DE10236300A1 - Low-power loss decoupling circuit for collocated current branches in vehicle has parasitic FET source-drain decoupling diodes, circuit elements that switch FET on if current branch carrying current - Google Patents

Abstract

The circuit arrangement has a decoupling diode for each current branch in the form of the parasitic source-drain-diode of a field effect transistor (T220) and circuit elements that switch the relevant field effect transistor to the conducting state when its associated current branch is supplied with current. A microprocessor (MP) detects current flow in a branch and drives the associated FET.

Description

The invention relates to a circuit arrangement for low-loss decoupling of merged current branches in a motor vehicle.

To certain lighting functions if necessary, for example in the event of a fault, also with the current other lighting function, it is necessary to that the corresponding current branches are merged. This is a Decoupling necessary, to prevent mutual interference of the current branches.

A commonly used way to Decoupling of current branches consists in the use of decoupling diodes. Especially when used in a motor vehicle, e.g. B. in the decoupling of supply lines for Lighting functions, however, the use of diodes is disadvantageous, because of the relatively high currents, quite large power losses arise, which not only wastes electrical energy, but also expensive cooling measures required become.

It is the object of the invention to create a circuit arrangement which has the aforementioned disadvantages avoids.

This object is achieved according to the invention solved, that the Decoupling diode each through the parasitic source-drain diode Field effect transistor is formed and that circuit elements are provided are, which the respective field effect transistor when energized control the current branch assigned to it.

Advantageous configurations and Further training is listed in the subclaims.

An embodiment of the circuit arrangement according to the invention is shown in the drawing and should be based on the following single figure closer explained become.

A section of is shown a control circuit for Lighting devices, for example in a trailer vehicle are arranged. The lighting device is only an example here a brake light shown; a realization of this circuit arrangement might control and monitor several lighting devices, all of which Functions controlled by the same microprocessor (MP) and all lights over the same bus line (S) can be supplied with voltage. The supply of lighting devices over a manifold (S) has the particular advantage that at one detected errors of a luminaire function, e.g. B. in the event of failure of Brake light (s), this function by controlling another Lamp groups can be simulated.

The lighting is controlled via a multi-core Connection from the tractor to the trailer vehicle, of which here only the brake light line is shown. As soon as a voltage signal with sufficient power on the brake light cable this about the parasitic Diode (DP) of the field effect transistor (T220), which is the function here decoupling diode, on the bus line (S) and can be assigned via an assigned circuit breaker (T200) energize the brake light.

The parasitic diode (DP) of the field effect transistor (T220) has quite good properties in terms of blocking capacity, forward voltage and forward current. It is in the direction of the river switched because the field effect transistor (T220) is installed inversely is. With the help of the control via the transistor (T221) becomes the field effect transistor (T220) one enough high gate voltage made to conduct. This reduces the voltage drop between source and drain of z. B. 0.7 V at Use as a diode depending on the current to a significantly lower value, so that with a current flow of exemplary 4 A the power loss of 2.8 W on the field effect transistor 0.16 W reduced.

In order to be able to check whether the Function is still present, it is necessary to use the field effect transistor (T220) again so that only still its parasitic Diode (DP) is effective. By suitable selection of the duty cycle let yourself keep the power loss low.

The functioning of the circuit arrangement shown can be described as follows:
The microprocessor recognizes via an input variable measurement on the voltage divider arrangement (ST) whether a voltage signal is present on the brake light line.

If this is the case, the voltage signal is present from the brake light line via the parasitic Diode (DP) of the field effect transistor (T220) also on the bus (S) so that the Microprocessor (MP) by controlling the circuit breaker (T200) the brake light can turn on.

As long as no voltage signal on the brake light line is present, the parasitic diode (DP) of the field effect transistor (T220) used as a decoupling diode, which when energized the manifold over a (not shown) supply line of another lighting function, the Brake light line decoupled from the manifold.

As soon as a voltage signal is present on the brake light line, such decoupling becomes unnecessary. On the diode (DP) of the field effect transistor (T220), however, as with every diode, there is a voltage drop of approx. 0.7 V, which leads to a noteworthy power loss at the diode (DP) at currents of several amperes, whereby at least cooling measures would have to be taken with a simple decoupling diode ,

In the circuit arrangement shown this power loss by turning on the field effect transistor (T220) minimized. This happens in which the microprocessor (MP) drives a first transistor T222, whereby a second transistor T221 a charge pump (LP) with the control input of the field effect transistor (T220) is connected, whereby this switches through and thus the voltage drop between source and drain reduced to approx. 0.04 V.

Since the microprocessor is switched on Field effect transistor (T220) can no longer measure input variables, the microprocessor briefly triggers the control at regular intervals interrupt to by evaluating the voltage signal at the voltage divider arrangement (ST) to check if there is still a voltage signal on the brake light line.

DP

parasitic diode

LP

charge pump

MP

microprocessor

S

manifold

ST

voltage divider

T200

breakers

T220

Feldeftekttransistor

T221, T222

transistor

Claims (5)

Circuit arrangement for low-loss decoupling of merged current branches in a motor vehicle, each with one decoupling diode per current branch, characterized in that the decoupling diode is in each case formed by the parasitic source-drain diode of a field-effect transistor (T220), and in that circuit elements are provided which correspond to the respective field-effect transistor Control (T220) when energizing the current branch assigned to it. Circuit arrangement according to claim 1, characterized in that too the circuit elements include a microprocessor (MP), which recognizes the energization of a current branch and the activation of the associated Field effect transistor (T220). Circuit arrangement according to claim 1, characterized in that the Circuit elements form a charge pump (LP), the output voltage connected to the control input of the field effect transistor (T220) can be. Circuit arrangement according to claim 1, characterized in that the Circuit arrangement part of a control device for control and monitoring of lighting functions in a trailer vehicle. Circuit arrangement according to claim 2, characterized in that the Microprocessor (MP) temporarily activates the field effect transistor (T220) interrupts to check whether a control signal is still present on the supply line.