GB2544820A

GB2544820A - A low voltage power supply using an earth connection on a terminal block

Info

Publication number: GB2544820A
Application number: GB1521417.4A
Authority: GB
Inventors: Bell Wayne; Moris Juan
Original assignee: Tridonic GmbH and Co KG
Current assignee: Tridonic GmbH and Co KG
Priority date: 2015-11-30
Filing date: 2015-11-30
Publication date: 2017-05-31
Anticipated expiration: 2035-11-30
Also published as: GB201521417D0; GB2544820B

Abstract

An electronic power supply device comprises an AC power input filter circuit 2 including a capacitor 18 and a leakage energy recovery circuit 14 configured to recover electric energy from a leakage current through the capacitor. The rectified output of the AC filter may be fed to a switched converter such as a power factor correction circuit. The leakage energy recovery circuit may comprise a low voltage power supply means 22 for driving an integrated circuit such as a microprocessor 12. The leakage energy recovery circuit may comprise a resonance circuit 16 in series with the capacitor. An inductance of the resonant circuit may be a primary winding 20.1 of a transformer 20. The capacitor may be a Y-capacitor of an EMI filter circuit. The electronic power supply device may be a switched mode power supply, a LED converter or an electronic ballast.

Description

A low voltage power supply using an earth connection on a terminal block

The invention relates to the field of low voltage power supply. Particularly the invention relates to a low voltage power supply from an earth connection in a terminal block of an electronic power supply, for example a switched mode power supply such as an LED converter.

In a purely resistive alternating current (AC) load circuit, voltage and current waveforms are in phase, changing polarity at the same instant in each cycle. All the power entering the load circuit is consumed or dissipated.

When electronic equipment is connected to AC mains it potentially may feed noise to the mains supply line and disturb other equipment also connected to the same mains supply line. Particularly in the field of switched mode power supplies the design engineer has to devise means to counter this problem.

Capacitor-based power line filtering is often used in an electronic device to decouple any common-mode noise produced by the electronic devices power supply, preventing it from reaching other equipment via the mains power line. The reliability of these line filter capacitors is critical to the safety of the users of the electronic device. Line filter capacitors are classified either as X-capacitors or Y-capacitors. X-capacitors are connected between phase line and neutral line, to protect against differential mode interference. Y-capacitors are designed to filter out commonmode noise, and are connected between line and earth. Y-capacitors are designed to fulfill enhanced electrical and mechanical reliability standards. Y-Capacitors must be tested to applicable standards such as EN 60384-14 (IEC 60384-14) to qualify them for use as Y-capacitors. For Y capacitors, ceramic types are less expensive than metallised film, but unstable over time and temperature and less mechanically stable.

Capacitance values are also limited to reduce the leakage current passing through the capacitor when an AC voltage is applied, and to reduce the energy stored to a safe limit when DC voltage is applied.

The leakage current through the Y-capacitor is an unwanted element and strict limits are applied in luminaries and their power supply units to restrict the leakage current. The leakage current also is a waste of electric energy which reduces the electric efficiency of the power supply unit, and thus also the luminary.

Therefore the efficiency of the electronic power supply may be improved.

The technical problem is solved by the electronic power supply device according to claim 1.

An electronic power supply device comprises an AC input filter circuit including at least one capacitor. The electronic power supply device further comprises a leakage energy recovery circuit which is configured to recover electric energy from a leakage current through the at least one capacitor.

The claimed electronic power supply device increases the efficiency of the power supply of an electronic device, as the conventionally unused energy caused by the leakage current through the capacitor of an AC input filter circuit is used to provide a low voltage power supply of the electronic power supply device. The energy contained in particular in a high frequency component of the leakage current is used as a source of power for a low voltage power supply (LVPS) of the electronic device which may be used to drive an integrated circuit (IC), a microprocessor, a diode or other electronic circuits. Known low power supply devices are designed around providing additional energy to a system as this would represent a reduced efficiency. The claimed solution is suited to harvest electric energy which usually only represents energy loss and uses the recovered electric energy to provide a low voltage power supply for the electronic power supply device. The electronic power supply device is able to provide a low voltage power supply even during standby mode of operation of the electronic device, as long as a line and a protective earth connection are present.

