Flyback converter device with two switching elements and method for operating the flyback converter device

Abstract

Flyback converter device (1) with an input device (4), wherein the input device (4) has a voltage input (2) for receiving a supply voltage, with an output device (8), wherein the output device (8) has a voltage output (3) for providing an output voltage, with a main transmission device (11), wherein the main transmission device (11) has a main input coil (12) and a main output coil (13), wherein the main input coil (12) is connected to the input device (4) and the main output coil (13) is connected to the output device (8), wherein the flyback converter device (1) is designed to charge the main transmission device (11) through the input device (4) in a conducting phase and to discharge the main transmission device (11) via the output device (8) in a blocking phase, with a low-side switching element (19), wherein the low-side switching element (19) is arranged between the main transmission device (11) and a ground (7), with a test device (14), wherein the test device (14) has a test output (15) for providing a test voltage as a reference voltage to the output voltage, whereby a reference variable for controlling the input device (4) is provided, wherein the flyback converter device (1) is designed such that in the blocking phase, the test device (14) is conductively connected to the main input coil (12) in order to at least partially discharge the main transmission device (11) into the test device (14) and to provide the test voltage, wherein the test voltage corresponds to the output voltage or is at least equivalent to it, so that the output voltage can be deduced from a measurement of the test voltage, wherein the flyback converter device (1) contains a control device (20) for controlling the input device (4), wherein the input device (4) is controlled on the basis of the test voltage, wherein the test device (14) has a test storage capacity (24) and a test diode device (25), wherein the test storage capacity (24) is connected on the one hand via the test diode device (25) to an output of the main input coil (12) and on the other hand to the ground (7), - wherein the flyback converter device (1) has an auxiliary resistor (26), wherein the auxiliary resistor (26) is arranged in parallel with the test storage capacitance (24), across which a voltage drops, which is fed to the test voltage via a voltage divider.

Description

[0001] The invention relates to a flyback converter device having the features of the preamble of claim 1. The invention also relates to a method for operating the flyback converter device.

[0002] Flyback converters are designed as DC-DC converters and are used to transfer electrical energy between an input and output side of galvanically isolated DC voltages. Since galvanic isolation is an important aspect of flyback converters, galvanic isolation must also be provided for testing the voltage on the output side with the goal of monitoring the input side.

[0003] From the literature it is known, on the one hand, to transmit corresponding measurement data from the output side to the input side via an optocoupler.

[0004] A half-bridge flyback current converter is known from US 2006 / 0 007 711 A1. The half-bridge flyback current converter comprises a high-side switch and a low-side switch that periodically conduct an input voltage to a primary winding of a transformer. When the high-side switch and the low-side switch are off, energy stored in the transformer is transferred to a secondary circuit and used to charge a bulk capacitor. A forward diode combines the input voltage with a voltage across the bulk capacitor to feed the secondary circuit. Therefore, the power consumption of the stray inductance is reduced and the circuit topology is simplified.

[0005] A fault detection device for a DC / DC converter is known from JP 2016- 92 939 A.

[0006] It is an object of the invention to propose a simple and robust method for controlling the input side of a flyback converter. This object is achieved by a flyback converter device having the features of claim 1 and by a method for operating the flyback converter device having the features of claim 10. Further advantages, effects, features, and embodiments are disclosed in the description and the subclaims.

[0007] The invention thus relates to a flyback converter device, which can also be referred to as a boost / buck converter or, in English, a flyback converter. The flyback converter is designed, in particular, as a DC-DC converter.

[0008] The flyback converter device has an input device, wherein the input device is designed as a first subcircuit and forms an input side. The input device has a voltage input for receiving a supply voltage. The supply voltage is designed, in particular, as a direct voltage. Preferably, one terminal of the voltage input is connected to a positive pole, and another terminal of the voltage input is connected and / or connectable to ground.

