.

The purpose, technical contents, features and effects achieved by the present invention will be more readily understood by the detailed description of the embodiments and the accompanying drawings.

The present invention creates a variable reference voltage that varies depending on the valley inductor current. Since the inductor chopping current should be controlled by the valley inductor current plus half of the sum of the peak inductor currents, this means that the peak inductor current is equal to twice the average inductor current minus the valley inductor current; therefore, the present invention defines a new reference current. Iref can be set to double the preset average inductor current Iavg minus this valley inductor current Ivally, as shown in the following relationship:

Iref=2*Iavg-Ivally.

Expressed by voltage, it can be expressed as the reference voltage Vref can be set to twice the preset average inductor voltage Vavg minus the valley inductor voltage Vvally, as shown in the following relationship:

Vref=2*Vavg-Vvally.

The present invention proposes an average inductor current type voltage control method and a variable reference voltage generating apparatus therefor according to the above relationship. First, the average inductor current type voltage control method of the present invention will be described in detail, which is applied to a DC to DC converter, and a DC-to-DC converter with a fixed cut-off time is taken as an example. Referring to FIG. 3, first, as shown in step S10, receiving twice the external preset current, which is the original reference current, that is, the average inductor current; converting the preset current to twice the preset Voltage. At the same time, as shown in step S12, the valley inductor current generated by one of the DC-to-DC converters is also converted into a valley voltage. Then, as shown in step S14, the double preset voltage is subtracted from the valley voltage to generate a reference voltage, as shown in the foregoing relationship, which is used to control the switching of the transistor switch in the DC-to-DC converter. in accordance with.

After the reference voltage is obtained, the reference voltage (Vref) and the inductor voltage (CS) generated by the inductor are compared as shown in step S16, and a comparison result is outputted to the transistor switch in the DC-to-DC converter. Wherein, the inductor voltage is compared with the reference voltage. When the inductor voltage is equal to the reference voltage, the comparison result is a cutoff signal, and the cutoff signal can turn off the transistor switch (OFF); thereby, the average inductor The current can be stably maintained at a predetermined value. Conversely, when the reference voltage and the inductor voltage are not equal, it means that the comparison result is a pilot signal, so that the transistor switch remains conductive.

In one step, the aforementioned two times the preset voltage, the valley voltage, the reference voltage, and the like are generated in a variable reference voltage generating device. The details of the variable reference voltage generating device are described below.

Referring to FIG. 4, a variable reference voltage generating device mainly includes a sample and hold valley inductor current unit 20 and a reference voltage generating unit 30; the sample holding valley inductor current unit 20 receives a valley of inductance generation. The value of the inductor current (CS) is converted to a valley voltage (Vvalley) to provide a reference voltage generating unit 30 electrically connected to the sample and hold valley inductor current unit 20, the reference voltage generating unit 30 receiving the external pre- Set the preset current twice (that is, the average inductor current, 2Iavg) and convert it to twice the preset voltage (2Vavg), and then subtract the second preset voltage from the valley voltage (2Vavg-Vvalley) to generate a Reference voltage (Vref). The generated reference voltage is in a comparator 40, and compared with the inductance voltage (CS) of the inductor in the converter, so that the comparator outputs a comparison result; that is, when the reference voltage and the inductor voltage are equal, the comparator 40 outputs a cutoff. The signal is controlled to turn off one of the transistor switches in the DC to DC converter. Of course, if the reference voltage and the inductor voltage become unequal, the comparator 40 has no output cutoff signal, which is referred to herein as a pilot communication number. The transistor switch remains on.

After understanding the overall variable reference voltage generating device architecture, the detailed circuit for the sample-holding valley-value inductor current unit 20 and the reference voltage generating unit 30 will be described later, but the scope of the present invention is not limited thereto. As shown in FIG. 4, the sample-holding valley inductor current unit 20 further includes a switch 21 connected to a capacitor 22 and an operational amplifier 23, and a gate of a transistor switch 24 is connected to the output of the operational amplifier 23. The source drain of the transistor switch 24 is connected to the resistor 25 and the reference voltage generating unit 30 respectively; when the switch 21 is turned on, the valley current inductor current of the induced current (CS) flows through the switch 21 and is operated. After the amplifier 23 and the transistor switch 24, they are converted into a valley voltage (Vvalley) by the resistor 25 and supplied to the reference voltage generating unit 30. The detailed circuit of the reference voltage generating unit includes an operational amplifier 31 that receives twice the preset current (2Iavg), and a gate of the transistor switch 32 is connected to the output terminal of the operational amplifier 31. The source and drain of the transistor switch 32 are respectively Connected to a current mirror 33 and a first resistor 34, the current mirror 33 is also connected to the second resistor 35, and is further connected between the current mirror 33 and the second resistor 35 to the sample and hold valley inductor current unit 20, The double preset voltage (2Vavg) generated by the conversion of the double preset current (2Iavg) can be subtracted (2Vavg-Vvalley) from the valley voltage (Vvalley) generated by the sample-holding valley inductor current unit 20 to output the reference voltage. (Vref) to the comparator 40.

Among them, all of the aforementioned transistor switches include transistor switches 24, 32, preferably using thin film transistors (TFTs).

