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Power mosfet having current detection means
| Details |
Inventors: Takahashi, Mitsuasa;
Assignee: NEC Corporation (Tokyo, JP)
Primary Examiner: Prenty; Mark V.
Assistant Examiner:
Attorney, Agent or Firm: Foley & Lardner
A power MOSFET includes a main MOSFET connected in series with a load resistor between a high voltage power supply voltage and ground, and a series circuit connected in parallel to the main MOSFET and composed of a sensing MOSFET and a converting MOSFET for converting a shunted current flowing through the sensing MOSFET into a detected voltage signal, which is supplied to one input of an operational amplifier. A gate of the main MOSFET and a gate of the sensing MOSFET are connected in common to an output of a gate drive circuit. The other input of the operational amplifier is connected to a reference voltage, so that the detected voltage signal is compared with the reference voltage. An output of the operational amplifier is fed back to the gate drive circuit, so that the gate drive circuit controls a gate voltage supplied to the gate of the main MOSFET and the gate of the sensing MOSFET, in order to prevent an overcurrent from flowing through the power MOSFET. |
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DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide a power MOSFET device which has overcome the above mentioned defects of the conventional ones.
Another object of the present invention is to provide a power MOSFET device having a means for detecting a load current of the power MOSFET with a high degree of sensitivity and a high degree of precision, which can be easily manufactured and which can easily modify the set value of the overcurrent detecting value.
The above and other objects of the present invention are achieved in accordance with the present invention by using a MOSFET as a current-to-voltage converting means for detecting a current value.
Specifically, according to the present invention, there is provided a power MOSFET device including a main MOSFET connected between a high voltage power supply side terminal and a low voltage power supply side terminal, and a series circuit composed of a sensing MOSFET and a current-to-voltage converting means, the series circuit being connected in parallel to the main MOSFET, the sensing MOSFET having a gate connected to a gate of the main MOSFET, the improvement characterized in that the current-to-voltage converting means is constituted of a MOSFET.
Preferably, the current-to-voltage converting MOSFET has a gate and a drain connected to each other.
More specifically, a back gate of the current-to-voltage converting MOSFET is connected to the above mentioned low voltage power supply side terminal.
In addition, the power MOSFET device further includes a reference voltage generating MOSFET having a gate and a drain connected to each other, and a voltage comparing means having a first input connected to receive an output voltage of the current-to-voltage converting means and a second input connected to a reference voltage generated by the reference voltage generating MOSFET.
In the power MOSFET device thus constructed, since it is possible to use, as a detection voltage value, a voltage not less than a threshold of the MOSFET, namely, since it is possible to utilize, as the detection voltage value, a voltage which is sufficiently larger than the offset of the operational amplifier, it is possible to realize the current detection having a high degree of precision
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