DC-DC converter overvoltage suppression control circuit

Abstract

The surge voltage applied to the switching element is suppressed to a set voltage value, and the occurrence of snubber circuit loss is suppressed. [Solution] A circuit configuration in which an auxiliary switch circuit is connected in series with a main switch circuit 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 required to suppress the surge voltage of the DC-DC converter, controls the capacitor voltage to a certain value or below, and suppresses and controls the overvoltage applied to the main switch circuit without causing snubber circuit loss.

Description

[Technical Field]

[0001] This invention relates to a new overvoltage suppression control circuit and control method that can suppress surge voltages caused by leakage inductance of high-frequency transformers and wiring inductance in DC-DC converters to below a set value, prevent the withstand voltage of switching elements from being exceeded, and suppress snubber circuit losses, without complicating the circuit configuration. [Background technology]

[0002] General DC-DC converters, which are widely used for applications requiring relatively small capacity, can be configured with a simple circuit consisting of one switch element and a high-frequency transformer, but there are two types: flyback converters and forward converters, which differ in the secondary circuit configuration of the transformer that provides isolation and converts to the required voltage range.

[0003] Figure 1 shows the typical circuit configuration for both converters. Figure (a) shows a flyback converter, and Figure (b) shows a forward converter. In either converter, 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 this voltage exceeds the element's withstand voltage, it could cause destruction of the element, so a snubber circuit is used to suppress this.

[0004] The primary circuit configuration of both converters is the same, and the control circuit operation for suppressing overvoltage applied to the switch element is the same for both converters. As shown in Figure (a) The description will be limited to flyback converters.

[0005] As shown in the figure, a typical snubber circuit uses a capacitor for absorbing snubber energy (snubber capacitor )When the switch is turned on, the snubber capacitor is connected via an inverse diode to prevent the energy stored in the snubber capacitor from flowing into the switch element. Also, since 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] FIG. 2 shows an example of a circuit in which a snubber circuit of a flyback converter is inserted in parallel with a switching element.

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

[0008] [Non-Patent Document 1] Tech Web Hand Book, "Fundamentals and Design Procedures of AC / DC Converters", TWHB-06-001, ROHM, p.3-21, 2021. [Non-patent document 2] Jiro Togawa, "Coil / Transformer Design for Switching Power Supplies," CQ Publishing, pp. 176, 87-97, 2012. [Non-patent document 3] Katsuya Hirachi, "Soft Switching: From Fundamentals to Applications," 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" Summary of the Invention [Problem to be solved by the invention]

[0010] This invention aims to solve the issues 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 leakage inductance or the magnitude of the load current, and by suppressing the occurrence of snubber circuit loss.

[0011] (Non-Patent Document 1) is an example of an explanatory article about DC-DC converters used in AC-DC converters, such as AC adapters, and describes the design procedure for relatively small-capacity power supplies, up to about 100W for the flyback type and up to about 1.5kW for the forward type, including snubber circuits.

[0012] (Non-Patent Document 2) provides detailed information on material selection and design methods for the coils and transformers that make up such switching power supplies, and provides useful information on designing DC-DC power supplies, such as transformer saturation and leakage inductance, the principles behind the resulting surge voltage, and methods for reducing noise. However, circuit loss due to snubber resistance in the circuit configuration cannot be avoided.

[0013] (Non-Patent Document 3) provides a detailed explanation of LLC DC-DC converters, which have been put to practical use as a control technology using soft switching control, a control circuit method for overcoming issues such as switching loss, surge voltage, and high-frequency noise 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 from an AC power source can be performed by soft switching control, output voltage control is frequency control and no transformer or the like is used. Because there is no , the converter's Output is DC supply It cannot be isolated from the power supply.

[0015] In (Patent Document 3), a step-up DC-DC converter is connected to the output of (Patent Document 2), and the switching pulse width of the step-up DC-DC converter is controlled in synchronization with the switching control of the resonant AC-DC converter, thereby enabling output control for any DC load at a constant switching frequency while maintaining the AC waveform sinusoidal.

