WO2004091086A1

WO2004091086A1 - Switched-mode power supply unit

Info

Publication number: WO2004091086A1
Application number: PCT/EP2004/003596
Authority: WO
Inventors: Heinz Dettmer
Original assignee: Z-Laser Optoelektronik Gmbh
Priority date: 2003-04-10
Filing date: 2004-04-05
Publication date: 2004-10-21
Also published as: EP1611666A1; ATE349799T1; EP1611666B1; DE502004002457D1

Abstract

The invention relates to a switched-mode power supply unit which supplies current to low voltage consumers from a network voltage source. Said switched-mode supply unit comprises a pulsed direct current-direct current converter (6) which is embodied as a resonance filter converter for the galvanic separation of the network side from the low voltage side. The converter (6) comprises a transformer provided with a primary winding (8) and a secondary winding (9). An electric insulation layer (16) is arranged between the primary winding (8) and the secondary winding (9). The primary winding (8) is serially connected to a pulse-controlled semi-conductor switch (VI) arranged in the electric circuit of an input voltage source (1). The secondary winding (9) is connected to connections (12a, 12b) for the low voltage consumer by means of a rectifier circuit. The insulation layer (16) is at least 0,2 mm thick (d) for the capacitive decoupling of primary windings (8) and secondary windings (9).

Description

Schαltnetzteil

The invention relates to a switching power supply for the power supply of low-voltage consumers from a mains voltage source, with a clocked ΘDC voltage-θDC voltage converter for the electrical isolation of the network side from the low-voltage side, the converter having a transformer with a primary winding and a secondary winding, between the primary winding and the secondary winding is arranged with an electrical insulation layer, the primary winding in the circuit of an input voltage source being connected in series with a clock-controlled semiconductor switch and the secondary winding being connected to connections for the low-voltage consumer via a rectifier circuit.

Such a switching power supply is known from practice. It has an input voltage source; which has a bridge rectifier which can be connected with its input connections to the mains voltage of the public AC network. With its output connections, the bridge rectifier is connected to an electrolytic capacitor, which smoothes the pulsating DC output voltage of the bridge rectifier. The input voltage source is connected to a primary winding of a transformer to form a circuit via a semiconductor switch. The semiconductor switch has a control input; which is connected to a control device for periodically interrupting the circuit. An approximately rectangular control voltage is applied to the control input via the control device. The periodic interruption of the circuit generates an electrical voltage in the secondary winding of the transformer, which is rectified with the aid of a rectifier circuit and supplied with electrical connections that can be connected to a low-voltage consumer. The switching frequency is greater than the mains frequency, which means that the transformer has relatively small dimensions in comparison to a transformer of the same power operated at mains frequency.

In order to enable safe electrical isolation between the primary winding and the secondary winding and in particular when an overcurrent occurs To prevent voltage in the AC network from breaking through the AC voltage from the primary winding to the secondary winding, an electrical paper insulation layer is arranged between the primary winding and the secondary winding, which has a thickness of about 0.1 millimeters. When designing the transformer, taking the required overvoltage resistance of the transformer into account, the smallest possible thickness of the insulation layer is sought in order to achieve a good magnetic coupling between the primary winding and the secondary winding, a low leakage inductance and a low component load and thus a low power loss.

The primary circuit is connected to the secondary winding via a radio interference suppression capacitor in order to comply with the radio interference voltage limit values prescribed by law. The switching power supply is housed in a grounded metallic housing. A coupling capacitance is formed between the housing and the switching power supply.

Such a switched-mode power supply must meet certain requirements for applications of protection class 1 regarding the interference frequency transmission and the immunity to interference, which relates to the burst voltage penetration to the low-voltage side, which is electrically isolated from the network side. If the housing of the switching power supply is arranged on an electrically insulated surface, static discharges (by touch) can generate leakage currents through the housing, the coupling capacitance, the low-voltage consumer and the radio interference suppression capacitor to the network. On the one hand, this can be uncomfortable for the user of the switching power supply if he perceives the leakage current as an electric shock. On the other hand, such a leakage current can also be used to connect a sensitive low-voltage consumer, e.g. a laser diode, can be damaged or even destroyed if the leakage current reaches the low-voltage consumer. Another disadvantage of the known switching power supply is that it still has relatively large dimensions.

