DC-DC converter overvoltage suppression control circuit

Abstract

This suppresses the surge voltage applied to the switching element to a set voltage value, while also reducing the occurrence of snubber circuit losses. [Solution] The circuit configuration involves connecting an auxiliary switch circuit in series with the main switch circuit. This ensures a drive power supply for the auxiliary switch circuit without complicating the drive circuit. The auxiliary switch circuit regenerates the charge stored in the capacitor necessary to suppress the surge voltage of the DC-DC converter, controlling the capacitor voltage to a certain value or lower, thereby suppressing and controlling the overvoltage applied to the main switch circuit without causing snubber circuit losses.

Description

Technical Field

[0001] The present invention relates to a new overvoltage suppression control circuit and control method that can suppress the generation of surge voltage generated by the leakage inductance of a high-frequency transformer and the inductance of wiring that constitute a DC-DC converter below a set value without complicating the circuit configuration, prevent the breakdown voltage of the switching element from being exceeded, and suppress the occurrence of snubber circuit loss.

Background Art

[0002] In general DC-DC converters that are widely used in applications with relatively small capacitances, a simple circuit consisting of one switching element and a high-frequency transformer can be configured. However, due to differences in the secondary circuit configuration of the transformer that converts to the required voltage range for insulation, there are flyback converters and forward converters.

[0003] FIG. 1 shows a typical circuit configuration of both converters. Figure (a) shows a flyback converter, and Figure (b) shows a forward converter. In both converters, when the switch is turned off, a large surge voltage is applied to the switching element due to the energy stored in the leakage inductance of the transformer. If the element breakdown voltage is exceeded, there is a risk of element destruction, and a snubber circuit is used to suppress this.

[0004] Note that the primary circuit configurations of both converters are the same, and the control circuit operations for the purpose of suppressing overvoltage applied to the switching element are the same for both converters. Therefore, in the following explanatory diagrams of the present invention, As shown in Figure (a) The explanation will be limited to the flyback converter.

[0005] As shown in the figure, a normal snubber circuit includes a capacitor for absorbing snubber energy (snubber capacitor) )Therefore, when the switch is turned on, the energy stored in the snubber capacitor is connected via an inverse diode to prevent it from flowing into the switching element. Additionally, because it is necessary to release the energy stored in the snubber capacitor in preparation for the next commutation, a snubber resistor is usually connected in parallel with the snubber capacitor.

[0006] Figure 2 shows an example circuit in which the snubber circuit of the flyback converter is connected in parallel with the switching element.

[0007] Figure (a) shows a circuit configuration in which the surge voltage applied to the switching element is absorbed by a snubber capacitor Cs and released by a snubber resistor to prepare for the next switching operation, while Figure (b) shows the snubber resistor r connected to a DC power supply. The basic operation is the same as in Figure 1(a), and the surge voltage can be suppressed, but it involves snubber circuit losses determined by the leakage inductance value and current value of the transformer. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Tech Web Handbook, "Fundamentals and Design Procedures for AC / DC Converters," TWHB-06-001, ROHM, pp. 3-21, 2021. [Non-Patent Document 2] Jiro Togawa, "Coil / Transformer Design for Switching Power Supplies," CQ Publishing, pp. 176, pp. 87-97, 2012. [Non-Patent Document 3] Katsuya Hirachi, "From Fundamentals to Applications of Soft Switching," Institute of Electrical Engineers of Japan, pp. 3-21, 2022. [Patent Documents]

[0009] [Patent Document 1] Patent No. 6667750: "DC-DC converter" [Patent Document 2] Patent No. 6775745: "AC-DC converter" [Patent Document 3] Patent No. 7333127: “Resonant type AC-DC power supply” [Patent Document 4] Patent No. 7352327: "Resonant Current Controlled DC Power Supply" [Patent Document 5] Patent No. 7452920: "Current-controlled AC-DC power supply" [Overview of the project] [Problems that the invention aims to solve]

[0010] This invention aims to solve the problems of snubber circuits in DC-DC converters by using a relatively simple circuit configuration to suppress the surge voltage applied to the switching element to a set voltage value, regardless of the value of the transformer's leakage inductance or the magnitude of the load current, while also suppressing the occurrence of snubber circuit losses.

