GB2613405A

GB2613405A - A flyback converter

Info

Publication number: GB2613405A
Application number: GB2202003.6A
Authority: GB
Inventors: Pressas Stavros
Original assignee: Petalite Ltd
Current assignee: Petalite Ltd
Priority date: 2021-12-02
Filing date: 2022-02-15
Publication date: 2023-06-07
Also published as: GB202202003D0

Abstract

A flyback converter has an input 12 for connection to a power supply 122 and an output 16 for connection to a load 18. The flyback converter includes an inductor, or flyback transformer, 11 with primary and secondary windings. A primary switch device 15 is connected in series with the primary winding and in parallel with the input. An output device 161 is connected in series with the secondary winding to block current of a first polarity and to pass current of a second polarity from the secondary winding. A blocking circuit 19 is connected between the secondary winding and the output diode, and includes a blocking circuit diode 191 to pass electrical current of the first polarity from the secondary winding to one or more circulating components of the blocking circuit such that the associated voltage is blocked from the output diode, and to block current of the second polarity from the secondary winding. The converter may include a snubber circuit 13. The output diode and blocking diode may be Schottky diodes. The load may be a battery, particularly for an electric vehicle, and the converter used in a battery charging circuit.

Description

A FLYBACK CONVERTER

FIELD

Embodiments relate to a flyback converter, which may be used, for example, as a battery charger.

BACKGROUND

Flyback converters are found in many different applications. In situations, however, in which the load on the flyback converter requires a high voltage (e.g. more than 500V) the voltage rating of the output diode used in a conventional flyback converter must be very high. This increases costs and can create difficulties in other parts of the circuit (for example, in relation to EMI).

There is a need to alleviate some of these problems

BRIEF DESCRIPTION OF THE INVENTION

A version provides a flyback converter having an input for electrical connection to an electrical power supply and an output for connection to a load, the flyback converter including: an inductor with a primary and a secondary winding; a primary switch device electrically connected in series with the primary winding and in parallel with the input; an output device electrically connected in series with the secondary winding, the output device configured to block electrical current of a first polarity and to pass electrical current of a second polarity from the secondary winding; an output capacitor electrically connected in parallel with the secondary winding and output diode, and in parallel with the output; and a blocking circuit electrically connected between the secondary winding and the output diode, the blocking circuit including a blocking circuit diode configured to pass electrical current of the first polarity from the secondary winding to one or more circulating components of the blocking circuit such that the associated voltage is blocked from the output diode, and to block electrical current of the second polarity from the secondary winding.

The output device may be an output diode.

The one or more circulating components may include one or more resistors.

The one or more circulating components may include one or more capacitors.

The blocking circuit may include a secondary output device electrically connected in series with the output device and in parallel with the one or more circulating components.

The secondary output device may be a secondary output diode.

The load may require a voltage of greater than 500V.

The flyback converter may further include a snubber circuit.

Another version provides a battery charger including a flyback converter as above, and a connector electrically coupled to the output and for connection to a battery.

The connector may be for connection to an electric vehicle which may include the battery.

BRIEF DESCRIPTION OF THE FIGURES

In order that the present disclosure may be more readily understood, preferable embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 is a circuit diagram of some versions; FIGURE 2 is a graph of voltages and currents in a conventional flyback converter; and FIGURE 3 is a graph of voltages and currents in a flyback converter of some versions described herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

In accordance with some versions of the technology, there is provided a flyback converter circuit 1.

The flyback converter circuit includes an inductor 11, which is split to form a transformer with a primary winding and a secondary winding (the inductor 11 may, therefore, be referred to as a flyback transformer 11, for example). The primary winding of the inductor 11 is connected in electrical communication with an electrical power supply 12 and may be connected in electrical communication with a snubber circuit 13. The electrical power supply 12 may, therefore, be configured to output electrical power to the inductor 11 and the inductor 11, in turn, may be configured to receive electrical power from the electrical power supply 12.

