RU2396686C2 - Stabilised voltage converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: there is performed removal of driving transformer, development of power transformer with minimum capacitor coupling of primary and secondary windings, introduction of additional windings (20), (21) to feed shapers (13), (14), which control power transistor switches (1), (2), and introduction of voltage detector (24) which, in case load current decreases below the specified limit, changes the parameters of timing RC - circuit (22), which leads to increase of commutation period of converter. Frequency reduction allows maintaining stable self-oscillations at no-load and automatic providing "soft commutation" mode within the whole load current change range.

EFFECT: simplifying and cheapening of voltage converter, enlarging allowable load current change range to zero value.

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Description

The present invention relates to a conversion technique and can be used in secondary power sources.

Known for simple and cheap self-oscillating voltage converters containing a transistor switch connected in series with the primary winding of the transformer, the secondary winding of which is loaded on a rectifier and a smoothing filter, and the control winding is connected to the input of the transistor switch.

Known self-oscillating stabilized voltage converters are single-circuit with a single transistor switch. A rectifier with a capacitive smoothing filter is used in the output circuit. The processes in such converters are significantly dependent on the magnitude of the load. In particular, when the load is reduced to zero, the switching frequency increases many times. In practice, such devices either use a rather powerful load, which reduces the efficiency, or a regime occurs with intermittent bursts of pulses. The latter increases the ripple of the output voltage [1].

Closest to the proposed one is a stabilized voltage converter containing the first and second transistor switches, shunted by antiparallel diodes and connected to the bipolar leads of the primary power source, a power transformer, the output windings of which are connected through a rectifier to a smoothing filter, the output of which is connected to the terminals for connecting the load, filter capacitor, the first output of which is connected to the output of the primary power source, and the second to the first output primary winding of the power transformer, the second output of the primary winding of the power transformer is connected to a common point of the transistor switches, an error signal amplifier, the first output of which is connected to the output of the smoothing filter, the second is connected to the source of the reference voltage, the output of the amplifier is connected to the input of the galvanic isolation element, and the output of the last connected to the modulating input of the second driver, the outputs of the first and second drivers are connected respectively to the control inputs of the transistor switches, defining transformer, the primary winding of which through an isolation capacitor with one output connected to the primary power source, and the other to the midpoint of the series-connected transistor switches, the control inputs and the first output of which are shunted by resistors respectively, the first and second secondary windings are connected respectively to the second terminals of the first and second transistor switches and to the power inputs of the first and second shaper [2].

However, in this converter, due to the introduction of a second transformer connected through an isolation capacitor parallel to the primary circuit of the power transformer, additional losses occur due to the magnetization current of the master transformer. If the primary power source is high voltage, for example a 220 V rectifier, then the master transformer must contain a significant number of turns, which makes it technologically difficult to ensure its miniature and reliability.

If a rectifier with a capacitive filter is used in such a converter, then when the load current changes over a wide range, a significant change in the duty cycle of the generated pulses is not required. If a push-pull rectifier with an LC filter is used, then when the load current changes over a wide range, a very large change in duty cycle is required. It increases even more with the change in voltage of the primary power source.

In this case, in the known converter, while maintaining a constant switching frequency, it is necessary to use output loading, which reduces the efficiency of the device. In such a self-oscillating converter, it is difficult to form a minimum pulse duration of less than 0.5-1.0 μs. While maintaining a constant switching frequency and stable idling, the switching period should be 12-15 μs. Only in this case can significant overload be avoided. However, such a switching period in full load mode leads to an unjustified increase in the dimensions of the transformer and the smoothing filter.

The technical result obtained by the implementation of the invention is to simplify and reduce the cost of the Converter while expanding the range of changes in the load current and increasing efficiency. This is achieved by the fact that the driving transformer and the decoupling capacitor are excluded from the circuit, a voltage detector is introduced, the power output connected to the output of the auxiliary rectifier, the common point to the common point of the first driver, and the output to the connection point of the output of the timing RC circuit and the input of the first driver , the first and second additional windings are introduced into the power transformer, which are respectively connected to the power inputs of the first driver, auxiliary rectifier and second driver and their General points, and the power transformer is made with minimal capacitive coupling between the primary and secondary windings.

This goal is also achieved by the fact that the voltage detector contains a transistor, the base of which is connected to the midpoint of the resistive voltage divider, the emitter of the transistor and the common point of the divider are combined, the collector is connected through the resistor to the output of the voltage detector, the input of which is connected to the output of the voltage divider.