[0011] (Non-Patent Document 1) is an example of an explanatory article on DC-DC converters used in AC-DC converters, such as those found in AC adapters. It describes relatively small-capacity power supplies, such as flyback type (around 100W) and forward type (around 1.5kW), and includes a snubber circuit in its design procedure.

[0012] Non-patent document 2 provides detailed information on material selection and design methods for coils and transformers that constitute such switching power supplies. It offers useful information for designing DC-DC power supplies, such as transformer saturation and leakage inductance, the principle of surge voltage generation resulting from these, and methods for reducing noise. However, circuit losses due to snubber resistance in the circuit configuration cannot be avoided.

[0013] Non-patent document 3 provides a detailed explanation of LLC-type DC-DC converters and other control technologies that have been put into practical use, utilizing soft switching control, a control circuit method designed to overcome issues such as switching losses, surge voltages, and high-frequency noise generation caused by hard switches.

[0014] (Patent Document 1) is a soft-switching controlled DC-DC converter, and (Patent Document 2) is an application of this to an AC-DC converter section. Although rectification conversion can be performed from an AC power supply by soft-switching control, the output voltage control is frequency control, and a transformer etc. is used Because they are not there and it is impossible to insulate from the Output is DC supply power supply of the converter.

[0015] (Patent Document 3) connects a boost-type DC-DC converter to the output of (Patent Document 2), and controls the switching pulse width of the boost-type DC-DC converter in synchronization with the switching control of the resonant AC-DC converter, thereby maintaining the AC current waveform in a sine wave shape and enabling output control for any DC load under a constant switching frequency.

[0016] (Patent Document 4) uses a buck-boost type DC-DC converter for (Patent Document 2), thereby obtaining better resonant current characteristics similar to (Patent Document 1), and by using a flyback type DC-DC converter for the buck-boost type DC-DC converter, an isolated output can be obtained.

[0017] (Patent Document 3) and (Patent Document 4) both use current discontinuous control, so without combining special PFC control, the amplitude of the AC current can be made to act as a sine wave proportional to the AC power supply voltage.

[0018] However, although the rectifier circuit sections of both use soft-switching control by resonance, the voltage of the resonance capacitor proportional to the amplitude of the AC power supply is no ha - output control is performed by hard switching control such as boost control or buck-boost control.

[0019] Therefore, in the case of using a flyback converter circuit in the DC-DC converter section (Patent Document 4), similar to a general circuit, since a surge voltage is generated at the time of switch-off due to the leakage inductance of the high-frequency transformer, it is necessary to use a snubber circuit, and the problems of the DC-DC converter remain.

[0020] On the other hand, for the further miniaturization and weight reduction of the DC-DC converter, in the future, faster hard-switching elements such as SiC and GaN tend to be used, and since the generation of surge voltage associated with switching control becomes larger, further reduction of the transformer leakage inductance and wiring inductance that cause it is required.

[0021] However, when the DC-DC switching frequency increases, it is necessary to use a thin wire to reduce the influence of skin resistance. As the occupancy rate of the conductor decreases, it becomes difficult to achieve tight coupling between the primary and secondary windings, and it is considered that further reduction of the transformer leakage inductance becomes more difficult.

[0022] Furthermore, when the device capacity of the DC-DC converter increases, the wire for ensuring insulation between the primary and secondary windings also becomes thicker, and it is also considered that the interlayer insulation thickness increases, making it more difficult to reduce the transformer leakage inductance.

[0023] These From this perspective, there is a limit to reducing the leakage inductance of the transformer. When increasing the current capacity and using high-speed switching elements in the future, it is difficult to suppress overvoltage only with the conventional snubber circuit, and countermeasures for this are an issue.

