RU2467460C1 - Output circuit of pulse voltage converter, method of its galvanic isolation, pulse converter of voltage and pulse source of supply - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: inventions relate to equipment of pulse voltage converters and may be used in design of their galvanically isolated output circuits. In an output circuit of a pulse voltage converter, comprising a device of galvanic isolation with a rectifier and a smoothing filter, the rectifier is connected to a key cascade via two or more separating capacitances, and a useful load is connected to the rectifier via two or more separating inductances. In the method for galvanic isolation suppression of DC current and currents of industrial frequencies is carried out using reactive resistances of a capacitance nature, and suppression of currents of internal frequencies of a pulse voltage converter is carried out using reactive resistances of an inductive nature. In a pulse voltage converter and in a pulse supply source, key cascades and output circuits are arranged as capable of implementing of previous technical solutions.

EFFECT: development of technical solutions for galvanic isolation of an output circuit of a pulse supply source and/or a pulse voltage converter, comprising circuits of useful load, differing with simplicity, compactness, reliability and increased efficiency, in contact with equipment, which has an electric contact with useful load circuits, both for good or faulty pulse source of supply and/or a pulse voltage converter.

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Description

The group of inventions relates to the technique of pulse voltage converters and, accordingly, power supplies and can be used in the design of their galvanically isolated output circuits.

There are various definitions of the term “galvanic isolation”, in particular galvanic isolation is the transfer of energy or a signal between electrical circuits without electrical contact between them, but there is no clear, generally accepted definition.

The term galvanic isolation is used to describe the conditions for the transfer of energy or signal between electrically isolated circuits, so the definition would be more correct: galvanic isolation is the controlled transfer of energy or signal between separated (isolated) electrical circuits.

In many devices, the flow of currents not dangerous for people and the device itself is allowed between galvanically isolated nodes, if necessary to improve the consumer properties of the product. So, for example, the metal cases of some switching power supplies are connected to the network conductors by small capacitors - of the order of 10 nF - which are an integral part of the input filter. Through them, current can flow from the phase wire in contact with the housing of several milliamps, which is structurally embedded in the parameters of this device and is not dangerous for people and the electrical circuits associated with it.

The definition of galvanic isolation used in this application is as follows: galvanic isolation is the separation (isolation) of electrical circuits by suppressing between them not determined by the design parameters of these current circuits with controlled transfer of energy or signals between them.

A device that provides galvanic isolation between circuits eliminates the flow between them of currents not determined by the design parameters of this device. Currently, an optocoupler is most often used to transmit a signal between circuits, provided they are galvanically isolated, and a transformer is used to transfer energy between circuits, but sometimes designs of devices with the so-called conditional galvanic isolation, in which isolation of electrical circuits is performed only when serviceable, are offered. elements of these devices.

Known capacitor voltage converter with current multiplication ["Capacitor voltage converter with current multiplication" // Radio, 1999, No. 1, p. 42-44 or see http://pc.fk0.pp.ru/pub/books/- hard / radio / 199901 / p42 (44.htm]. The converter includes an output circuit with positive and negative terminals X2, X3, a switching transistor VT3, an ammeter PA1.

The output circuit of this device can be considered galvanically isolated from the network formally (conditionally), i.e. only if all the elements of the circuit are in good working order, since standing up of individual elements, for example, VT3 transistor, VD3 or VD4 diodes, will lead to the connection of the output circuit to the network, which can lead to the flow of currents that are not determined by the design parameters of this device, hazardous to people and working elements scheme. For example, a breakdown of the VD3 diode leads to the connection of the network connector X1 and the “positive” output terminal X2 through it, which can be life-threatening when touching the terminals X2 and X3, while the device will remain operational.

Known switching power supply based on a PWM controller NCP1200 [see http://pdf1.alldatasheet.com/datasheet-pdf/view/174811/-ONSEMI/NCP1200.html], the output circuit of which includes a galvanic isolation device made in the form of a pulse transformer, a rectifier and a smoothing filter.