It is therefore the task of creating a switching power supply of the type mentioned at the outset which, with compact dimensions, enables a low leakage current and a low interference emission with high immunity to interference (burst, surge, HF field, HF inflow). This object is achieved in that the insulation layer for the capacitive decoupling of primary winding and secondary winding has a thickness of at least 0.2 millimeters and that the converter is designed as a resonance flyback converter.

Surprisingly, the thickness of the insulation layer arranged between the primary winding and the secondary winding is therefore chosen to be greater than would actually be required to meet the overvoltage resistance of the transformer. This measure advantageously achieves a very low coupling capacitance between the primary winding and the secondary winding, so that the leakage current is reduced accordingly. The associated reduction in the magnetic coupling between the primary winding and the secondary winding, which leads to a greater power loss in the transformer, is deliberately accepted. The converter, which is designed as a resonance flyback converter, results in a sinusoidal course of the control signal for the semiconductor switch, as a result of which the steepness of the switched transformer currents decreases so much in comparison with the switching power supply known from the prior art, in which the semiconductor switch is controlled with a rectangular control signal. that an interference suppression capacitor connecting the primary winding to the secondary winding can be dispensed with. As a result, the electrical capacitance between the primary and the secondary side of the switching power supply is additionally reduced by a factor K = C _κ / (C _κ + C _E ), where C _κ is the coupling capacitance between the primary and the secondary side of the switching power supply and C _E which mean the capacitance of the interference suppression capacitor. These measures reduce the leakage current and the burst voltage penetration from the primary side to the secondary side to a value that hardly affects sensitive consumers.However, the emission of interference frequencies is extremely low due to the low steepness of the transformer currents, so that Environment of the switching power supply is hardly disturbed. Because of the low leakage current, the switching power supply is particularly suitable as a power supply for laser diodes. The switching power supply can also be used advantageously in medical devices that come into contact with patients. Since a suppressor capacitor is saved, the switching power supply enables compact dimensions. In an advantageous manner, the switching power supply can also be used to operate a mobile phone. there Is avoided by the low leakage current that the user of the mobile phone feels a disturbing tingling in the ear when making a call when the mobile phone is connected to the switching power supply.

In an advantageous embodiment of the invention, the thickness of the insulation layer is at least 0.3 millimeters, preferably at least 0.35 millimeters and in particular at least 0.4 millimeters. The switched-mode power supply enables an even smaller leakage current, which can be in the picoampere range.

An even greater distance between the primary and secondary windings and thus an even lower leakage current can be achieved in that the thickness of the insulation layer is at least 0.5 millimeters, possibly at least 0.6 millimeters and possibly at least 0.7 millimeters. Such a wall thickness of the insulation layer is particularly useful for larger switching power supplies.

It is advantageous if the secondary winding is arranged on the outer circumference of the primary winding. This enables an even lower interference frequency radiation. In principle, however, it is also conceivable that the primary winding and the secondary winding are arranged next to one another in the axial direction and that the insulation layer is arranged in a plane approximately perpendicular to the axial direction between the primary winding and the secondary winding.

In an expedient embodiment of the invention, the primary winding is connected at one end to a pole of the input voltage source and at the other end to the semiconductor switch, the primary winding having a plurality of winding layers and the winding layer, the end of which is connected to the semiconductor switch, being a soft magnetic one and / or ferritic transformer core and the winding layer, the end of which is connected to the pole of the input voltage source, faces the secondary winding. The side of the primary winding, which is connected to the semiconductor switch and on which the potential fluctuations occur when switching, is thus arranged away from the secondary winding, so that the interference occurring when switching the primary current is not or only to a very small extent transferred to the secondary winding. Good shielding of the secondary winding against the interference voltages occurring on the primary winding can also be achieved in that the secondary winding only partially covers the primary winding, and in that between the secondary winding and the end face of the primary winding, on which the end of the primary winding connected to the semiconductor switch is arranged a distance is provided. Also in this embodiment, the side of the primary winding, the potential fluctuations at the on switching disposed of ^'the secondary winding removed.

If the secondary winding has a larger number of turns, it is advantageous if the secondary winding has a plurality of winding layers lying one on top of the other, and if the radial dimension or thickness of the winding body formed by these winding layers is greater than its axial dimension or length. The winding on the low-voltage side is thus designed as a narrow upright winding, so that there can be a correspondingly large distance between the end face of the secondary winding on which the end of the primary winding connected to the semiconductor switch is arranged and the secondary winding.

