Protective circuitry for electronic device

A protective circuitry (20) is connected between a power input port (11) and an electronic component (12) of an electronic device. The protective circuitry includes a field effect transistor (21) and a detection unit (25). The field effect transistor has a gate and a drain both electrically connected to an anode of the power input port, and a source electrically connected to a cathode of the power input port via the electronic component. The detection unit has two conductive pads spaced to each other. One pad is electrically connected to the gate and the other pad is electrically connected to the cathode of the power input port.

BACKGROUND

1. Technical field

The present invention relates generally to protective circuitry for electronic devices, and more particularly to a protective circuitry which can protect an electronic device from water damage by automatically switching off power to electronic components of the electronic device.

2. Description of the Related Art

Electronic devices may be damaged when they come into contact with water and/or are subjected to high humidity environments. Thus, protecting electronic devices from water or humidity is a problem. However, currently, most electronic devices lack this protection. When these electronic devices contact water or are placed in a damp environment, the electronic components within the electronic device may short circuit and destroy or damage the electronic device.

Therefore, there is room for improvement within the art.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS

The present protective circuitry is particularly suitable for electronic devices, such as mobile phones, personal digital assistants (PDAs), palm computers, and the like.

Referring now toFIGS. 1 and 2, a protect circuit20is incorporated on a circuit board substrate10of an electronic device (not shown). The circuit board substrate10incorporates a plurality of electronic components12for cooperatively achieving a desirable function of the electronic device, a plurality of connecting circuits15for electrically connecting the electronic components12, and at least one protective circuitry20electrically connected between a power input port11and the electronic components12. The power input port11is used to electrically connect with a power supply, e.g., a battery, to provide a working voltage Vccto the electronic components12. The power input port11has an anode, and a cathode.

The protective circuitry20includes a field effect transistor (FET)21, an adjustable resistor R1, and a detection unit25. The FET21can be but not limited to a metal oxide semiconductor field effect transistor (MOSFET), and has three terminals, i.e., a gate G, a drain D, and a source S. The FET21has two different modes depending on the voltages at the terminals. When the voltage between the gate G and the source S (VGS) is smaller than a threshold voltage Vth, the FET21is in a cut-off mode, and there is no current flow between the drain D and the source S. When VGSis larger than Vth, the FET21is in a turn-on mode, and there is current flow between the gate G and the source S. The drain D is electrically connected to the anode of the power input port11. The adjustable resistor R1is electrically connected in series between the anode of the power input port11and the gate G. The detection unit25includes two conductive pads spaced to each other. One pad of the detection unit25is electrically connected to the cathode of the power input port11, and the other pad of the detection unit25is electrically connected to the gate G. The detection unit25is preferably located where water or moisture is prone to enter the electronic device, such as a joint between the covers of the electronic device. The electronic components12are electrically connected between the source S and the cathode of the power input port11.

In use, a power supply is electrically connected to the power input port11of the circuit board substrate10to enable operation of the electronic device. When there is no water in the electronic device, there is no conduction between the two pads of the detection unit25. The FET21devides a VGSlarger than Vth, thereby making the FET21work on a turn-on mode. Therefore, the electronic component20can get power supply via the FET21.

Referring toFIG. 3, when there is water in the electronic device, the two pads of the detection unit25are electrically connected to each other by the water, and act as a resistor Rpadelectrically connected between the gate G and the cathode of power input port11. Since the resistor Rpadhas a voltage dividing function and divides part of the voltage, the VGSis reduced and becomes smaller than the Vth. Then, the FET21automatically switches to the cut-off mode. Therefore, there is no current flowing through the electronic components12, and the electronic components12are shut down.

The pads of the detection unit25can be bar shaped as shown inFIG. 2. In addition, the pads may be patterned as shown inFIGS. 4 and 5to increase the sensitivity of the detection unit25. As shown inFIG. 4, one pad251has a circular main portion and a plurality of leaves outwardly radially protruding from the main portion. The leaves are equally spaced to each other. The other pad252has a hole defined therein. The hole has a shape and size corresponding to that of the pad251to receive the pad251. As shown inFIG. 5, one pad253is a toothed strip having leaves on two opposite sides. The other pad255has a hole defined therein. The hole has a shape and size corresponding to that of the pad253to receive the pad253.