The most characteristic and closest analogue of the claimed technical solution is the output circuit of a pulsed voltage converter of a pulsed power supply with a key stage, including a galvanic isolation device based on a pulsed transformer, a rectifier and a smoothing filter [Raymond Mek, Switching power supplies, Moscow, Dodeka-XXI Publishing House , 2008, p. 20]. A pulse transformer is used to transfer energy from a pulse converter to other elements of the output circuit and to ensure their galvanic isolation from the rest, as a rule, galvanically connected to the network of nodes of the pulse converter. After rectification and smoothing by the filter, a constant voltage determined by the design of the switching power supply unit is present at the load.

The main disadvantage of this output circuit is the presence of a pulse transformer, which entails an increase in the size of the pulse power supplies that include this circuit, low efficiency at low powers (less than 80% at 1-20 W - see “Methodology and program for calculating the pulse transformer of a push-pull converter ”// Radio, 2006, No. 6, p. 35), the complexity of modernization, a decrease in the operating range of output voltages and currents and, as a result, an increase in cost.

The problem solved by the first invention of a group of technical solutions connected by a single inventive concept, and the technical result achieved, consist in creating the next technical solution of the output circuit of a switching power supply, an integral part of which is a switching voltage converter, and / or a switching voltage converter, characterized by simplicity, compactness, reliability and increased efficiency, providing a controlled transfer of energy from a key element of a switching power supply and / or a pulse voltage converter in their output circuits and excluding the occurrence of equalizing and other, not determined by the design parameters of the pulse power supply and / or pulse voltage converter electric currents that can damage circuit components or hit people touching equipment that has electrical contact with the chains payload, both for serviceable and faulty switching power supply and / or switching voltage converter.

To solve the problem and achieve the claimed technical result in the output circuit of a pulse voltage converter with a key stage, including a galvanic isolation device with a rectifier and a smoothing filter, the rectifier is connected to the key stage through two or more separation capacitors, and the payload is connected to the rectifier through two or more decoupling inductances. In addition, the payload can be connected to the separation inductors using an additional smoothing filter.

There are various methods for galvanically decoupling the output circuits of switching power supplies and / or switching voltage converters [see, for example, previous sources of information], the essence of which is to separate (isolate) the output circuits from other nodes of the switching power supplies and / or switching voltage converters for suppressing the flow between them not determined by the design parameters of these circuits and the pulse current converter with the controlled transfer of energy or signals.

The most common, transformer method of galvanic isolation of the key stage of a pulsed power supply and / or a pulse converter and its output circuit is the suppression of the currents flowing between them that are not determined by the parameters of their structures due to their mechanical separation, while for the transfer of energy, the energy of the pulse converter is converted into magnetic energy induction, and then back into the energy of an electric current in the output circuit [see http://pdf1.alldatasheet.com/datasheetpdf/view/174811/-ONSEMI/NCP1200.html].

In the general case, the transformer method of galvanic isolation of the output circuit of a switching power supply is implemented in the output circuit of a switching voltage converter [see book by Raymond Mack, Switching Power Supplies - Figure 1.7]. The method consists in the controlled transfer of energy (and / or signal) between separated (isolated) electrical circuits by converting the energy of an alternating electric current from one circuit into electromagnetic induction energy and converting electromagnetic induction energy into electric current energy in a second circuit.

The disadvantages of this method are the sufficient complexity of its hardware implementation, mainly due to the design of a pulse transformer, and energy loss of electromagnetic induction, leading to a total loss of energy, which leads to a decrease in the efficiency of a switching power supply and / or a pulse voltage converter.

The problem solved by the second invention of the group and the technical result achieved are to create another method for galvanically decoupling the output circuit of a switching power supply and / or a switching voltage converter, the features of which are determined by the capabilities of their output circuits made according to the first invention of the group.

To solve the problem and achieve the claimed technical result in a method of galvanically decoupling the output circuit of a pulse voltage converter, which consists in suppressing currents flowing through this circuit that are not determined by the parameters of its design with controlled transfer of energy from the pulse voltage converter to its output circuit, suppressing direct current and currents industrial frequencies are carried out using capacitive reactances, and current suppression GOVERNMENTAL frequency pulse voltage converter is carried out using inductive reactances. Additionally, the suppression of the currents flowing through the output circuit that are not determined by the design parameters is carried out to levels that do not affect the operation of the voltage converter and the output circuit itself and do not cause damage to people touching the payload or equipment that has electrical contact with it.