In an advantageous embodiment of the invention, an auxiliary voltage winding is arranged between the primary winding and the secondary winding, and is connected to control electronics for the semiconductor switch in such a way that it can be used as a power supply for the control electronics. As a result, the control electronics can be supplied with a low operating voltage compared to the mains voltage.

In a preferred embodiment, the connections for the low-voltage consumer are connected to measurement signal inputs of a voltage measurement device, the measurement signal output of which is connected to a comparison device having a reference voltage source, the comparison device being connected to the control electronics via a controller to form a closed control circuit, and between the controller and an optical coupler is preferably arranged in the control electronics. The electrical voltage applied to the secondary winding is therefore regulated by measuring and comparing it with a reference voltage, and by the If a control deviation occurs, the control signal for the semiconductor switch is changed in such a way that the control deviation is reduced or eliminated. The optocoupler enables electrical isolation between the primary winding and the secondary winding.

The clock frequency of the converter is preferably greater than 25 kHz. The transformer can then have very compact dimensions.

It is advantageous if the semiconductor switch, the control circuit and the input voltage source are arranged on one side of the transformer and the rectifier circuit and optionally the measuring device and the control circuit on the opposite other side of the transformer. The secondary side of the switching power supply is then even better shielded from electromagnetic interference that occurs on the primary side.

In a preferred embodiment of the invention, the switching power supply has a housing; in the inner cavity of which the input voltage source and the converter are arranged, the housing being electrically conductively connected to one of the connections for the low-voltage consumer. The switching power supply then meets even higher requirements for radio interference suppression. The housing is preferably made of metal. But it can also consist of an electrically insulating material, such as plastic, which is provided with an electrically conductive coating.

The housing is preferably tubular, the electrical circuit formed by the input voltage source and the converter and the low voltage consumer being arranged one behind the other in the axial direction of the housing in its inner cavity and preferably being spaced apart from one another by a space. The switched-mode power supply preferably faces the low-voltage consumer with its secondary side.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing. It shows: Fig. 1 is a circuit diagram of a resonance flyback converter and a transformer switching power supply, and

2 shows a cross section through the transformer of the switching power supply.

A switched-mode power supply for the power supply of low-voltage consumers from a mains voltage source, namely the public AC voltage network, has an input voltage source or input stage, designated as a whole in FIG. 1, which has a bridge rectifier 2, which with its input connections 3a, 3b has a fuse F1 with the mains voltage source via a fuse F1 is connectable. The output connections or poles 4a, 4b of the bridge rectifier 2 are connected via an EMC filter 5 to a first electrolytic capacitor C4, which is used to smooth the mains AC voltage rectified by the bridge rectifier 2.

The input voltage source 1 feeds one in Fig.! generally designated mit clocked DC-to-DC voltage converter which has a transformer 7 with a primary winding 8, a secondary winding 9 and an auxiliary voltage winding 10 for galvanic isolation of the network side from the low-voltage side, which has a soft magnetic core 1 designed as a laminated core 1 are arranged. Instead of the laminated core, a core 11 made of ferrite material can also be provided. A closed magnetic circuit is formed in the core 11, which passes through the primary winding 8, the secondary winding 9 and the auxiliary voltage winding 10. The primary winding 8 of the transformer 7 is connected with its one winding connection to a first pole 4a of the input voltage source 1 and with its other winding connection to a drain connection of a clock-controlled semiconductor switch VI designed as a field effect transistor. The source connection of the semiconductor switch VI is connected via a first ohmic resistor R9 to a second pole 4b of the input voltage source 1 or input stage.

The secondary winding 9 of the transformer 7 is connected with one winding connection via a rectifier Dl with a first connection 12a and with its other winding connection with a second connection 12b for the low voltage consumption connected. A second electrolytic capacitor C3, which serves as a buffer and for screening, is connected in parallel with the connections 12a, 12b.