[0016] In (Patent Document 4), by using a step-up / step-down DC-DC converter in contrast to (Patent Document 2), it is possible to obtain superior resonance current characteristics similar to (Patent Document 1), and by using a flyback DC-DC converter instead of the step-up / step-down DC-DC converter, it is possible to obtain an isolated output.

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

[0018] However, the rectifier circuit of both uses soft switching control by resonance, but the voltage of the resonance capacitor, which is proportional to the amplitude of the AC power supply, is controlled by voltage boost control or voltage boost / buck control. Noha The output is controlled by hard switching control.

[0019] For this reason, when a flyback converter circuit is used in the DC-DC converter section (Patent Document 4), a surge voltage occurs when the switch is turned off due to the leakage inductance of the high-frequency transformer, just like in general circuits, so a snubber circuit must be used, and issues with DC-DC converters remain.

[0020] On the other hand, the DC-DC converter Further In order to reduce size and weight, there is a trend towards using faster hard-switching elements such as SiC and GaN. However, the surge voltages generated by switching control will increase, so there is a need to further reduce the transformer leakage inductance and wiring inductance that cause these surges.

[0021] However, as the DC-DC switching frequency increases, it becomes necessary to use thinner wire to reduce the effect of skin resistance, and as the conductor area decreases, it becomes more difficult to achieve close coupling between the primary and secondary windings, making it even more difficult to reduce transformer leakage inductance.

[0022] Furthermore, as the device capacity of DC-DC converters increases, the wire used to ensure insulation between the primary and secondary windings will also become thicker, which may increase the thickness of the interlayer insulation, making it more difficult to reduce transformer leakage inductance.

[0023] These From this perspective, there is a limit to how much leakage inductance can be reduced in transformers, and with the increase in current capacity and the use of high-speed switching elements in the future, it will become difficult to suppress overvoltage using only conventional snubber circuits, making it an issue to find countermeasures.

[0024] In (Patent Document 5), a transformer is driven by a new current-type full-bridge power supply, and is proposed as a DC-DC power supply with a larger capacity. As the current increases, snubber circuit loss leads to large heat generation and reduced efficiency, so an overvoltage suppression circuit is added that can suppress and control the overvoltage applied to the switching element to a set value without generating snubber circuit loss.

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

[0026] In the same figure, when the main switch S1 is turned off, The main switch S1 is connected to the DC power supply voltage Eb plus the primary voltage v1 of the transformer, Absorbs commutation energy due to leakage inductance of high frequency transformers The voltage due to this is also superimposed Voltage of snubber capacitor Cs but Exceeding the set voltage At this point Auxiliary switch S2 on By making The current of the regenerative inductor Lc flows into the DC power supply, and the energy absorbed by the snubber capacitor Cs is regenerated to the DC power supply, and when the voltage of the snubber capacitor falls below the set voltage, switch S2 is turned off. The voltage applied to the main switch S1 is The voltage is suppressed and controlled to 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 set arbitrarily, regardless of the leakage inductance value of the high-frequency transformer, and snubber circuit loss can be suppressed.

[0028] Snubber measures used in (Patent Document 5) to Although this requires additional circuitry, it can be said to be an effective 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 becomes even more complicated due to the additional snubber circuit configuration and the need to secure a drive power supply to drive the auxiliary switch S2. Therefore, it is thought that application to a general DC-DC converter with a small power supply capacity would be difficult in terms of size, cost, etc. [Means for solving the problem]

[0030] The present invention provides a means for simplifying the drive circuit of the above-mentioned overvoltage suppression control circuit in order to solve the problems of snubber circuits in DC-DC converters with relatively small capacity, such as flyback converters and forward converters. (1) Basic circuit operation of overvoltage suppression control

