Electric power conversion systems – Current conversion – With voltage multiplication means
Reexamination Certificate
2000-03-27
2001-01-30
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
With voltage multiplication means
C307S110000
Reexamination Certificate
active
06181584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor device with an internal power supply circuit, together with a liquid crystal device and electronic equipment that use the same, and, in particular, to the prevention of erroneous operation in the event of a power supply emergency, such as when a battery is removed.
2. Description of Related Art
In a liquid crystal display device, voltages are applied to a liquid crystal that is sandwiched between substrates on which electrodes are formed, to provide a display. This type of liquid crystal display device has recently become common in various types of electronic equipment, such as personal computers, word processors, portable telephones, and electronic organizers.
Electronic equipment that has such a liquid crystal display device has countermeasures such that the screen is momentarily blanked when power is turned off in a predetermined sequence. However, a phenomenon called momentary lighting can occur if the display is ended in a different sequence such as the battery is removed abruptly when the display is being driven or the electronic equipment is forcibly terminated. This phenomenon causes a momentary blanking of the screen when the battery is removed while the display is being driven, followed by the display artifacts such as horizontal lines on the screen for a while, by way of example.
The present inventors have analyzed the causes of this momentary lighting phenomenon and have devised this invention in the light thereof.
SUMMARY OF THE INVENTION
An objective of this invention is to provide a semiconductor device with an internal power supply circuit that makes it possible to prevent erroneous operation such as momentary lighting caused in the event of a power supply emergency, together with a liquid crystal device and electronic equipment that use this semiconductor device.
According to an aspect of the present invention, there is provided a semiconductor device with a power supply circuit, wherein the power supply circuit comprises:
a booster circuit to which first and second power supply potentials are supplied from an external power source, for boosting the absolute value of a difference between the first and second power supply potentials and for charging the boosted potential in a capacitor in the booster circuit; and
a discharge circuit for causing the discharge of the potential charged into the capacitor, before the first and second power supply potentials become equal, based on a signal that becomes active in the event of a power supply emergency when the absolute value of a difference between the first and second power supply potentials falls below a predetermined value.
If, for example, the power supply fails after a battery is removed, the first and second power supply potentials supplied from the external power source become equal, at a level such as ground, after a certain time has elapsed.
Erroneous operation such as momentary lighting can occur when the time required for discharging the charge on the capacitor within the booster circuit, after the battery is removed and thus the power supply fails, is longer than the time taken until the first and second power supply potentials become equal.
This erroneous operation such as momentary lighting can be prevented by discharging the output potential of the booster circuit before the first and second power supply potentials become equal, based on a signal that becomes active in the event of the power supply emergency when the absolute value of the difference between the first and second power supply potentials falls below a predetermined value.
The booster circuit may comprise a switching circuit for turning one end of the capacitor on and off, based on a logic signal during boosting; and the discharge circuit may cause the switching circuit to be forcibly turned on in the event of the power supply emergency, regardless of the logic of the logic signal, to cause the discharge of the potential charged into the capacitor.
During the boosting, the switching circuit turns on and off a connection at one end of the capacitor, based on the logic signal. The charge on the capacitor can be discharged by forcibly turning on the switching circuit regardless of the logic of the logic signal, in the event of the power supply emergency.
The discharge circuit may comprise:
a comparator for comparing a potential of the predetermined value with a potential of the external power source; and
a logic gate circuit that controls the turning on and off of the switching circuit during a normal power supply operation, based on the logic of the logic signal, and causes the switching circuit to be forcibly turned on in the event of power supply emergency, based on the output logic of the comparator.
In this manner, it is possible to force the switching circuit on in the event of the power supply emergency, by providing the semiconductor device with an internal comparator that detects the power supply emergency and by giving precedence to the output logic of that comparator.
A power-on reset signal that becomes active in the event of the power supply emergency may be input to the discharge circuit. In this case, the discharge circuit may comprise a logic gate circuit that controls the turning on and off of the switching circuit during a normal power supply operation, based on the logic of the logic signal, and causes the switching circuit to be forcibly turned on in the event of power supply emergency, based on the logic of the power-on reset signal.
It is therefore possible to force the switching circuit on in the event of the power supply emergency, by using a power-on reset signal that is supplied from outside the semiconductor device, instead of providing a comparator within the semiconductor device as described above, and by giving precedence to the logic of that power-on reset signal.
The power supply circuit may comprise:
a potential generation circuit for generating a plurality of different potentials, based on the output potential of the booster circuit;
a drive circuit for outputting a drive potential selected from among the plurality of different potentials; and
a drive control circuit for controlling the drive circuit by controlling the selection of the drive potential from among the plurality of different potentials.
Since the absolute value of the output potential of the booster circuit falls in this case, the absolute values of the plurality of different potentials generated by the potential generation circuit also fall in a similar manner. It is therefore possible to prevent erroneous operation of the drive circuit even when the drive potential is selected from a plurality of different potentials, because there is a fall in the absolute values of all the drive potentials. Moreover, it is not necessary to discharge all of the different potentials. Discharging the potential of the booster circuit on which the different potentials depend is only required.
The drive control circuit may comprise:
a logic circuit to which the first and second power supply potentials are input, for outputting a logic signal;
a group of level shifters to which are input the first potential and an output potential from a regulator, for shifting the level of an output of the logic circuit; and
a selection signal generation circuit for generating a selection signal to be input to the drive circuit, based on an output of the group of level shifters.
In this case, it is possible to prevent erroneous operation such as momentary lighting, even in the event of the power supply emergency and the unstable output of the group of level shifters.
Other aspects of this invention relate to liquid crystal devices or items of electronic equipment that use the above described semiconductor device. Since the absolute values of drive voltages can be made to drop rapidly in such liquid crystal devices or items of electronic equipment, erroneous operation such as momentary lighting does not occur therein.
REFERENCES:
patent: 4186436 (1980-01-01), Ishiwatari
patent: 5757632
Koizumi Norio
Tsuchiya Masahiko
Oliff & Berridg,e PLC
Seiko Epson Corporation
Vu Bao Q.
Wong Peter S.
LandOfFree
Semiconductor device with internal power supply circuit,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor device with internal power supply circuit,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor device with internal power supply circuit,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2512065