The DC-DC converter ό is designed as a resonance flyback converter and has a first capacitor C5; which forms a series resonant circuit with the primary winding 8. For this purpose, the capacitor C5 is connected with its one pole to the winding connection of the primary winding 8 connected to the drain connection of the semiconductor switch VI and with its other pole to a first node 13, which is connected via a second resistor R8 to the second pole 4b of the input voltage source is. The first node 1 3 is also connected to the base of a first transistor V2 of control electronics for the semiconductor switch VI. The collector of transistor V2 is connected to a second account point 14, which is connected on the one hand via a diode D7 to the gate connection of the semiconductor switch VI and on the other hand to the collector of a second transistor V3 of the control electronics. The emitters of the transistors V2, V3 are connected to the second pole 4b of the input voltage source 1. The base of the second transistor V3 is connected via a third resistor Rl 2 at the source connection of the semiconductor switch VI and via a fourth resistor Rl 1 to a voltage divider connection of a voltage divider R4, RI O, connecting the first pole 4a to the second pole 4b of the input voltage source 1. R7 connected. Another voltage divider connection of the voltage divider R4, Rl 0, R7 is connected via a resistor R6 to the gate connection of the semiconductor switch VI. This voltage divider connection is also connected via a second capacitor C1 to a first connection of the auxiliary voltage winding 10. A second connection of the auxiliary voltage winding 10 is connected to the second pole 4b of the input voltage source. Via the auxiliary voltage winding 10, the control electronics are supplied with an operating voltage that is less than the mains voltage with little loss. The voltage applied to the auxiliary voltage winding 10 is dimensioned such that magnetic saturation of the soft magnetic material of the transformer core 11 is avoided. The resonance circuit formed from the primary winding 8 and the capacitor C5 results in a sinusoidal current profile with low steepness in the primary circuit. As a result, an interference suppression capacitor between the primary winding 8 and the secondary winding 9 can be saved, as a result of which the coupling capacitance between the primary winding 8 and the secondary winding 9 is reduced accordingly. Nevertheless, the switching power supply has only a very low interference signal emission even without an interference suppression capacitor

It can be seen in FIG. 2 that the primary winding 8 has a plurality of winding layers and that the auxiliary voltage winding 10 is arranged on the outer circumference of the primary winding 8. It can also be seen that the secondary winding 9 is arranged on the auxiliary voltage winding 10. A first electrical insulation layer 15 is arranged between the primary winding 8 and the auxiliary voltage winding 10, the thickness of which in the radial direction is approximately 0.1 millimeter. A second electrical insulation layer 16 is arranged between the auxiliary voltage winding 10 and the secondary winding 9, the thickness d of which in the radial direction is approximately 0.35 millimeters. On its outer circumference, the secondary winding 9 is covered by a third electrical insulation layer 19, which serves as a cover layer. Primarily through the second insulation layer 16, the primary winding and secondary winding are largely capacitively decoupled. This measure, in combination with the lack of interference suppression capacitor between the primary winding 8 and the secondary winding 9, results in a very low coupling capacitance between the primary side and the secondary side of the transformer 7 and thus a correspondingly low leakage current, which is typically less than 1 microampere. The coupling capacity is typically less than 25 picofarads.

In order to reduce the burst voltage penetration from the primary side to the secondary side of the transformer, the winding position of the primary winding, the end 1 8 of which is connected to the semiconductor switch VI, is the soft magnetic transformer core 1 1 and the winding position, the end 19 of which is connected to the first pole 4a is connected to the input voltage source 1, facing the auxiliary voltage winding 10 and the secondary winding 9. 2 that the secondary winding 9 only partially covers the auxiliary voltage winding 9 and the primary winding 8, and that between the secondary winding 9 and the end face of the primary winding 8, at which the end 18 of the primary winding 8 connected to the semiconductor switch VI is arranged, a distance a is provided.

In Fig. 1 it can be seen that the connections 12a, 12b for the low-voltage consumer is connected to an integrated circuit D4, which is a reference voltage source and a comparison device for comparing the between has the output voltage applied to the terminals 12α, 12b with a reference voltage. The integrated circuit D4 also contains a regulator which generates a control voltage which is dependent on the deviation between the measured output voltage and the reference voltage and which feeds a light-emitting diode of an optocoupler OI. A photocell of the optocoupler OI arranged in the radiation area of the light-emitting diode is connected to a control input of the control electronics in order to regulate the output voltage present between the connections 12a, 12b.

The power supply unit for the power supply of low-voltage consumers from the public network has a transformer 7, a clocked converter ό for the electrical isolation of the network side and the low-voltage side and a grounded housing. The coupling capacity between the windings of the transformer 7 is reduced by a special winding layer structure. A switching method is selected for the clocked converter 6 in which the steepness of the switched transformer currents is low. The clock frequency of the converter ό is selected to be greater than 25 kHz.