The electrical power supply 12 may be a DC power supply, in that the electrical power provided by the electrical power supply 12 to the inductor 11 may be DC electrical power. The electrical power supply 12 may include a rectifier 121 which may be configured to receive electrical power from an AC power source 122 and to convert that electrical power from AC to DC. The rectifier 121 may be a full-wave bridge rectifier for example. The AC power source 122 may be a mains electrical power source for example (and may be a single phase of a three phase mains electrical power source, for example). In some versions, the AC power source 122 is part of the electrical power supply 12 and, in some versions, it is not. Accordingly, the electrical power supply 12 may be configured for electrical connection to the AC power source 122. The electrical power supply 12 may be associated with an input inductance 124, Lin, (e.g. in series with a live output of the AC power source 122) and an input capacitance 125, Cin (e.g. in parallel across the output of the rectifier 121). The rectifier 121 may, therefore, have an output which includes a positive and a negative output, the positive output may be configured to be coupled in electrical communication with a terminal (e.g. a second terminal) of the inductor 11 (e.g. the primary winding thereof). The negative output may be coupled in electrical communication with ground. Accordingly, the primary winding of the inductor 11 may be connected in parallel with the electrical power supply 12 (as first terminal of the primary winding may be connected in electrical communication with ground via a primary switch device 15).

The output of the rectifier 121 (which may be the output of the electrical power supply 12) may be configured to be coupled in electrical communication with a drive circuit 14. In some versions, therefore, the positive output of the rectifier 121 (which may be a positive output of electrical power supply 12) is configured to be coupled in electrical communication with the drive circuit 14. The electrical power supply 12 and/or the drive circuit 14 may include one or more circuit components to modify the output of the electrical power supply 12 (e.g. the positive output therefrom) for use by one or more components of the drive circuit 14. The one or more circuit components of the electrical power supply 12 and/or drive circuit 14 are depicted, by way of example only, as part of the electrical power supply 12 but it will be appreciated that this need not be the case. These one or more components may include a potential divider circuit which may include a first potential divider resistor 123a and a second potential divider resistor 123b. The first and second potential divider resistors 123a,b may be electrically connected in series between the output of the electrical power supply 12 (e.g. the positive output of the rectifier 121) and ground. The drive circuit 14 (or one or more components thereof) may be connected in electrical communication between the first and second potential divider resistors 123a,b. In some versions a capacitor 123c, which may be part of the potential divider circuit, is connected in electrical communication in parallel with one of these resistors 123a,b (e.g. with the second potential divider resister 123b, which may be connected to ground and the drive circuit 14 (or one or more components of the drive circuit 14). In the depicted and some other versions, the output of the potential divider circuit is labelled as Div and is an input to the drive circuit 14 (or to one or more components of the drive circuit 14 in instances in which the potential divider circuit is part of the drive circuit 14, for example).

As will be understood, therefore, the signal, e.g. Div, representative of the output of the electrical power supply 12 is provided to the drive circuit 14.

The output from the electrical power supply 12 (e.g. from the positive output of the rectifier 121) may be configured to be coupled in electrical communication with the snubber circuit 13 (which, as described, may also be connectable in electrical communication with the inductor 11).

The snubber circuit 13 may be configured to attenuate voltage spikes which might otherwise damage a primary switch device 15 of the flyback converter 1 (e.g. due to leakage inductance of the inductor 11) and/or may be configured to re-circulate current from the inductor 11.

The snubber circuit 13 could take a number of different forms. In the depicted and some other versions, for example, the snubber circuit 13 includes first and second snubber diodes 134,135, (D1snb, D2snb), a snubber inductor 133, Lsnb, and a snubber resistor 137, Rsnb, all connected in electrical communication in series with each other and in parallel with the primary switch device 15. In particular, the first snubber diode 134 may have its cathode connected in electrical communication with the output of the electrical power supply 12 (e.g. the positive output) and may be in electrical communication with the inductor 11 (e.g. the primary winding thereof, and may be connected to the second terminal of the primary winding). The anode of the first snubber diode 134 may be connected in electrical communication with the cathode of the second snubber diode and may be connected in electrical communication with a snubber capacitor 136, Csnb. The snubber capacitor 136 may be connected in electrical communication with the first and second snubber diodes 134,135 and the inductor 11 (e.g. the first terminal of the primary winding which is different to the second terminal of the primary winding to which the positive output of the electrical power supply 12 is connectable). The anode of the second snubber diode 135 may be connected in electrical communication with the snubber inductor 133 and the snubber resistor 137 (which may be connected in parallel with each other). The snubber inductor 133 and snubber resistor 137 may be connected in electrical communication with ground, and this may be via a shunt circuit.

