Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific quantity comparison means
Reexamination Certificate
2002-07-29
2004-10-12
Toatley, Jr., Gregory J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific quantity comparison means
C361S091200
Reexamination Certificate
active
06804096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electronic circuit (hereinafter, referred to as “load driving circuit”) for controlling the power feed to the load which circuit has a function of detecting an abnormal state such as the disconnection and the short circuit of the load.
2. Description of the Related Art
FIG. 1
is a schematic diagram for conceptually describing the structure of a conventional load driving circuit in a high side driver configuration which circuit is used in the electronic control unit (ECU) mounted in a vehicle and has a load disconnection and/or short circuit detection function. The circuit of
FIG. 1
comprises a battery
1
having its negative electrode connected to ground; a load driving circuit IC (integrated circuit)
100
having its positive power terminal or pin
101
connected to the positive electrode of the battery
1
and its negative power or ground pin
103
connected to ground; a load
2
connected between an output terminal
102
of IC
100
and the ground; and a pull-up resistor
3
connected between positive power pin
101
and output pin
102
of IC
100
for pulling up the IC output pin
102
.
In the load driving circuit IC
100
, between its positive power
101
and output
102
pins, there are connected the drain and source of an N-channel power MOSFET
111
and the cathode and anode of a protection diode
112
, respectively. Between the gate and the source of FET
111
there is connected a diode
117
to prevent the reverse biasing of the FET
111
gate. The IC
100
further comprises a charge pump
109
having its input voltage supplied from the positive electrode of battery
1
through a dedicated pin
104
of IC
100
to provide a charge voltage Vc; a switch circuit
110
connected between the output of charge pump
109
and the gate of FET
111
to effect connection and disconnection between them; a buffer
108
having its input connected to a power feed control signal input pin
105
to receive a binary power feed control signal Sa from a not-shown external controller and its output connected to a control terminal of switch circuit
110
so as to control the switching operation thereof; an inverter
114
having its input connected to the buffer
108
output to provide an inverted version {overscore (Sa)} of signal Sa; a discharging NPN transistor
14
having its gate connected to the inverter
114
output and its emitter connected to the ground pin
103
; a resistor
116
connected between the collector of discharging transistor
14
and the node including the gate of power FET
111
; and a comparator
113
having its non-inverting input connected to the power output pin
102
, its inverting input supplied with a reference voltage Vr and its output Sc connected to a comparator output pin
106
which is connected to the above-mentioned not-shown controller.
In thus structured load driving circuit, if the power feed control signal Sa is at the high level that indicates that the battery voltage Vb should be supplied to the load
2
, then the switch
110
is on (i.e., conductive) and the transistor
115
is off(i.e., nonconductive), holding the power FET
111
on, which means that the load
2
is electrically connected to the battery
1
through the FET
111
. If the power feed control signal Sa is at the low level that indicates that the battery voltage Vb should not be supplied to the load
2
, then the switch
110
is off and the transistor
115
is on, holding the power FET
111
off, which means that the load
2
is not connected to the battery
1
. For this purpose, the charge pump circuit
109
is so arranged as to use the battery voltage Vb supplied through an IC pin
104
and generate a raised voltage Vc higher than the battery voltage Vb by more than the threshold voltage Vt of the power FET
111
: i.e., Vc>Vb+Vt.
Since the load driver IC
100
is provided with the comparator
113
and has the external pull-up resistor
3
, the IC
100
can detect abnormalities such as a disconnection and a short circuit of the load
2
. Though a short circuit can be always detected by monitoring the level of the comparator
113
output or the IC pin
106
, the abnormality detection is preferably performed while the power FET
111
is off. If the FET
111
is off for example, then the current from the battery
1
flows mainly through either of the following two current paths in response to the connection condition of the load
2
. That is, the current flows through:
in case of disconnection of the load
2
,
the first path comprising the battery
1
positive electrode, the pull-up resistor
3
, the power output pin
102
, the diode
117
, the resistor
116
, the discharging transistor
115
, the ground pin
103
and the battery
1
negative electrode; and
in cases other than disconnection of the load
2
,
the second path comprising the battery
1
positive electrode, the pull-up resistor
3
, the load
2
and the battery
1
negative electrode.
If the load
2
is normally connected, then the FET
111
being off causes the current to flow through the second path. In this case, The level of the power output pin
102
, i.e., Vo, is given by Vb·R
2
/(R
2
+R
3
). Here, R
2
and R
3
are the resistor values of the load
2
and the pull-up resistor
3
, respectively. (Hereinafter, we make it a rule to express the resistance value of an element denoted by a reference numeral “N” with a form of “RN”.) Since the resistance R
3
of the resistor
3
is usually set to a sufficiently large value as compared with the resistance value R
2
of the load
2
, the output pin
102
level is close to 0V. If a disconnection exists in the load
2
when the load is viewed from its both ends, then the FET
111
being off causes the current to flow through the first path, resulting in the level Vo of the IC pin
102
being equal to the voltage drop due to diode
117
, resistor
116
and transistor
115
. The voltage drop is roughly given by Vb·R
116
/(R
3
+R
116
).
Thus, as long as the condition that R
2
<R
3
<R
116
is met, it is possible to correctly detect the disconnection and the normal connection of the load
2
from the output Sc of the comparator
113
by setting the reference voltage Vr of the comparator
113
to a medium value between Vb·R
2
/(R
2
+R
3
) and Vb·R
116
/(R
3
+R
116
).
For this purpose, it is a possible solution that the resistance value R
3
is set to a relatively large value and the resistance value R
116
is set to a still larger value. However, this solution causes the impedance of the discharge path through which the electric charges are drawn out of the gate capacitance of the power FET
111
to be large, which disadvantageously results in increases in the turn-off time of the power FET
111
(i.e., a speed-down of the load driving operation) and the switching loss of the power FET
111
.
Considering the foregoing, we makes it an object of the invention to provide a load driving circuit capable of detecting abnormality such as disconnection of the load with a high accuracy and driving the load at a high speed with low power consumption.
It is another object of the invention to provide a load driver IC which enables the detection of abnormality such as disconnection of the load with a high accuracy while driving the load at a high speed with low power consumption.
SUMMARY OF THE INVENTION
According to an aspect of the invention, a circuit for controlling a feed of a power supply voltage of a power supply to a load which circuit has a function of detecting a load driving state such as disconnection and short circuit is provided. The circuit comprises: a MOSFET connected in series with the power supply and the load for effecting an on/off operation; a circuit (such as a charge pump circuit) responsive to a feed control signal given from external for supplying a driving voltage to the gate to turn the MOSFET on; a resistor connected between the power supply and the load for causing a voltage drop during an off period of the MOSFET; a detection circuit or a comparato
Denso Corporation
Harness Dickey & Pierce PLC
Kitov Z
Toatley , Jr. Gregory J.
LandOfFree
Load driving circuit capable of raised accuracy detection of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Load driving circuit capable of raised accuracy detection of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Load driving circuit capable of raised accuracy detection of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3300237