DC-DC converter

Abstract

DC-DC converter with an output-side storage capacitor arrangement for providing an operating voltage for an inductive load and for at least one further electronic circuit and / or electronic component of a vehicle electronics, wherein the storage capacitor arrangement is connected to the DC-DC converter via a reverse-biased diode (6) and the output-side storage capacitor arrangement is connected to a parallel circuit consisting of an electrolytic capacitor (1), a ceramic capacitor (2) and a circuit arrangement is formed with a series connection of a hybrid electrolytic capacitor (3) and a suppressor diode (4) and a resistor (5) connected in parallel to the hybrid electrolytic capacitor (3), wherein the hybrid electrolytic capacitor (3) has a lower series resistance than the electrolytic capacitor (1) and a larger capacitance than the ceramic capacitor (2), so that in the event of energy being fed back from the inductive load into the storage capacitor arrangement, the hybrid electrolytic capacitor (3) absorbs a large proportion of the energy and thus prevents a voltage increase at an output terminal above a value at which connected components can be destroyed, wherein the output terminal is the cathode terminal of the diode (6) and the inductive load can be connected to the output terminal.

Description

[0001] The invention relates to a DC-DC converter with an output-side storage capacitor arrangement.

[0002] From DE 10 2007 001 414 B3 such a DC-DC converter is known, in which the storage capacitor arrangement is formed with an electrolytic capacitor.

[0003] In automotive electronics, such DC-DC converters are used to operate solenoid-actuated fuel injectors. The electrolytic capacitor provides an operating voltage for this inductive load, enabling a relatively large electrical current to be supplied briefly and easily when the solenoid is activated. Furthermore, it is known to feed electrical energy back into the electrolytic capacitor after the solenoid is switched off, so that the stored energy can be used during the next solenoid activation.

[0004] As shown and described in detail in DE 10 2007 001 414 B3, electrolytic capacitors frequently used in automotive electronics have, in addition to their desired large capacitance, a parasitic series internal resistance, which is often referred to as ESR (equivalent series resistance).

[0005] When a DC-DC converter supplies power to a load, energy is drawn from the electrolytic capacitor. The current to the load flows through this internal resistance, causing a corresponding voltage drop that reduces the voltage across the load. If the load is inductive, such as the solenoid assembly in a solenoid valve, then switching off the power supply from the electrolytic capacitor results in the dissipation of the magnetic energy stored in the solenoid. With a control circuit that allows this energy to be fed back into the electrolytic capacitor, a current now flows in the opposite direction through the capacitor's internal resistance, thus increasing its terminal voltage.

[0006] However, currently available, inexpensive electrolytic capacitors in the can form with a capacitance ≥ 500 µF and a rated voltage of ≥ 60 V have the characteristic that their series resistance increases significantly with rising negative temperatures. The series resistance (ESR) guaranteed by the supplier of ≤ 100 mΩ at 25°C can increase to a value of up to 1000 mΩ at -40°C. With a nominal voltage across the electrolytic capacitor of 65 V and an assumed ESR of ∼ 700 mΩ and a peak current of 5 A, the terminal voltage rises to a value of 65 V + 700 mΩ * 5 A = 68.5 V.

[0007] In particular, if the operating voltage provided by the DC-DC converter for the electrolytic capacitor is also used as a supply voltage for at least one other electronic circuit or component of the vehicle electronics, this other electronic circuit or its components must be dimensioned so that the described voltage increase does not exceed their maximum connection voltage. Otherwise, such components can be damaged or even destroyed. However, there is also the additional problem that the maximum reverse voltage of many currently used semiconductors decreases at low temperatures.

[0008] The currently common solution involves either designing the components directly connected to the electrolytic capacitor for a higher nominal voltage (e.g., 90V-100V technology) or installing additional ceramic capacitors or MLCCs (multi-layer ceramic chip capacitors) in parallel with the electrolytic capacitor. These ceramic capacitors exhibit very low resistance even at low temperatures. Their number is determined by the maximum voltage swing across the inductive load and the energy fed back into the circuit. Assuming a nominal voltage of 65V, the available capacitance values ​​for cost-effective components approved for automotive applications are around 2.2 µF. Therefore, if the ceramic capacitors require a capacitance of 25 µF, approximately 11 units must be used in parallel. This results in higher costs due to their space requirements on the circuit board and, of course, the component costs themselves.

