Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific quantity comparison means
Reexamination Certificate
2000-10-23
2001-10-16
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific quantity comparison means
C307S127000
Reexamination Certificate
active
06304422
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a polarity reversal protection circuit that includes a first semiconductor switch and a polarity reversal protection diode that are connected in series with a load and that includes a second semiconductor switch that is connected in parallel with the polarity reversal protection diode. When the supply voltage terminals are properly connected to the circuit, the second semiconductor switch is switched on at least during the times that the first semiconductor switch is turned on.
The problem with power semiconductor switches and, in particular, MOS semiconductor switches by comparison with a relay is its diode, dictated by the technology, between the source connection and the drain connection of the MOS semiconductor switch. This diode, which is integrated in the MOS semiconductor switch and is also referred to as an inverse diode, is forward biased in the event of polarity reversal of the operation voltage and thus leads to the current flow through the load elements connected to the source connection or drain connection. In order in this case to afford effective protection of the load elements and of the MOS semiconductor switch against polarity reversal, it is regularly the case that a polarity reversal protection circuit is connected in series with the MOS semiconductor switch. In this case, the polarity reversal protection diode is biased such that during normal operation, that is to say correct connection of the supply voltage to the terminals of the circuit configuration, a current flow can take place through the polarity reversal protection diode. In contrast, the polarity reversal protection diode is in the off state in the event of polarity reversal, that is to say when the operational voltage is incorrectly connected to the terminals of the circuit configuration.
FIG. 1
illustrates a circuit configuration which is suitable for this purpose. The operating voltage V can be applied to two terminals
2
,
3
in order to supply a load
16
with voltage, in a manner controlled by a semiconductor switch
12
. By way of example, the load
16
may be the lamp of a motor vehicle headlight, which is switched on as required by the driver. In detail, the series circuit formed by the polarity reversal protection diode
10
already mentioned, the semiconductor switch
12
and the load
16
is present between the terminals
2
and
3
. The anode connection of the polarity reversal protection diode
10
is connected to the terminal
2
and the cathode connection of the polarity reversal protection diode
10
is connected to the drain connection D of the semiconductor switch
12
, which is designed as a MOS semiconductor switch in the present case. The source connection S is connected to one terminal of the load
16
, the other terminal of which is connected to the terminal
3
. An inverse diode
14
is connected in parallel with the load path of the semiconductor switch
12
and thus between the drain connection D and source connection S thereof. The anode connection of the inverse diode
14
is connected to the source connection S and the cathode connection is connected to the drain connection D. The semiconductor switch
12
is controlled at its control connection or gate connection G by a control device
20
, which is known sufficiently to a person skilled in the art.
The circuit configuration illustrated in
FIG. 1
shows a so called highside switch. Specifically, the semiconductor switch
12
is connected to the positive pole of the supply voltage terminal during normal operation by way of the polarity reversal protection diode
10
.
FIG. 1
illustrates normal operation, that is to say that the positive pole of the supply voltage V is connected to the terminal
2
and the negative pole to the terminal
3
.
What is problematic with the circuit configuration illustrated in
FIG. 1
is the power loss that is caused by the polarity reversal protection diode
10
and that is consumed continuously during normal operation because the current flow must necessarily flow through the forward biased polarity reversal protection diode
10
. The power losses are extremely high primarily when the semiconductor switch
12
is intended to switch high currents. In this case, the voltage drop across the polarity reversal protection diode
10
is often unacceptably high, because this reduces the effective voltage across the load
16
.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to improve the polarity reversal protection circuit illustrated in
FIG. 1
, and, in particular, of considerably reducing the power loss that inevitably occurs therein during normal operation.
With the foregoing and other objects in view there is provided, in accordance with the invention a polarity reversal protection circuit with a further controllable semiconductor switch connected in parallel with a polarity reversal protection diode, which switch is switched on by a control circuit during normal operation at least during the switched on times of the semiconductor switch. The further controllable semiconductor switch is switched off in the event of polarity reversal of the supply voltage.
This solution has the decisive advantage that during normal operation, that is to say with the supply voltage connected to the terminals in the correct manner, the polarity reversal protection diode
10
is bridged and so the power loss which occurs in the circuit configuration is one which is caused merely by the voltage drop of the switched on semiconductor switch. The power loss of the switched on further semiconductor switch is considerably smaller than the power loss caused by the polarity reversal protection diode.
In accordance with an added feature of the invention, the two semiconductor switches mentioned, that is to say the power semiconductor switch for switching on the current for the load and the semiconductor switch which is connected in parallel with the polarity reversal protection diode and can have smaller dimensions, are each realized by MOS transistors.
In accordance with an additional feature of the invention, the inverse diode that is present in any case in MOS semiconductor switches is expediently provided as the polarity reversal protection diode of the polarity reversal protection circuit.
In this case, the source connection of the further semiconductor switch is connected to that terminal of the supply voltage during normal operation at which a positive potential can be tapped off. The drain connection of the further semiconductor switch is connected to the drain connection of the power semiconductor switch and the source connection of the power semiconductor switch is connected via the load to the second terminal of the supply voltage, at which a negative potential or reference ground potential can be tapped off. The gate connection of the further semiconductor switch can be driven by means of the abovementioned control circuit in such a way that, during normal operation, the further semiconductor switch is always switched on or is in the on state at least when the power semiconductor switch is also in the on state. In contrast, in the event of polarity reversal, the further semiconductor switch is blocked and is thus switched off, with the result that the polarity reversal protection diode can fulfill its blocking function.
In accordance with another feature of the invention, the entire polarity reversal protection circuit may be designed as a monolithically integrated circuit configuration. However, the polarity reversal protection circuit according to the invention is not restricted to this, but rather, may also be constructed in discrete form or be integrated in a plurality of semiconductor chips. The two semiconductor switches of the polarity reversal protection circuit according to the invention may be integrated in different semiconductor bodies.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and descri
Gantioler Josef-Matthias
Sander Rainald
Xu Chihao
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Sherry Michael J.
Stemer Werner H.
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