[0009] The flyback converter device has an output device, wherein the output device is designed as a second subcircuit and forms an output side. The output device has a voltage output for providing an output voltage. The voltage output has a first terminal, wherein a positive voltage is output at the first terminal, and a second terminal, wherein a second ground is present at the second terminal, which is galvanically connected to the ground of the input device. The output voltage and the input voltage are, in particular, galvanically isolated direct voltages. It is provided that the input device and the output device are galvanically isolated from one another.

[0010] The flyback converter device has a main transmission device, wherein the main transmission device comprises a main input coil and a main output coil. The main input coil is connected to the input device, and the main output coil is connected to the output device. The main input coil and the main output coil are preferably magnetically coupled to one another and / or can be coupled to one another. A magnetic field can be temporarily stored and / or a magnetic voltage can be built up in the main transmission device. The main transmission device preferably has at least one core, wherein the core has an air gap.

[0011] The flyback converter device is designed to charge the main transmission device through the input device during a conducting phase, with the supply voltage applied to the main input coil and another end of the main input coil connected to ground. In particular, a magnetic voltage builds up in the main transmission device, particularly in the air gap.

[0012] During a blocking phase, with the main input coil isolated from ground, the main transmission device is discharged via the output device. During the blocking phase, energy is thus transferred from the input device via the main transmission device to the output device.

[0013] The flyback converter device has a low-side switching element, wherein the low-side switching element is arranged in series with the main input coil and is configured to connect the main input coil to ground. For example, the switching element is configured as a MOSFET. The low-side switching element allows the input device to be switched between the conducting phase and the blocking phase.

[0014] Within the scope of the invention, it is proposed that the flyback converter device comprise a test device, wherein the test device is particularly designed as a third subcircuit. The test device comprises a test output for providing a test voltage. The test device is preferably galvanically connected to the input device and / or galvanically isolated from the output device.

[0015] The flyback converter device is designed to conductively connect the test device to the main input coil in the blocking phase in order to at least partially discharge the main transmission device into the test device and provide the test voltage. The energy stored in the main transmission device is thus preferably largely transferred to the output device, but at least partially also passed to the test device so that the latter can provide a test voltage which is a relative value for the output voltage of the output device. The test voltage corresponds to the output voltage or is, for example, proportional to it after a voltage divider or is at least equivalent to it, so that the output voltage can be deduced from a measurement of the test voltage. In particular, the flyback converter device is designed to disconnect the test device from the main transmission device in the conducting phase.

[0016] It is therefore an advantage of the invention that the test device can provide the test voltage as a reference voltage to the output voltage, wherein the test device does not have to be galvanically isolated from the input device. This test voltage can therefore be measured without the interposition of an optocoupler or a similar galvanically isolating element. The invention thus makes it possible to dispense with such an optocoupler and still provide a reliable reference variable for controlling the input device. Such a reference variable is necessary because, without control of the input device, the voltage at the output device would rise uncontrollably in a load-free state of the output device.

[0017] According to the invention, the flyback converter device comprises a control device for controlling the input device. It is provided that the control device controls the input device based on the test voltage.

[0018] In particular, the test voltage forms one or the reference variable for the control device.

[0019] The flyback converter device is preferably implemented such that the unloaded output voltage is equal to the test voltage, so that the value of the test voltage can be adopted without change instead of the actual value of the output voltage.

[0020] In a preferred development of the invention, the flyback converter device has a high-side switching element, wherein the high-side switching element is arranged between the voltage input and the main transmission device, in particular the main input coil. The high-side switching element has the function of isolating the main transmission device, in particular the main input coil, from the voltage input during the blocking phase, so that no energy can be supplied to the main transmission device during the blocking phase. Thus, the energy stored in the main transmission device is distributed between the output device and the test device, wherein the test voltage is predetermined by the proportion of energy distributed to the test device. In particular, the separation ensures that the output voltage and the test voltage are the same or at least equivalent.

[0021] In a further preferred embodiment of the invention, the flyback converter device has a reverse discharge branch. The reverse discharge branch connects ground to the input of the main input coil. A reverse discharge diode device is arranged in the reverse discharge branch, wherein the reverse discharge diode device is directed in the forward direction toward the input. The reverse discharge branch enables a compensating current to be applied to the input of the main input coil, so that energy can be transferred from the main transmission device to the output device and / or to the test device.

