# Patent

## Title
DC-to-DC voltage regulator and its operating method thereof

## Abstract

A method for operating the DC-to-DC voltage regulator including plural active switches and plural inductors is disclosed. The method including the steps of: turning on the first active switch, and then turning off the first active switch when the current flowing in the first inductor is equal to zero; turning on the third active switch, and then turning off the third active switch when the current flowing in the second inductor is equal to zero; turning on the second active switch, and then turning off the second active switch when the current flowing in the first inductor is equal to zero; and turning on the fourth active switch, and then turning off the fourth active switch when the current flowing in the second inductor is equal to zero.

## Background
The present application is based on, and claims priority from, Taiwan Application Serial Number 100144816, filed 2011 Nov. 6, the disclosure of which is hereby incorporated by reference herein in its entirety
TECHNICAL FIELD
The present disclosure relates to a DC-to-DC voltage regulator, and more particularly, to an operating method for controlling the active switches in the voltage regulator.
TECHNICAL BACKGROUND
Conventionally, the voltage converting circuits can have their applications in solar energy systems, being in parallel with the household electricity, so that they have a wide range of DC voltage at the input terminals thereof. For household usage, the solar cell modules can be connected in parallel or in series to each other to supply the home appliances with electricity of proper DC voltages. However, throughput of the solar energy system can be affected once one of the solar cell modules was out of order for some how, so a DC-to-AC voltage converter was included in a solar cell module. Low-voltage power generation of the solar cell module can be transferred to an AC power by the DC-to-AC voltage converter and then in paralleled with the household electricity; thereby, reliability and efficiency of the household power supply system can be improved.
The DC-to-AC voltage converter in solar cell modules can be constructed by a DC-to-DC voltage converting circuit of high-frequency switching in the first stage and a DC-to-AC voltage converting circuit of low-frequency switching in the second stage. With regard to the DC-to-DC voltage converting circuit therein, it is based on the pulse-width-modulation (PWM) mechanism. The PWM technique to operate the DC-to-DC voltage converting circuit is of slow response and not in the soft-switching condition for all possible loading scenarios. Therefore, it is in need to develop an operating method for controlling the active switches in the DC-to-DC voltage converting circuit to improve its performance.
TECHNICAL SUMMARY
According to one aspect of the present disclosure, an embodiment provides a DC-to-DC voltage regulator having input and output terminals, the voltage regulator comprising: a push-pull DC-to-DC converting unit comprising first and second active switches and configured to convert a voltage V1 at the input terminal to a square-wave signal of voltage; an isolation transformer having two primary windings and one secondary winding, wherein the primary windings are coupled to the first and second active switches, respectively; a resonant unit comprising a capacitor and first and second inductors, the first inductor coupled to the secondary winding of the isolation transformer; third and forth active switches coupled to a terminal of the second inductor; first and second rectifiers coupled to the third and forth active switches, respectively; and an output stage of full-wave rectification comprising four passive switches and a plurality of connection joints and configured to provide a voltage V2 at the output terminal, wherein the connection joints are coupled to the resonant unit, the isolation transformer, and the first and second rectifiers, respectively.
According to another aspect of the present disclosure, another embodiment provides a method for operating the DC-to-DC voltage regulator according to the foregoing embodiment, the method comprising the steps of: turning on the first active switch, and then turning off the first active switch when the current flowing in the first inductor is equal to zero; turning on the third active switch, and then turning off the third active switch when the current flowing in the second inductor is equal to zero; turning on the second active switch, and then turning off the second active switch when the current flowing in the first inductor is equal to zero; and turning on the fourth active switch, and then turning off the fourth active switch when the current flowing in the second inductor is equal to zero.
Further scope of applicability of the present application will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from this detailed description.



BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present disclosure and wherein:
FIG. 1 shows a circuit diagram of a DC-to-DC voltage regulator according to an embodiment of the present disclosure.
FIG. 2 shows a flowchart of the operating method for controlling the active switches in the DC-to-DC voltage converter.
FIG. 3 plots the control signals of the active switches Q1/Q2/Q3/Q4 and the flowing currents of the first and second inductors Lr1 and Lr2 in the operating method.
FIG. 4A shows the current path in the DC-to-DC voltage regulator in the dashed line in the step 210.
FIG. 4B shows the current path in the DC-to-DC voltage regulator in the dashed line in the step 220.
FIG. 4C shows the current path in the DC-to-DC voltage regulator in the dashed line in the step 230.
FIG. 4D shows the current path in the DC-to-DC voltage regulator in the dashed line in the step 240.



DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
For further understanding and recognizing the fulfilled functions and structural characteristics of the disclosure, several exemplary embodiments cooperating with detailed description are presented as the following.
FIG. 1 shows a circuit diagram of a DC-to-DC voltage regulator according to an embodiment of the present disclosure, which is also used to describe the operating method for the DC-to-DC voltage regulator. As shown in FIG. 1, the DC-to-DC voltage regulator 100 has input and output terminals and is configured to convert a DC voltage V1 at the input terminals to a DC voltage V2 at the output terminals. The DC-to-DC voltage regulator includes a DC-to-DC converting unit 110, an isolation transformer TR, a resonant unit 120, third and forth active switches Q3 and Q4, first and second rectifiers D1 and D2, and an output stage 130. Each element in the DC-to-DC voltage regulator 100 is going to be described below in detail.
The isolation transformer TR having a first primary winding, a second primary winding, and a secondary winding, in which the turns ratio of the first primary winding to the second primary winding is 1:1, while the turns ratio of the secondary winding to the primary winding is n:1, where n is more or less than 1. In other words, the number of turns among the windings of the isolation transformer TR is in the ratio 1:1:n, and a center tap is formed between the first and second primary windings. If n is more than 1, the isolation transformer TR can be used for stepping up the voltage; otherwise, it can be used for stepping down the voltage.
The DC-to-DC converting unit 110 can serve as an input stage of the DC-to-DC voltage regulator 100, and includes a first active switch Q1 and a second active switch Q2. In the embodiment, the active switches are formed of MOSFETs. The positive terminal of the input voltage V1 is connected to the center tap of the primary windings in the isolation transformer TR, and its negative terminal is connected to the first and second active switches Q1 and Q2. The other terminal of the first active switch Q1 is connected to the negative terminal of the first primary winding, while the other terminal of the second active switch Q2 is connected to the positive terminal of the second primary winding. Due to the switching control of push-pull operation between the first and second active switches Q1 and Q2, the DC-to-DC converting unit 110 can convert the input voltage V1 at the input terminals to a square-wave signal of voltage, so as to facilitate the electro-magnetically inductive coupling effect in the isolation transformer TR.
The resonant unit 120 can be composed of a capacitor Cr, a first inductors Lr1 and a second inductors Lr2, in which the first and second inductors Lr1 and Lr2 are connected to one of two terminals of the capacitor Cr, to respectively form a LC serial resonant circuit. The resonance frequencies of the LC serial resonant circuits can be used to control the operational states, “On” or “Off”, of the active switches in the embodiment, which will be described later in more detail. Moreover, the first inductor Lr1 is connected to one of two terminals of the secondary winding in the isolation transformer TR.
The third and forth active switches Q3 and Q4 can also be implemented by MOSFETs and are connected to one of two terminals of the second inductors Lr2, as to control the current flowing in the secondary winding of the isolation transformer TR. It will be described later in more detail.
The first rectifier D1 is connected to the third active switch Q3, while the second rectifier D2 is connected to the forth active switch Q4. The first and second rectifiers can be implemented by clamping diodes, so as to clamp the current direction of the secondary winding in the isolation transformer TR. Thereby, the current can be limited to flow in only one direction to avoid fault operation of the DC-to-DC voltage regulator 100 caused by the current in the opposite direction. It will be described later in more detail.
The output stage 130 can be implemented by a full-wave rectifier circuit, which includes four passive switches D3/D4/D5/D6. Each two of the passive switches D3/D4/D5/D6 are cascaded and then the cascades are connected in parallel, forming two cascade and two parallel connection joints. As shown in FIG. 1, the passive switches D3 and D4 are cascaded with a cascade connection joint formed between them, the passive switches D5 and D6 are cascaded with another cascade connection joint formed between them, and then the two cascades are connected in parallel with two parallel connection joints formed at both sides, respectively. In other words, the connection joints of the passive switches D3/D4/D5/D6 include two cascade and two parallel connection joints, which are further connected to the resonant unit 120, the isolation transformer TR, and the first and second rectifiers D1 and D2, respectively. In the embodiment, the two cascade connection joints are connected to the other terminals of the capacitor Cr and the secondary winding, respectively, while the two parallel connection joints are connected to the other terminals of the first and second rectifiers D1 and D2, respectively. After that, the voltage V2 at the output terminals of the DC-to-DC voltage regulator 100 can be extracted from the two parallel connection joints of the output stage 130.
An appropriate method of operation can be applied to each active switch in the foregoing embodiment to realize DC-to-DC voltage conversion in a high-frequency switching mode, wherein the operating frequency is variable with a maximum of 200 KHz. By proper designation of switching frequency for the active switches and turns ratio for the isolation transformer TR, the DC voltage V1 at the input terminals of the DC-to-DC voltage regulator 100 can be increased to the DC voltage V2 at its output terminals. But it is not limited thereby; the DC-to-DC voltage regulator 100 can also produce a DC voltage decrease from V1 to V2 without limitations on its allowable voltage range. The DC-to-DC voltage regulator 100 according to the embodiment can have its applications in the DC-to-DC voltage conversion unit of high-frequency switching mode for the pre-stage of solar cell modules; but it is not limited thereby.
Regarding the DC-to-DC voltage regulator as set forth in the previous embodiments, an operating method 200 is then provided to control the On or Off states of the active switches Q1/Q2/Q3/Q4 in the DC-to-DC voltage regulator 100. Please refer to FIG. 2, showing a flowchart of the operating method 200 which includes the following steps. In step 210, the first active switch Q1 is turned on and kept in its On state, and then it is turned off when the current flowing in the first inductor Lr1 is equal to zero. In step 220, the third active switch Q3 is turned on and kept in its On state, and then it is turned off when the current flowing in the second inductor Lr2 is equal to zero. In step 230, the second active switch Q2 is turned on and kept in its On state, and then it is turned off when the current flowing in the first inductor Lr1 is equal to zero. In step 240, the forth active switch Q4 is turned on and kept in its On state, and then it is turned off when the current flowing in the second inductor Lr2 is equal to zero. The steps are going to be described in more detail.