The shunt circuit is, as depicted and in some other examples, a part of the snubber circuit 13 although this need not be the case. The shunt circuit may include a shunt resistor 138, Shunt, which is connected in electrical communication with the primary switch device 15, and one or more components of the snubber circuit 13 (such as the snubber inductor 133 and snubber resistor 137).

The shunt resistor, 138, may also be connected in electrical communication with ground (e.g. between these other components and ground). The shunt circuit may, therefore, be viewed as having an input (to which one or more components of the snubber circuit 13 and the primary switch device 15 are connected) and an output (which is connected to ground).

The input to the shunt circuit may be connectable in electrical communication with the drive circuit 14. This may be via one or more components which may modify the input to the shunt circuit for use by the drive circuit 15 (as such these one or more components may form part of the drive circuit 14 itself in some versions). These one or more components may be in the form of a shunt potential divider, which may be a low-pass filter (e.g. a low-pass RC filter), for example. The shunt potential divider may include a shunt divider resistor 131 and a shunt divider capacitor 132 connected in series with each other. The shunt divider resistor 131 may be connected in electrical communication between the shunt input and with the drive circuit 14 (or may be so connectable).

The shunt divider capacitor 132 may be connected in electrical communication between the shunt divider resistor 131 (and drive circuit 14) and ground. Accordingly, an input to the drive circuit 14 may include a signal, VShunt, representative of the voltage across the shunt resistor 138 and so the current therethrough.

As indicated above, the primary switch device 15 may be connected in electrical communication between the inductor 11 (e.g. the primary winding and, for example, the first terminal of that winding) and ground (which may be via the shunt circuit, e.g. shunt resistor 138).

Accordingly, the primary winding of the inductor 11 may be connected in series between the positive output of the electrical power supply 12 and the primary switch device 15 (which may, in turn, be connected in series between the inductor 11 and ground). As such the primary switch device 15 is electrically connected in series with the primary winding and in parallel with an input of the flyback converter 1 (which may be connected to the output of the electrical power supply 12 -defined as the positive output and ground).

The primary switch device 15, MOS, may be a MOSFET device (e.g. a SiC MOSFET), for example. As depicted, and in some other versions, the primary switch device 15 is driven by the drive circuit 14 (i.e. actuated between on and off (e.g. open and closed) states). The primary switch device 15 is configured to connect, selectively, the inductor 11 (e.g. the primary winding thereof and, in particular, the first terminal thereof) with ground (e.g. via the shunt circuit). The primary switch device 15 may include an input which is connectable in electrical communication with the drive circuit 14 to control the actuation of the primary switch device 15.

As will be appreciated, the electrical power supply 12 and snubber circuit 13, along with the primary switch device 15 may be considered to be input-side parts of the flyback converter 1. These input-side parts are connectable in electrical communication with the inductor 11 (e.g. the primary winding thereof).

We turn the output-side part(s) of the flyback converter 1.

The flyback converter 1 may include a bias circuit 17 which is connected in electrical communication with the inductor 11 (e.g. with the secondary winding thereof). The bias circuit 17 may, therefore, be connected in electrical communication with a first secondary winding (wherein the secondary winding mentioned herein may include multiple windings). The bias circuit 17 may be configured to output, to the drive circuit 14, a signal, Bias, representative of the current through the secondary winding (e.g. through the first secondary winding but, by extension, also through any other secondary winding) of the inductor 11. The bias circuit 17 may include a potential divider circuit which may be in the form of a low-pass filter (e.g. a low pass RC filter). The potential divider circuit may include a bias divider resistor 171 connected in series with a bias divider capacitor 172 across the first secondary winding of the inductor 11 (i.e. across an output of the inductor 11).

