Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2001-07-12
2003-04-08
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S427000, C327S432000, C327S434000
Reexamination Certificate
active
06545515
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a low side switch for driving a load such as a lamp, a light-emitting diode (LED), and an inductor. In particular, the present invention relates to a semiconductor switch capable of reducing a leakage current during an OFF time.
2. Description of the Related Art
Conventionally, as a procedure for driving a load such as a lamp and a coil, a method generally is used for driving a load by turning on/off a switch provided on a low potential side of a load as shown in FIG.
7
. In
FIG. 7
, reference numeral
31
denotes a power supply,
32
denotes a load such as a lamp and a coil, and
30
denotes a switch. As the switch
30
, a transistor mainly is used. Among transistors, an N-type power MOSFET, which may be used as a low side switch, mostly is used.
Furthermore, the above-mentioned systems generally are provided with various protection functions. In order to realize a load short protection function, an overcurrent protection function, and the like among the protection functions, it is required to detect a voltage on a low potential side of a load (i.e., a potential of a drain terminal in the case of using a MOSFET as a switch).
FIG. 8
shows a conventional example in which a MOSFET is used as a switch, and a function of detecting a voltage of a drain terminal is incorporated.
In
FIG. 8
, reference numeral
31
denotes a power supply,
32
denotes a load such as a lamp and a coil, and
34
denotes an input terminal of a system. Furthermore, reference numeral
21
denotes a MOSFET that functions as a switch for driving the load
32
. Reference numeral
25
denotes a drain electrode of the MOSFET
21
, and a potential of the drain electrode
25
is assumed to be V
D
. Furthermore, reference numeral
24
denotes a gate electrode of the MOSFET
21
, and the MOSFET
21
is turned on/off based on a potential of the gate electrode
24
. Reference numeral
26
denotes a source electrode of the MOSFET
21
, which is grounded. Herein, reference numeral
40
denotes a switching portion, and elements contained therein can be formed on the same semiconductor substrate.
In the switching portion
40
, a voltage detection circuit
22
is connected in parallel to the MOSFET
21
between the drain electrode
25
and the source electrode
26
. The voltage detection circuit
22
can detect the potential V
D
of the drain electrode
25
by connecting a resistive element
28
(resistance Ra) and a resistive element
29
(resistance Rb) in series as resistors for detecting a drain voltage. More specifically, the potential V
D
of the drain electrode
25
can be detected only by monitoring a potential V
C
of an output signal (voltage detection signal)
23
of the voltage detection circuit
22
. The relationship between V
D
and V
C
can be expressed as follows:
V
C
=Rb
/(
Ra+Rb
)×
V
D
(more specifically,
V
D
=V
C
×(
Ra+Rb
)/
Rb
)
A drain voltage is detected in this manner, and is used for controlling various functions such as a load short protection function and an overcurrent protection function.
Furthermore, reference numeral
27
denotes a control circuit. The control circuit
27
receives the voltage detection signal V
C
output from the voltage detection circuit
22
to control the gate electrode
24
of the power MOSFET
21
.
However, in the conventional example, even if a leakage current of the power MOSFET
21
is small during an OFF time of the power MOSFET
21
, a current flows through the resistive elements
28
and
29
connected between the drain and the source, so that a leakage current flows. In this case, a current of about (power supply voltage)/(total resistance of the load
32
and the resistive elements
28
,
29
for detecting a voltage) flows.
When a leakage current is large, a current consumed by the system is increased. Furthermore, in the case where a load is an LED, the LED may emit light even during an OFF time.
In order to minimize a leakage current, a method of increasing a resistance of the resistive elements
28
and
29
for detecting a voltage is considered easily. However, in the case where the voltage detection signal V
C
is received by a MOSFET or a transistor, when the resistance of the resistive elements
28
and
29
for detecting a voltage is prescribed to be too large, a current flowing as the voltage detection signal V
C
becomes too small, which may cause inconvenience for control. Furthermore, in order to increase a resistance, a tip area also is increased.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a voltage detection circuit and a semiconductor device in which a leakage current is reduced without increasing a tip area, and various protection functions with respect to a load are ensured.
In order to achieve the above-mentioned object, the voltage detection circuit of the present invention is connected in parallel to a first switching element for controlling a power supply to a load and includes a second switching element and a voltage detedction portion connected in series to each other, wherein the second switching element is connected to a high potential side of the first switching element, and the voltage detection portion detects a voltage of a high potential electrode of the first switching element when the second switching element is conducting.
In the above-mentioned voltage detection circuit, the voltage detection portion is composed of at least two resistive elements, and detects a voltage of the high potential electrode of the first switching element based on a division ratio of the resistance of the resistive elements. In this case, it is preferable that the resistive element is a polysilicon resistor formed on an oxide film of the same substrate as that of the first switching element.
Alternatively, the voltage detection portion is composed of at least two Zener diodes.
Furthermore, the second switching element is composed of an N-channel MOSFET. In this case, it is preferable that a backgate of the N-channel MOSFET is at the same potential as that of a source or at a ground potential. Alternatively, the second switching element is composed of a bipolar transistor or an N-channel MOSFET with a high withstand voltage.
In order to achieve the above-mentioned object, the semiconductor device of the present invention includes: a first switching element for controlling a power supply to a load; the above-mentioned voltage detection circuit; and a control circuit that brings the first switching element into conduction or out of conduction in accordance with a control signal from outside, and brings the first switching element out of conduction based on a voltage detection signal output from the voltage detection circuit.
In the above-mentioned semiconductor device, the second switching element of the voltage detection circuit is brought into conduction or out of conduction in accordance with the control signal from outside.
Furthermore, the first switching element is composed of an N-channel MOSFET, an insulating gate type bipolar transistor, or a bipolar transistor.
Furthermore, it is preferable that the first switching element, the second switching element, and the voltage detection circuit are formed on the same semiconductor substrate.
Furthermore, the first switching element is composed of an N-channel vertical MOSFET with a high withstand voltage, using an N-type silicon substrate as a drain electrode.
Furthermore, the first switching element and the second switching element of the voltage detection circuit are both composed of an N-channel vertical MOSFET with a high withstand voltage, using the same N-type silicon substrate as a drain electrode.
Alternatively, the second switching element of the voltage detection circuit is formed on the same semiconductor substrate as that of the first switching element while being electrically insulated with an insulator from the first switching element.
According to the above-mentioned configuration, a volta
Takada Kouji
Takahashi Satoru
Yamaguchi Seiki
Lam Tuan T.
Merchant & Gould P.C.
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