Advantageous embodiments of the electronic power supply device are claimed in the dependent claims.

The electronic power supply device according to a preferred embodiment has the leakage energy recovery circuit comprising a resonance circuit arranged in series to the at least one capacitor as part of the leakage energy recovery circuit. The resonance circuit uses the high frequency components contained in the leakage current in order to harvest electric energy which is then used for the low voltage power supply.

Preferably the capacitor is a Y-capacitor of an electromagnetic interference (EMI) filter circuit as the AC input filter circuit.

The electronic power supply device of an advantageous embodiment has a rectified output signal of the AC mains filter circuit being fed to a switched converter circuit, such as a power factor correction (PFC) circuit. A preferred embodiment of the electronic power supply device is designed such that a center frequency of the resonance circuit is in the order of magnitude of, or in particular tuned to a switching frequency of a switched converter circuit.

An advantageous electronic power supply device according to an aspect of the invention includes a transformer in the leakage energy recovery circuit configured to couple out a voltage from the resonance circuit. The transformer further provides electric isolation between the low voltage power supply on one hand and the AC supply input of the electronic power supply device on the other hand.

Preferably the electronic power supply device includes a primary winding of the transformer simultaneously being an inductive element (inductance, coil) of the resonance circuit. The electronic power supply device may include a secondary winding of the transformer to couple the voltage from the resonance circuit and apply the voltage, for example, to a rectifier circuit.

The electronic power supply device according to an advantageous embodiment comprises the leakage energy recovery circuit including a low voltage power supply means. The low voltage power supply means is configured to provide an output voltage in a range from 3 to 12 V, and/or to supply an output current in a range from 1 mA to 5 mA. The low voltage power supply device is therefore suited to supply an integrated circuit (IC) , a microprocessor, an application specific circuit (ASIC) or similar circuit with the required energy, either for constant power supply or at least for a start-up process of the electronic circuit.

The electronic power supply device may be a switched mode power supply device. According to another aspect the switched mode power supply device is an electronic ballast or a LED converter.

The description of embodiments of the invention refers to the enclosed drawings in which

Fig. 1 provides a general overview of major elements of an AC driven switched mode power supply device, and

Fig. 2 is simplified schematic circuit diagram of a preferred embodiment of a electronic power supply device with a low voltage power supply.

In the figure same numerals denote the same or corresponding elements. For sake of conciseness the description of the figures omits repeating the description of same reference signs for different figures.

In fig. 1 a general overview of major elements of an AC driven switched mode power supply device 1' is provided. Although the invention is discussed with reference to a switched mode power supply device, the invention can be applied to any system which has an input terminal connected via a capacitor to protective earth and require a low voltage power supply with limited power supply capability.

Generally in a resistive AC load circuit, voltage and current waveforms are in phase and change polarity at the same time instant in each cycle. All the power entering the load circuit is consumed or dissipated.

In case of a reactive AC load circuit including reactive circuit elements as capacitors or inductors being present, electric energy stored in in a reactive circuit element results in a phase difference between the AC current and voltage waveforms. During each cycle of the AC voltage, extra energy, in addition to any energy consumed in the load, is temporarily stored in the load in electric or magnetic fields, and then returned to the power grid a fraction of the period later.

Electronic circuits containing exclusively resistive loads such as incandescent lamps have a power factor around 1.0, circuits containing inductive or capacitive loads such as electric motors, and transformers, fluorescent lamp ballasts, often have a power factor below 1. A circuit with a low power factor will use higher currents to transfer a given quantity of real power than a circuit with a high power factor. A linear load does not change the shape of the waveform of the current, but may change the relative timing (phase) between voltage and current.