Therefore, the bias divider resistor 171 may be connected in electrical communication between a terminal of the first secondary winding of the inductor 11 (i.e. with a terminal of an output of the inductor 11, which may be a first output) and an output of the bias circuit, Bias, which is configured for connection to the drive circuit 14. The bias divider capacitor 172 may be connected in electrical communication between, on the one hand, the bias divider 171 and output of the bias circuit, Bias, and, on the other hand, another terminal of the first secondary winding of the inductor 11 (i.e. with another terrninal of the output of the inductor 11, which may be the first output). The other terminal of the secondary winding of the inductor 11 may be connected in electrical communication with ground and so the bias divider capacitor 172 may be connected in electrical communication with ground.

The flyback converter 1 includes an output circuit 16. The output circuit 16 includes an output diode 161, Schottky2, and an output capacitor 162, Gout.

In the depicted and some other versions, the flyback converter 1 is implemented as a battery charger circuit which is configured to recharge a battery. Accordingly, in the depicted and some other examples, the output circuit 16 may include an output which is configured for connection to a battery 18, Bat. This is depicted, for convenience, as part of the output circuit 16 but this does not need to be the case. In some versions, the flyback converter 1 is put to another application (which may be an application requiring an output voltage of more than about 500V, for example). Therefore, the battery 18 is an example of a load and references to the battery 18 may be references to a different load, for example.

The battery 18 may be a battery 18 with an output voltage of more than 500V, for example.

Moreover, there may be one or more other components associated with the output of the output circuit 16. These components may include, for example, a filter inductor 181, Lf, and a filter capacitor 182, Cf. These components may be viewed as part of the battery 18 or part of the output circuit 16, for example. The filter capacitor 182 and filter inductor 181 may form, for example an LC filter This is one example of a filter circuit which may be associated with the output of the output circuit 16, for example. The filter circuit may be configured to smooth the electrical power provided to the battery 18. Other forms of filter circuit may be used and, indeed, in some applications and versions, there may be no filter circuit.

Accordingly, in the depicted and some other versions, the output of the output circuit 16 is electrically connected in parallel with the inductor 11 and may be electrically connected in parallel with the secondary winding of the inductor 11 (e.g. a second secondary winding). The filter circuit may be electrically connected between the output of the output circuit 16 and the inductor 11. The output capacitor 16 and output diode 161 may be electrically connected between the filter circuit (which may not be provided in some versions) and the inductor 11.

As such, in the depicted and some other versions, the inductor 11 includes the second secondary winding. A first terminal of the second secondary winding is connected in electrical communication with an anode of the output diode 161. A cathode of the output diode 161 is connected in electrical communication with the output capacitor 162 and a first terminal of the output of the output circuit 16 (e.g. a first terminal of the battery 18). The output capacitor 162 may be connected in electrical communication with the cathode of the output diode 161 and the first terminal of the output of the output circuit 16 (as described), and also in electrical communication with a second terminal of the second secondary winding and a second terminal of the output of the output circuit 16 (e.g. a second terminal of the battery 16)-such that the output capacitor 162 is electrically connected in parallel with the output and the second secondary winding, for example.

Accordingly, the output capacitor 162 may be electrically connected in parallel with the secondary winding of the inductor 11 and the output diode 161 (on the one hand), and in parallel with the output of the output circuit 16 (on the other hand).

Therefore, the output diode 161 may be electrically connected in series with the secondary winding of the inductor 11 (e.g. the second secondary winding), and the output diode may be configured to block electrical current of a first polarity and to pass electrical current of a second polarity from the secondary winding of the inductor 11.

In versions with the filter circuit, then the filter circuit may be located between the output diode 161 and output capacitor 162 on the one hand and the output of the output circuit 16 (e.g. the battery 18) on the other hand. For example, the filter inductor 181, Lf, may be electrically connected in series between the cathode of the output diode 161 and the output of the output circuit 16 (e.g. the first terminal of the output). The filter capacitor 182, Of, may be electrically connected in parallel with the output capacitor 162, Cout, and/or the output of the output circuit 16 (e.g. the battery 18).