[0031] FIG. 4 is a diagram showing the basic operating principle of an overvoltage suppression control circuit for a DC-DC converter according to the present invention. This DC-DC converter is configured so that, for a DC power supply 100, the primary current of a high-frequency transformer 300 is controlled by a switch control circuit section 200, and the secondary current is passed through a rectifying and smoothing section 400 to control the output of a DC load 500. The circuit is configured so that the auxiliary switch S2 is connected in series with the main switch S1 of the flyback DC-DC converter, and a bootstrap operation is performed to ensure a drive power supply for the auxiliary switch S2. The surge voltage due to the leakage inductance of the high-frequency transformer is absorbed by a capacitor Cs, and the absorbed energy is then regenerated into the DC power supply Eb.

[0032] FIG. 5 is an operating mode diagram of a specific half-bridge circuit configuration including a drive circuit in which a main switch circuit S1 and an auxiliary switch circuit S2 are configured using switch circuits in which MOSFETs and diodes are connected in anti-parallel as semiconductor switches, the auxiliary switch circuit S2 is connected in series to the upper stage of the main switch circuit S1, and a capacitor Cs is connected across the series switch circuit, and shows an explanatory diagram of means for securing a drive power supply for the auxiliary switch circuit S2.

[0033] Figure 1(a) shows that both switches S1 and S2 are in the off state, and Figure 1(b) shows that when the main switch S1 is turned on, a current flows that charges capacitor CB2 of the auxiliary switch drive circuit with the voltage VB of the drive power supply for the main switch S1, thereby ensuring drive power for the auxiliary switch S2. Depending on the direction of the load current, current flows through the paths shown in Figure 1(c) and Figure 1(d), and the state returns to Figure 1(a) where both switches S1 and S2 are off, and when the main switch S1 is turned on, the drive power for the auxiliary switch S2 is ensured.

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

[0035] Therefore, in principle, this overvoltage suppression control circuit can control the voltage of the snubber capacitor to any set value using the auxiliary switch without causing any snubber circuit loss, so it can suppress and control the surge voltage value that occurs when the main switch circuit is turned off.

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

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

[0038] Figure 7 shows the operating waveforms of an A-Type DC-DC converter, which consists of six operating modes as shown, depending on the switching signals (S1) and (s2) of the two switch circuits and the current path state.

[0039] FIG. 8 shows the current paths in the operation modes (1), (2)-1, (2)-2, and (3)-1 out of these six operation modes.

[0040] The operating principle of the A-Type DC-DC converter circuit of the present invention is as follows: in operation mode (1), the main switch S1 is turned on, current flows through the high frequency transformer, and when the main switch S1 is turned off, an ON signal is sent to the auxiliary switch S2. In operation mode (2)-1, the current due to the commutation energy of the leakage inductance of the high frequency transformer flows into the snubber capacitor Cs via the diode Ds2 of the upper switch circuit. After this current becomes zero, in operation 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 becomes equal to or lower than the set voltage value Vp, the auxiliary switch S2 is turned off. In operation mode (3)-1, By routeCurrent flows, and when this current becomes zero, the operation mode becomes (3)-2, the primary current i1 decreases and becomes zero, the operation mode becomes (4), and this state 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 starts to flow when the main switch S1 is turned off, as the current in the excitation circuit of the high frequency transformer is combined with the current in the leakage inductance, and reaches a peak at the end of operation mode (2)-1. After operation mode (3)-1, in which the free-foiling current flows, the excitation current of the high frequency transformer becomes the DC voltage of the secondary side DC capacitor Cd. flow When it decreases to zero, the secondary current i2 stops flowing, the operation mode (4) is entered, and all current stops flowing. This state continues until an ON signal is input to the main switch S1 in the next cycle.