If a switched mode power supply (SMPS) has an AC current input, then the first stage as shown in fig. 1 is to convert the input AC current to a DC current by rectification. A rectifier circuit 4 produces an unregulated DC voltage which is then fed to a large filter capacitor. The rectifier circuit 4 is a non- linear circuit, so the input AC current is highly non-linear. That means that the input current to the rectifier circuit 4 has energy at harmonics of the frequency of the voltage. The current drawn from the mains supply by the rectifier circuit occurs in short pulses around the AC voltage peaks. These pulses have significant high frequency energy which reduces the power factor.

To further correct a low power factor of the basic switched mode power supply 1 as shown in fig. 1, a more elaborate SMPS 1 can use a dedicated power factor correction circuit 6 (PFC circuit 6) to ensure that the input current follows a sinusoidal shape of the AC input voltage and thereby to correct the power factor. A basic SMPS 1 incorporates a simple full-wave rectifier circuit 4 connected to a large energy storing capacitor. Such SMPS 1 draws current from the AC line in short pulses when the instantaneous mains voltage exceeds the voltage over this energy storing capacitor. During the remaining portion of the AC cycle the energy storing capacitor provides energy to the power supply. As a result, the input current of such basic SMPS 1 has high harmonic content and relatively low power factor. This creates extra load on utility lines, might increase heating of building wiring, the utility transformers and may cause stability problems in some applications such as in emergency generator systems or aircraft generators. Harmonics can be removed by filtering, but the AC supply input filter circuit 2 (EMI filter circuit 2) mean further costs.

Unlike a displacement power factor created by linear inductive or capacitive loads, the distortion by the rectifier circuit 4 cannot be corrected by addition of a single linear component. Additional circuits are required to counteract the effect of the brief current pulses. For example arranging a switched converter circuit 6 for example a current regulated boost chopper stage, after the rectifier circuit 4 for charging the storage capacitor can correct the power factor, but increases the complexity and cost.

The electronic power supply device 1 in fig. 1 further includes a converter 8, for example a boost converter, for generating the desired DC output voltage UL and DC output current IL for driving a load 10. In fig. 1 the converter 8 generates output voltage UL and the output current IL to drive one or more light emitting diodes 10 as load. The load may also be a gas discharge lamp or any other circuit requiring a DC power supply. The converter 8 also provides a potential barrier between the high voltages on the first side of converter 8 towards the AC supply input lines 3, 5 and 7 and the low voltages on the second side of the converter 8 towards the load 10 and the load connecting lines 21, 23.

The converter 8 further may internally generate also a DC low voltage Ulves and/or a low current Ilvps for supplying one or more integrated circuits 12. This secondary function as a low voltage power supply also integrated into the converter 8 is usually implemented using additional auxiliary windings of a transformer forming part of the converter 8. The power for driving the integrated circuit 12 via the low voltage power supply lines 25, 27 is also drawn from the AC power supply via the AC supply input filter 2, the rectifier circuit 4 and the PFC circuit 6.

Fig. 2 is simplified schematic circuit diagram of a preferred embodiment of an electronic power supply device 1, in the depicted case a switched mode power supply device 1 with a low voltage power supply 14 according to an embodiment.

The electronic power supply device 1 in fig. 2 is depicted only partially in order to show the AC supply input filter 2 according to the invention and the low voltage power supply 14 of the invention more clearly.

As shown for the rectifying circuit 4 in fig. 2, the power factor correction circuit 6 and the converter circuit 8 correspond to the respective units in fig. 1. The same reasoning applies for the load 10 and the integrated circuit 12.

The load 10 can be a light emitting means comprising one or more LEDs. The integrated circuit 12 can be a microcontroller, an ASIC, a light emitting diode or a similar assembly.

