Low voltage DC converter with active clamping

Abstract

The invention relates to electrical engineering, in particular to a DC-DC converter transformer, the primary winding of which is connected to a DC voltage source by means of a switch, a clamping element being connected in parallel to said primary winding, said element consisting of a series capacitor and a switch. The starting ends of the first secondary winding and the second secondary winding are connected with each other. Ends of the first secondary winding and the second secondary winding are both connected to diodes, and the diodes are joined to each other. A common starting point of the secondary winding and a common connection point of the diodes are connected to the L-shaped LC filter. A control electrode of the switch is connected to the pulse width modulation controller. Wherein the number of turns of one secondary winding is larger than that of the other secondary winding. The technical result is a reduction in dynamic and static losses.

Description

[0001] The present invention relates to the field of electrical engineering, particularly to a DC-DC converter, which can be used in secondary power supply systems to convert, regulate and stabilize a DC output voltage electrically isolated from a DC input voltage, and to reduce static and dynamic power losses.

[0002] DC-DC converters with active clamping are known [1].

[0003] The disadvantage of known DC-DC converters with active clamping is the difficulty of obtaining a low output voltage of a single volt, the possibility of power switches to be turned on at zero current, which leads to an increase in dynamic losses at turn-on, and a decrease in static losses at low output voltage due to the voltage of the rectifier diode in the on state being proportional to the output voltage.

[0004] The closest in technical essence to the proposed device is a DC-DC converter with active clamping given in [1], which contains a primary winding of a transformer connected through a power regulating key to the terminals of a source of input DC voltage, a clamping element connected in parallel to the primary winding, consisting of a series capacitor and an additional switch, the transformer is used to provide electrical isolation and obtain the required DC output voltage, the secondary windings of the transformer are connected through rectifier diodes to the input terminals of an L-type LC filter, and the load is connected to the output terminals of the filter.

[0005] The purpose of the present invention is to eliminate the above disadvantages.

[0006] The said purpose is achieved in a low-voltage DC converter with active clamping, in which the primary winding of a transformer is connected through a power regulating key to the terminals of a source of input DC voltage, a clamping element is connected in parallel to the primary winding, and at the same time, two secondary windings of the transformer with different numbers of turns are connected in parallel in phase after being connected in series with diodes, and are connected to the input terminals of an L-type LC filter, and the load is connected to the output terminals of the filter.

[0007] Figure 1 、 2 The basic circuit diagram of the proposed embodiment of a low-voltage DC-DC converter with active clamping is shown in Figures 1, 2 and 3. Figure 1 The basic circuit diagram of a low-voltage DC-DC converter with active clamping is shown in Figure 1; Figure 2 The basic circuit diagram of a low-voltage DC-DC converter with active clamping, in which the active clamping is implemented by introducing a small linear inductance into the circuit of one of the secondary windings of the transformer with a larger number of turns, is shown in Figure 2; Figure 3 The basic circuit diagram of a low-voltage DC-DC converter with active clamping, in which a synchronous rectifier is used instead of a rectifier diode, is shown in Figure 3.

[0008] wherein (a) the primary winding of the transformer is connected through a power regulating key to the terminals of a source of input DC voltage, (b) a clamping element is connected in parallel to the primary winding, (c) two secondary windings of the transformer with different numbers of turns are connected in parallel in phase after being connected in series with diodes, and are connected to the input terminals of an L-type LC filter, and (d) the load is connected to the output terminals of the filter. Figure 1), the start of the primary winding 1 of the transformer 2 is connected to the positive pole of the input DC voltage source, and the end of the primary winding 1 is connected to the negative pole of the input DC voltage source through the power control switch 3 realized in the form of a MOSFET field effect transistor. The clamping element is connected in parallel to the primary winding 1 of the transformer 2 and consists of a series capacitor 4 and an additional switch 5 realized in the form of a MOSFET field effect transistor. The start of the first secondary winding 6 is connected to the start 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 being connected to a common connection point. The common start of the secondary windings of the transformer and the common connection point of the anodes of the diodes 8 and 9 are connected to the input of the L-shaped LC filter 10, and in parallel to the output connected to the load 11. The control electrodes of the switches 3 and 5 are connected to the pulse width modulation controller 12.

[0009] We will consider the operation of the proposed low voltage DC-DC converter with active clamping on the basis of the following assumptions: ideal clamping element, stable mode of operation and continuous change of the magnetic flux in the core of the transformer 2. We denote by D the duration of the on state of the clamping element 3 relative to the period T. In this case, during the phase of the on state of the switch 3 for the duration DT, the energy is transferred through the secondary winding with a greater number of turns, which in this case is the secondary winding 6. In this case, the energy is transferred through the forward biased diode 8, the secondary winding 6 and the L-shaped LC filter to the load, while the diode 9 is blocked and is in the reverse biased state with a voltage equal to the voltage difference between the secondary windings 6 and 7, i.e. (n1-n2)V IN , where n1 is the ratio of the number of turns of the windings 6 and 1, and n2 is the ratio of the number of turns of the windings 7 and 1. When the power regulation switch 3 is off, the additional switch 5 of the clamping element is on, and the voltage on all windings of the transformer is reversed, and a voltage V IN is established on the primary winding 1 of the transformer 2, which is equal to the average voltage on the capacitor 4 of the clamping element, i.e. V IN = D / (1-D). Thus, at the input of the L-shaped LC filter, an alternating polarity voltage will be generated, which during the duration DT of the on state of the power regulation switch 3 will be a positive voltage with a value equal to n1V IN , and during the duration (1-D)T of the on state of the additional switch 5 of the clamping element will be a negative voltage with a value equal to n2V IND / (1-D).

[0010] Thus, the output voltage (n1-n2) V is established on the load IN D, flowing through the power control switch 3 is equal to (n1-n2) I L Thus, the low output voltage depends mainly on the transformation ratio difference of any values of n1 and n2, which makes it possible to ensure a good coupling coefficient between the primary and secondary windings of the transformer 2 in the case of a significant difference between the input voltage (tens of volts) and the output voltage (single volt) values. The time delay of the energy transfer to the output circuit when the power regulation switch 3 is on, makes the current and voltage fronts on the power regulation switch 3 separate, thus reducing the dynamic losses when on. This is achieved by connecting in series with the secondary winding 6 of the transformer 2 a small linear inductance 13. Figure 2

[0011] The forward voltage drop on the diodes in the on state becomes very significant under the low output voltage conditions achieved in the proposed device, which has a significant impact on the efficiency. In order to reduce this impact, it is proposed to use synchronous rectifiers 14, 15 implemented on MOSFET field effect transistors, with their own control circuit 16, instead of rectifying diodes, as shown in Figure 3

[0012] Thus, the proposed low voltage DC converter is able to form a low voltage DC output voltage from a high DC input voltage, while reducing the static and dynamic power losses, compared to known devices.

[0013] 1. A.s. No. 892614 (CCCP) MKI H02M3 / 335 "Single stroke constant voltage regulator" A.G. Polikarpov, E.F. Shcherbinaenko.​​

Claims

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

2. The low-voltage DC-DC converter with active clamping according to claim 1, characterized in that, The rectifier element is made in the form of a diode.

3. The low-voltage DC-DC converter with active clamping according to claim 1, characterized in that, The linear inductor is connected in series with the primary winding of the transformer.

4. The low-voltage DC-DC converter with active clamping according to claim 1, characterized in that, The rectifier element is made in the form of a MOSFET field-effect transistor with its own control circuit.

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