[0042] Here, the voltage Vs1 applied to the main switch S1 in a flyback converter is When the main switch S1 is turned off, the action of the transformer's magnetizing inductance causes current i2 to flow on the secondary side of the transformer, and the voltage at the output end of the DC-DC converter is added as secondary side voltage v2 to the transformer, and voltage v1 multiplied by the transformation ratio appears as the primary side 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 of capacitor Cs rises to an even higher voltage due to the commutation energy caused by the transformer's leakage inductance, so the above set voltage must be an appropriate voltage value Vp that is below the withstand voltage of the switch element used at Eb + V1 or above.

[0043] In the operating mode from the point when 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 basically there is no snubber circuit loss.

[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 so that the voltage fluctuation of the snubber capacitor Cs during one switching cycle can be ignored, the voltage vs1 applied to the main switch S1 can be kept almost at 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 it impossible to control the current. Therefore, it goes without saying that the operating period T12 from operating modes (1) to (3) must be set to be shorter than the switching control period T including operating mode (4). (3) Circuit operation of B-Type DC-DC converter

[0046] The B-Type DC-DC converter shown in FIG. 9 is connected to a DC power source 100 via a high frequency transformer 300, and is connected to a switching control circuit 200, which is configured by connecting two semiconductor switches in series via a diode D2, and is connected to a switch circuit 210-2 and a snubber capacitor 220-3, which is configured by connecting five diodes D1 to D5 and a regenerative inductor Lc. TaCs The main switch S1 of the lower switch circuit of 210-2 controls the output of the DC-DC converter. Uto In both cases, the charge and discharge control of the capacitor 220 that absorbs surge voltage caused by the commutation energy of the leakage inductance of the high frequency transformer is performed by separate switch paths for the charge path and the discharge path.

[0047] Figure 10 shows the operating waveforms of the B-Type DC-DC converter, which consists of six operating modes as shown in the figure, 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 the six operating modes (1), (2)-1, (2)-2, and (3)-1.

[0049] The operating principle of the B-Type DC-DC converter circuit of the present invention is as follows: In operation mode (1), when the main switch S1 is turned on and current flows through the high frequency transformer, the drive power supply for the auxiliary switch S2 is secured, and when the main switch S1 is turned off, an ON signal is sent to the auxiliary switch S2; in operation mode (2)-1, 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 becomes conductive; and in operation mode (2)-2, current iLc from the capacitor flows into the DC power supply via the regenerative inductor Lc and diode D5 as a regenerative current; when the capacitor voltage becomes equal to or lower than the set Vp value, the auxiliary switch S2 is turned off, and the diode D4, the regenerative inductor Lc, and diode D5 via the route When the current flows and becomes zero, the operation mode (3)-2 is entered, the primary current i1 decreases to zero, and the operation mode (4) is entered, and this state 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 starts to flow when the main switch S1 is turned off, combining with the current i1 in the excitation circuit of the high frequency transformer and the current in the leakage inductance, and reaches a peak at the end of operation mode (2)-1. During operation 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 side DC capacitor Cd and flows to zero, and in operation mode (4) all current stops flowing, and this state continues until an ON signal is input 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 operation mode (4), the excitation current will continue to increase, making it impossible to control the current. Therefore, the operation period T12 from operation modes (1) to (3) must be set to be shorter than the switching control period T, just like the circuit operation in Figure 6.

[0052] As a result, even in the B-Type DC-DC converter shown in Figure 9, there is basically no snubber circuit loss, and the voltage vs1 applied to the main switch S1 can be kept almost at the set voltage value Vp.

[0053] It goes without saying that the switching period T must also be set so that all currents become zero, so that the excitation current of the high frequency transformer does not enter a continuous operation mode.

[0054] When the DC-DC converter of the present invention is operated with discontinuous current, the rectified output voltage from a single-phase power supply via a filter circuit can be connected as a DC power supply, allowing it to function 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 as (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 figure, the power supply line inductor La includes the power supply line impedance, and the filter circuit is intended to remove the switching frequency components of the DC-DC converter.