[0009] US 5,369,547 A discloses an electrolytic capacitor comprising a metal container with an inner and an outer surface, which acts as the cathode of the capacitor, a porous coating comprising an oxide of one of the following elements: ruthenium, iridium, nickel, rhodium, platinum, palladium, and osmium, arranged on the inside of the container in electrical communication with the container, an anode selected from the group consisting of tantalum, aluminum, niobium, zirconium, and titanium, arranged within the porous coating and spaced apart from the container, and an electrolyte within the container which is in contact with the porous coating and the electrode.

[0010] US 2009 / 0002908A1 discloses a protective circuit comprising an energy storage device, a melting element, and a surge modulation unit. The energy storage device stores and supplies a first energy. The melting element is connected in series with the energy storage device to form a partial circuit. The surge modulation unit is connected in parallel to the partial circuit, such that when the partial circuit begins to experience a surge, the absolute value of a modulation current flowing through the surge modulation unit is instantaneously increased, thus applying a second energy, instantaneously released from the energy storage device, to cut off the melting element.

[0011] DE 10 2016 100 061 A1 discloses a circuit comprising a first differential input pair and a second differential input pair. The first differential input pair is activated according to an output of the second differential input pair and receives a first temperature-dependent voltage and an output signal. The second differential input pair is activated according to an output of the first differential input pair and receives a second temperature-dependent voltage and the output signal. The circuit couples a capacitive element to a first voltage supply according to the output of the first differential input pair and the capacitive element to a second voltage supply according to the output of the second differential input pair to generate an output signal.

[0012] DE 41 26 865 A1 discloses a circuit arrangement for starting and operating high-pressure gas discharge lamps, comprising at least one DC / DC converter (D) which is current- or power-controlled and is supplied from a DC voltage source (B), which generates a lamp supply voltage and which has a charging capacitor (CL1) at its output, with an additional charging capacitor (CL2) in parallel to the charging capacitor (CL1) and with an ignition device (Z) for generating an ignition voltage in the connection between the at least one DC / DC converter (D) and the high-pressure gas discharge lamp (GDL), characterized in that a Zener diode (D1) is arranged in series with the additional charging capacitor (CL2), and that this series arrangement is in parallel with the charging capacitor (CL1).

[0013] The object of the present invention is to provide a DC-DC converter with which the disadvantages explained above can be avoided and, in particular, an undesirable voltage increase in the freewheeling phase with an inductive load can be reduced.

[0014] The problem is solved by a DC-DC converter according to claim 1. Advantageous embodiments are specified in the dependent claims.

[0015] The DC-DC converter with an output-side storage capacitor arrangement serves to provide an operating voltage for an inductive load and for at least one further electronic circuit and / or electronic component of a vehicle electronics system, wherein the storage capacitor arrangement is connected to the DC-DC converter via a reverse-biased diode 6.

[0016] The DC-DC converter includes a ceramic capacitor in addition to the electrolytic capacitor and a circuit arrangement consisting of a series circuit of a hybrid electrolytic capacitor and a suppressor diode, and a resistor connected in parallel to the hybrid electrolytic capacitor.

[0017] Hybrid electrolytic capacitors offer a high capacitance value relative to their size, with low ESR across the entire desired temperature range, but only a comparatively low rated voltage. This is compensated for according to the invention by the series suppressor diode. The resistor connected in parallel to the hybrid electrolytic capacitor ensures that a small current always flows through the suppressor diode, thus eliminating any switching delay.

[0018] The hybrid electrolytic capacitor has a lower series resistance than the electrolytic capacitor and a larger capacitance than the ceramic capacitor, so that in the event of energy being fed back from the inductive load into the storage capacitor arrangement, the hybrid electrolytic capacitor absorbs the largest proportion of the energy and thus prevents a voltage increase at an output terminal above a value at which connected components could be destroyed, where the output terminal is the cathode terminal of the diode and the inductive load can be connected to the output terminal.