[0024] (Patent Document 5) proposes a DC-DC power supply with a larger capacity by driving a transformer with a new current-mode full-bridge power supply. Since a large snubber circuit loss causes significant heat generation and efficiency reduction when the current increases, an overvoltage suppression circuit is added that can suppress the overvoltage applied to the switching element to a set value without generating a snubber circuit loss.

[0025] Figure 3 shows the basic circuit diagram when this overvoltage suppression control circuit is applied to a flyback DC-DC converter, and consists of a step-down chopper circuit composed of an auxiliary switch S2, a regenerative inductor Lc, and a diode.

[0026] In the same diagram, when the main switch S1 is turned off, The main switch S1 has a high voltage, which is the DC power supply voltage Eb plus the primary voltage v1 of the transformer, Absorbs commutation energy due to leakage inductance in high-frequency transformers. The resulting voltage is also superimposed. Voltage of snubber capacitor Cs but Exceeding the set voltage At that point Turn on auxiliary switch S2. By doing so The current from the regenerative inductor Lc flows into the DC power supply, and the energy absorbed by the snubber capacitor Cs By regenerating the power to a DC power supply and turning off switch S2 when the snubber capacitor voltage falls below the set voltage, The voltage applied to the main switch S1 The voltage is controlled to maintain the set voltage.

[0027] By adding this overvoltage protection circuit to the DC-DC converter, the overvoltage value applied to the main switch can be arbitrarily set regardless of the magnitude of the leakage inductance of the high-frequency transformer, and the occurrence of snubber circuit losses can be suppressed.

[0028] Snab countermeasures used in (Patent Document 5) to Although it requires additional circuitry, it can be considered an effective and fundamental solution for DC-DC converters with large device capacities.

[0029] However, the step-down chopper circuit that constitutes the overvoltage suppression control circuit shown in Figure 3 is further complicated in addition to the added snubber circuit configuration, in order to secure the drive power supply that drives the auxiliary switch S2. Therefore, it is considered difficult to apply it to a typical DC-DC converter with a small power supply capacity due to size, cost, etc. [Means for solving the problem]

[0030] The present invention provides a means to simplify the drive circuit of the overvoltage suppression control circuit described above, in order to solve the snubber circuit problem in DC-DC converters with relatively small capacitance, such as flyback converters and forward converters. (1) Operation of the basic circuit for overvoltage suppression control

[0031] Figure 4 shows the basic operating principle of the overvoltage suppression control circuit of the DC-DC converter according to the present invention. The DC-DC converter is configured such that the primary current of the high-frequency transformer 300 is controlled by the switch control circuit section 200 with respect to the DC power supply 100, and the output of the DC load 500 is controlled by the secondary current via the rectifier and smoothing section 400. The circuit configuration ensures the drive power of the auxiliary switch S2 by bootstrap operation through a circuit configuration in which the auxiliary switch S2 is connected in series with the main switch S1 of the flyback DC-DC converter, and the circuit configuration allows the surge voltage due to the leakage inductance of the high-frequency transformer to be absorbed by the capacitor Cs, and the absorbed energy to be regenerated to the DC power supply Eb.

[0032] Figure 5 is an operating mode diagram of a specific half-bridge circuit configuration that includes a drive circuit in which a MOSFET and a diode are connected in antiparallel as semiconductor switches to form a main switch circuit S1 and an auxiliary switch circuit S2, with the auxiliary switch circuit S2 connected in series to the upper stage of the main switch circuit S1 and a capacitor Cs connected across both ends of the series switch circuit. The diagram also illustrates the means for securing the drive power supply for the auxiliary switch circuit S2.

[0033] Figure (a) shows both switches S1 and S2 in the off state. Figure (b) shows that when the main switch S1 is turned on, the voltage VB of the drive power supply for the main switch S1 generates a current that charges the capacitor CB2 of the auxiliary switch's drive circuit, thus securing the drive power supply for the auxiliary switch S2. Depending on the direction of the load current, current flows through the paths shown in Figures (c) and (d), returning the system to the state shown in Figure (a) where both switches S1 and S2 are off. When the main switch S1 is turned on, the drive power supply for the auxiliary switch S2 is secured.