The output of the output circuit 16 may include a connection to ground via a ground capacitor 183, Cgnd. The ground capacitor 183 may be connected between ground and the second terminal of the output of the output circuit 16 and/or the second terminal of the second secondary winding of the inductor 11, for example.

The output diode 161 may be a Schottky diode (e.g. a SiC Schottky diode), for example. In some versions, the output diode 161 may be a switch device, such as a MOSFET device (which may be applicable for load (e.g. battery 18) voltages of less than 100y). The output diode 161 may, therefore, be referred to as an output device 161, for example, which has the functionality to block electrical current in one direction and pass electrical current in the opposing direction.

The output circuit 16 includes a blocking circuit 19. The blocking circuit 19 is configured to block a voltage from being applied to the output diode 161 when the primary switch device 15 is in its on (or closed) state.

The blocking circuit 19 is connected in electrical communication with the inductor 11 (e.g. with the second secondary winding thereof). The blocking circuit 19 is connected in electrical communication between the output diode 161 and the inductor 11.

The blocking circuit 19 may be configured to circulate an electrical current therethrough when the electrical current is of a polarity (a first polarity) which would be blocked by the output diode 161 (the output diode being configure to pass an electrical current of a second polarity therethrough).

The blocking circuit 19 includes a blocking circuit diode 191, Dres, which is configured to pass an electrical current of the first polarity and to block an electrical current of the second polarity. The blocking circuit diode 191, Dres, may be connected to the inductor 11 and this may be to the second terminal of the second secondary winding of the inductor 11, for example. In particular, an anode of the blocking circuit diode 191, Dres, may be connected in electrical communication with the inductor 11 (e.g. with the second terminal of the second secondary winding of the inductor 11).

A cathode of the blocking circuit diode 191, Dres, may be connected in electrical communication with the anode of the output diode 161. The cathode of the blocking circuit diode 191, Dres, may be connected in electrical communication with one or more circulating components 192 of the blocking circuit 19 through which the electrical current is to circulate. The one or more circulating components 192 may include a capacitor and/or a resistor. The one or more circulating components 192 may, therefore, be electrically connected between the blocking circuit diode 191, Dres, (e.g. the cathode thereof) and the inductor 11 (e.g. the first terminal of the second secondary winding).

When electrical current of the first polarity flows through the output circuit 16 (or a part thereof such as the blocking circuit 19), the current is effectively short-circuited (i.e. circulated) through the one or more circulating components 192. This, therefore, means that the output diode 161 is not exposed to the associated voltage.

The blocking circuit 19, moreover, includes a secondary output diode 193, Schottky1, which is electrically connected in parallel with the one or more circulating components 192, and electrically connected in series between the inductor 11 (e.g. between the first terminal of the second secondary winding thereof) and the output diode 161.

The secondary output diode 193 may be a Schottky diode (e.g. an Schottky SiC diode). In some versions, the secondary output diode 193 may be a switch device, such as a MOSFET device (which may be applicable for load (e.g. battery 18) voltages of less than 100V). The secondary output diode 193 may, therefore, be referred to as a secondary output device 193, for example, which has the functionality to block electrical current in one direction and pass electrical current in the opposing direction.

When the electrical current flows in the opposite direction (i.e. with the second polarity), the current will flow through both the secondary output diode 193 and the output diode 161 (and not through the blocking circuit diode 191 or one or more circulating components 192).

The blocking circuit 19, therefore, provides a bypass flow path for electrical current in one direction (i.e. the first polarity of current) to reduce the voltage to which the output diode 191 is exposed. However, when electrical current is flowing in the opposite direction, the current can flow through the output diode 161 (and the secondary output diode 193).

Accordingly, the blocking circuit 19 may be electrically connected between the secondary winding of the inductor 11 and the output diode 161. The blocking circuit 19 may include a blocking circuit diode 191 configured to pass electrical current of the first polarity from the secondary winding of the inductor 11 to one or more circulating components 192 of the blocking circuit 19 such that the associated voltage is blocked from the output diode 161, and to block electrical current of the second polarity from the secondary winding of the inductor 11.