A typical pulse converter includes a constant voltage source, a key stage, and an output circuit, typically made using a pulse transformer [see http://pdf1.-alldatasheet.com/datasheet-pdf/view/174811/ONSEMI/NCP1200.html]. The primary winding of the pulse transformer is connected to the key stage of the pulse converter, the voltage from the secondary winding is rectified, filtered and supplied to the load.

A typical pulse converter is known, which includes a constant voltage source, a key stage and an output circuit, made, as a rule, with transformer galvanic isolation [see Raymond Mack book, Switching Power Supplies - Figure 1.7.].

The disadvantage of this converter is its high cost, large dimensions, low efficiency at low powers — less than 80% at 1-20 W (see “Methodology and program for calculating a pulse transformer of a push-pull converter” // Radio, 2006, No. 6, p. 35) as well as difficulties with subsequent modernization, requiring the replacement of a pulse transformer and limited possibilities for changing the output voltage.

The problem solved by the third invention of the group and the technical result achieved are similar to the first two inventions of the group, adjusted for the object - a pulse voltage converter.

To solve the problem and achieve the claimed technical result in a pulsed voltage converter, including a constant voltage source, a key stage and an output circuit, the latter is made according to the above-described inventions in terms of design and method of galvanic isolation. In addition, the converter includes at least one additional output circuit, performed similarly to the first (main).

There is a need for compact, reliable and efficient switching power supplies that suppress currents not determined by their technical and operational parameters that can lead to damage to the working elements of the source or to electric shock to people who touch the devices connected to it.

Known transformer power source, which includes a linear transformer connected to an industrial network, a rectifier and an adjustable voltage regulator with an output circuit ["Low-voltage rectifier" // Radio, 1971, No. 4, p.52-53]. The galvanic isolation of the output circuit of this device from the industrial network is carried out by decoupling the entire electrical circuit carried out by the transformer.

Until the 80s of the last century, transformer power supplies were used everywhere, and then they began to be replaced by switching power supplies due to a number of advantages, for example, lower weight, dimensions, etc.

Pulse transformers have significantly smaller dimensions at the same power compared to linear transformers. At the same time, pulse transformers have a number of disadvantages: high price - up to 50% of the cost of the power supply, large dimensions compared to other components of switching power supplies, low efficiency at low powers (about 80% at 1-20 W - see article “Methodology and program for calculating a pulse transformer of a push-pull converter” // Radio). In addition, the power and dimensions of the switching power supply is determined by the power of the pulse transformer, which leads to a compromise between miniaturization and power. The presence of a pulse transformer makes it difficult to upgrade a pulse power supply, since this almost always requires the replacement of a pulse transformer. The design of the pulse transformer determines the output parameters of the entire power supply, which limits the range of possible tuning of the latter.

In switching power supplies intended for operation from an alternating current main, the mains voltage is rectified by means of a rectifier and a filter, the DC voltage obtained is converted by a pulse converter to a rectangular high-frequency voltage, which is transformed to the required values, then rectified and filtered. The galvanic isolation of the output circuits and the transfer of energy to them from a pulse converter is carried out by a pulse transformer.

In particular, a typical switching power supply is known, including a network rectifier, a pulse converter, a key stage and an output circuit with a load element of the output stage in the form of a primary transformer winding [see Raymond Mack book, Switching Power Supplies - FIG. 1].

A disadvantage of the known power source, as well as that of a pulsed voltage converter, is its high cost, large dimensions, low efficiency at low powers, as well as difficulties with modernization, requiring the replacement of a pulse transformer, and limited adjustment possibilities.

The problem solved by the fourth invention of the group and the technical result achieved are similar to the first three inventions of the group, adjusted for the object - a switching power supply.

To solve the problem and achieve the claimed technical result in a switching power supply, including a network rectifier, a switching voltage converter, a key stage and an output circuit, a switching converter and an output circuit are made according to the above-described inventions with the possibility of implementing a galvanic isolation method. Additionally, the power source includes at least one additional output circuit, made similar to the first (main).