[0022] In a preferred development of the invention, the control device has a PWM module for controlling the at least one switching element, in particular the low-side switching element and / or the high-side switching element. For example, it can be provided that when the PWM output has a high signal, the respective switching element is closed and the main input coil is connected to ground and the voltage input, and when the PWM output has a low signal, the respective switching element is opened, so that the main input coil is disconnected from ground and the voltage input. It is provided that the control device of the PWM module monitors, in particular controls and / or regulates, based on the test voltage. For example, a frequency or a duty cycle can be adjusted as a manipulated variable.

[0023] In a circuit-related development of the invention, the output device has a main storage capacitor, which is arranged in parallel with the main output coil. Furthermore, the output device has a main diode device, wherein the main diode device is arranged between the main storage capacitor and the voltage output.

[0024] The test device has a test storage capacitor, which is arranged in parallel circuitry. Furthermore, the test device has a test diode device, which is arranged between the auxiliary output coil and the test output for the test voltage. The energy from the main transmission device is transferred to the main storage capacitor and / or test storage capacitor. In particular, during the conduction phase, the test device is separated from the main input coil by the test diode device.

[0025] The flyback converter device, in particular the test device, has an auxiliary resistor, wherein the auxiliary resistor is arranged in parallel with the test storage capacitance. The auxiliary resistor forms, in particular, a constant load in the test device. In the output device, however, a variable load is present at the voltage output. Nevertheless, the test voltage forms a reference value for the output voltage, since the energy from the main transmission device is always distributed to the output device / test device, so that with a larger load on the output device, more energy is transferred to the output device and less energy to the test device. The flyback converter device can be operated in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM).

[0026] A further subject of the invention relates to a method for operating the flyback converter device as described above, wherein in a conducting phase the main transmission device is charged by the input device and in a blocking phase the main transmission device is discharged via the output device and the test device, so that the test voltage is provided in the test device.

[0027] Further features, advantages, and effects of the invention will become apparent from the following description of preferred embodiments of the invention and the accompanying figures. These show: Fig. 1 is a schematic circuit diagram of a flyback converter device as an embodiment of the invention; Fig. 2 the flyback converter device in the Fig. 1 during a lead phase; Fig. 3 the flyback converter device in the Fig. 1 during a blocking phase with current flow; Fig. 4 the flyback converter device in the Fig. 1 during the blocking phase without current flow; Fig. 5 is a schematic diagram of a simulation model of the flyback converter device; Fig. 6 Signal curves from the simulation model of the Fig. 5; Fig. 7 Signal curves from the simulation model of the Fig. 5.

[0028] The Fig. Figure 1 shows a schematic circuit diagram of a flyback converter device 1 as an exemplary embodiment of the invention. The flyback converter device 1 has the function of providing an output voltage Vout at a voltage output 3 based on a supply voltage Vin at a voltage input 2. The input voltage 2 and the output voltage 3 are galvanically isolated from each other.

[0029] The flyback converter device 1 has an input device 4, wherein the input device 4 comprises the voltage input 2, which is connected to a voltage source 5. The voltage input 2 has a first input with a positive pole 6 and a second input, which forms a ground 7.

[0030] The flyback converter device 1 further comprises an output device 8, wherein the output device 8 comprises the voltage output 3 for providing the output voltage Vout. The voltage output 3 has a second positive pole 9 and a second ground 10, which, however, is galvanically isolated from the first ground 7.

[0031] The flyback converter device 1 has a main transmission device 11, wherein the main transmission device 11 has a main input coil 12 and a main output coil 13. The main input coil 12 is connected to the input device 4 by circuitry, and the main output coil 13 is connected to the output device 8 by circuitry. The two coils 12, 13 are arranged relative to one another in a similar way to a transformer. For example, the coils 12, 13 are arranged parallel to one another, but with an air gap in a core to store a magnetic field and / or build up a magnetic voltage.

