DE102021214676A1 - Flyback converter device with two switching elements and method for operating the flyback converter device - Google Patents

Abstract

Flyback converters are designed as DC voltage converters and are used to transmit electrical energy between an input side and an output side of galvanically isolated DC voltages. A flyback converter device 1 is proposed with an input device 4, with an output device 8, with a main transmission device 11, with the main transmission device 11 having a main input coil 12 and has a main output coil 13, wherein the flyback converter device 1 is designed to charge the main transmission device 11 through the input device 4 in a conduction phase and to discharge the main transmission device 4 via the output device 8 in a blocking phase, with a low-side switching element 19, the low Side switching element 19 is arranged between the main transmission device 11 and a ground 7, and with a test device 14, the test device 14 having a test output 15 for providing a test voltage, the flyback converter device 1 being designed so that in the blocking phase the test device 14 with the main input coil 12 is conductively connected in order to at least partially discharge the main transmission device 11 into the test device 14 and to provide the test voltage.

Description

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.

Flyback converters are designed as DC converters and are used to transmit electrical energy between an input side and an 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 aim of checking the input side.

On the one hand, it is known from the literature to transmit corresponding measurement data from the output side to the input side via an optocoupler.

It is an object of the invention to propose a simple and robust way of controlling an 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 and features as well as exemplary embodiments are disclosed in the description and in the dependent claims.

The invention thus relates to a flyback converter device, in which case the flyback converter device can also be referred to as a buck/boost point or in English as a flyback converter. The flyback converter is designed in particular as a DC voltage converter.

The flyback converter device has an input device, the input device being designed as a first sub-circuit and forming an input side. The input device has a voltage input for accepting a supply voltage. The supply voltage is in particular in the form of a direct voltage. One connection of the voltage input is preferably connected to a positive pole, and another connection of the voltage input is and/or can be connected to ground.

The flyback converter device has an output device, the output device being designed as a second sub-circuit and forming an output side. The output device has a voltage output for providing an output voltage. The voltage output has a first connection, with a positive voltage being output at the first connection, and a second connection, with a second ground being present at the second connection, which is formed galvanically with respect to the ground of the input device. The output voltage and the input voltage are, in particular, galvanically isolated direct voltages. Provision is made for the input device and the output device to be designed to be electrically isolated from one another.

The flyback converter device has a main transmission device, the main transmission device comprising 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 and/or can be coupled to one another. A magnetic field can be temporarily stored in the main transmission device and/or a magnetic voltage can be built up. The main transmission device preferably has at least one core, the core having an air gap.

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

In an off phase, with the main input coil isolated from ground, the main transmission device is discharged through the output device. During the blocking phase, energy is therefore transferred from the input device via the main transmission device to the output device.

The flyback converter device has a low-side switching element, the low-side switching element being arranged and configured in series with the main input coil, the main input coil being grounded to switch. For example, the switching element is designed as a mosfet. The input device can be switched between the conducting phase and the blocking phase by the low-side switching element.

In the context of the invention, it is proposed that the flyback converter device has a test device, with the test device being designed in particular as a third sub-circuit. The testing device has a test output for providing a test voltage. The testing device is preferably electrically connected to the input device and/or electrically isolated from the output device.

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 to provide the test voltage. Thus, the energy stored in the main transmission device is preferably largely transferred to the output device, but at least partially also transferred to the test device, so that it 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 e.g. proportional to it after a voltage divider or is at least equivalent to it, so that conclusions can be drawn about the output voltage by measuring the test voltage. In particular, the flyback converter device is designed to separate the testing device from the main transmission device in the conducting phase.

It is therefore an advantage of the invention that the test device can provide the test voltage as a reference voltage for the output voltage, with the test device not having to be electrically isolated from the input device. Thus, this test voltage can be measured without the interposition of an opto-coupler or a similar galvanically isolating element. The invention means that such an optocoupler can be dispensed with and a reliable reference variable for controlling the input device can nevertheless be provided. Such a command variable is necessary because without control of the input device, the voltage at the output device would rise in an uncontrolled manner when the output device was in a load-free state.

