Low-voltage DC converter with active clamping

Abstract

The invention relates to electrical engineering, and more particularly to DC-to-DC converters. A primary winding of a transformer is connected via a switch to a DC voltage source. Connected in parallel to said primary winding is a clamping element consisting of a capacitor and a switch, connected in series. The starts of a first and a second secondary winding are connected. The ends of the first and second secondary windings are connected to diode cathodes, and the diode anodes are joined. The common points of the starts of the secondary windings and of the diode anodes are connected to an L-type LC filter. Control electrodes of switches are connected to a pulse width controller. One of the secondary windings has more turns than the other. The technical result is a reduction in dynamic and static losses.

Description

[0001] Low Voltage DC-DC Converter with Active Clamping

[0002] The invention relates to electrical engineering, in particular to DC to DC converters, and can be used in secondary power supply systems for converting, regulating and stabilising a DC output voltage, galvanically separated from the DC input voltage, and reducing static and dynamic power losses.

[0003] DC / DC converters with active clamping are known

[0001] .

[0004] The disadvantage of the known DC-DC converter with active clamping is the difficulty of obtaining a low output voltage of a few volts, the possibility of turning on the power switch to a zero current value, which leads to an increase in dynamic losses when it is turned on, and a decrease in static losses at a low output voltage level due to the voltages on the rectifier diodes in the conducting state, commensurate with the output voltage level.

[0005] The closest in technical essence to the proposed device is a DC / DC converter with active clamping given in [1], containing a primary winding of a transformer connected via a power regulating key to the terminals of an input DC voltage source, in parallel to which a clamping element is connected, consisting of a series-connected capacitor and an additional key, a transformer implementing electrical isolation and obtaining the required level of DC output voltage, secondary windings connected via rectifier diodes to the input of an L-shaped LC filter, to the output of which a load is connected. The purpose of the invention is to eliminate the said disadvantages.

[0006] The stated goal is achieved by the fact that in a low-voltage DC / DC converter with active clamping, the primary winding of the transformer of which is connected via a power regulating key to the terminals of the input DC voltage source, in parallel to which a clamping element is connected, and two secondary windings with a different number of turns with series-connected diodes are connected in phase and in parallel and are connected to the input terminals of an L-shaped LC filter, to the output terminals of which a load is connected.

[0007] Fig. 1, 2 and 3 show the basic electrical circuit diagrams of embodiments of the proposed low-voltage DC / DC converter with active clamping. Fig. 1 shows the basic electrical circuit diagram of the low-voltage DC / DC converter with active clamping; Fig. 2 shows the basic electrical circuit diagram of the low-voltage DC / DC converter with active clamping with the introduction of a small linear inductance into the circuit of one of the secondary windings of the transformer with a large number of turns; Fig. 3 shows the basic electrical circuit diagram of the low-voltage DC / DC converter with active clamping using synchronous rectifiers instead of rectifier diodes.

[0008] In it (Fig. 1), the beginning of the primary winding 1 of the transformer 2 is connected to the positive pole of the input source of direct voltage, and the end of the primary winding 1 through the power regulating key 3, implemented in the form of a MOSFET field-effect transistor, is connected to the negative pole of the input source of direct voltage. A clamping element is connected in parallel to the primary winding 1 of the transformer 2, consisting of a series-connected capacitor 4 and an additional key 5, implemented in the form of a MOSFET field-effect transistor. The beginning of the first secondary winding 6 is connected to the beginning of the second secondary winding 7. The end of the first secondary winding is connected to the cathode of the diode 8, and the end of the second secondary winding 7 is connected to the cathode of the diode 9, the anodes of the diodes 8 and 9 are united in a common connection point.The common points of the beginnings of the secondary windings of the transformer and the common connection points of the anodes of the diodes 8 and 9 are connected to the input of the L-shaped LC filter 10, in parallel to the output terminals of which the load 1 1 is connected. The control electrodes of the keys 3, 5 are connected to the pulse-width controller 12.