[0032] The flyback converter device 1 comprises a test device 14, wherein the test device 14 has a test output 15 for providing a test voltage VFB. The test device 14 is connected to the output side of the main input coil 12 and to ground 7. The flyback converter device 1 has a reverse discharge branch 16 with a reverse discharge diode device 17, wherein the reverse discharge branch 16 connects the ground 7 to the input side of the main input coil 12. The forward direction of the reverse discharge diode device 17 is oriented toward the main input coil 12.

[0033] Furthermore, the flyback converter device 1, in particular the input device 4, has a high-side switching element 18 and a low-side switching element 19. The high-side switching element 18 is arranged in series between the voltage input 2, in particular the positive pole 6, and the input side of the main input coil 12. The low-side switching element 19 is arranged in series with the main input coil 12 between its output side and ground 7 and enables the main input coil 12 to be connected to ground 7.

[0034] The flyback converter device 1 has a control device 20 for controlling the input device 4, in particular the switching elements 18, 19. The input device 4 is controlled based on the test voltage VFB from the test output 15. The control device 20 comprises, in particular, a PWM module 21 for controlling the switching elements 18, 19 with a switching signal. In particular, the switching elements 18, 19 can be controlled, in particular switched on and off, by changing the frequency and / or duty cycle of the respective switching signal.

[0035] The output device 8 has a main storage capacitor 22, wherein the main storage capacitor 22 is arranged in circuitry parallel to the main output coil 13. The main storage capacitor 22 has the task of enabling energy transfer from the main transmission device 11 and keeping the output voltage Vout constant at the voltage output 3, and temporarily stores energy. Furthermore, the output device 8 has a main diode device 23, wherein the main diode device 23 is arranged between the main output coil 13 and the positive pole 9, so that current can flow from the main output coil 13 to the voltage output 3, but the opposite direction is blocked.

[0036] The test device 14 has a test storage capacitance 24, wherein the test storage capacitance 24 is arranged between the input side of the main input coil 12 and ground 7. The test storage capacitance 24 has the function of enabling energy transfer from the main transmission device 11 and keeping the test voltage VFB constant over time. Furthermore, the test device 14 has a test diode device 25, wherein the test diode device 25 is connected between the output side of the main input coil 12 and the test output 15 and / or the test storage capacitance 24 such that current can flow in the direction of the test output 15 or the test storage capacitance 24, but is blocked in the opposite direction.

[0037] Furthermore, the test device 14 also has an auxiliary resistor 26, which is arranged in parallel with the test storage capacitor 24, as well as a voltage divider 27 for tapping the test signal VFB, wherein the voltage divider 27 is connected in parallel with the auxiliary resistor 26 and / or the test storage capacitor 24. The test signal VFB corresponds to the test voltage and is transmitted to the control device 20 as a reference variable for controlling the input device 4, in particular the switching elements 18, 19.

[0038] The Fig. 2 shows the flyback converter device 1 of the Fig. 1 in a conducting phase (tone), with the switching elements 18, 19 being conductive and shown as solid lines. Thus, the main input coil 12 is connected on the input side to the voltage input 2, in particular the positive pole 6, and is connected to ground 7 via a further resistor 28. A clockwise current flows in the input device 4, and the main transmission device 11 is charged. Due to the current direction, the reverse discharge diode device 17 is in a blocking state, so that the reverse discharge branch 16 is non-conductive and has been omitted from the illustration. No energy is transferred to the output device 8, since the main diode device 23 prevents a corresponding current flow. The voltage output 3 is supplied with the output voltage from the main storage capacitor 22.Likewise, no energy is transferred to the test device 14, so the test diode device 25 is operated in the reverse direction and has been omitted from the illustration. The test storage capacitor 24 supplies the auxiliary resistor 26, so that the test voltage is present at the test output 15.