This goal is achieved in that the power transformer is made with a partitioned separate winding of the primary and secondary windings.

Figure 1 shows a diagram of the proposed voltage Converter; figure 2 - diagrams explaining the operation of the circuit; figure 3 is an embodiment of a voltage detector and input nodes of the shaper.

In FIG. and the following notation is used in the text: 1 - the first transistor switch, 2 - the second transistor switch, 3, 4 - antiparallel diodes, 5 - the primary power source, 6 - power transformer, 7 - output winding of the power transformer, 8 - push-pull rectifier, 9 - smoothing LC filter, 10 - load, 11 - primary winding of the power transformer, 12 - filtering capacitor, 13 - first shaper, 14 - second shaper, 15 and 16 - starting resistors, 17 - error signal amplifier, 18 - voltage reference source , 19 - galvanic cell junction 20 - the first additional winding of the power transformer 21 - the second additional winding of the power transformer 22 - RC-time-setting circuit 23 - auxiliary rectifier 24 - voltage detector. The timing RC circuit 22 is implemented on the elements R2, C1, the auxiliary rectifier 23 - on the elements VD1, C2, the voltage detector 24 - on the elements VT3, R4, R5, R6.

The device contains first 1 and second 2 transistor switches, shunted by antiparallel diodes 3 and 4 and connected to bipolar leads of the primary power source 5, a power transformer 6, the output winding of which 7 through a push-pull rectifier 8 is connected to a smoothing LC filter 9, to the output of the last and the midpoint of the output winding 7 is connected to the load 10, the primary winding 11 of the power transformer 6 with the first output through the filter capacitor 12 is connected to the output of the primary power source 5, and the second output sub is connected to the midpoint of the transistor switches 1 and 2 connected in series, the first 13 and second 14 drivers, the outputs are connected to the control inputs of the first 1 and second 2 transistor switches connected through the starting resistors 15, 16 to the output of the primary power source 5, the first driver 13, to the input of which a timing RC circuit 22 and an auxiliary rectifier 23 are connected, connected to the output of the first additional winding 20, a voltage detector 24, the input of which is connected to the output of the auxiliary rectifier 23, the output is connection point RC- output of timing circuit 22 and the input of the first driver. The voltage detector 24 contains a transistor VT3, to the base of which is connected the midpoint of the resistive voltage divider R5, R6. The emitter of the transistor VT3 and the common point of the divider R5, R6 are combined. The collector of transistor VT3 through a resistor R4 is connected to the output of the voltage detector 24. The input of the detector 24 is connected to the output of the divider R5, R6.

The device operates as follows.

The voltage of the primary power source 5 is supplied to the transistor switches 1 and 2. Due to the presence of high-resistance starting resistors 15, 16, the transistor switches are opened, and the current begins to flow through the filter capacitor 12 and the primary winding 11 of the power transformer 6. This leads to the appearance of voltage on the additional windings 20 , 21, which, in turn, activates the shapers 13, 14, and the latter leads to a periodic alternate unlocking of the transistor switches 1 and 2. Shapers 13, 14 with the help of timing RC-circuits determine yayut time of open state of each of the transistor switches 1 and 2.

The voltage pulses on the transistor switch 2 are shown in figa. Voltage pulses arising on the primary winding 11 of the power transformer 6 are fed to its secondary winding 7, then to a push-pull rectifier 8 and a smoothing LC filter 9. At the input of the filter 9, pulses are formed having different amplitude and duration, but equal area (Fig. 2c). At load 10, there is a constant voltage equal to the average value for the period from the voltsecond area of the pulses at the input of the filter 9. In this case, the current in the primary winding flows continuously (Fig.2b), and energy is transmitted to the output almost continuously through the transformer 6.

The output voltage is stabilized by means of a mismatch signal amplifier 17, which transmits a mismatch voltage through the galvanic isolation element 19 to the input of the second shaper 14. This voltage affects the processes during the RC master circuit 22 of the shaper 14 and, therefore, the duration of the on state of the transistor switch 1 The construction of the formers 13, 14 allows to reduce the duration of the pulse of the key 1 to increase the duration of the key 2. Moreover, the duration of the switching period it is maintained almost constant if the voltage of the primary power source 5 changes by (+ 10-15)%, and the load current changes in the range (100-5)% of the nominal value.

In this converter, as well as in the known one, the mode of “soft switching” of transistor switches is carried out at a voltage close to zero, which dramatically reduces dynamic losses and switching noise.