[0034] Furthermore, if the auxiliary switch S2 is connected in series with the main switch S1, then, as will be described later, such bootstrap circuit operation is possible in principle even if a diode is connected in series.

[0035] Therefore, this overvoltage suppression control circuit, in principle, does not cause snubber circuit losses, and the voltage of the snubber capacitor can be controlled to any set value by an auxiliary switch, thus suppressing the surge voltage value that occurs when the main switch circuit is turned off.

[0036] As a specific circuit configuration example that realizes the basic control principle of the overvoltage suppression circuit of the DC-DC converter according to the present invention, the control operating principle of a DC-DC converter circuit that combines two overvoltage suppression control circuits, A-Type and B-Type, with the DC-DC converter circuit will be explained. (2) Circuit operation of the A-Type DC-DC converter

[0037] The A-Type DC-DC converter shown in Figure 6 is constructed by connecting two switch circuits in series, each consisting of a semiconductor switch with a diode connected in antiparallel. Power is supplied from a DC power supply 100 via a high-frequency transformer 300, and the output of the DC-DC converter is controlled by the main switch S1 of the lower switch circuit 210-1 of the switching control circuit section 200. The charge and discharge of the capacitor 220, which absorbs the surge voltage caused by the commutation energy of the leakage inductance of the high-frequency transformer, is controlled by the diode Ds1 and the upper switch circuit. This can be constructed with an extremely simple circuit consisting only of two sets of switch circuits and a snubber capacitor.

[0038] Figure 7 shows the operating waveform of an A-Type DC-DC converter, and consists of the six operating modes shown, depending on the switching signals (S1) and (S2) of the two switch circuits and the current path state.

[0039] Figure 8 shows the current paths in operation modes (1), (2)-1, (2)-2, and (3)-1, among these six operating modes.

[0040] The operating principle of the A-Type DC-DC converter circuit of the present invention is as follows: In operating mode (1), when the main switch S1 is turned on, current flows to the high-frequency transformer, and when the main switch S1 is turned off, an ON signal is given to the auxiliary switch S2. In operating mode (2)-1, after the current due to the commutation energy of the leakage inductance of the high-frequency transformer flows through the diode Ds2 of the upper switch circuit to the snubber capacitor Cs becomes zero, in operating mode (2)-2, a regenerative current flows from the snubber capacitor Cs to the DC power supply via the high-frequency transformer, and when the voltage of the snubber capacitor Cs falls below the set voltage value Vp, the auxiliary switch S2 is turned off, and in operating mode (3)-1, the diode Ds1 of the lower switch circuit... RouteWhen current flows and this current becomes zero, the system enters operating mode (3)-2, the primary current i1 decreases to zero, and the system enters operating mode (4), which is maintained until the next ON signal is given to the main switch S1.

[0041] On the other hand, the secondary current i2 of the high-frequency transformer begins to flow when the main switch S1 is turned off, as the current in the excitation circuit of the high-frequency transformer combines with the leakage inductance current, peaking at the end of operating mode (2)-1, and after operating mode (3)-1 in which free-foiling current flows, the excitation current of the high-frequency transformer becomes the DC voltage of the secondary DC capacitor Cd. flow When the secondary current i2 decreases to zero, it stops flowing, entering operating mode (4), and all current stops flowing. This state continues until an ON signal is applied to the main switch S1 in the next cycle.

[0042] Here, the voltage Vs1 across the main switch S1 is, in the flyback converter, When the main switch S1 is turned off, current i2 flows to the secondary side of the transformer due to the action of the transformer's excitation inductance, the voltage at the output terminal of the DC-DC converter is added as the secondary voltage v2 of the transformer, and a voltage v1 multiplied by the transformation ratio appears as the primary voltage of the transformer. In addition to the high voltage obtained by adding this voltage v1 to the DC power supply voltage Eb, the voltage across capacitor Cs rises to an even higher voltage due to the commutation energy caused by the transformer's leakage inductance. Therefore, the above set voltage needs to be an appropriate voltage value Vp that is Eb + V1 or higher and less than or equal to the breakdown voltage of the switch element used.