[0019] In advantageous embodiments of the DC-DC converter according to the invention, the electrolytic capacitor has a nominal voltage of 50V to 70V and / or the hybrid electrolytic capacitor has a nominal voltage of 30V to 40V.

[0020] The invention is explained in more detail below using an exemplary embodiment and a figure. This figure shows... Fig. 1 the storage capacitor arrangement of a DC-DC converter according to the invention.

[0021] A DC-DC converter typically converts the energy from an input energy source into electrical energy stored in an output capacitor, via intermediate storage as magnetic energy in an inductor. The voltage across the output capacitor is regulated to a predetermined value by pulsed current flowing through the inductor. The DC-DC converter can be configured as a buck converter, boost converter, or inverting converter, and as a primary-switched or secondary-switched converter.

[0022] The output capacitor serves as a storage capacitor and is located in the storage capacitor arrangement according to the invention. Fig.The capacitor bank consists of an electrolytic capacitor 1, a ceramic capacitor 2 connected in parallel, and a series circuit consisting of a hybrid electrolytic capacitor 3, a suppressor diode 4, and a resistor 5 connected in parallel with the hybrid electrolytic capacitor 3. The capacitor bank is connected to the DC-DC converter via a reverse-biased diode 6. The resistor 5 conducts the suppressor diode 4, resulting in a current of approximately 1 mA. The suppressor diode 4 has a clamping voltage of approximately 40 V at a current of 1 mA. The cathode terminal of the diode 6 is also the output terminal of the DC-DC converter, to which an inductive load, in particular, can be connected.

[0023] In the event of energy being fed back into the storage capacitor arrangement from an inductive load, the hybrid electrolytic capacitor 3 takes over the largest share due to its lower series resistance compared to the electrolytic capacitor 1 and its larger capacitance compared to the ceramic capacitor 2, so that the voltage at the output terminal cannot rise to a value that could destroy other connected components.

[0024] The suppressor diode 4 must be designed such that its dynamic internal resistance (change in reverse voltage with current change) is as low as possible. Additionally, the suppressor diode 4 must be able to absorb a high pulse energy. The reverse current (leakage current) through the suppressor diode 4 must be at least ten times smaller than the current through the parallel resistor 5 to prevent voltage spikes above the nominal voltage from occurring across the series-connected hybrid electrolytic capacitor 3. Typical reverse currents of suppressor diodes are up to 25 µA in the temperature range up to 125°C.

[0025] Typical cup sizes for hybrid electrolytic capacitors are 8 x 8 mm with a height of 6 mm (100µF / 35V) or 10 x 10 mm with a height of 10 mm (220µF / 35V).

[0026] The peak power dissipation of the suppressor diode 4 must be greater than the maximum value of the peak regenerative current multiplied by the clamping voltage of the suppressor diode 4.

Claims

[1] DC-DC converter with an output-side storage capacitor arrangement for providing an operating voltage for an inductive load and for at least one further electronic circuit and / or electronic component of a vehicle electronics, wherein the storage capacitor arrangement is connected to the DC-DC converter via a reverse-biased diode (6) and the output-side storage capacitor arrangement is connected to a parallel circuit of an electrolytic capacitor (1), a ceramic capacitor (2) and a circuit arrangement is formed with a series connection of a hybrid electrolytic capacitor (3) and a suppressor diode (4) and a resistor (5) connected in parallel to the hybrid electrolytic capacitor (3), wherein the hybrid electrolytic capacitor (3) has a lower series resistance than the electrolytic capacitor (1) and a larger capacitance than the ceramic capacitor (2), so that in the event of energy being fed back from the inductive load into the storage capacitor arrangement, the hybrid electrolytic capacitor (3) absorbs a large proportion of the energy and thus prevents a voltage increase at an output terminal above a value at which connected components can be destroyed, wherein the output terminal is the cathode terminal of the diode (6) and the inductive load can be connected to the output terminal. [2] DC-DC converter according to claim 1, characterized by, that the electrolytic capacitor (1) has a nominal voltage of 50V to 70V. [3] DC-DC converter according to claim 1 or 2, characterized by , that the hybrid electrolytic capacitor (3) has a nominal voltage of 30V to 40V.

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