FIG. 3 plots the control signals of the active switches Q1/Q2/Q3/Q4 and the flowing currents of the first and second inductors Lr1 and Lr2 in the operating method 200. In order to facilitate knowing the operation of the DC-to-DC voltage regulator 100 according to the operating method 200 in the embodiment, all the active switches Q1/Q2/Q3/Q4 can be turned off and then the steps 210, 220, 230 and 240 proceed in sequence.
Of all the active switches Q1/Q2/Q3/Q4, only the first active switches Q1 is turned on in the first step 210, so that the current path flowing in the DC-to-DC voltage regulator 100 can be illustrated as the dashed line in FIG. 4A. Due to the On state of the first active switch Q1, the current I1-1 can be conducted to flow into the isolation transformer TR through the positive terminal of the first primary winding, and then its secondary-winding current I2-1 can be produced according to the electro-magnetically inductive coupling effects in the transformer. The current I2-1 may follow along the path of the first inductor Lr1, the capacitor Cr and the passive switches D3. With the closed state of the passive switches D6, the DC-to-DC voltage regulator 100 can output the DC voltage V2 at its output terminals. The capacitor Cr can be charged to store electrical energy due to the current I2-1. The current I2-1 may increase and then decrease sinusoidally, in accordance with the current curve of the first inductor Lr1 as shown in FIG. 3. Once the current I2-1 or the current flowing in the first inductor Lr1 is equal to zero, the first active switch Q1 can be turned off so as to proceed to the next step of switching the active switches in sequence.
In the next step 220, the third active switches Q3 is turned on so that the current path flowing in the DC-to-DC voltage regulator 100 can be illustrated as the dashed line in FIG. 4B. Due to the On state of the third active switches Q3, the energy stored in the capacitor Cr can be discharged to form the new current I2-2, which flow along the path of the second inductor Lr2, the third active switches Q3 and the first rectifier D1. With the closed state of the passive switches D4, the DC-to-DC voltage regulator 100 can output the DC voltage V2 at its output terminals. The current I2-2 may increase and then decrease sinusoidally, in accordance with the current curve of the second inductor Lr2 as shown in FIG. 3. Once the current I2-2 or the current flowing in the second inductor Lr2 is equal to zero, the third active switches Q3 can be turned off so as to proceed to the next step of switching the active switches in sequence.
In the next step 230, the second active switches Q2 is turned on so that the current path flowing in the DC-to-DC voltage regulator 100 can be illustrated as the dashed line in FIG. 4C. Due to the On state of the second active switches Q2, the current I1-2 can be conducted to flow into the isolation transformer TR through the negative terminal of the second primary winding, and then its secondary-winding current I2-3 can be produced according to the electro-magnetically inductive coupling effects in the transformer. The current I2-3 may follow along the path of the passive switches D4, the capacitor Cr, the first inductor Lr1 and the passive switches D5, so that the DC-to-DC voltage regulator 100 can output the DC voltage V2 at its output terminals. Again, the capacitor Cr can be charged to accumulate electrical energy due to the current I2-3. The current I2-3 may increase and then decrease sinusoidally, in accordance with the current curve of the first inductor Lr1 as shown in FIG. 3. Once the current I2-3 or the current flowing in the first inductor Lr1 is equal to zero, the second active switches Q2 can be turned off so as to proceed to the next step of switching the active switches in sequence.
In the next step 240, the forth active switches Q4 is turned on so that the current path flowing in the DC-to-DC voltage regulator 100 can be illustrated as the dashed line in FIG. 4D. Due to the On state of the forth active switches Q4, the energy stored in the capacitor Cr can be discharged to form the new current I2-4, which flow along the path of the second rectifiers D2, the forth active switches Q4, the second inductor Lr2, the capacitor Cr and the passive switches D3, so that the DC-to-DC voltage regulator 100 can output the DC voltage V2 at its output terminals. The current I2-4 may increase and then decrease sinusoidally, in accordance with the current curve of the second inductor Lr2 as shown in FIG. 3. Once the current I2-4 or the current flowing in the second inductor Lr2 is equal to zero, the forth active switches Q4 can be turned off so as to be ready for the next cycle of switching the active switches in sequence.
In the embodiment, the active switches Q1/Q2/Q3/Q4 can be operated according to the control signals in FIG. 3, respectively. The On-state duration of each active switch Q1/Q2/Q3/Q4 is based on its corresponding resonance frequency of the resonant unit 120. When the resonance current in the resonant unit 120 is equal to zero, the active switch at the primary-winding side of the isolation transformer TR is turned off and the active switch at its secondary-winding side can be turned on and kept for a proper On-state duration; thereby, the switching loss happened in the Off state of the active switches can be minimized. Moreover, the resonant unit 120 is disposed at the secondary-winding side of the isolation transformer TR with a higher voltage than its primary-winding side, so the operating loss happened in the On state of the active switches can be lowered. Consequently, such kind of voltage converting unit can have improved conversion efficiency.
It can be inevitable for an active switch to have energy lost in its switching operation, such as switching loss and turning-on loss. However, in the embodiments according to the present disclosure, only one of the active switches in the DC-to-DC voltage regulator 100 can be switched on and stay in the On state at every single time. As to the conventional full-bridge DC-to-DC voltage regulators, at least two active switches are switched and stay in the On state at every single time. Therefore, it may be of low-loss advantage for the DC-to-DC voltage regulators according to the embodiments.
With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the disclosure, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present disclosure.