[0043] In the operating mode from the moment the main switch S1 is turned off, the commutation energy of the leakage inductance of the high-frequency transformer is stored in the snubber capacitor Cs and then regenerated to the DC power supply, so there are basically no snubber circuit losses.

[0044] Furthermore, since the auxiliary switch S2 is turned off when the voltage of the snubber capacitor Cs falls below the set voltage value Vp, if the value of the snubber capacitor Cs is selected such that the voltage fluctuation of the snubber capacitor Cs during one switching cycle is negligible, the voltage vs1 applied to the main switch S1 can be kept to approximately the set voltage value Vp.

[0045] In addition, As shown in Figure 7, If the next switch operation begins before the excitation current of the high-frequency transformer becomes zero, the excitation current will increase continuously, making current control impossible. Therefore, it goes without saying that the operating period T12 for operating modes (1) to (3) must be set to be shorter than the switching control period T that includes operating mode (4). (3) Circuit operation of the B-Type DC-DC converter

[0046] The B-Type DC-DC converter shown in Figure 9 is configured to receive a DC power supply 100 via a high-frequency transformer 300, and a switching control circuit section 200 consisting of a switch circuit 210-2 with five diodes D1-D5 and a regenerative inductor Lc, and a snubber capacitance. TaCs The circuit section 220 is configured, and the main switch S1 of the lower switch circuit of 2 10-2 controls the output of the DC-DC converter. Uto In both cases, the charge and discharge control of the capacitor 220, which absorbs surge voltage due to the commutation energy of the leakage inductance of the high-frequency transformer, is performed by using separate switch paths for the charging and discharging paths.

[0047] Figure 10 shows the operating waveform of a B-Type DC-DC converter, and consists of the six operating modes shown, depending on the switching signals (S1) and (S2) of the two switch circuits and the current path state.

[0048] Figure 11 shows the current paths in operation modes (1), (2)-1, (2)-2, and (3)-1, among these six operating modes.

[0049] The operating principle of the B-Type DC-DC converter circuit of the present invention is as follows: In operating mode (1), when the main switch S1 is turned on and current flows to the high-frequency transformer, the drive power for the auxiliary switch S2 is secured. When the main switch S1 is turned off, an ON signal is given to the auxiliary switch S2. In operating mode (2)-1, the current i1 due to the commutation energy of the leakage inductance of the high-frequency transformer flows into the snubber capacitor Cs via diode D1, the high-frequency transformer, and diode D3. After this current becomes zero, the auxiliary switch S2 conducts. In operating mode (2)-2, the current iLc from the capacitor flows as a regenerative current to the DC power supply via the regenerative inductor Lc and diode D5. When the capacitor voltage falls below the set Vp value, the auxiliary switch S2 is turned off, and diode D4, regenerative inductor Lc, and diode D5 via a route through When current flows and this current becomes zero, the device enters operating mode (3)-2, the primary current i1 decreases to zero, and the device enters operating mode (4), which is maintained until the next ON signal is given to the main switch S1.

[0050] On the other hand, the secondary current i2 of the high-frequency transformer begins to flow when the main switch S1 is turned off, as the current i1 in the excitation circuit of the high-frequency transformer combines with the leakage inductance current. It peaks at the end of operating mode (2)-1, and during the intervals of operating modes (2)-2, (3)-1, and (3)-2, the excitation current of the high-frequency transformer decreases due to the DC voltage of the secondary DC capacitor Cd and flows down to zero. In operating mode (4), no current flows at all, and this state continues until an ON signal is applied to the main switch S1 in the next cycle.