In a preferred development of the invention, the flyback converter device has a control device for controlling the input device. Provision is made for the control device to control the input device on the basis of the test voltage. In particular, the test voltage forms one or the reference variable for the control device.

The flyback converter device is preferably implemented in such a way that the no-load output voltage is equal to the test voltage, so that the value of the test voltage can be accepted without change instead of the actual value of the output voltage.

In a preferred development of the invention, the flyback converter device has a high-side switching element, with the high-side switching element being 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 separating the main transmission device, in particular the main input coil, from the voltage input during the blocking phase, so that no energy can be subsequently supplied to the main transmission device during the blocking phase. The energy stored in the main transmission device is thus distributed to the output device and the test device, the test voltage being predetermined by the proportion of the 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.

In a further preferred configuration of the invention, the flyback converter device has a flyback discharge branch. The reverse discharge path connects ground to the input to the main input coil. A reverse discharge diode device is arranged in the reverse discharge branch, the reverse discharge diode device being directed in the flow direction toward the input. The blocking discharge branch makes it possible for a compensating current to be present at the input of the main input coil, so that the energy can be recharged from the main transmission device to the output device and/or to the test device.

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 with a high signal of the PWM output, the respective switching element is closed and the main input coil is connected to ground and to the voltage input, and if the PWM output has a low signal, the respective switching element is open, so that the main input coil is isolated from ground and the voltage input. It is provided that the control device controls the PWM module on the basis of the test voltage, in particular controls and/or regulates it. For example, a frequency or a duty cycle can be adjusted as a manipulated variable.

In a further development of the invention in terms of circuitry, the output device has a main storage capacitance which is arranged in parallel with the main output coil in terms of circuitry. Furthermore, the output device has a main diode device, the main diode device being arranged between the main storage capacitance and the voltage output.

Alternatively or additionally, the test device has a test storage capacity, with the test storage capacity being arranged in parallel with the circuitry. Furthermore, the test device has a test diode device, the test diode device being 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 capacity and/or test storage capacity. In particular, in the conduction phase, the test device is separated from the main input coil by the test diode device.

In a further development of the invention, the flyback converter device, in particular the test device, has an auxiliary resistor, the auxiliary resistor being arranged in parallel with the test storage capacitance. In particular, the auxiliary resistance forms a constant load in the test device. In the output device, on the other hand, there is a variable load 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 transmitted to the output device and less energy to the test device.

The flyback converter device can be operated both in continuous conduction mode (CCM) and in discontinuous conduction mode (DCM).

Another subject matter of the invention relates to a method for operating the flyback converter device as described above, with the main transmission device being charged by the input device in a conducting phase and the main transmission device being discharged via the output device and the test device in a blocking phase, so that in the test device the Test voltage is provided.

• 1 ein schematisches Schaltbild von einer Sperrwandlervorrichtung als ein Ausführungsbeispiel der Erfindung;
• 2 die Sperrwandlervorrichtung in der 1 während einer Leitphase;
• 3 die Sperrwandlervorrichtung in der 1 während einer Sperrphase mit Stromfluss;
• 4 die Sperrwandlervorrichtung in der 1 während der Sperrphase ohne Stromfluss;
• 5 ein schematisches Schaltbild von einem Simulationsmodell der Sperrwandlervorrichtung;
• 6 Signalverläufe aus dem Simulationsmodell der 5;
• 7 Signalverläufe aus dem Simulationsmodell der 5.

Further features, advantages and effects of the invention result from the following description of preferred exemplary embodiments of the invention and the attached figures. These show:

• 1 a schematic circuit diagram of a flyback converter device as an embodiment of the invention;
• 2 the flyback device in the 1 during a lead phase;
• 3 the flyback device in the 1 during a blocking phase with current flow;
• 4 the flyback device in the 1 during the blocking phase without current flow;
• 5 a schematic circuit diagram of a simulation model of the flyback converter device;
• 6 Signal curves from the simulation model 5 ;
• 7 Signal curves from the simulation model 5 .