Returning to the wider flyback converter 1, as described herein, the flyback converter 1 may include the drive circuit 14. This drive circuit 14 may be configured to receive a number of inputs regarding the operation of the components of the flyback converter 1 and to output a drive signal, Drive, to control the operation of the primary switch device 15 (e.g. to actuate the primary switch device 15).

The drive circuit 14 could take different forms and could be configured to drive the operation of the primary switch device 15 (and so control the output of the flyback converter 1, which is the output of the output circuit 16, for the avoidance of doubt).

In the depicted and some other examples, the drive circuit 14 is configured to receive as input(s) one or more of the signal representative, Bias, of the current through the secondary winding; the signal, Div, representative of the output of the electrical power supply 12 is provided to the drive circuit 14; and the signal, VShunt, representative of the voltage across the shunt resistor 138.

The drive circuit 14 may be configured to control the flyback converter 1 in a Quasi Resonant (or Boundary) Conduction Mode.

The drive circuit 14 may include a zero current detection comparator 141, ZCD_Comp. The zero current detection comparator 141 may have a first input (e.g. an inverting input) configured to be connected in electrical communication with the bias circuit 17 to receive the signal, Bias, representative of the current through the secondary winding. The zero current detection comparator 141 may have a second input (e.g. a non-inverting input) configured to be connected in electrical communication with a reference current 142, which is OA in this instance (e.g. a connection to ground).

The drive circuit 14 may include a peak current comparator 143, Ipeak_Comp. The peak current comparator 14 may have a first input (e.g. an inverting input) configured to be connected in electrical communication with the electrical power supply 12 to receive the signal, Div, representative of the output of the electrical power supply 12 is provided to the drive circuit 14. The peak current comparator 143 may have a second input (e.g. a non-inverting input) configured to be connected in electrical communication with the shunt circuit to receive the signal, VShunt, representative of the voltage across the shunt resistor 138. As will be appreciated, these voltages are representative of the electrical current output by the electrical power supply 12 and which is passing through the primary switch device 15, respectively.

An output of the zero current detection comparator 141 and an output of the peak current comparator 143 may be connected to a latch or flip-flop device 144 of the drive circuit 14 In the depicted and some other examples, the latch or flip-flop device 144 may be an SR latch 144. The output of the zero current detection comparator 141 may be connected in electrical communication with the S input of the SR latch 144 and the output of the peak current comparator 143 may be connected in electrical communication with the R input of the SR latch 144. An output of the latch or flip-flop device 144 (which may the Q output of the SR latch 144) may be the drive signal, Drive, for driving operation of the primary switch device 15. In some versions, the output of the latch or flip-flop device 144 may be connected in electrical communication with one or more other components between the latch or flip-flop device 144 and the primary switch device 15. This may include, for example, a buffer 151 (which may be considered to be a part of the primary switch device 15 or the drive circuit 14).

Accordingly, operation of the flyback converter 1 depicted and according to some versions described herein is such that the primary switch device 15 is actuated (by the drive circuit 14) to its on state when the output current through the output diode 161 drops substantially to zero (as sensed by the bias circuit 17). The primary switch device 15 is actuated (by the drive circuit 14) to its off state when the current through the primary switch device 15 reaches a peak current defined as a proportion of the current output by the electrical power supply 12 (as determined, for example, using the signal, Div, representative of the output of the electrical power supply 12 is provided to the drive circuit 14 and the signal, VShunt, representative of the voltage across the shunt resistor 138).

With the primary switch device 15 in its on state, the voltage across the primary winding of the inductor 11 is effectively reflected to the secondary winding The resulting electrical current would conventionally have been blocked entirely by the output diode 161. However, in versions described herein, the resulting current is blocked from reaching the output diode 161 by the blocking circuit 19 (e.g. the current flows through the blocking circuit diode 191 and one or more circulating components 192, and the secondary winding (e.g. the second secondary winding) of the inductor 11).

With the primary switch device 15 in its off state, electrical current flows through the secondary winding of the inductor 11 in a direction (i.e. polarity) to pass through the output diode 161 (and the secondary output diode 193) and the flyback converter 1 operates substantially as a conventional flyback converter 1.