The invention is illustrated by drawings, where

- figure 1 shows a circuit diagram of the output circuit of a pulse voltage converter with inductive-capacitive galvanic isolation;

- figure 2 shows a fragment of the output circuit using an additional smoothing filter;

- figure 3 shows a typical diagram of a switching power supply based on a PWM controller NCP1200;

- figure 4 is a diagram of a switching power supply using inductance-capacitive galvanic isolation based on a PWM-based NCP1200 controller;

- figure 5 shows an example of the use of inductive-capacitive galvanic isolation to bridge pulse voltage converters;

- figure 6 is an example of the use of inductive-capacitive galvanic isolation to half-bridge pulse voltage converters.

- Fig.7 - switching power supply with inductive-capacitive galvanic isolation;

- Fig. 8 shows a switching power supply (switching voltage converter) with three output circuits;

- figure 9 for comparison shows a typical output circuit of a pulse Converter with transformer galvanic isolation.

The pulse converter 1 contains a constant voltage source (not shown conventionally), a key stage 2 and an output circuit 3, including a galvanic isolation device 4 and 4 'with a rectifier 5 and a smoothing filter 6, while the rectifier 5 is connected to the key stage 2 through two or more separation capacitances 7 and 7 ', which are an element of galvanic isolation, and a payload 8 is connected to the rectifier 5 through two or more isolation inductances 9 and 9', which are also an element of galvanic isolation and, at the same time, electric cops smoothing filter 6. The payload 8 may be connected to the separating inductors 9 and 9 'using an additional smoothing filter 10. The pulse transducer 1 may include at least one additional output circuit 3', formed similarly to circuit 3.

The method of galvanically decoupling the output circuit 3 of the pulse voltage converter 1 with a controlled transfer of energy from the converter to its output circuit consists in suppressing direct current and industrial frequency currents using capacitive reactances - dividing capacitors 7 and 7 ', and suppressing the natural frequencies of the pulse converter 1 using reactances of an inductive nature - separation inductances 9 and 9 '. The suppression of currents not determined by the design parameters flowing through the output circuit 3 is carried out to levels that do not affect the operation of the pulse converter 1 and the output circuit 3 itself and do not cause damage to people touching the payload 8 (its circuits) or equipment having electrical contact with it .

The obtained galvanic isolation of the payload circuits of a switching power supply and / or a switching voltage converter can be qualified as inductive-capacitive.

The switching power supply (see FIGS. 4, 7 and 8) includes a network rectifier 11, a switching converter 1 with a key stage 2 and an output circuit 3, which are made according to the aforementioned technical solutions, while it may include at least one additional output circuit 3 ', made in a similar manner.

Let us analyze the essential features of inventions.

In contrast to transformer isolation, which provides energy transfer, DC separation of circuits, separation of current circuits of industrial frequencies and separation of circuits for natural frequencies of operation of pulse converters 1, in inductive-capacitive galvanic isolation made according to the inventions, separation of key cascade circuits 2 and rectifier 5 for direct current, industrial frequency current, and energy transfer are implemented using capacitors 7 and 7 ', and the separation of rectifier 5 and payload circuits ki 8 for currents of natural frequencies of operation of pulse converters 1 - using inductors 9 and 9 '. The parameters of the used capacitances 7 and 7 'and inductances 9 and 9' depend on the frequency of operation of the pulse converter 1 - with increasing frequency their values decrease.

Inductive-capacitive galvanic isolation effectively suppresses currents that are not determined by the design parameters to levels that do not affect the operation of the pulse converter 1 and the output circuit 3 itself and do not cause damage to people touching the payload circuits 8 or equipment that has electrical contact with them. The level of current suppression depends on the ratings of the inductive-capacitive isolation elements.

The payload can be connected to the separation inductors 9 and 9 'using an additional smoothing filter 10, which can be used commercially available chokes for line filters, as a result of which it is possible to reduce the values of the inductances 9 and 9'.

The implementation of the output circuit 3 of the pulse voltage Converter 1 according to the invention allowed us to create simple, compact and reliable switching voltage converters and switching power supplies that differ from analogues, for example, with transformer isolation with higher efficiency, smaller dimensions, having a larger range of output parameters, a larger margin power, and when equipped with additional appropriate output circuits 3 ', you can get any number of required output voltages.

Each conductor (in the simplest version there are two of them - see Fig. 1) connecting the rectifier 5 and the key stage 2 of the pulse voltage converter 1 is connected through isolation capacitors 7 and 7 ', so there is no direct contact between them.