The electronic power supply device 1 is fed by a mains input with via a phase line 3, a neutral line 5 and is earthed by a protective earth line 7. However, any other AC supply voltage can be used for feeding the electronic power supply device 1.

The AC supply voltage input lines 3, 5, 7 inputted to the electronic power supply device 1 are fed to an AC supply input filter 2. The AC supply input filter 2 is adapted to attenuate radio frequency (high frequency) components between the mains input lines 3, 5, 7 and the electronic power supply device 1. AC supply input filter 2, (also: line filter, EMI filter, RFI filter) is employed to attenuate emissions in either direction. The AC supply input filter 2 reduces unintentional conducted emission from the electronic power supply device 1, for example to a level compliant with regulatory restrictions. This is particularly important for switched mode power supplies. The AC supply input filter 2 also prevents unwanted electromagnetic interference from entering the electronic power supply device 1 to a level sufficiently low to guaranty correct functioning of the electronic power supply device 1. The AC mains input filter 2 can comprise resistors, inductances (chokes) and capacities. The capacities used in known AC supply input filter 2 as well as in the inventive AC supply input filter 2 are of two specific varieties.

An X capacitor 24 is arranged between phase input line 3 and the neutral input line 5 and attenuates differential mode interference. Electromagnetic interference can be differential mode interference, which refers to interference signals which appear on either the phase input line 3 or the neutral input line 5.

An Y-capacitor 26 is arranged between the neutral input line 5 on one hand and the protective earth line 7 on the other hand and attenuates common mode interference. Common mode interference refers to interference signals which appear identically on the phase input line 3 and the neutral input line 5. Known is also arranging a corresponding Y capacitor 28 between the phase line 3 and the protective earth line 7.

However the Y-capacitors 26, 28 cause a leakage current due to capacitive coupling. Capacitive coupling refers to a transfer of energy within an electric network by means of the capacitance between circuit nodes. This capacitive coupling over the Y-capacities 26, 28 to the protective earth line 7 results in an unwanted leakage current as the accidental effect.

According to a preferred embodiment of the inventive electronic power supply device 1 shown in fig. 2, a resonance circuit 16 is arranged in series with the Y-capacitor 28. The resonance circuit 16 is shown as a parallel resonance circuit comprising a capacitor 18 and transformer 20, or particularly, a primary winding 20.1 of the transformer 20. The resonance circuit 16 is designed to have a center frequency with a value in the magnitude of the switching frequency of the switched converter circuit 8 (power factor correction circuit). The resonance circuit 16 is even more advantageously tuned to the center frequency (resonance frequency) which corresponds to the switching frequency of the switched converter circuit 8. Thus the resonance circuit 16 is most suited to harvest high frequency components of a signal on the phase line 3 whose frequency corresponds to or is in the close vicinity of the switching frequency of the switched converter circuit 8. There may exist further signal components of the signal on the phase line 3 whose frequency is for example at twice the frequency of the AC supply line 3. However, tuning the center frequency of the resonance circuit 16 to the switching frequency of the switched converter circuit 8 yields a good result for acquiring leakage power of the leakage current through the Y capacity 28.

The resonance circuit 16 forming part of the electronic power supply device 1 and its leakage energy recovery circuit 14 comprises besides the capacitor 28 a transformer 20. A secondary winding 20.2 of the transformer 20 is used to couple a voltage from the resonance circuit 16. The voltage coupled from the resonance circuit 16 is fed to a low voltage power supply means 22 configured to provide an output voltage for driving a load requiring only limited power supply such as an integrated circuit 12.

The low voltage power supply means 22 is provided with the voltage induced in the secondary winding 20.2, which can be fed to a low voltage rectifying circuit for rectifying the AC voltage induced in the secondary winding 20.2 of the transformer 20. The low voltage rectifying circuit converts alternating electric current, which periodically reverses polarity, to direct current. Because of the alternating nature of the input current corresponding to an AC sine wave, the process of rectification alone produces a DC current that, though unidirectional, consists of pulses of current.