The 1 shows a schematic circuit diagram of a flyback converter device 1 as an embodiment of the invention. The flyback converter device 1 has the function of providing an output voltage Vout at a voltage output 3 starting from a supply voltage Vin at a voltage input 2 . The input voltage 2 and the output voltage 3 are electrically isolated from each other.

The flyback converter device 1 has an input device 4 , the input device 4 including the voltage input 2 which is connected to a voltage source 5 . The tension one Gang 2 has a first input with a positive pole 6 and a second input which forms a ground 7 .

The flyback converter device 1 also has an output device 8, the output device 8 having 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 (ground), which, however, is electrically isolated from the first ground 7 .

The flyback converter device 1 has a main transmission device 11 , the main transmission device 11 having a main input coil 12 and a main output coil 13 . The main input coil 12 is connected to the input device 4 in terms of circuitry, and the main output coil 13 is connected to the output device 8 in terms of circuitry. The two coils 12, 13 are arranged in a manner similar to that of a transformer. For example, the coils 12, 13 are arranged parallel to one another, but with an air gap being present in a core in order to store a magnetic field and/or to build up a magnetic tension.

The flyback converter device 1 has a test device 14, the test device 14 having a test output 15 for providing a test voltage VFB. The testing device 14 is connected to the output side of the main input coil 12 and to the ground 7 .

The flyback converter device 1 has a reverse discharge path 16 with a reverse discharge diode device 17 , the reverse discharge path 16 connecting the ground 7 to the input side of the main input coil 12 . The conducting direction of the reverse discharge diode device 17 is oriented in the direction of the main input coil 12 .

Furthermore, flyback converter device 1 , in particular 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 the ground 7 and makes it possible to switch the main input coil 12 to ground 7 .

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 includes 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 the duty cycle of the respective switching signal.

The output device 8 has a main storage capacitance 22, the main storage capacitance 22 being arranged in parallel with the main output coil 13 in terms of circuitry. The task of the main storage capacity 22 is to allow energy to be reloaded from the main transmission device 11 and to keep the output voltage Vout at the voltage output 3 constant and temporarily stores energy. Furthermore, the output device 8 has a main diode device 23, the main diode device 23 being 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.

The test device 14 has a test storage capacitance 24 , the test storage capacitance 24 being arranged between the input side of the main input coil 12 and the ground 7 . The function of the test storage capacity 24 is to allow energy to be reloaded from the main transmission device 11 and to keep the test voltage VFB constant over time. Furthermore, the test device 14 has a test diode device 25, the test diode device 25 being connected between the output side of the main input coil 12 and the test output 15 and/or the test storage capacitance 24 in such a way that current can flow in the direction of the test output 15 or the test storage capacitance 24, but in opposite direction is blocked.

Furthermore, the test device 14 also has an auxiliary resistor 26, which is arranged in parallel with the test memory capacitor 24 in terms of circuitry, and a voltage divider 27 for tapping off the test signal VFB, the voltage divider 27 being parallel to the auxiliary resistor 26 and/or the test memory capacitor capacity 24 is switched. The test signal VFB corresponds to the test voltage and is transferred to the control device 20 as a reference variable for checking the input device 4, in particular the switching elements 18, 19.

The 2 shows the flyback converter device 1 of FIG 1 in a conducting phase (Ton), the switching elements 18, 19 being rendered conductive and shown as solid lines. The main input coil 12 is thus connected on the input side to the voltage input 2 , in particular to the positive pole 6 , and is connected to ground 7 via a further resistor 28 . In the input device 4 there is a current flow in the clockwise direction, the main transmission device 11 is charged. Due to the direction of the current, 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 flow of current. The voltage output 3 is supplied with the output voltage from the main storage capacity 22 . Likewise, there is no transfer of energy to the test device 14, so that the test diode device 25 is operated in the reverse direction and has been omitted from the illustration. The test storage capacity 24 supplies the auxiliary resistor 26 so that the test voltage is present at the test output 15 .

