Electric heating – Heating devices – With protective means for heater
Reexamination Certificate
1998-11-17
2001-02-20
Paschall, Mark (Department: 3742)
Electric heating
Heating devices
With protective means for heater
C219S492000, C219S497000, C361S035000
Reexamination Certificate
active
06191396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to heater abnormality detecting circuits, and more particularly to a CRT heater abnormality detecting circuit used, for example, for television receivers, display units and so on.
2. Description of the Prior Art
In a conventional heater abnormality detecting circuit
1
shown in
FIG. 3
, normality or abnormality is determined based on a level of a bias voltage detected by a micro-computer
2
. That is, if the heater
3
is normal, a fly back pulse (FB pulse) extracted on a heater winding
4
is supplied to the heater
3
through a heater register R
1
, and also rectified by a diode D
1
so that a voltage taken by an electrolytic capacitor C
1
is voltage-divided by resistors R
2
and R
3
. Accordingly, an electric current flows through the resistor R
3
and a diode D
2
is turned on, thereby causing a bias current flowing through the resistor R
3
. That is, there is a decrease in level of a bias voltage detected by the micro-computer
2
.
On the other hand, in the event that the heater be short circuited, an FB pulse extracted on the heater winding
4
is supplied to the heater resistor R
1
, and also to a ground through the short-circuited heater
3
. Due to this, the diode D
2
will not turn on with a result that the micro-computer
2
detects a bias voltage that is dropped in voltage from a bias B through a resistor R
4
. Accordingly, the bias voltage is higher in level as compared with the case that the heater
3
is normal.
In this prior art, however, the FB pulse is rectified by the diode D
1
so that a voltage taken by electrolytic capacitor C
1
is voltage-divided by the resistors R
2
and R
3
. Also, the diode D
2
is provided in order to prevent a bias current from flowing into the micro-computer
2
(prevention against reverse current flow). Thus there is a necessity to provide an element to extract as a voltage an FB pulse, an element to prevent against current reverse flow, and so on Thus, the number of parts required is increased, resulting in mounting up of cost.
Furthermore, the electrolytic capacitor C
1
and the resistor R
2
might form a CR circuit. Due to a presence of a time constant of this CR circuit, the determination of normality or abnormality on the heater
3
is delayed by several msecs. Thus there is a disadvantage that there is delay in detecting an abnormality in the heater
3
resulting in possible smoking from the heater resistor R
1
.
SUMMARY OF THE INVENTION
Therefore, it is a primary object of the present invention to provide a novel heater abnormality detecting circuit.
It is another object of the present invention to provide at low cost a heater abnormality detecting circuit which can rapidly detect an abnormality.
An abnormality detecting circuit according to the present invention, comprises: a fly back pulse extracting means for extracting a fly back pulse out of heater winding of a fly back transformer; and a detecting means to be inputted with the fly back pulse extracted by the extracting means, the extracting means determining whether or not the fly back pulse has been inputted in a predetermined time period.
In a preferred embodiment, the fly back pulse extracting means includes a resistor means connected in series to the heater winding. The fly back pulse extracting means includes level reducing means for reducing in voltage level the fly back pulse outputted from the resistor means, and the detecting means receiving the fly back pulse reduced in voltage level from the level reducing means.
The level reducing means includes, concretely, a voltage-dividing means including a first resistor having one end directly connected to one end of the resistor means and the other end, and a second resistor having one end connecting to the other end of the first resistor and the other end connected to a reference potential, whereby the fly back pulse is supplied from connection point between the first resistor and the second resistor to the detecting means.
The fly back pulse, extracted through the heater winding of the fly back transformer (FBT) by the fly back extracting means, is supplied to the heater and also to the detecting means. The fly back pulse is preferably given to the detecting means through the level reducing means, such as a voltage-dividing means (voltage-dividing resistor). The detecting means is, for example, a micro-computer. The micro-computer determined as to whether or not a level-reduced fly back pulse is inputted in a predetermined time period. The fly back pulse, when the heater is normal, is inputted for example every 63 micro-seconds. If there is an abnormality such as short circuit in the heater, no fly back pulse is inputted to the detecting means. It is therefore possible to detect heater abnormality by detecting a time period that a fly back pulse is inputted.
According to the present invention, the number of component parts is reduced as compared with that of the conventional, and hence cheap in cost. Also, because no time constant circuit is included, detection of abnormality is rapidly made.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3774069 (1973-11-01), Yasumatsuya
patent: 4281372 (1981-07-01), Kornrumpf
patent: 4814878 (1989-03-01), Kishi et al.
patent: 5708254 (1998-01-01), Ikegami et al.
Funai Electric Co. Ltd.
Paschall Mark
LandOfFree
Heater abnormality detecting 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 Heater abnormality detecting circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heater abnormality detecting circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2606843