[0039] In the Fig. 3, the flyback converter device 1 is shown in a blocking phase (Toff, I>0), wherein the switching elements 18, 19 interrupt the connection of the main input coil 12 to the voltage input 2 and to ground 7, so that the switching elements 18, 19 are shown as gaps. However, a current flow is now possible from the main output coil 13 to the voltage output 3 or to the main storage capacitance 22, as well as from the output side of the main input coil 12 to the test output 25 or the test storage capacitance 24. The diode devices 23, 25 are now operated in the forward direction, so that they are no longer shown as gaps, but as continuous lines. The reverse discharge diode device 17 is also operated in the forward direction, so that the reverse discharge branch 16 can transmit a discharge current to the main input coil 12.During the blocking phase, energy is transferred from the main transmission device 11 to the output device 8, and energy is transferred from the main transmission device 11, in particular the main input coil 12, to the test device 14. In the output device 8, a current flows from the main output coil 13 to the main storage capacitor 22 or to the voltage output 3 and / or from the main input coil 12 to the test storage capacitor 24 and / or the test output 15.

[0040] In principle, this could lead to this state in the Fig. 3, the conduction phase can be returned to. This would correspond to a CCM mode. Optionally, the flyback converter device 1 can be continued in a DCM mode during the blocking phase, as shown in the Fig. 4 (TOFF, I=0). The switching elements 18, 19 are still open. However, the current flow from the main output coil 13 to the voltage output 3 or from the main input coil 12 to the test output 15 has been terminated, so that, to prevent current flow in the opposite direction, the diode devices 17, 25 operate in the reverse direction again, so that they are again shown as gaps in the circuit. The current flow, however, occurs from the main storage capacitor 22 to the voltage output 3 or from the test storage capacitor 24 to the test output 15.

[0041] After a certain time, the switching elements 18, 19 are closed again via the control by the PWM module 21, so that the main transmission device 11 can be charged again ( Fig. 1). Simulated implementation examples:

[0042] The Fig. 5 shows a circuit diagram of a first embodiment of the flyback converter device 1. The following Fig. 6, shows the signal waveforms from the simulation of the flyback converter device 1.

[0043] The simulation parameters are as follows: 1) Vinmin = 4.5V 2) Switching frequency Fsw: 150kHz, 3) Vout :16V 4) Lp : 3.3uH (main transmission device 11) 5) Iout : 0 to 500mA 6) Operating mode: DCM

[0044] The signal curves show: 6.1 Control voltage 6.2 Load current 6.3 Input voltage Vin 6.4 Output voltage at the voltage output & output voltage at the auxiliary resistor 26 / test memory capacity 24

[0045] In the signal curve 7.4 it can be seen that the voltage in the test device 14 is equal to the voltage in the output device 8, so that the test signal is suitable as a reference variable for controlling the input device 4.

[0046] The Fig.7 shows signal curves of a second simulation, wherein a standard component in the form of a self-holding assembly 29 was used for the main transmission device 11.

[0047] The simulation parameters are as follows: 1) Vinmin = 4.5V 2) Switching frequency Fsw: 150kHz, 3) Vout :16V 4) Part Number: MSD1260T-332ML; 5) Iout : 0 to 500mA 6) Operating mode: DCM

[0048] Assembly 29: Core: MSD1260T-332ML Type: SMT Make: COILCRAFT Lm: 3.3 ±20% uH DCR: 0.02 Llk: 0.2uH Isat: 11.5A Irms:3.6A

[0049] The signal curves show: 7.1 Control voltage 7.2 Load current 7.3 Input voltage Vin 7.4 Output voltage at the voltage output & output voltage at the auxiliary resistor 26 / test memory capacity 24

[0050] In the unloaded state, the output voltage is 16.514 V, and in the loaded state, 11.576 V. The signal curve 8.4 shows that the voltage in the test device 14 is at least sufficiently similar to the voltage in the output device 8, so that the test signal is suitable as a reference variable for controlling the input device 4.