In the 3 the flyback converter device 1 is shown in a blocking phase (Toff, I>0), the switching elements 18, 19 interrupting the connection of the main input coil 12 to the voltage input 2 and to the ground 7, so that the switching elements 18, 19 are shown as gaps. On the other hand, a current flow is now possible from the main output coil 13 to the voltage output 3 or to the main storage capacitance 22 and 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 flow direction, so that these 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 path 16 can transmit a discharge current to the main input coil 12 . In the blocking phase, energy is transmitted from the main transmission device 11 to the output device 8 and energy is transmitted from the main transmission device 11, in particular the main input coil 12, to the testing device 14. A current flow takes place in the output device 8 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.

In principle, from this from this state in the 3 , be returned to the conducting phase. This would correspond to a CCM mode. Optionally, the flyback converter device 1 is continued in the blocking phase in a DCM mode, as is shown in FIG 4 is shown (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 is terminated, so that, in order to avoid a current flow in the opposite direction, the diode devices 17, 25 work in the reverse direction again, so that they can again be used as a Gaps in the circuit are shown. In contrast, the current flow takes place from the main storage capacity 22 to the voltage output 3 or from the test storage capacity 24 to the test output 15.

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 ( 1 ).

Simulated examples:

The 5 shows a circuit diagram of a first embodiment of the flyback converter device 1. The following 6 , shows the signal curves from the simulation of the flyback converter device 1.

1. 1) Vinmin = 4.5V
2. 2) Schaltfrequenz Fsw: 150kHz,
3. 3) Vout :16V
4. 4) Lp : 3.3uH (Hauptübertragungseinrichtung 11)
5. 5) lout : 0 to 500mA
6. 6) Betriebsart: DCM

The simulation parameters are as follows:

1. 1) Vinmin = 4.5V
2. 2) Switching frequency Fsw: 150kHz,
3. 3) Vout :16V
4. 4) Lp : 3.3uH (main transmission equipment 11)
5. 5) out : 0 to 500mA
6. 6) Operating mode: DCM

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 storage capacity 24

It can be seen in signal curve 7.4 that the voltage in test device 14 is equal to the voltage in output device 8, so that the test signal is suitable as a reference variable for checking input device 4.

The 7 shows signal curves of a second simulation, a standard component in the form of a self-retaining assembly 29 being used for the main transmission device 11 .

1. 1) Vinmin = 4.5V
2. 2) Schaltfrequenz Fsw: 150kHz,
3. 3) Vout :16V
4. 4) Part Number: MSD1260T-332ML;
5. 5) lout : 0 to 500mA
6. 6) Betriebsart: DCM

The simulation parameters are as follows:

1. 1) Vinmin = 4.5V
2. 2) Switching frequency Fsw: 150kHz,
3. 3) Vout :16V
4. 4) Part Number: MSD1260T-332ML;
5. 5) out : 0 to 500mA
6. 6) Operating mode: DCM

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

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

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 resistance 26/ test storage capacity 24

In the unloaded state, there is an output voltage of 16,514 V, in the loaded state 11.576 V. In the signal curve 8.4 it can be seen 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 can be used as a reference variable for Control of the input device 4 is suitable.

• - kein Optokoppler
• - Verwendung von Off-the-Shelf-Baugruppe 29 ist möglich
• - mechanisch robustes Design
• - hohe Lebensdauer (verglichen mit der begrenzten Lebenszeit von einem Optokoppler)
• - kann über einen weiteren Spannungsbereich wie z.B. 4.5 V... 70 V arbeiten
• - das PWM-Modul kann unspezifisch gewählt werden
• - schematisch ähnlich zu konventionellen Sperrwandlern
• - Gute Regulierung, da die Kontrolleinrichtung 20 in einem Strom-Mode ist.