[0051] In addition, As shown in Figure 10, If the next switch operation begins before the excitation current of the high-frequency transformer becomes zero in operating mode (4), the excitation current will increase continuously, making current control impossible. Therefore, the operating period T12 for operating modes (1) to (3) must be set to be shorter than the switching control period T, as is the case with the circuit operation shown in Figure 6.

[0052] As described above, even in the B-Type DC-DC converter shown in Figure 9, there are basically no snubber circuit losses, and the voltage vs1 applied to the main switch S1 can be kept to approximately the set voltage value Vp.

[0053] Furthermore, it goes without saying that the switching period T must also be set so that all currents are zero, preventing the excitation current of the high-frequency transformer from entering a continuous operation mode.

[0054] When the DC-DC converter of the present invention is to operate with discontinuous current, by connecting the rectified output voltage obtained from a single-phase power supply via a filter circuit as a DC power supply, it can be made to operate as an AC-DC converter power supply with a sinusoidal current waveform proportional to the sinusoidal single-phase voltage waveform.

[0055] Figure 12 shows examples of circuit configurations for (a) an AC-DC converter power supply using an A-Type DC-DC converter and (b) a B-Type DC-DC converter power supply.

[0056] In the diagram, the power line inductor La includes the power line impedance, and the filter circuit is intended to remove the switching frequency component of the DC-DC converter.

[0057] Furthermore, by selecting the circuit constants of the DC output filter of the full-wave rectifier circuit shown in the figure according to the switching frequency, the characteristics of the resonant circuit operation described in (Patent Document 4) can also be expected.

[0058] In addition, the overvoltage suppression control circuit of the DC-DC converter of the present invention, compared to the AC-DC converter using discontinuous current control shown in (Patent Document 5), makes it possible to easily secure a drive power supply for the auxiliary switch by using the same combination circuit configuration as the B-Type for the PFC switch circuit and the auxiliary switch for snubber control, even when configuring an AC-DC converter power supply that includes a continuous current control PFC converter in the DC power supply section. [Effects of the Invention]

[0059] The present invention addresses the problem of snubber circuit losses occurring even when surge voltage is suppressed, as the surge voltage applied to the main switch element changes depending on the value of the transformer's leakage inductance, the current value, and the switching speed when the main switch that controls the current of the DC-DC converter is turned off. The effects of the present invention include the following:

[0060] 1) The value of the overvoltage suppression voltage can be arbitrarily set to be less than or equal to the allowable value (Vp) of the switch element. 2) Since the commutation energy of the leakage inductance of a high-frequency transformer can be regenerated into the DC power supply, snubber losses do not occur, and thus an improvement in efficiency can be expected. 3) By configuring the circuit to connect the auxiliary switch circuit and the main switch circuit in series, which constitute the overvoltage suppression control circuit, the drive power for the auxiliary switch can be easily secured by the bootstrap operation when the main switch circuit is turned on. 4) An A-Type DC-DC converter can be constructed using two switch circuits with semiconductor elements and diodes connected in antiparallel, and a snubber capacitor, resulting in an extremely simple circuit configuration. 5) In a B-Type DC-DC converter, the regenerative current from the snubber energy absorbed by the snubber capacitor does not pass through the transformer, thus eliminating any impact on the secondary current. 6) By connecting the rectified output via a filter circuit to a single-phase power supply as the DC power supply for the DC-DC converter of the present invention, a high power factor AC-DC converter power supply can be easily realized. [Brief explanation of the drawing]