The use of the blocking circuit 19 as described herein seeks to reduce the voltage rating requirements for the output diode 161 and secondary output diode 193. This means that lower cost and more readily available diodes may be used, for example. The same is true for the primary switch device 15.

For example, figure 2 shows the voltage across and current through the primary switch device 15 (MOS) and the output diode 161 (Schottky2) for a conventional flyback converter of the same topology as described but without the blocking circuit 19. Figure 3 shows the voltage across and current through the primary switch device 15 (MOS) and the output diode 161 (Schottky2) for a flyback converter 1 with the blocking circuit 19, as described. In the example represented in Figure 3 there the AC power source 122 is a 240 Vrms power source 122, and the battery voltage is 950 Vdc. The flyback converter 1 may be a 2.4 KW peak converter (providing a 1.2 KW average battery 18 charging power). The flyback converter 1 may be a 1-10 KW peak converter. The flyback converter 1 may be a 2-8 KW peak converter. The flyback converter 1 may be a 4-6 KW peak converter. The flyback converter 1 may be up to a 50 KW peak converter.

Versions may also permit a higher degree of flexibility on choosing the flyback transformer turns ratio. In particular, the turns ration for the inductor 11 (e.g. in the form of a transformer) may be mainly limited by a maximum reverse voltage capability of the primary switch device 15 and a maximum reverse voltage capability of the output diode 161. Therefore, if the maximum reverse voltage applied in accordance with versions of the described technology (as a result of use of the described blocking circuit 19) is reduced, then the flexibility of choosing the transformer turns ratio is higher.

Some versions seek to provide a flyback converter 1 with reduced voltage overshoots and ringing on both the primary switch device 15 and the output diode 161, thus reducing both the conducting and the radiated electromagnetic interference. Therefore, an input EMI converter filter can be simpler and this may reduce the stresses and the switching losses of the power semiconductors devices. This may allow the minimising of the snubber circuit 13 component ratings, thus increasing the converter 1 efficiency and the power density, and reducing its cost.

In some example, a conventional flyback converter may have required an output diode rated at 1700 V. However, if the conventional flyback converter is modified in accordance with versions described herein, then the output diode 161 and the secondary output device 193 may be rated at 1200 V each.

Some versions may be used, for example, in a battery charger and the battery charger may be configured to charge a battery 18 in a vehicle, for example. The battery charger may, therefore, include a connector for connection to the vehicle (the connector being in electrical communication with the output of the output circuit 16).

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The invention may also broadly consist in the parts, elements, steps, examples and/or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and/or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein.

Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure.

Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

Claims

CLAIMS1. A flyback converter having an input for electrical connection to an electrical power supply and an output for connection to a load, the flyback converter including: an inductor with a primary and a secondary winding; a primary switch device electrically connected in series with the primary winding and in parallel with the input; an output device electrically connected in series with the secondary winding, the output device configured to block electrical current of a first polarity and to pass electrical current of a second polarity from the secondary winding; an output capacitor electrically connected in parallel with the secondary winding and output diode, and in parallel with the output; and a blocking circuit electrically connected between the secondary winding and the output diode, the blocking circuit including a blocking circuit diode configured to pass electrical current of the first polarity from the secondary winding to one or more circulating components of the blocking circuit such that the associated voltage is blocked from the output diode, and to block electrical current of the second polarity from the secondary winding.
2. A flyback converter according to claim 1, wherein the output device is an output diode.
3. A flyback converter according to any preceding claim, wherein the one or more circulating components include one or more resistors.
4. A flyback converter according to any preceding claim, wherein the one or more circulating components include one or more capacitors.
5. A flyback converter according to any preceding claim, wherein the blocking circuit includes a secondary output device electrically connected in series with the output device and in parallel with the one or more circulating components.
6. A flyback converter according to any preceding claim, wherein the secondary output device is a secondary output diode.
7. A flyback converter according to any preceding claim, wherein the load requires a voltage of greater than 500V.
8 A flyback converter according to any preceding claim, further including a snubber circuit.
9. A battery charger including a flyback converter according to any preceding claim, and a connector electrically coupled to the output and for connection to a battery.
10. A battery charger according to claim 9, wherein the connector is for connection to an electric vehicle which includes the battery.