[0051] The advantages of the flyback converter device are: - no optocoupler - Use of off-the-shelf assembly 29 is possible - mechanically robust design - long service life (compared to the limited service life of an optocoupler) - can operate over a wider voltage range such as 4.5 V... 70 V - the PWM module can be selected non-specifically - schematically similar to conventional flyback converters - Good regulation, since the control device 20 is in a current mode. Reference symbol 1 flyback converter device 2 voltage input 3 Voltage output 4 Entrance facility 5 Voltage source 6 Positive pole 7 Mass 8 Exit device 9 second positive pole 10 second mass 11 Main transmission device 12 Main input coil 13 Main output coil 14 Test facility 15 Test output 16 Barrier discharge branch 17 Blocking discharge diode device 18 High-side switching element 19 Low-side formwork element 20 Control device 21 PWM module 22 main memory capacity 23 Main diode device 24 test memory capacity 25 Test diode device 26 Auxiliary resistor 27 voltage dividers 28 further resistance 29 Main transmission device assembly 11 Vin supply voltage Vout output voltage

Claims

[1] Flyback converter device (1) with an input device (4), wherein the input device (4) has a voltage input (2) for receiving a supply voltage, with an output device (8), wherein the output device (8) has a voltage output (3) for providing an output voltage, with a main transmission device (11), wherein the main transmission device (11) has a main input coil (12) and a main output coil (13), wherein the main input coil (12) is connected to the input device (4) and the main output coil (13) is connected to the output device (8), wherein the flyback converter device (1) is designed to charge the main transmission device (11) through the input device (4) in a conducting phase and to discharge the main transmission device (11) via the output device (8) in a blocking phase, with a low-side switching element (19), wherein the low-side switching element (19) is arranged between the main transmission device (11) and a ground (7), with a test device (14), wherein the test device (14) has a test output (15) for providing a test voltage as a reference voltage to the output voltage, whereby a reference variable for controlling the input device (4) is provided, wherein the flyback converter device (1) is designed such that in the blocking phase, the test device (14) is conductively connected to the main input coil (12) in order to at least partially discharge the main transmission device (11) into the test device (14) and to provide the test voltage, wherein the test voltage corresponds to the output voltage or is at least equivalent to it, so that the output voltage can be deduced from a measurement of the test voltage, wherein the flyback converter device (1) contains a control device (20) for controlling the input device (4), wherein the input device (4) is controlled on the basis of the test voltage, wherein the test device (14) has a test storage capacity (24) and a test diode device (25), wherein the test storage capacity (24) is connected on the one hand via the test diode device (25) to an output of the main input coil (12) and on the other hand to the ground (7), - wherein the flyback converter device (1) has an auxiliary resistor (26), wherein the auxiliary resistor (26) is arranged in parallel with the test storage capacitance (24), across which a voltage drops, which is fed to the test voltage via a voltage divider. [2] Flyback converter device (1) according to claim 1, characterized bya high-side switching element (18), wherein the high-side switching element (18) is arranged between the voltage input (2) and the main transmission device (11). [3] Flyback converter device (1) according to one of the preceding claims, characterized by a reverse discharge branch (16), wherein a reverse discharge diode device (17) is arranged in the reverse discharge branch (16), wherein the reverse discharge branch (16) is connected on the one hand to the ground (7) and in the flow direction of the reverse discharge diode device (17) to an input of the main transmission device (11). [4] Flyback converter device (1) according to claim 2, characterized by that the control device (20) has a PWM module (21) for controlling the low-side switching element (19) and / or the high-side switching element (18), wherein the PWM module (21) is controlled on the basis of the test voltage. [5] Flyback converter device (1) according to one of the preceding claims, characterized byin that the output device (8) has a main storage capacitance (22), wherein the main storage capacitance (22) is arranged in parallel with the main output coil (13), and a main diode device (23), wherein the main diode device (23) is arranged between the main output coil (13) and the main storage capacitance (22). [6] Flyback converter device (1) according to one of the preceding claims, characterized by that it can be operated in a CCM mode or in a DCM mode. [7] Method for operating the flyback converter device (1) according to one of the preceding claims, characterized byin that in a conducting phase the main transmission device (11) is charged by the input device (4) and in a blocking phase the main transmission device (11) discharges via the output device (8) and the test device (14), so that in the test device (14) the test voltage is provided as a reference voltage to the output voltage, whereby a reference variable for controlling the input device (4) is provided, wherein the input device (4) is controlled on the basis of the test voltage.

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