Output controller

Details Output controller Output controller

2001-02-13

2002-07-23

Berhane, Adolf Deneke (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S316000

Reexamination Certificate

active

06424131

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a power control device utilized in a power semiconductor device.
BACKGROUND ART
An output circuit in a driver of such as motor or actuator, a power source circuit, or the like, includes a circuit breaker for cutting off an output current in order to protect circuit elements from excess current or control the output current so as to avoid exceeding a predetermined value.
FIG. 13
shows one conventional example of the circuit breaker. An output transistor
1
is a transistor for driving a load
3
. A register
101
for detecting current is connected in series with the output transistor
1
. The potential difference across the resistor
101
, namely the voltage drop due to the current flowing through the output transistor
1
(hereinafter referred to as output current) is compared with a reference voltage
102
through a differential amplifier
103
. The reference voltage
102
is set to be equal to the voltage drop due to a control target amount of the output current. The comparison result of the differential amplifier
103
is outputted to a control circuit. The control circuit cuts off the output transistor
1
when the output current is larger than the control target amount, that is to say, when the output of the differential amplifier
16
is negative. The output transistor
1
which has been once cut off is held under the cutoff condition by the control circuit. The control circuit allows the output transistor
1
to conduct the current again in the case of receiving a signal indicating the directions to conduct the current from the outside or when the output of the differential amplifier
103
becomes positive after a predetermined time has passed. Thus, the output current avoids substantially exceeding the control target amount.
In the above-described conventional example of
FIG. 13
, however, the resistor
101
is connected in series with the output transistor
1
. Therefore, there is the problem of narrowing the range of the output voltage or spending the wasted power.
FIG. 14
shows another conventional example of the circuit breaker. In the conventional example, the above-described problem with the conventional example is solved as follows.
In the second conventional example, an auxiliary transistor
2
is connected in parallel to the output transistor
1
and the current-detecting resistor
101
is connected in series with the auxiliary transistor
2
. The current I
2
outputted by the auxiliary transistor
2
(hereinafter referred to as adjusting current) is smaller by a predetermined ratio than the output current I
1
outputted by the output transistor
1
applied with the common input. For example, in the case where the output transistor
1
and the auxiliary transistor
2
are monolithically formed such as an integrated circuit or the like, the structure of the auxiliary transistor
2
is substantially the same as the output transistor
1
but the size thereof is smaller than the output transistor
1
. In that case, the ratio of the currents outputted by the respective transistors applied with the common input voltage substantially equals to the ratio of the sizes of the transistors.
By utilizing the current-detecting resistor
101
, the adjusting current I
2
is controlled so as not to exceed the control target value in the same way as the first conventional example. When the voltage drop across the resistor
101
is sufficiently small to be ignorable in comparison with the voltage inputted to the output transistor
1
, the current ratio I
1
/I
2
is substantially equal to the size ratio of the transistors. After all, the current I
1
is proportional to the current I
2
, and the proportional coefficient is substantially determined by the size ratio of the transistors and substantially independent of the input voltage, the temperature of the environment and the like. Accordingly, the output current I
1
can be controlled so as not to exceed an amount larger than the above-described control target amount by the inverse of the above-described ratio. In the second conventional example, since the resistor
101
is not connected in series with the output transistor
1
, the range of the output voltage can be widened in comparison with the first conventional example and, at the same time, the wasted power can be reduced.
When the voltage drop across the resistor
101
is large and not ignorable in comparison with the voltage inputted to the output transistor
1
, the voltage between gate and source (hereinafter referred to as gate voltage) of the output transistor
1
is larger than the auxiliary transistor
2
by the voltage drop across the resistor
101
. Thus, the ratio I
1
/I
2
of the output current I
1
to the adjusting current I
2
depends on not only the size ratio of transistors but also either of the voltage between source and drain or the gate voltage, and parameters such as the threshold value of the gate voltage. Accordingly, the relation between the output current I
1
and the adjusting current I
2
is, in general, non-linear. In particular, the output current I
1
tends to increase more largely than the adjusting current I
2
beyond the ratio determined by the size ratio of the transistors, and the current ratio I
1
/I
2
in the region of the large gate voltage is several times or more larger than the size ratio of the transistors.
FIG. 16A
is a diagram showing a graph representing the changes of the output current I
1
and the adjusting current I
2
with respect to the gate voltage of the output transistor
1
in the second conventional example. Here, the vertical axis of the figure is normalized in order that the difference from the proportionality may be easily seen. In fact, if the curve corresponding to the output current I
1
and the curve corresponding to the adjusting current I
2
agree with each other, the relation between the output current I
1
and the adjusting current I
2
is proportional. As shown in
FIG. 16A
, in the second conventional example, the output current I
1
and the adjusting current I
2
do not agree particularly in the region of the large gate voltage. In addition, the difference between the above-described two curves changes greatly owing to a change of the threshold value of the gate voltage caused by the temperature. Since the current ratio I
1
/I
2
changes depending on the gate voltage and the temperature in that manner, the output current I
1
varies from a predetermined value even if the adjusting current I
2
is controlled so as to be set at a predetermined control target value. Therefore, the second conventional example cannot make the control precision of the output current I
1
sufficiently high and secure sufficient reliability.
FIG. 15
shows the third conventional example of the circuit breaker. This conventional example has an output transistor
1
and a parallel-connected auxiliary transistor
2
in the same way as the second conventional example. In the third conventional example, the voltages between drain and source are different from each other between the output transistor
1
and the auxiliary transistor
2
in contrast with the second conventional example, though the gate voltages of the transistors are the same. In the output transistor
1
in particular, the voltage between drain and source tends to reduce remarkably owing to a voltage drop across the load
3
.
FIG. 16B
is a diagram showing a graph representing the changes of the output current I
1
and the adjusting current I
2
with respect to the gate voltage in the third conventional example. The vertical axis of
FIG. 16B
is normalized in the same way as FIG.
16
A. As shown in
FIG. 16B
, in the third conventional example, the output current I
1
and the adjusting current I
2
do not agree when the gate voltage is raised to a certain level. In particular, the output current I
1
shows a change to become saturated together with the increase of the gate voltage. Accordingly, the control precision of the output current I
1
cannot be made high sufficiently in the third conventional example simil

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