Discharge lamp lighting circuit

Details Discharge lamp lighting circuit Discharge lamp lighting circuit

2001-12-06

2003-06-24

Clinger, James (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

C315S119000

Reexamination Certificate

active

06583585

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a technique for preventing a starting pulse from being supplied to a discharge lamp in a state in which the discharge lamp is not surely connected to a socket and also simplifying a circuit configuration therefor.
Recently, a small-size discharge lamp (metal halide lamp etc.) has received attention as a light source substituting for an incandescent lamp and, for example, as a configuration of a lighting circuit in the case of being applied to a light source of a lamp for vehicle, the lighting circuit comprising a DC power source, a power source part (switching power source circuit), a DC-AC conversion circuit and a starting circuit has been known.
On starting a discharge lamp, a starter transformer is required as a circuit for generating a starting pulse with high voltage, and a primary side circuit including a primary winding of the transformer is provided with a capacitor for accumulating an electric charge and a switch element for discharging this electric charge. Incidentally, as the switch element, a separately excited type configuration for receiving a signal from another circuit to control the conduction timing as a thyristor element and a self-excited type configuration for conducting at the time when a voltage across an element becomes a defined value as typified by a self-breakdown type element such as a spark gap element have been known.
By the way, with regard to selection of any of the two kinds of the switch elements, it is related to a form of a lighting control circuit (ballast circuit) and a starting circuit (starter circuit) of the discharge lamp. For example, when both the circuits are mounted on the same circuit board without a cord and are housed in one case, any of the two kinds of the switch elements may be used, but when both the circuits are arranged at a distant place and are wired by a cord, the self-excited type configuration becomes advantageous. The reason is because in the separately excited type configuration, disturbance noise is superimposed on a control signal for turning on or off the switch element and a malfunction of the switch element is feared. Also, with regard to wiring, in the separately excited type configuration, a signal line is required for electric charge supply of a primary side capacitor and control of a switch element in addition to two power supply lines.
In recent years, miniaturization of starter circuit components has developed and, for example, a form of integrating the starter circuit with the discharge lamp or a form of holding the starter circuit within a valve socket for discharge lamp connection has been used in application to a discharge lamp for vehicle. That is, the starter circuit tends to be arranged immediately near to the discharge lamp and be located at a place distant from the ballast circuit and thus, the self-excited type configuration using the self-breakdown type element is in the mainstream and there is no trouble of a malfunction and also, there is a cost merit in which two wirings of connection between the ballast circuit and the starter circuit will do.
FIG. 7
shows only the main part in a conventional configuration example, and shows a configuration of an output stage of a ballast circuit of a lighting circuit A and a starter circuit.
In a transformer C constructing a starter circuit B, one end of a secondary winding c
2
of the transformer is connected to a power supply terminal ta
1
and the other end is connected to an output terminal to. Also, in a primary winding c
1
of the transformer C, one end of the primary winding is connected to an electric charge supply source D within a ballast circuit and a spark gap element E is connected to the other end side which is connected to the electric charge supply source d through the element. Incidentally, a capacitor F is interposed between connection terminals of a primary side circuit of the transformer C and the electric charge supply source D.
The other terminal ta
2
of a pair of power supply terminals ta
1
, ta
2
is connected to an output terminal to′ and connections between the terminal and the output terminal to and a discharge lamp G are made through a connecting member H such as a socket (for example, a base part of the discharge lamp is fitted and coupled to the socket and each the terminal to, to′ is individually connected to each electrode terminal of the discharge lamp G, respectively).
The present circuit is formed into a configuration of a four-terminal connection in the case of electrical connections between the ballast circuit and the starter circuit, but as a circuit in which this is formed into a configuration of a three-terminal connection, a configuration example shown in
FIG. 8
is given.
In a lighting circuit A′, one end of a primary winding c
1
of a transformer C and one end of a secondary winding c
2
are connected to a power supply terminal ta
1
and also are connected to one end of a capacitor F. As a result of this, connection terminals of a ballast circuit and a starting circuit B can be reduced by one (incidentally, in the present example, a reference potential of an electric charge supply source D is grounded, but the grounding may be performed anywhere as long as a feeding path to the capacitor F can be formed).
By the way, since a starting pulse supplied to a discharge lamp is a high voltage, it is necessary to take measures against the case of turning on a lighting switch in a state in which the discharge lamp is not connected to a lighting circuit. This is because, for example, a breakdown may be caused when a high voltage is applied to a connection terminal within a valve socket and this state is left for a long time, or an operator may accidentally touch a connection terminal of a socket to trigger an electric shock accident when replacement operations of the discharge lamp are performed with forgetting that there is in a state of turning on the lighting switch.
Hence, there is considered a method constructed so that a feeding path for accumulating an electric charge in a capacitor within a starter circuit is formed when a discharge lamp has been connected using high voltage connection means (a valve socket etc.) and the feeding path is not formed when the discharge lamp has been disconnected from the high voltage connection means.
FIG.
9
and
FIG. 10
show a main part of such a configuration example, and both the figures are based on the circuit example of FIG.
8
.
Differences between a circuit example I shown in FIG.
9
and the circuit of
FIG. 8
in the configuration are as follows.
A valve socket J is interposed between a lighting circuit and a discharge lamp G, and three terminals k
1
, k
2
, k
3
are provided within the socket J.
Three terminals g
1
, g
2
, g
3
are provided in a connection part (base part) of the discharge lamp G to the valve socket J, and the terminals g
1
, g
2
of the three terminals are respectively connected to each electrode terminal of the discharge lamp G and the terminal g
3
is connected to the terminal g
2
.
In a state in which the discharge lamp G is connected to the valve socket J, the terminal g
1
is connected to the terminal k
1
and the terminal k
2
is connected to the terminal g
2
.
With respect to an electric charge supply source D, one end of the electric charge supply source D is connected to a connection point of a spark gap element E and a capacitor F and the other end is connected to the terminal k
3
.
In a state in which the discharge lamp G is connected to the valve socket J, the terminal k
2
is connected to the terminal k
3
and both the terminals are connected to a power supply terminal ta
2
.
Thus, in the present circuit I, when the discharge lamp G is disconnected from the valve socket J and the terminals k
2
and k
3
become a non-connection state, a feeding path to the capacitor F is not formed, so that generation of a starting pulse is prohibited.
Also, differences between a circuit example L shown in FIG.
10
and the circuit of
FIG. 8
in the configuration are as follo

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