DE10129550A1 - Electronic protection circuit for automobile electronics, has source-drain path of MOSFET switched into conduction dependent on onboard network voltage polarity - Google Patents

Abstract

The protection circuit has the source-drain path of a MOSFET (T1) used for connecting the automobile electronics to the onboard network voltage, the gate terminal (G) of the MOSFET supplied with a conduction signal when the network voltage has the correct polarity. The source and drain terminals (S,D) of the MOSFET are coupled to respective inputs of a comparator (IC1), the comparator output fed to the gate terminal.

Description

The invention relates to an electronic circuit arrangement for a motor vehicle to protect electronics against reverse polarity and electrical system ripples, the Electronics with the source-drain path of a MOS transistor in series on the Vehicle electrical system voltage is present, and if the polarity is correct Electrical system voltage of the MOS transistor via a signal at its gate connection is switched through.

In the simplest case, it can be used as a protective measure against polarity reversal a polarity reversal protection diode connected between voltage source and electronics be provided. The disadvantage is that there is a relatively high voltage drop across the Diode results, which also leads to a high power dissipation with larger currents.

For larger currents, it is therefore more advantageous to use electronics instead of Reverse polarity protection diode upstream of a MOS transistor with correct polarity switches through and connects the electronics to the vehicle electrical system voltage. For this is the Gate connection of the MOS transistor simply with a node of the Electronics connected, the one with the correct connection the MOS transistor controlling potential. Such a circuit is suitable because of its Low resistance for very high currents with low power loss of the MOS Transistor. The disadvantage here is, however, in contrast to one Circuit arrangement with a reverse polarity protection diode that smaller Voltage fluctuations, hereinafter referred to as electrical system ripples, can act freely on the electronics.

It is the object of the invention to provide an inexpensive circuit arrangement create the advantages of the aforementioned circuit arrangements with each other connects and avoids their disadvantages.

This object is achieved in that with the source connection and the drain of the MOS transistor each have an input Comparator is connected, and that the comparator output to the gate Connection of the MOS transistor is performed.

The invention is explained in more detail below with reference to the drawing.

Show it

Fig. 1 shows an embodiment of the circuit arrangement according to the invention,

Fig. 2 shows a first circuit arrangement according to the prior art,

Fig. 3 shows a second circuit arrangement according to the prior art.

In order to protect an electronic circuit against reverse polarity and vehicle electrical system ripple, the simplest possibility, which is shown in FIG. 2, is to insert a reverse polarity protection diode (D2) into the voltage supply lines of the electronics. The disadvantage of this circuit arrangement is that, depending on the type, a voltage drop between 0.4 V and 1 V occurs at the polarity reversal protection diode (D2) and the full load current flows through the polarity reversal protection diode (D2). Large power losses occur with larger currents.

The circuit arrangement shown in FIG. 3 is advantageous for larger load currents. An N-channel MOS transistor (T1) is used in inverse connection. If the polarity is correct, the electronics are supplied with the vehicle electrical system voltage, which is reduced by the flow voltage of the parasitic diode (D1) of the MOS transistor (T1) in the first moment. When the electronics are in operation, the gate (G) of the MOS transistor ( 1 ) is activated via a circuit point of the electronics with a suitable potential; the MOS transistor (T1) becomes conductive and bridges the internal diode (D1) with a low resistance with its channel path. With normal dimensioning, the voltage drop across the MOS transistor (T1) is less than 0.1 V. Because of its low impedance, the circuit is suitable for very high currents with low power loss in the MOS transistor (T1). A disadvantage compared to the circuit arrangement of FIG. 2 is that on-board electrical system ripples can have an unimpeded effect on the electronics.

The circuit arrangement according to the invention shown in FIG. 1 extends the circuit arrangement shown in FIG. 3 by means of a comparator circuit controlling the MOS transistor. Through this simple and inexpensive extension, this circuit arrangement additionally protects the electronics against on-board electrical system ripples and also against general unloading processes, e.g. B. of buffer capacitors of the electronics, which feed back currents into the vehicle electrical system.

The circuit arrangement already described with reference to FIG. 3 has been supplemented in FIG. 1 by a comparator (IC1), one with the source connection (S) and the drain connection (D) of the MOS transistor (T1) Input of a comparator (IC1) is connected, and wherein the comparator output is led to the gate terminal (G) of the MOS transistor (IC1). A resistor (R) connected to the comparator output serves as a pull-up resistor for adapting the potential present at the gate connection (G).

The electronics to be protected are purely exemplary with an additional one Capacitor (C1) has been added. This component is representative of Components (e.g. buffer capacitors, battery packs) which return currents can feed into the vehicle electrical system.

The comparator (IC1) checks the current flow in the MOS transistor (T1). Normally" the source terminal (S) of the MOS transistor (T1) has a higher potential than the drain connection (D); the output signal of the comparator (IC1) positive and the gate (G) of the MOS transistor (T1) is driven and thus the MOS transistor (T1) switched through.

If the vehicle electrical system voltage (Ub1) drops, for example due to a vehicle electrical system ripple, would normally the capacitor (C1) over the channel resistance of the MOS Unload transistor (T1) back into the vehicle electrical system. The measuring circuit (here by IC1 stylized) registers the reversing current flow through the discharge current of the Capacitor (C1) in the MOS transistor (T1) and switches it off. At the MOS Transistor (T1) sets a negative voltage; the parasitic diode (D1) lies in the reverse direction. If the vehicle electrical system voltage (Ub1) rises again, or the battery discharges Buffer capacitor (C1) so that the vehicle electrical system voltage (Ub1) is at least as large as the voltage at the capacitor (UC1), the comparator (IC1) switches the MOS transistor (T1) on again.

It should be added that the circuit arrangement shown in FIG. 1 represents the invention very schematically. An implementation of this circuit may contain additional, in particular passive, components for suitable dimensioning of the potentials, but the inventive basic principle, namely the feedback of a signal proportional to the voltage difference between the source (S) and the drain connection (D) to the gate (G) of the MOS transistor is retained. Reference symbol C1 (buffer) capacitor
D drain terminal (of the MOS transistor)
D1 parasitic diode (of the MOS transistor)
D2 reverse polarity protection diode
G gate connection (of the MOS transistor)
IC1 comparator
R resistance
S source connection (of the MOS transistor)
T1 MOS transistor
Ub1 vehicle electrical system voltage
UC1 voltage at the capacitor

Claims (1)

Electronic circuit arrangement for a motor vehicle to protect electronics against reverse polarity and electrical system ripples
the electronics with the source-drain path of a MOS transistor being connected in series to the vehicle electrical system voltage,
and wherein when the vehicle electrical system voltage is correctly polarized, the MOS transistor is switched through via a signal at its gate connection,
characterized by
that an input of a comparator (IC1) is connected to the source connection (S) and the drain connection (D) of the MOS transistor (T1), and that the comparator output is connected to the gate connection (G) of the MOS Transistor (IC1) is performed.