Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2003-02-11
2004-06-08
Vo, Tuyet T. (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S307000, C315S279000
Reexamination Certificate
active
06747421
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to self oscillation circuits, for use in inverters for driving cold cathode lamps and the like.
2. Description of the Related Art
In order to light up backlights of televisions, notebook computers, desktop computers, PDAs and the like using liquid crystal display devices, inverters of high tension AC output are required. The inverters of this kind have been used from discrete construction type, but ICs of exclusive type have been desired to be employed from among light, thin, short and small size type ICs.
FIG. 11
shows a self oscillation circuit in a conventional Loyer system. In such a self oscillation circuit, in order to self oscillation, an F winding
4
(normally, it is called a detection winding or feedback winding) is provided for detection of resonance frequency in a winding type transformer, and with its signal, transistors
6
and
8
are driven with its own oscillation frequency, namely, resonance frequency type transformer
2
, whereby the oscillation continues while always automatically tracking to the resonance frequency of winding type transformer
2
.
Furthermore, in U.S. Pat. Ser. No. 6,316,881 and U.S. Pat. Ser. No. 6,259,615, self oscillation circuits are disclosed where a plurality of switch networks are controlled of their make and break according to resonance oscillation at a secondary side of a tank circuit and a DC signal is converted to an AC signal.
The ICs of this kind, which are recently in the market, are of separate excitation system without exception. For this reason, the present situation is such that a deterioration of efficiency due to changes, such as ambient environment temperature and the like, because of such system, and a total evaluation bring about undesired results. Now, the reason for employing the separate excitation system results from giving a priority to the installation rather than merely to the performance. Namely, for the elimination of a feedback winding that detects resonance frequency of the transformer, as well as the convenience of keeping a creeping distance between a high tension portion and a low tension portion in a case of laying out a substrate with the transformer having input
2
terminals and output
2
terminals. Under the circumstances, if the self commutation system can be materialized by using a transformer without the feedback winding, it is not subjected to environment temperature, and the oscillation frequency always are automatically tracks to the resonance frequency of the transformer; it is constantly driven at optimum efficiency; and also its layout can be easily arranged on account of the absence of the feedback winding when component parts are arranged in the circuit.
However, in the self oscillation circuit eliminating the feedback winding that is employed in the winding type transformer, a system of detecting a resonance frequency from the secondary side of the winding type is generally employed. For this reason, there is a need for increasing the number of windings at the secondary side in order to generate a required voltage at the secondary side of the winding type since high resonance voltage is not generated at the primary side, and which results in a large size winding type transformer and at the same time, increases cost and deteriorates efficiency, which are problems.
A primary object of the present invention is to provide a self oscillation circuit that has a high efficiency with stability.
Furthermore, another object of the present invention is to operate the transformer efficiently by producing it in smaller size in the self oscillation circuit using the transformer.
SUMMARY OF THE INVENTION
The present, invention is constructed in such a way that, a drive circuit is connected to a transformer having a resonance circuit at its primary side. In the drive circuit, a switching circuit for turning on and off the DC voltage is provided in the drive circuit. In the drive circuit, the switching circuit is turned on and off on the basis of a feedback signal of resonance voltage at the primary side induced in the primary winding at an input side of the transformer, a direction of flowing electric current to the transformer is converted to a clockwise direction or a counter-clockwise direction, and is input, as an AC signal to the primary winding at the input side of the transformer. A phase detecting means detects a phase of a resonance wave form at the primary side of a winding type transformer and outputs a phase signal. A control circuit connected to the drive circuit outputs a drive signal that controls the switching circuit by on-off manner on the basis of the output signal of the phase detecting means.
REFERENCES:
patent: 6259615 (2001-07-01), Lin
patent: 6292339 (2001-09-01), Brooks
patent: 6316881 (2001-11-01), Shannon et al.
patent: 6326740 (2001-12-01), Chang et al.
patent: 6509700 (2003-01-01), Nakatsuka et al.
patent: 6515427 (2003-02-01), Oura et al.
Vo Tuyet T.
Wenderoth , Lind & Ponack, L.L.P.
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