[0009] The operating principle of the proposed low-voltage DC / DC converter with active clamping will be considered based on the assumption of ideal key elements, steady-state operation, and continuous change in magnetic flux in the core of transformer 2. Let D be the duration of the on state of switch 3 relative to the period T. In this case, at the stage of the closed state DT of switch 3, energy is transferred to the load through the secondary winding, which has a larger number of turns, let us assume that this is secondary winding 6. In this case, energy is transferred to the load through the forward-biased diode 8, secondary winding 6, and the L-shaped LC filter, while diode 9 is locked and is under reverse bias equal to the difference in voltages on secondary windings 6 and 7, i.e. VIN, where p / is the ratio of turns of windings 6 and 1, and P2 is the ratio of turns 7 and 1. When the power regulating switch 3 is switched off, the additional switch 5 of the clamping element is switched on and a polarity reversal of voltages occurs on all windings of the transformer, and a voltage VIND / (1-D) equal to the average voltage on the capacitor 4 of the clamping element is established on the primary winding 1 of the transformer 2. This voltage is transformed into the secondary windings 6, 7 of the transformer 2 in the form of a voltage with a negative sign, which leads to switching the current of the choke of the L-shaped LC filter to the diode, which is under a lower negative voltage, in our case diode 9, since the number of turns of the secondary winding 7 is less than the number of turns of the secondary winding 6. In this time interval (lD)T, the conducting state of the additional key 5 of the clamping element, the reverse voltage on the locked diode 8 is equal to (P1-P2) VD / (1-D).Thus, at the input of the L-shaped LC filter there is a voltage of different polarity equal to HzU in the time interval DT, the switched-on state of the regulating switch 3, and a negative voltage -r^V^D / -D) in the time interval (lD)T, the switched-on state of the additional switch 5 of the clamping element.

[0010] As a result, the output voltage (ni-n2) V is established on the load. IND, and the current through the power regulating key 3 is equal to (п1-П2)1 - Thus, the low output voltage is determined mainly by the difference in the transformation ratios at any values ​​of r and П2, which allows for a good coupling coefficient between the primary and secondary windings of the transformer 2 with a significant difference in the values ​​of the input (tens of volts) and output (units of volts) voltages. The time delay in the transfer of energy to the output circuit when the power regulating key 3 is turned on leads to the separation of the current and voltage fronts on the power regulating key 3 and a decrease in the dynamic losses when it is turned on. This is achieved by introducing a small linear inductance 13 in series with the secondary winding 6 of Fig. 2.

[0011] At low output voltage, which is realized in the proposed device, direct voltage drops on the diodes in the conducting state are significant, which affects the efficiency. To reduce this effect, it is advisable to use synchronous rectifiers 14, 15 realized on MOSFET field-effect transistors with their own control circuit 16, Fig. 3, instead of rectifier diodes.

[0012] Thus, the proposed low-voltage DC / DC converter, in comparison with the known device, allows the formation of a low-voltage DC output voltage from a high DC input voltage with a reduction in static and dynamic power losses.

[0013] 1. A. s. No. 892614 (USSR) MKI H02M3 / 335 “Single-stroke constant voltage regulator” A.G. Polikarpov, E.F. Sergienko.

Claims

Invention formula 1. A low-voltage DC / DC converter with active clamping, comprising a transformer having a primary winding connected through a power regulating key to the terminals of a DC input voltage source, in parallel to which a clamping element is connected, consisting of a series-connected capacitor and an additional key, secondary windings with rectifier elements connected to an L-shaped LC filter, characterized in that two secondary windings of the transformer with series-connected rectifier elements are connected in phase and in parallel and are connected to the input terminals of the L-shaped LC filter, to the output terminals of which a load is connected, wherein one of the secondary windings of the transformer has a greater number of turns than the other.

2. A low-voltage DC / DC converter with active clamping according to claim 1, characterized in that the rectifier elements are made in the form of diodes.

3. A low-voltage DC / DC converter with active clamping according to claim 1, characterized in that a linear inductance is connected in series with one of the transformer windings.

4. A low-voltage DC / DC converter with active clamping according to claim 1, characterized in that the rectifier elements are made in the form of MOSFET field-effect transistors with their own control circuit. 6

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