Energy is transferred from the key stage 2 of the pulse voltage converter 1 to its output circuit 3 due to the bias current in the capacitors 7 and 7 'arising from their charge and discharge, or the change of their charge to the opposite (depending on the type of the key stage 2 of the pulse converter 1 )

Capacitors 7 and 7 'isolate the rectifier 5, and therefore the payload 8, from the output stage 2 of the pulse voltage converter (power source) 1 for direct current. In the event of a malfunction of the pulse voltage converter 1, which is part of the switching power supply, a power frequency voltage can be applied to the capacitors 7 and 7 '. The capacitance of the capacitors 7 and 7 'is chosen so that they have a high resistance for industrial frequency currents and actually isolate the rectifier 5 from them, and therefore the payload 8. For example, a capacitor with a capacity of 10,000 pF at a frequency of 50 Hz has a reactance of 318,310 Ohm, at a voltage of 220 V connected to the capacitor with an industrial frequency of 50 Hz, the current through it will not exceed 0.7 mA (negligible current), while at a frequency of 500,000 Hz for a sinusoidal current, its reactance is only 31 Ohms (for imp snogo - even less), which does not prevent transmission through this energy frequency.

Separating capacitors 7 and 7 'in the simplest version should be one for each connecting rectifier 5 and output stage 2 of the pulse voltage converter (power source) 1 conductor, but to increase the reliability of the circuit, each capacitor 7 and 7' can be made in the form of two and more series capacitors with high breakdown voltage. The payload 8 is connected to the rectifier 5 through two or more isolation inductances 9 and 9 ', which are part of the output smoothing filter 6 and isolate the payload 8 from the pulse currents of the natural frequencies of the switching power supply. For example, at a frequency of 500,000 Hz, an inductance of 10 mH has a reactance for sinusoidal currents of 31416 ohms. With a voltage of 300 V applied to it, the current through it does not exceed 10 mA - the permissible current.

For pulsed currents, an inductance resistance of 10 mH at a frequency of 500,000 Hz will be higher than 31416 Ohms, since the amplitude of the sinusoidal component in the pulses is always less than the amplitude of the pulses themselves. In the manufacture of pulse converter controllers, there is a tendency to increase the conversion frequency. Modern controllers operate at a frequency of 1 MHz and higher, which further reduces the value of inductances 9 and 9 '.

The absence of a pulse transformer for pulse voltage converters (power sources) 1 allows a wide range of changes in their output voltages and currents, which can be used to convert direct or alternating current energy to the required type of energy by changing the pulse-width modulation of the pulses of the key stage 2.

The implementation of the inventions will consider the following examples.

Example 1. Switching power supply based on the NCP1200 PWM controller.

Figure 3 illustrates the standard switching circuit recommended by the manufacturer, and the use of inductive-capacitive galvanic isolation for this circuit is illustrated in Fig. 4.

The power source operates as follows: on the inductor L1 high-voltage pulses are released, which charge the capacitors C4 and C5. During the charge of capacitors C4 and C5, energy is accumulated in the chokes L2 and L3. In the intervals between pulses, the capacitors C4, C5 and the inductors L2, L3 are discharged, the diode D2 (the same rectifier 5) provides a channel for the discharge current to flow in the inductors L2, L3.

The use of inductive-capacitive galvanic isolation allows, if necessary, changing the output voltage from almost zero to 15-20 V only by replacing the Zener diode D8, to increase the current more than 600 mA, you only need to install the key transistor M1 on the radiator.

Tests of the circuit of FIG. 4 showed an increase in efficiency relative to the circuit with traditional transformer isolation by 5-10 percent. The rather high capacitances of the capacitors C4 and C5 are due to the low frequency of the NCP1200P60 chip - 60 kHz. The inductances L2 and L3 are less than those necessary for isolating the rectifier 5 for currents with a frequency of 60 kHz from the payload, but the presence of an EMI Filter at the input of a switching power supply will allow them to be used in this case, since the EMI Filter prevents the formation of a closed circuit for currents with frequencies of 60 kHz due to its inductances (10-20 mH). Instead of inductors L2 and L3, some standard line filter chokes can be used for a switching power supply.