[0057] In addition, by selecting the circuit constants of the DC output filter of the full-wave rectifier circuit in the figure in accordance with the switching frequency, it is possible to expect the characteristics of the resonant circuit operation in (Patent Document 4).

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

[0059] The present invention addresses the problem that the overvoltage suppression control circuit of a DC-DC converter is difficult to design a snubber circuit to suppress the surge voltage that occurs when the main switch that controls the current of the DC-DC converter is turned off, as the surge voltage applied to the main switch element varies depending on the value of the leakage inductance of the transformer, the current value, and the switching speed, and even if the surge voltage can be suppressed, snubber circuit loss still occurs, and the effects of the present invention include the following.

[0060] 1) The value of the overvoltage suppression voltage can be set arbitrarily to a value below the allowable value (Vp) of the switching element. 2) The commutation energy of the leakage inductance of the high-frequency transformer can be regenerated into the DC power supply, so no snubber loss occurs, and efficiency can be expected to improve. 3) By configuring the circuit so that the auxiliary switch circuit and the main switch circuit that make up the overvoltage suppression control circuit are connected in series, the drive power supply for the auxiliary switch can be easily secured by bootstrap operation when the main switch circuit is turned on. 4) The A-Type DC-DC converter can be configured with two switches, each consisting of a semiconductor element and a diode connected in antiparallel, and a snubber capacitor, making the circuit configuration extremely simple. 5) In the B-Type DC-DC converter, the regenerative current of the snubber energy absorbed by the snubber capacitor does not pass through the transformer, so there is no effect on the secondary current. 6) By connecting the rectified output of a single-phase power supply via a filter circuit as the DC power supply for the DC-DC converter of the present invention, an AC-DC converter power supply with a high power factor can be easily realized. [Brief explanation of the drawings]

[0061] [Figure 1]Typical DC-DC converter circuits and snubber circuits (a) Flyback converter circuit (b) Forward converter circuit [Figure 2] Examples of configurations of switching element parallel snubber circuits: (a) Parallel snubber circuit 1 (snubber resistor connected to a capacitor) (b) Parallel snubber circuit 2 (snubber resistor connected to a DC power supply) [Figure 3] Surge voltage control and snubber loss reduction circuit using a step-down chopper circuit [Figure 4] Basic principle 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] Operation waveform of the A-Type overvoltage suppression control circuit of the present invention [Figure 8] Each operation 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] Operating waveforms of the B-Type overvoltage suppression control circuit of the present invention [Figure 11] Each operation mode of the B-Type overvoltage suppression control circuit of the present invention [Figure 12] AC-DC converter circuit 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] Control system for AC-DC converter 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 this invention (Idr=1.5A) [Figure 15] Switching control operation waveforms of multiple B-Type AC-DC converter circuits (Idr=1.5A) DETAILED DESCRIPTION OF THE INVENTION

[0062] FIG. 13 shows an example of an embodiment of an overvoltage suppression control circuit for a DC-DC converter according to the present invention, in which the full-wave rectified output of a single-phase power supply is passed through a filter circuit for removing switching harmonic components to form a DC power supply. This is a control system for an AC-DC converter power supply.

[0063] In the figure, the DC-DC converter section shows the a) A Type and b) B Type 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 by 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 that they use a B Type regenerative inductor Lc. A single-phase AC power supply with a voltage of Va = 200 V and a frequency of 60 Hz is added, and the transformation ratio of the high-frequency transformer is An LED light (forward voltage drop VF = 170V, resistance RF = 10 ohms) was connected as the DC load at 1, and the control conditions were a DC current reference value Idr = 1.5A and a set voltage Vpr = 600V to suppress overvoltage.