In this case, the switching period is chosen optimal to minimize the volume of the transformer and the elements of the LC filter, providing a given level of output voltage ripple.

If the load current decreases from 5% to zero, then the change in the duty cycle of the generated pulses leads to a decrease in the amplitude of the positive pulses on the additional winding 20, which is detected by the voltage detector 24, the output of which affects the output of the timing RC circuit 22. This leads to an increase in the duration of the open state of the transistor switch 1, which, in turn, leads to a further decrease in the amplitude of the positive pulses on the winding 20. Due to the positive feedback in the conversion hardly lowered abruptly set stable switching frequency that allows the output voltage to stabilize at a final key pulse duration 1 and avoid power loss in podgruzku. It is essential that, as in the known converter, the "soft switching" mode is automatically supported in the entire range of the load current.

The processes in the Converter in the absence of load are shown in Fig.2 g, d, e.

With significant load currents, the voltage across the capacitor C2 is sufficient to maintain the transistor VT3 in the open state. The transition base - emitter of transistor VT2 is shunted by resistors R3, R4, connected in parallel. In this case, the pulse duration of the driver 13 and the transistor switch 1 is minimal. If the load current of the converter approaches zero, then the voltage on the capacitor C2 decreases, the transistor VT3 is turned off, and the resistor R4 is disconnected from the base-emitter circuit of the transistor VT2. This leads to an increase in the duration of the open state of the transistor VT2, the power transistor switch VT1 and the switching period of the entire Converter. Since it is not necessary to accurately record the moment of transition to an increased period value (it can range from (3-5)% to (8-10)% of the nominal current value), the temperature stability of the voltage detector on the VT3 transistor does not play a significant role.

It was possible to generate stable self-oscillations in the converter circuit without a master transformer provided that a power transformer with a minimized capacitive coupling between the primary and secondary windings is implemented. This condition can be fulfilled either by sectioned separate winding of the primary and secondary windings, or by winding the windings on different rods of the magnetic circuit. Separate winding of the windings into separate sections of the frame is preferable as the most technologically advanced and does not lead to an increase in the size and cost of the transformer.

A prototype stabilized voltage converter with an input voltage of ~ 220 V, 50 Hz, and output parameters of 5 V, 10A has been developed and tested. Output voltage ripple <1% of Uout, efficiency = 0.8. The switching period under load is 8 μs, at idle increases to 14-15 μs. This reduces load losses by up to 1% of power output.

Information sources

1. Sources of power for electronic equipment. Directory under. ed. G.S. Naivelt. M .: Radio and communications, 1985, p. 347.

2. Guter L.R. Stabilized voltage converter. RF patent No. 2309520, Н02М 3/338. Bulletin “Inventions. Utility Models ”No. 30, 2007

Claims (3)

1. A stabilized voltage converter containing the first and second transistor switches, shunted by antiparallel diodes and connected to the bipolar terminals of the primary power source, a power transformer, the output winding of which is connected through a push-pull rectifier to a smoothing LC filter, the output of which and the midpoint of the output winding are connected load filtering capacitor, the first output of which is connected to the output of the primary power source, and the second to the first output of the primary winding power transformer, the second terminal of the primary winding of the power transformer is connected to a common point of the transistor switches, the first and second drivers, outputs connected to the control inputs of the first and second transistor switches, an RC timing circuit is connected to the input of the first driver, and an auxiliary circuit is connected to its power supply rectifier, transistor switches connected via starting resistors to the output of the primary power source, an error signal amplifier, the first output of which is connected to with the smoothing LC filter, the second with a voltage reference source, the amplifier output with an input of a galvanic isolation element, and the output of the latter is connected to the modulating input of the second driver, characterized in that a voltage detector is inserted into it, the power output connected to the output of the auxiliary rectifier, common point - to the common point of the first shaper, and the output - to the connection point of the output of the timing RC circuit and the input of the first shaper, the first and second additional coils are introduced into the power transformer they are respectively connected to the power inputs of the first shaper, auxiliary rectifier and second shaper and their common points, and the power transformer is made with minimal capacitive coupling between the primary and secondary windings. 2. The stabilized voltage converter according to claim 1, in which the voltage detector contains a transistor, to the base of which is connected the midpoint of the resistive voltage divider, the emitter of the transistor and the common point of the divider are combined, the collector through a resistor connected to the output of the voltage detector, the input of which is connected to the output of the divider voltage. 3. The stabilized voltage converter according to claim 1, in which the power transformer is made with a partitioned separate winding of the primary and secondary windings.

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