Actively switchable diode to prevent current backfeed in redundant power supplies in automobiles

Abstract

The invention relates to a method for minimizing the power loss of redundant power supplies in automobiles, wherein an active switching element in the form of a FET T1 is used, wherein the body diode of the FET T1 is provided to be designed as an actively switchable diode.

Description

[0001] The invention relates to an actively switchable diode for preventing current feedback in redundant power supplies in automobiles. State of the art

[0002] In the automotive industry, safety and redundancy in the supply, for example the battery, are very important.

[0003] Fig. 1 shows a prior art circuit structure that provides a redundant power supply.

[0004] Terminal 30 directly protects the battery supply. Terminal 15 protects the battery supply via the ignition switch.

[0005] S1 is a switching element. S1 can be a mechanical switch, an electronic switch, or a mechanical relay.

[0006] D1 and D2 are electronic diodes. D1 and D2 ensure the supply to the two terminals T30 and T15.

[0007] F1 and F2 are fuses. If one of the two fuses, F1 or F2, blows, meaning an electrical connection is established, current flows back from T15 to T30 or from T30 to T15.

[0008] D1 and D2 are designed to prevent this current backflow from T15 to T30 or from T30 to T15.

[0009] Diodes D1 and D2 also prevent a negative voltage to S1. A negative voltage to S1 can occur due to faults or incorrectly applied battery voltage. Disclosure of the invention

[0010] If redundant power supplies are used in an automobile, they can be connected via diodes for lower currents to prevent unwanted current flow. However, implementation with "simple" diodes is difficult or even impossible for currents above 5A due to the high power losses.

[0011] The invention therefore proposes using an active switching element, e.g., in the form of a FET, instead of a diode. The body diode of this switching element can ensure conduction at low current flows and immediately at the beginning of the current flow. At higher current flows or later, the switching element can be actively switched to conduction. Drawings

[0012] It shows Fig. 1: a circuit from the state of the art in schematic representation, Fig. 2: a circuit according to the invention in schematic representation, Fig. 3: an extension of the circuit according to the invention in a schematic representation. Description

[0013] Fig. Figure 2 shows a circuit 10 according to the invention with the following components: a battery voltage Vbat, a first FET T1 with an integrated body diode, a control FET T2, a comparator 16, and resistors R1 and R2. This circuit is implemented at both terminals 15 and 30.

[0014] If currents <2A flow, transistor T1 is high-impedance, and the full battery voltage drops across T1. (Right?)

[0015] If larger currents flow, for example, due to a turn-on process, the power dissipation across transistor T1 becomes excessive. Comparator 16 detects the higher currents and actively switches on transistor T1 via transistor T2. The drain of T2 is connected to the drain of T1. T1 thus becomes low-resistance, meaning it conducts. This bypasses the internal body diode and minimizes power dissipation. If the current drops to 0A, transistor T1 is deactivated again.

[0016] Resistors R1 and R2 ensure that transistor T1 is only turned on by comparator 16 when the currents flowing through resistors R1 and R2 are positive. If the currents are negative, i.e., the potential at the drain of transistor T1 is negative, transistor T1 should be high-impedance.

[0017] Fig. 3 shows a possible implementation of the invention with the following components: a battery voltage Vbat, a first FET T1 with an integrated body diode, a control FET T2, a comparator 16, resistors R1, R2, R3, R4, R5, R6 and capacitors C1, C2, C3 and C4.

[0018] R3 and R4 ensure the dielectric strength of the comparator 16, even against higher voltages.

[0019] The capacitor C1 stabilizes the comparator 16, in which C1 prevents disturbances from easily causing the comparator 16 to oscillate.

[0020] C4 could be used as a "speed-up capacitor" for R4. The capacitance of C4 should be significantly smaller than that of C1 to avoid subjecting the comparator to voltage spikes across C4. Therefore, C1 should always be significantly larger than C4. R5 is intended for current limiting.

[0021] R6 and R7 at the output of comparator 16 are important for open collector comparators.

[0022] Resistors R6 and R7 at the output of comparator 16, as well as resistor R8, are designed to ensure a defined current through R1 and R2. This allows a defined, but small, offset voltage to be used for one of the comparator inputs.

[0023] C3 is the support C of the supply voltage of the comparator

Claims

[1] Method for minimizing the power loss of redundant power supplies in automobiles, wherein an active switching element in the form of a FET T1 is used, wherein the body diode of the FET T1 is intended to be designed as an actively switchable diode. [2] Method according to claim 1, characterized by that for current flows <2A T1 is high-resistance to ensure permeability. [3] Method according to claim 1, characterized by that at currents >2A the switching element T1 is actively switched on, whereby the internal body diode is bridged in order to minimize the conduction loss in T1. [4] Circuit 10 with a first FET T1, wherein T1 has an integrated body diode, a control FET T2, a comparator 16 and resistors R1 and R2 for carrying out the method according to claims 1 to 3.

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