When the reference voltage generated by the variable reference voltage generating device of the present invention is directly applied to the actual circuit, as shown in FIG. 5, when the transistor switch M0 is turned on (ON), the input power source Vin has a current flowing through the inductor L, The energy is stored on the inductor L. When the transistor switch M0 receives the above-mentioned cutoff signal, the transistor switch M0 is turned off (OFF), and the induced current on the inductor L is released to the resistor R1 to stabilize the voltage. Output.

In summary, the present invention is a design for adding a variable reference voltage in a DC-to-DC converter. The reference voltage varies with the inductor current of the inductor current ripple, and then with the effect of the average inductor current. The reference voltage is dynamically adjusted to replace the conventional adjustment technique using peak current and independent inductance values, and does not need to sense the high side induced current. Furthermore, since the present invention uses the average inductor current as the reference voltage, the average inductor current is controlled by the fixed off-time DC-to-DC converter operating in the continuous conduction mode, so it is not directly affected by the inductance used in the converter. It can effectively improve the accuracy of voltage adjustment.

The embodiments described above are merely illustrative of the technical spirit and the features of the present invention, and the objects of the present invention can be understood by those skilled in the art, and the scope of the present invention cannot be limited thereto. That is, the equivalent variations or modifications made by the spirit of the present invention should still be included in the scope of the present invention.

10. . . Feedback circuit

12. . . Control circuit

20. . . Sample and hold valley inductor current unit

twenty one. . . Toggle switch

twenty two. . . Capacitor

twenty three. . . Operational Amplifier

twenty four. . . Transistor switch

25. . . Resistor

30. . . Reference voltage generating unit

31. . . Operational Amplifier

32. . . Transistor switch

33. . . Current mirror

34. . . First resistor

35. . . Second resistor

40. . . Comparators

Figure 1 is a simplified circuit diagram of a conventional step-down DC to DC converter.

Figure 2 is a waveform diagram of the existing inductor voltage, wherein (a) shows that the inductor L has a large average induced current, and the peak-to-average error is small; and (b) shows the inductor L. When it is small, there is a lower average induced current, and the peak-to-average error is relatively large.

Fig. 3 is a flow chart showing the voltage control method of the present invention.

Figure 4 is a circuit diagram of a variable reference voltage generating device used in the present invention.

Figure 5 is a schematic diagram of the reference voltage generated by the present invention applied directly to the actual circuit.

Claims (15)

An average inductor current type voltage control method is applied to a DC to DC converter, and the voltage control method comprises the steps of: converting a second average inductor current received to an external to a preset voltage; and generating an inductor The valley inductor current is converted to a valley voltage; and the double preset voltage is subtracted from the valley voltage to generate a reference voltage as a basis for controlling the switching of the transistor switch. The method for controlling an average inductor current type voltage according to claim 1, further comprising: comparing the reference voltage with an inductance voltage of the inductor, and outputting a comparison result. The method of claim 2, wherein when the reference voltage is equal to the inductor voltage, the comparison result is a cutoff signal, and the transistor switch is turned off. The method of claim 3, wherein the reference voltage is not equal to the inductor voltage, and the comparison result is a pilot signal to keep the transistor switch turned on. The average inductor current type voltage control method according to claim 1, wherein the DC to DC converter is a fixed off time DC to DC converter. The average inductor current voltage control method according to claim 1, wherein the double preset voltage, the valley voltage, and the reference voltage are generated in a variable reference voltage generating device. A variable reference voltage generating device is applied to a DC to DC converter, the variable reference voltage generating device comprising: a sample and hold valley inductor current unit, which receives a valley inductor current generated by an inductor and converts the same a valley voltage; and a reference voltage generating unit electrically connected to the sample-holding valley inductor current unit, the reference voltage generating unit receiving an external preset second-time average inductor current converted to twice the preset voltage, and The double preset voltage is subtracted from the valley voltage to generate a reference voltage. The variable reference voltage generating device of claim 7, wherein the reference voltage is further measurable by a comparator, compared with an inductance voltage of the inductor, to cause the comparator to output a comparison result. The variable reference voltage generating device of claim 8, wherein when the reference voltage is equal to the inductor voltage, the comparator outputs a cutoff signal to control a transistor switch in the DC to DC converter to be turned off. The variable reference voltage generating device of claim 9, wherein when the reference voltage is not equal to the inductor voltage, the comparator output is a pilot communication number to keep the transistor switch turned on. The variable reference voltage generating device of claim 7, wherein the direct current to direct current converter is a fixed off time DC to DC converter. The variable reference voltage generating device of claim 7, wherein the sampling and holding valley inductor current unit further comprises a switching switch connected to an operational amplifier and a capacitor, and a gate of a transistor switch is connected to the output of the operational amplifier. The source drain of the transistor switch is connected to the resistor and the reference voltage generating unit, respectively. The variable reference voltage generating device of claim 12, wherein the transistor-on relationship is a thin film transistor. The variable reference voltage generating device of claim 7, wherein the reference voltage generating unit further comprises an operational amplifier receiving the double preset current, and a gate of a transistor switch is connected to an output end of the operational amplifier, the electric The source drains of the crystal switches are respectively connected to the first resistor and a current mirror, and the current mirror is also connected to the second resistor, and the current mirror and the second resistor are further connected to the sample and hold the valley inductor And the current unit is configured to subtract the double preset voltage generated from the valley voltage generated by the sample-holding valley inductor current unit to output the reference voltage. The variable reference voltage generating device of claim 14, wherein the transistor-on relationship is a thin film transistor.