Claims

claims

1. Switching power supply for the power supply of low-voltage consumers from a mains voltage source, with a clocked DC-DC converter (6) for the electrical isolation of the network side from the low-voltage side, the converter (6) being a transformer (7) with a primary winding (8) and one Secondary winding (9), an electrical insulation layer (1 ό) being arranged between the primary winding (8) and the secondary winding (9), the primary winding (8) in the circuit of an input voltage source (1) with a clock-controlled semiconductor switch (VI) in Is connected in series, and wherein the secondary winding (9) is connected via a rectifier circuit with connections (12a, 12b) for the low-voltage consumer, characterized in that the insulation layer (16) for the capacitive decoupling of primary winding (8) and secondary winding (9) Thickness (d) of at least 0.2 millimeters, and that the transducer (ό) a Is designed as a resonance flyback converter.

2. Switching power supply according to claim 1, characterized in that the thickness of the insulation layer (16) is at least 0.3 millimeters, preferably at least 0.35 millimeters and in particular at least 0.4 millimeters.

3. Power supply according to claim 1 or 2, characterized in that the thickness of the insulation layer (16) is at least 0.5 millimeters, possibly at least 0.6 millimeters and possibly at least 0.7 millimeters.

4. Switching power supply according to one of claims 1 to 3, characterized in that the secondary winding (9) is arranged on the outer circumference of the primary winding (8).

5. Switched-mode power supply according to claim 4, characterized in that the primary winding (8) is connected at one end to a pole (4a) of the input voltage source (1) and at the other end to the semiconductor switch (VI), that the primary winding (8 ) has several winding layers and that the winding layer, the end (1 8) of which is connected to the semiconductor switch (VI), is a soft magnetic and / or ferritic transforma- Tor core (1 1) and the winding length, the end (19) of which is connected to the pole (4α) of the input voltage source (1), faces the secondary winding (9).

ό. Switched-mode power supply according to one of Claims 1 to 5, characterized in that the secondary winding (9) only partially covers the primary winding (8), and that between the secondary winding (9) and the end face of the primary winding (8), on which the semiconductor switch (VI) connected end of the primary winding (8) is arranged, a distance (a) is provided.

7. Switching power supply according to one of claims 1 to 6, characterized in that the primary winding (8) and the secondary winding (9) on a soft magnetic and / or ferritic core (1 1) are arranged side by side in the axial direction and that the insulation layer (lό) is arranged in a plane approximately perpendicular to the axial direction between the primary winding (8) and the secondary winding (9).

8. Switched-mode power supply according to one of claims 1 to 7, characterized in that the secondary winding (9) has a plurality of winding layers lying one on top of the other, and that the radial dimension or thickness of the winding body formed by these winding layers is greater than its axial dimension or length.

9. Switched-mode power supply according to one of claims 1 to 8, characterized in that an auxiliary voltage winding (10) is arranged between the primary winding (8) and the secondary winding (9), which is connected to control electronics for the semiconductor switch (VI) in such a way that it can be used as a power supply for the control electronics.

10. Switched-mode power supply according to one of claims 1 to 9, characterized in that the connections (12a, 12b) for the low-voltage consumer are connected to measurement signal inputs of a voltage measurement device, the measurement signal output of which is connected to a comparison device having a reference voltage source, and that the comparison device for forming a closed control loop via a controller with the Control electronics is connected, wherein an optocoupler (OI) is preferably arranged between the controller and the control electronics

1 1. Switching power supply according to one of claims 1 to 10, characterized in that the clock frequency of the converter (ό) is greater than 25 kHz.

12. Switching power supply according to one of claims 1 to 1 1, characterized in that the semiconductor switch (VI), the control circuit and the input voltage source (1) on one side of the transformer (7) and the rectifier circuit and optionally the measuring device and the control circuit the opposite other side of the transformer (7) are arranged.

1 3. Switching power supply according to one of claims 1 to 12, characterized in that it has a housing, in the inner cavity of which the input voltage source, and the converter (ό) are arranged, and that the housing is electrically conductive with one of the connections (12a, 12b ) is connected to the low voltage consumer.

14. Switching power supply according to one of claims 1 to 1 3, characterized in that the housing is preferably tubular, and that the electrical circuit formed by the input voltage source (1) and the converter (ό) and the low voltage consumer in the axial direction of the housing are arranged one behind the other in the inner cavity and are preferably spaced apart by an intermediate space.