[0061] [Figure 1]Typical DC-DC converter circuits and snubber circuits (a) Flyback converter circuit (b) Forward converter circuit [Figure 2] Examples of configurations for parallel snubber circuits with switching elements: (a) Parallel snubber circuit 1 (capacitor connection of snubber resistor) (b) Parallel snubber circuit 2 (DC power supply connection of snubber resistor) [Figure 3] Surge voltage control and snubber loss reduction circuit using a step-down chopper circuit [Figure 4] Basic principles of the overvoltage suppression control circuit of the present invention [Figure 5] Bootstrap circuit operation diagram for auxiliary switch [Figure 6] DC-DC converter with overvoltage suppression control circuit according to the present invention (Type A) [Figure 7] Operating waveform of the A-Type overvoltage suppression control circuit of the present invention [Figure 8] Each operating mode of the A-Type overvoltage suppression control circuit of the present invention [Figure 9] DC-DC converter with overvoltage suppression control circuit according to the present invention (Type B) [Figure 10] Operation waveform of the B-Type overvoltage suppression control circuit of the present invention [Figure 11] Each operating mode of the B-Type overvoltage suppression control circuit of the present invention [Figure 12] AC-DC converter circuits using the DC-DC converter with overvoltage suppression control circuit of the present invention: (a) A-Type AC-DC converter circuit (b) B-Type AC-DC converter circuit [Figure 13] AC-DC converter control system using the overvoltage suppression control circuit of the present invention [Figure 14] Switching control operation waveform of the A-Type AC-DC converter circuit of the present invention (Idr=1.5A) [Figure 15] Switching control operation waveforms of multiple B-Type AC-DC converter circuits (Idr=1.5A) [Modes for carrying out the invention]

[0062] Figure 13 shows an example of an embodiment of the overvoltage suppression control circuit for the DC-DC converter of the present invention, illustrating a control system for an AC-DC converter power supply that uses a full-wave rectified output of a single-phase power source, passed through a switching harmonic component removal filter circuit to obtain a DC power supply.

[0063] In the same figure, the DC-DC converter section shows the a) Type A and b) Type B overvoltage suppression control circuits shown in Figure 11, and the effectiveness of these circuits will be verified by simulation analysis.

[0064] Figures 14 and 15 show the operating waveforms obtained from simulation analysis under each circuit constant and operating condition.

[0065] The main circuit constants of the two AC-DC power supplies are the same except for the use of a regenerative inductor Lc in the B type. When a single-phase AC power supply with voltage Va=200V and frequency 60 Hz is applied, the transformation ratio of the high-frequency transformer is In step 1, an LED light (forward voltage drop VF = 170V, resistance RF = 10 ohms) was connected as a DC load, and the control conditions were set to a DC current reference value Idr = 1.5A and an overvoltage suppression setting voltage Vpr = 600V.

[0066] Figure 14 shows the simulation results for a Type A AC-DC converter power supply. From Figure (a), the characteristics of the AC-DC power supply show that the DC current id can be controlled to the reference value Idr = 1.5A, and the AC power supply current ia at that time can be controlled to be sinusoidal. Figure (b) shows an enlarged view of the time axis with the peak value of the AC current, and the operating waveform is the same as in Figure 6. It can be confirmed that the peak value of the voltage vs1 applied when the main switch is turned off is suppressed to the set value Vp = 600V.

[0067] Figure 15 shows the simulation results for a Type B AC-DC converter power supply. From Figure 15(a), it can be seen that the DC current id can be controlled to the reference value Idr = 1.5A, and the AC power supply current ia at that time can be controlled to be sinusoidal. Figure 15(b) shows an enlarged view of the time axis with the peak value of the AC current, and the operating waveform is the same as in Figure 9. It can be confirmed that the peak value of the voltage vs1 applied when the main switch is turned off is suppressed to the set value Vp = 600V. [Explanation of symbols]

[0068] 100 … DC power supply 110 … DC power supply for DC-DC converter 120 ... Rectified DC power supply for AC-DC converter 200 ... DC-DC converter overvoltage suppression switching control circuit 210-1 … Switching control circuit of A-Type overvoltage suppression DC-DC converter 210-2 … Switching control circuit for B-Type overvoltage suppression DC-DC converter 220 ... Capacitor (snubber capacitor) 300 ... Transformer (High-frequency transformer) 400... Rectifier and smoothing circuit for DC-DC flyback converter 500... DC load 510 … General DC load 520…LED load 600 ... Control system 610 … DC-DC converter control system 620 … Overvoltage protection control system