## Claims

1. A DC-to-DC voltage regulator having input and output terminals, the voltage regulator comprising:
a push-pull DC-to-DC converting unit comprising first active switch and second active switch and configured to convert a voltage V1 at the input terminal to a square-wave signal of voltage;
an isolation transformer having two primary windings and one secondary winding, wherein the primary windings are coupled to the first and second active switches, respectively;
a resonant unit comprising a capacitor and first inductor and second inductor, the first inductor coupled to the secondary winding of the isolation transformer;
third active switch and fourth active switch coupled to a terminal of the second inductor;
first rectifier and second rectifier coupled to the third active switch and fourth active switch, respectively; and
an output stage of full-wave rectification comprising four passive switches and a plurality of connection joints and configured to provide a voltage V2 at the output terminal, wherein the connection joints are coupled to the resonant unit, the isolation transformer, and the first and second rectifiers, respectively.

2. The DC-to-DC voltage regulator of claim 1, wherein the turns ratio of the two primary windings is 1, while the turns ratio of the secondary winding to the primary winding is more than 1 in the isolation transformer.

3. The DC-to-DC voltage regulator of claim 1, wherein the first and second inductors are coupled to a terminal of the capacitor, and each two of the passive switches are cascaded and the cascades are connected in parallel, forming two cascade and two parallel connection joints, wherein the two cascade connection joints are coupled to the other terminals of the capacitor and the secondary winding, respectively, and the two parallel connection joints are coupled to the other terminals of the first and second rectifiers, respectively.

4. The DC-to-DC voltage regulator of claim 1, wherein the first rectifier comprises a first clamping diode and the second rectifier comprises a second clamping diode.

5. A method for operating the DC-to-DC voltage regulator of claim 1, the method comprising the steps of:
(A) turning on the first active switch, and then turning off the first active switch when the current flowing in the first inductor is equal to zero;
(B) turning on the third active switch, and then turning off the third active switch when the current flowing in the second inductor is equal to zero;
(C) turning on the second active switch, and then turning off the second active switch when the current flowing in the first inductor is equal to zero; and
(D) turning on the fourth active switch, and then turning off the fourth active switch when the current flowing in the second inductor is equal to zero.

6. The method of claim 5, wherein the steps of (A), (B), (C) and (D) are taken in the alphabetical sequence.

7. The method of claim 6, wherein all the active switches are turned off before the step (A) is initiated.

8. A method for operating the DC-to-DC voltage regulator of claim 3, the method comprising the steps of:
(A) turning on the first active switch, and then turning off the first active switch when the current flowing in the first inductor is equal to zero;
(B) turning on the third active switch, and then turning off the third active switch when the current flowing in the second inductor is equal to zero;
(C) turning on the second active switch, and then turning off the second active switch when the current flowing in the first inductor is equal to zero; and
(D) turning on the fourth active switch, and then turning off the fourth active switch when the current flowing in the second inductor is equal to zero.

9. The method of claim 8, wherein the steps of (A), (B), (C) and (D) are taken in the alphabetical sequence.

10. The method of claim 9, wherein all the active switches are turned off before the step (A) is initiated.