Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-06-20
2003-01-07
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S082000
Reexamination Certificate
active
06504309
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a driver circuit for a self-scanning light-emitting element array, more particularly to a driver circuit without using current sources. The present invention further relates to a self-scanning light-emitting element array using such driver circuit.
BACKGROUND ART
A light-emitting element array in which a plurality of light-emitting elements are arrayed on the same substrate is utilized as a light source of a printer, in combination with a driver circuit. The inventors of the present invention have interested in a three-terminal light-emitting thyristor having a pnpn-structure as a component of the light-emitting element array, and have already filed several patent applications (for example, Japanese Patent Publication Nos. 1-238962, 2-14584, 2-92650, and 2-92651.) These publications have disclosed that a self-scanning function for light-emitting elements may be implemented, and further have disclosed that such self-scanning light-emitting element array has a simple and compact structure for a light source of a printer, and has smaller arranging pitch of light-emitting elements.
When such a self-scanning light-emitting element array is utilized for a printer, the light emission by the elements due to a transfer operation is not desirable. Then, a self-scanning light-emitting element array has proposed, which can be escaped from the effect of light emission due to the transfer operation (see Japanese Patent Publication No. 2-263668). According to this self-scanning light-emitting array, a shift portion for a transfer function and a light-emitting portion for a light-emitting function are separated and the light-emitting thyristors are used in both portions, and the light emission of the thyristors of the shift portion is shielded by covering the thyristors by metal or the like.
Alternatively, the light output during a transfer operation may be sufficiently suppressed by using a light-emitting thyristor having a characteristic such that the light output is small in a low current area as shown in an example of I-L characteristic of FIG.
1
. In the figure, an abscissa designates a current (mA) and an ordinate a light output (&mgr;W), and an arrow A shows a light emission during a transfer operation (hereinafter referred to as a transfer light-emission) and an arrow B a light emission during a write operation (hereinafter referred to as a write light-emission).
In such a case, it is unnecessary that the shift portion and light-emitting portion are separated, and a light-emitting element array serving as both the shift and light-emitting portions may be used for a light source of a printer.
In such self-scanning light-emitting element array, two kinds of currents, i.e. a current I
t
required for the transfer operation (hereinafter referred to as a transfer current) and a current I
w
required for the write operation (hereinafter referred to as a write current).
Referring to
FIG. 2
, there is shown an equivalent circuit diagram of a conventional self-scanning light-emitting element array to which the transfer current I
t
and writing current I
w
are applied. This self-scanning light-emitting element array is a two-phase (&phgr;
1
and &phgr;
2
) driving type. In
FIG. 2
, T
1
, T
2
, T
3
, . . . designate light-emitting thyristors, D
1
, D
2
, D
3
, . . . coupling diodes, and R
1
, R
2
, R
3
, . . . gate load resistors. Each cathode of thyristors is connected a substrate electrode, each anode of odd-numbered thyristors T
1
, T
3
, . . . is connected to a clock pulse &phgr;
1
line
11
, and each anode of even-numbered thyristors T
2
, T
4
, . . . is connected to a clock pulse &phgr;
2
line
12
. Each gate of thyristors is connected to a power supply V
GK
line
14
via the load resistors R
1
, R
2
, R
3
, . . . respectively, and neighboring gate electrodes are connected to each other via the diode D
1
, D
2
, D
3
, . . . , respectively. Each of lines
11
,
12
and
14
is connected to a driver circuit
62
via terminals
21
,
22
and
24
. The gate of light-emitting thyristor T
1
is connected to a start pulse &phgr;
s
terminal
23
.
In
FIG. 2
, reference numeral
10
designates the part integrated as a self-scanning light-emitting element array chip. The driver circuit
62
is added to the chip
10
externally.
The terminals
21
,
22
and
23
of the chip
10
are connected to pulse voltage sources
51
,
52
and
53
via current limiting resistors
41
,
42
and
43
, respectively, and the terminal
24
is connected to a voltage source
60
. A pulse current source
31
is connected in parallel with the series circuit of the resistor
41
and the pulse voltage source
51
, and a pulse current source
32
is connected in parallel with the series circuit of the resistor
42
and the pulse voltage source
52
.
In the self-scanning light-emitting element array having the structure described above, the transfer current I
t
is generated by the resistors
41
,
42
and the pulse voltage sources
51
,
52
. In order to cause a desired thyristor to be in a write light-emission condition, the thyristor is turned on by a transfer operation and the required write current I
w
is applied thereto by the pulse current sources
31
or
33
.
FIG. 3
shows the wave shapes of the voltages generated by the pulse voltage sources and the currents generated by the current sources, and the conditions of the transfer light-emission and write light-emission of the thyristors. “V (numeral)” designates the voltage generated by the pulse voltage source referenced by the numeral in parentheses, “i (numeral)” the current generated by the pulse current source referenced by the numeral in parentheses, and “L(T
n
)” the light output of the n-th thyristor T
n
.
The light-emitting thyristors T
1
is turned on, when the pulse voltage v (
53
) of the voltage source
53
for the start pulse is at L (Low) level, and the pulse voltage v(
51
) of the voltage source
51
for the clock pulse &phgr;
1
is at H (High) level. In the wave shape of the light output L(T
1
), “a” designates the light output level of transfer light-emission, and “b” the light output level of write light-emission.
As described above, the on-state of the light-emitting thyristors is transferred by the repetition of the two-phase clock pulses &phgr;
1
and &phgr;
2
after the thyristor T
1
is turned on. The turned-on thyristor emits the light, but the light output thereof is extremely small. The write currents i(
31
) or i(
32
) is applied to the thyristor from the pulse current sources
31
or
32
in order to cause the thyristor to be in a write light-emission condition.
According to the conventional self-scanning light-emitting element array described above, there is a problem such that the pulse current source has a complicated circuit and a characteristic which varies widely.
Also, the turned-on thyristor T
5
, for example, is in “no-writing stage” in
FIG. 3
, but a current is flowed via the thyristor T
5
to hold it on-state, so that the thyristor emits the light slightly. The light-emission in “no writing” state causes a noise, so that its light output is desirable as small as possible. In order to decrease its light output, each resistance of the resistors
41
and
42
which determines the magnitude of the transfer current I
t
is required to be enlarged. However, the problem is caused in that the increase of the resistance make the speed of the transfer operation slow.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a driver circuit which can realize the same structure as a pulse current source in a simple circuit.
Another object of the present invention is to provide a driver circuit which has a function such that a light output may be decreased without lowering the speed of a transfer operation in “no-writing” state.
Further object of the present invention is to provide a self-scanning light-emitting element array which comprises such driver circuit.
A drive circuit according to the present invention is for a self-scanning light-emitting elem
Lee Wilson
Nippon Sheet Glass Co. Ltd.
RatnerPrestia
Wong Don
LandOfFree
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