The low voltage rectifying circuit may have the topology of a half-wave rectifier or preferably of a full-wave rectifier. The rectifier can comprise one or more diodes 30.1, 30.2 30.3, 30.4, in particular Schottky-diodes, for converting the input AC voltage with alternating polarity to a rectified, steady state, positive or negative polarity output low voltage signal Ulvps or output current signal Ilvps-

As a low voltage power supply usually requires a steady, constant DC current, the output of the low voltage rectifier circuit can be smoothed by an electronic filter. A capacitor 32 can be arranged to generate a steady DC current from the output of the low voltage rectifying circuit.

In fig. 2 a Zener diode 34 is shown to be arranged in parallel to the capacitor 34 in order to regulate the output voltage Ulvps. The Zener diode 34 of the depicted embodiment acts as shunt regulator by providing an alternate path to device ground connector through a variable resistance. The Zener diode 34 maintains a constant, voltage Ulvps when the current through the Zener diode 34 is sufficient to operate the Zener diode 34 in the breakthrough region of the I-U- diagram of the Zener diode 34. This regulator topology is one example suitable for very simple low-power applications where the currents involved are very small and the load is permanently connected across the Zener diode 34 as in present application.

According to an embodiment the low voltage Ulvps can be in a range from 3 to 12 V, and an output current Ilvps can be in a range from 1 mA to 5 mA.

The voltage Ulvps or the current Ilvps provided by the low voltage power supply 14 can be used to drive an integrated circuit 12 such as a microcontroller. The low voltage power supply 14 according to an aspect of the invention can be employed as a source of constant power to an integrated circuit 12. According to another aspect, the low voltage power supply 14 may provide a suitable start-up power supply for an integrated circuit 12.

Thus the electronic power supply device according to the invention uses electric energy due to a leakage current over the Y capacity 28 to provide an additional low voltage power Ulvps. The transformer 20 additionally ensures galvanic isolation between the primary side of the transformer 20 being connected with the AC mains supply lines 3, 5 and 7 on a mains potential level, for example 230V, and a secondary side of the transformer 20 which is on a low voltage power level, for example 3 to 12 V.

Claims

Patent Claims:

1. An electronic power supply device, comprising an AC supply input filter circuit (2) which includes at least one capacitor (15), and a leakage energy recovery circuit (14) configured to recover electric energy from a leakage current through the capacitor (18).

2. The electronic power supply device according to claim 1, characterized in that the leakage energy recovery circuit (14) comprises a resonance circuit (16) in series to the capacitor (18).

3. The electronic power supply device according to claim 2, characterized in that a center frequency of the resonance circuit (16) is in the order of magnitude of or tuned to a switching frequency of a switched converter circuit, such as a power factor correction circuit (6).

4. The electronic power supply device according to claim 2 or 3, characterized in that the capacitor (18) is a Y-capacitor of an EMI filter circuit.

5. The electronic power supply device according to any of claims 1 to 4, characterized in that the leakage energy recovery circuit (14) comprises a transformer (20) configured to couple out a voltage from the resonance circuit (16).

6. The electronic power supply device according to claim 5, characterized in that a primary winding (20.1) of the transformer (20) is an inductance of the resonance circuit (16).

7. The electronic power supply device according to any claims 1 to 6, characterized in that a rectified output signal of the AC mains supply filter (2) is fed to a switched converter, such as a power factor correction circuit (6).

8. The electronic power supply device according to any of claims 1 to 7, characterized in that the leakage energy recovery circuit (14) comprises a low voltage power supply means (22) configured to provide an output voltage in a range from 3 to 12 V, and/or to supply an output current in a range from 1 mA to 5 mA.

9. The electronic power supply device according to any of claims 1 to 8, characterized in that the electronic power supply device(1) is an electronic ballast or a LED converter.