Electricity: electrical systems and devices – Safety and protection of systems and devices – Load shunting by fault responsive means
Reexamination Certificate
2002-01-29
2004-11-09
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Load shunting by fault responsive means
C361S091100
Reexamination Certificate
active
06816348
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to an input protection circuit for protecting internal circuitry of a handheld electric device. More specifically, the present invention discloses an input protection circuit with low power consumption.
2. Description of the Prior Art
In modern society, people hope to receive all kinds of information via handheld electric devices, such as a personal digital assistant (PDA), a mobile phone, etc. These handheld electric devices have complex internal circuitry for dealing with great amount of data. The internal circuitry must have a certain threshold voltage to provide a direct current (DC) bias voltage for operating regularly. When a DC voltage exceeds the threshold voltage or a reverse DC voltage inputs to the internal circuitry, the internal circuitry will be damaged and the handheld electric device will have abnormal operation.
For preventing improper damages of the internal circuitry, the handheld electric device has an input protection circuit for protecting the internal circuitry. Please refer to
FIG. 1
of a diagram of an input protection circuit
12
applied in a handheld electric device
10
according to the prior art. The handheld electric device
10
has a direct current (DC) power supply
24
for providing DC power. The DC power supply
24
inputs the DC power to an internal circuitry
14
through the input protection circuit
12
of the handheld electric device
10
for protecting the internal circuitry
14
of the handheld electric device
10
. The input protection circuit
12
, electrically connected between the DC power supply
24
and the internal circuitry
14
, has a power socket
16
. The power socket
16
comprises a positive input node
16
A and a ground node
16
B, respectively electrically connected to two output nodes
24
A and
24
B of the DC power supply
24
for inputting the DC power provided from the DC power supply
24
to the input protection circuit
12
. The input protection circuit
12
further comprises two power connection channels
21
and
23
, respectively electrically connected to the positive input node
16
A and the ground node
16
B of the power socket
16
and the positive input node
14
A and the ground node
14
B of the internal circuitry
14
for forming electric connection between the DC power supply
24
and the internal circuitry
14
.
The prior art input protection circuit
12
further comprises a power diode D
1
and a pnp-type bipolar junction transistor (BJT) Q
1
respectively connected to the power connection channel
21
for controlling the DC power inputting through the power connection channel
21
to the internal circuitry
14
so as to protect the internal circuitry
14
. A base of the pnp-type BJT Q
1
electrically connects to an npn-type BJT Q
2
functioning as a control transistor, and a base of the npn-type BJT Q
2
electrically connects to an output node
20
A of an overvoltage protective circuit
20
. The overvoltage protective circuit
20
further comprises two input nodes
20
B and
20
C respectively connected to two power connection channels
21
and
23
.
An operation principle of the prior art input protection circuit
12
can be described as follows. A BJT can utilize a base current to turn the current between a collector and an emitter on and off. When a DC voltage provided by the DC power supply
24
is below a threshold voltage of the internal circuitry
14
, the power diode D
1
, the transistor Q
1
, and the control transistor Q
2
are all turned on so that the current provided by the DC power supply
24
flows into the internal circuitry
14
through the power connection channel
21
. When a DC voltage provided by the DC power supply
24
exceeds the threshold voltage of the internal circuitry
14
, the overvoltage protective circuit
20
with the two input nodes
20
B and
20
C electrically connecting between the power connection channel
21
and
23
will detect a overvoltage between the positive node
16
A and the ground node
16
B. Then, the overvoltage protective circuit
20
draws the base current out of the control transistor Q
2
through the output node
20
A so as to reduce the on current flux between the collector and the emitter of the control transistor Q
2
, and even turning off the control transistor Q
2
. Current reduction or elimination between the collector and the emitter of the control transistor Q
2
causes the base current of the transistor Q
1
to be reduced or turned off thereby causing the current between the emitter and the collector of the transistor Q
1
to be reduced or turned off. This prevents the DC current caused by exceeding the threshold voltage from flowing from the DC power supply
24
into the internal circuitry
14
through the transistor Q
1
.
If the output node
24
A of the DC power supply
24
which will connect with the positive input node
16
A is connected to the ground node
16
B, and if the output node
24
B of the DC power supply
24
which will connect with the ground node
16
B is connected to the ground node
16
A, the power diode D
1
positioned at the power connection channel
21
will be turned off so as to protect the internal circuitry
14
.
A defect of the prior art input protection circuit
12
is the utilization of the BJT to control the transistor Q
2
. When the voltage of the DC power supply
24
is below the threshold voltage, the control transistor Q
2
stays on so as to turn on the transistor Q
1
. Thus, the DC power of the DC power supply
24
is electrically connected to the internal circuitry
14
. The overvoltage protective circuit
20
outputs a current from the output node
20
A to the base of the control transistor Q
2
because the BJT must use the base current to control the transistor Q
2
. As a result, the overvoltage protective circuit
20
must consume power to maintain normal operation. Volume of the prior art overvoltage protective circuit
20
cannot be lessened because the overvoltage protective circuit
20
consumes power for preventing the prior art input protection circuitry
12
from overheating. Furthermore, the power diode D
1
positioned at the power connection channel
21
must admit the DC power to pass from the DC power supply
24
to the internal circuitry
14
, meaning that the power diode D
1
must be a diode with a large volume and the ability to bear high DC power. The above-mentioned reasons increase power consumption of the prior art input protection circuit
12
and do not allow the whole volume of the input protection circuit
12
to be lowered.
SUMMARY OF INVENTION
It is therefore a primary objective of the claimed invention to provide an input protection circuit with low power consumption to effectively lessen a volume of the input protection circuit.
The claimed invention discloses an input protection circuit for protecting internal circuitry of a handheld electric device. The internal circuitry has a positive input node and a ground node. The input protection circuit comprises a power socket having a positive input node and a ground node, a bipolar junction transistor (BJT), a metal-oxide semiconductor (MOS) transistor for controlling the on and off states of the BJT, and an overvoltage protective circuit. The power socket is used to electrically connect with two output nodes of a direct current (DC) power supply whose ground node is electrically connected to the ground node of the internal circuitry. An emitter of the BJT is electrically connected to the positive input node of the power socket, and a collector is electrically connected to the positive input node of the internal circuitry. When a reverse DC voltage or a DC voltage exceeding a threshold inputs from the positive input node and the ground node of the power socket, the overvoltage protective circuit will turn off the MOS transistor thereby turning off the BJT to prevent damages of the internal circuitry. When a DC voltage below the threshold inputs from the positive input node and the ground node of the power socket, the overvoltage protective circuit will tu
Chen Chung-Ho
Huang Chien-Hao
Sheh Gin-Yuan
Compal Electronics Inc.
Hsu Winston
Nguyen Danny
Sircus Brian
LandOfFree
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