Rectifier 5 can be made using one or several diodes, their number is determined by the type of key stage 2 of the pulse converter 1. For example, for a bridge or half-bridge key stage 2, the best results are obtained by using a diode bridge of four diodes, for a key stage on one transistor one diode, although with a diode bridge, the circuit is operational.

Several output voltages of a switching power supply are obtained by parallel connection of several output circuits 3 and 3 '- see Fig. 8 - illustrates the receipt of three voltages. The voltage polarity depends on the connection of the output circuits 3 and 3 'to a common wire - in Fig. 8, the lower output circuit 3 has a voltage inverse to the other two circuits 3'. The voltage and current in the output circuits 3 and 3 'depend on the capacitances of their capacitors 7 and 7' and the values of the inductors 9 and 9 '.

Example 2. A pulse converter based on a bridge circuit using inductive-capacitive galvanic isolation - see figure 5.

The power source operates as follows: due to the operation of the keys of the pulse converter 1, the voltage applied to the capacitors 7 and 7 'of the output circuit 3 is reversed with the frequency of the pulse converter 1, which causes charge-discharge currents to flow through the capacitors 7 and 7'. The charge-discharge circuit of capacitors 7 and 7 'includes reactors 9 and 9' and payload 8. Rectifier 5 provides the same current direction through reactors 9 and 9 'and payload 8 in all charge-discharge cycles of capacitors 7 and 7'.

Example 3. A pulse converter based on a half-bridge circuit using inductive-capacitive galvanic isolation - see Fig.6.

The principle of operation of a pulse converter based on a half-bridge circuit using inductive-capacitive galvanic isolation is similar to the principle of operation of a pulse converter based on a bridge circuit.

Other embodiments of the inventions illustrating inductive-capacitive galvanic isolation, using the essential features of the above technical solutions, adjusted for their design features and the specifics of their use, are also possible.

As a result of the use of the group of inventions, the technical problem of the galvanic isolation of the payload circuits of switching power supplies, of which pulsed voltage converters, and / or pulse voltage converters, was solved, was solved. Technical solutions are characterized by simplicity, compactness, reliability and increased efficiency, provide controlled energy transfer from a key element of a pulsed power supply and / or a pulsed voltage converter to their output circuits and exclude the appearance of equalizing and other, not determined by the design parameters of a pulsed power supply and / or pulsed voltage transducer of electric currents, capable of damaging circuit components or striking people touching equipment that has electrical Critical contact with the payload for both a working and a faulty switching power supply and / or switching voltage converter.

Claims (8)

1. The output circuit of a pulse voltage converter with a key stage, including a galvanic isolation device with a rectifier and a smoothing filter, characterized in that the rectifier is connected to the key stage through two or more isolation capacitors, and the payload is connected to the rectifier through two or more isolation inductances. 2. The output circuit according to claim 1, characterized in that the payload is connected to the separation inductors using an additional smoothing filter. 3. The method of galvanic isolation of the output circuit of a pulse voltage converter, which consists in suppressing currents flowing through this circuit that are not determined by its design parameters during a controlled transfer of energy from a pulse voltage converter to its output circuit, characterized in that the DC and current frequencies of industrial frequencies are suppressed with using capacitive reactances, and suppressing the natural frequencies of the pulse frequency converter dissolved using inductive reactances. 4. The method according to claim 3, characterized in that the suppression of the currents flowing through the output circuit that are not determined by the design parameters is carried out to levels that do not affect the operation of the pulse converter and the output circuit itself and do not cause damage to people touching the payload or equipment having electrical contact with her. 5. A pulse converter comprising a constant voltage source, a key stage and an output circuit, characterized in that the output circuit is made according to claim 1 or 2 with the possibility of implementing the method according to claim 3 or 4. 6. The Converter according to claim 5, characterized in that it includes at least one additional output circuit made according to claim 1 or 2, with the possibility of implementing the method according to claim 3 or 4. 7. Switching power supply, including a network rectifier, a pulse converter, a key stage and an output circuit, characterized in that the output circuit is made according to claim 1 or 2 with the possibility of implementing the method according to claim 3 or 4. 8. The power source according to claim 7, characterized in that it includes at least one additional output circuit made according to claim 1 or 2, with the possibility of implementing the method according to claim 3 or 4.

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