Claims

1. In a DC-DC converter circuit that connects a DC power supply to a main switch circuit via the primary winding of a transformer, controls the current flowing through the transformer by the switching action of the main switch circuit, and obtains the required isolated DC output voltage via the transformer, As a circuit configuration in which an auxiliary switch circuit connected to a capacitor that suppresses surge voltage generated by the leakage inductance of the transformer is connected in series with the main switch circuit, The bootstrap operation when the main switch circuit is ON secures the drive power for the auxiliary switch circuit. When the main switch circuit is off, an ON signal is given to the auxiliary switch circuit, and when the voltage charged to the primary capacitor falls below a set value, an OFF signal is given to the auxiliary switch circuit. When the main switch circuit is turned off, the energy stored by the leakage inductance of the transformer is absorbed by the capacitor and then regenerated into the DC power supply, An overvoltage suppression control circuit for a DC-DC converter, characterized by suppressing the generation of surge voltage applied to the main switch circuit.

2. In the overvoltage suppression control circuit for a DC-DC converter according to claim 1, the main switch circuit and the auxiliary switch circuit are configured using a switch circuit in which a semiconductor switch and a diode are connected in antiparallel, From the moment the main switch circuit is off, an ON signal is given to the auxiliary switch circuit, and from the moment the voltage charged to the primary capacitor falls below a set value, an OFF signal is given to the auxiliary switch circuit. This ensures that a current path is secured that allows current to flow from the primary winding of the transformer to the capacitor through the diode of the auxiliary switch circuit, and from the capacitor to the DC power supply via the semiconductor switch of the auxiliary switch circuit and the primary winding of the transformer. From the moment the auxiliary switch circuit is turned off, until the current in the primary winding of the transformer becomes zero via the diode of the main switch circuit, a current path is secured that allows for free-foiling operation. An overvoltage suppression control circuit for a DC-DC converter, characterized by suppressing the generation of surge voltage applied to the main switch circuit.

3. In the overvoltage suppression control circuit for a DC-DC converter according to claim 1, the main switch circuit and the auxiliary switch circuit are configured using the semiconductor switch, The circuit configuration involves connecting the auxiliary switch circuit and the main switch circuit in series via the diode 2, The circuit configuration includes: a circuit connecting the DC power supply to the main switch circuit via diode 1 and the transformer, a circuit connecting the primary winding of the transformer to the main switch circuit terminal via diode 3 to the capacitor, a circuit connecting the auxiliary switch circuit to the connection terminal of diode 2, a circuit connecting diode 4 from the negative side of the DC power supply, and a regenerative inductor and diode 5 connected in series to the positive side of the DC power supply. When the main switch circuit is off, an ON signal is given to the auxiliary switch circuit, and when the voltage charged to the primary capacitor falls below a set value, an OFF signal is given to the auxiliary switch circuit. Until then, a current path is secured that allows current to flow from the primary winding of the transformer to the capacitor through diode 3 and from the capacitor through the auxiliary switch circuit to the DC power supply via the regenerative inductor and diode 5. From the moment the signal of the auxiliary switch circuit is turned off, until the current in the regenerative inductor becomes zero via diode 4, a current path is secured that allows free-foiling operation. An overvoltage suppression control circuit for a DC-DC converter, characterized by suppressing and controlling the voltage applied to the main switch circuit.

4. As the DC power supply for the overvoltage suppression control circuit of the DC-DC converter according to claims 1 to 3, a full-wave rectified power supply with a circuit configuration in which a filter circuit that removes the switching harmonic components of the DC-DC converter is connected to the AC side or DC side of the full-wave rectifier circuit is connected to the AC power supply, An overvoltage suppression control circuit for a DC-DC converter, characterized by suppressing the voltage applied to the main switch circuit of the DC-DC converter, which constitutes an AC-DC converter that obtains a DC output voltage with a high power factor from an AC power source.

Images