The advantages of the flyback converter device are:

• - no optocoupler
• - Use of off-the-shelf assembly 29 is possible
• - Mechanically robust design
• - long lifetime (compared to the limited lifetime of an optocoupler)
• - Can operate over a wider voltage range such as 4.5V...70V
• - the PWM module can be selected unspecifically
• - Schematically similar to conventional flyback converters
• - Good regulation since the controller 20 is in a current mode.

Reference List

1

flyback device

2

voltage input

3

voltage output

4

entrance facility

5

voltage source

6

positive pole

7

Dimensions

8th

exit facility

9

second positive pole

10

second mass

11

main transmission facility

12

main input coil

13

main output coil

14

testing facility

15

test output

16

blocking discharge branch

17

reverse discharge diode device

18

high-side switching element

19

Low-side scarf element

20

control device

21

PWM module

22

main storage capacity

23

main diode device

24

test memory capacity

25

test diode setup

26

auxiliary resistance

27

voltage divider

28

further resistance

29

Assembly for the main transmission device 11

vintage

supply voltage

Vout

output voltage

Claims (10)

Flyback converter device (1) with an input device (4), the input device (4) having a voltage input (2) for accepting a supply voltage, with an output device (8), the output device (8) having a voltage output (3) for providing an output voltage having, 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) with the input device (4) and the main output coil (13) with the output device ( 8) is connected, wherein the flyback converter device (1) is designed to charge the main transmission device (11) through the input device (4) in a conduction phase and to discharge the main transmission device (4) via the output device (8) in a blocking phase, with a low -Side switching element (19), the low-side switching element (19) being arranged between the main transmission device (11) and a ground (7), characterized by a test device (14), the test device (14) having a test output ( 15) for providing a test voltage, the flyback converter device (1) being designed so that in the blocking phase the test device (14) is conductively connected to the main input coil (12) in order to at least partially convert the main transmission device (11) into the test device (14 ) to discharge and provide the test voltage. Flyback converter device (1) after claim 1 , characterized by a control device (20) for controlling the input device (4), wherein the input device (4) is controlled on the basis of the test voltage. Flyback converter device (1) after claim 1 or 2 , characterized by a high-side switching element (19), wherein the high-side switching element (19) is arranged between the voltage input (2) and the main transmission device (11). Flyback converter device (1) according to one of the preceding claims, characterized by a reverse discharge branch (16), a reverse discharge diode device (17) being arranged in the reverse discharge branch (16), the reverse discharge branch (16) being connected on the one hand to the mass (7) and in the direction of flow of the Blocking discharge diode device (17) is connected to an input of the main transmission device (11). Flyback converter device (1) after claim 3 , characterized in 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), the PWM module (21) is controlled based on the test voltage. Flyback converter device (1) according to one of the preceding claims, characterized in that the output device (8) has a main storage capacitance (22), the main storage capacitance (22) being arranged in parallel with the main output coil (13), and a main diode device (23), wherein the main diode means (23) is arranged between the main output coil (13) and the main storage capacitance (22). Flyback converter device (1) according to one of the preceding claims, characterized in that the test device (14) has a test storage capacitance (24) and a test diode device (25), the test storage capacitance (24) being 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 connected to the ground (7). Flyback converter device (1) after claim 7 , characterized by an auxiliary resistor (26), the auxiliary resistor (26) being arranged in parallel with the test storage capacitance (24). Flyback converter device (1) according to one of the preceding claims, characterized in that it can be operated in a CCM operating mode or in a DCM operating mode. Method for operating the flyback converter device (1) according to one of the preceding claims, characterized in that the main transmission device (11) is charged by the input device (4) in a conducting phase and the main transmission device is charged in a blocking phase (11) discharges via the output device (8) and the test device (14), so that the test voltage is provided in the test device (14).

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