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

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

[0068] 100 … DC power supply 110... DC-DC converter DC power supply 120... Rectified DC power supply for AC-DC converter 200... Overvoltage suppression switching control circuit for DC-DC converter 210-1 … A-Type Overvoltage Suppression DC-DC Converter Switching Control Circuit 210-2 … B-Type Overvoltage Suppression DC-DC Converter Switching Control Circuit 220... Capacitor (snubber capacitor) 300... Transformer (high frequency transformer) 400 ... Rectification and smoothing circuit of 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 and control system

Claims

1. A DC-DC converter circuit is provided which is connected to a DC power supply via a primary winding of a transformer and controls the current flowing through the transformer by the switching action of the main switch circuit, thereby obtaining a required isolated DC output voltage via the transformer, A circuit configuration in which an auxiliary switch circuit is connected in series to an upper stage of the main switch circuit, and capacitors are connected to both ends of the series switch circuit, In the output control of the DC-DC converter, a bootstrap circuit operates when the main switch circuit is turned on to charge a drive circuit capacitor of the auxiliary switch circuit from the drive power supply of the main switch circuit, thereby securing a drive power supply for the auxiliary switch circuit, during output control of the DC-DC converter, the main switch circuit is turned off, and at the point in time when the energy stored in the exciting inductance of the transformer is transferred to the secondary side of the transformer, the commutation energy of the leakage inductance of the transformer is absorbed by the capacitor via the auxiliary switch circuit that is in the on state, thereby suppressing the surge voltage applied to the main switch circuit; When the secondary current flowing through the transformer increases and the primary current decreases to zero, a regenerative current flows from the capacitor, which has been charged to a voltage higher than the voltage of the DC power supply, to the DC power supply, regenerating the commutation energy. When the voltage of the capacitor drops to a set voltage, the auxiliary switch circuit is turned off and the voltage of the capacitor is controlled, An overvoltage suppression control circuit for a DC-DC converter, characterized in that the main switch circuit controls the output of the DC-DC converter and ensures the drive power supply for the auxiliary switch circuit, and the auxiliary switch circuit can suppress losses due to the commutation energy and suppress and control the generation of surge voltages applied to the main switch circuit.

2. 2. The overvoltage suppression control circuit for a DC-DC converter according to claim 1, wherein 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, An overvoltage suppression control circuit for a DC-DC converter, characterized in that the main switch circuit controls the output of the DC-DC converter and ensures the drive power supply for the auxiliary switch circuit, and the auxiliary switch circuit can suppress losses due to the commutation energy and suppress and control the generation of surge voltages 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 a switch circuit in which a semiconductor switch and a diode are connected in antiparallel, and a series switch circuit connected in series to an upper stage of the main switch circuit via the auxiliary switch circuit and a diode 2 is connected in series to both ends of the series switch circuit, In a circuit configuration in which a circuit is added from the DC power supply to a terminal connected to the main switch circuit via a primary winding of the transformer through diodes 1 and 2, to the capacitor via diode 3, a circuit is added which connects diode 4 from the negative side of the DC power supply to the connection terminal of the auxiliary switch circuit and diode 2, and a circuit is added which connects a regenerative inductor in series with diode 5 to the positive side of the DC power supply, An overvoltage suppression control circuit for a DC-DC converter, characterized in that the main switch circuit controls the output of the DC-DC converter and ensures the drive power supply for the auxiliary switch circuit, and the auxiliary switch circuit can suppress losses due to the commutation energy and suppress and control the generation of surge voltages applied to the main switch circuit.

4. As the DC power supply of the overvoltage suppression control circuit of the DC-DC converter according to any one of claims 1 to 3, a full-wave rectified power supply having a circuit configuration in which a filter circuit for removing switching harmonic components of the DC-DC converter is connected to the AC side or DC side of a full-wave rectifier circuit is connected to an AC power supply, An overvoltage suppression control circuit for a DC-DC converter, characterized in that the main switch circuit controls the output of the DC-DC converter, which configures and controls an AC-DC converter that obtains a DC output voltage at a high power factor from an AC power source, and ensures the drive power supply for the auxiliary switch circuit, and the auxiliary switch circuit can suppress losses due to the commutation energy and suppress and control the generation of surge voltages applied to the main switch circuit.

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