Radiant energy – Photocells; circuits and apparatus – Signal isolator
Reexamination Certificate
2000-01-13
2003-01-14
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Signal isolator
C257S080000
Reexamination Certificate
active
06507035
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photocoupler device integrally including a light emitting element, and an output photodetector and a monitor photodetector for receiving light emitted by the light emitting element. The present invention also relates to a fabrication method thereof.
In another aspect, the present invention relates to a lead frame for the photocoupler device.
2. Description of the Related Art
In a photocoupler device, an optical signal is transmitted from a light emitting element on a primary side to a photodetector on a secondary side while the primary side and the secondary side are electrically isolated from each other. The light emitting element and the photodetector are mounted on a lead frame, an optical path therebetween is made of a light-transmissive resin, and the optical path is covered with a light-shielding resin.
In recent years, a photocoupler device including two photodetectors, one for signal transmission and the other for monitoring, has been proposed. Specifically, an extra photodetector is provided on the primary side in order to monitor an emission output level of the light emitting element, and to feed the monitoring result back to the light emitting element. This solves the problem of nonlinearity in temperature characteristics, etc., which is specific to light emitting elements, thereby stabilizing the emission output level.
FIG. 10
is a plan view showing one example of the conventional photocoupler device.
FIG. 11
is a cross-sectional view of the photocoupler device shown in FIG.
10
. As shown in
FIGS. 10 and 11
, a light emitting element
101
is mounted on a primary side lead frame
102
a
via an electrically conductive paste or the like, and connected to a lead frame
103
for connecting a line by an Au wire
104
or the like. An output photodetector
105
is mounted on a secondary side lead frame
102
b
, and is connected to a lead frame
106
for connecting a line by an Au wire
104
or the like. A photodetector
107
for monitoring (hereinafter, referred to as “monitor photodetector
107
”) is mounted on the primary side lead frame
102
a
in the same manner as the light emitting element
101
, and connected to a lead frame
108
for connecting a line by the Au wire
104
or the like.
The light emitting element
101
, the output photodetector
105
, and the monitor photodetector
107
are placed on the same plane, and are covered with a light-transmissive resin layer
109
which is made of a transmissive potting resin such as a silicone resin. Additionally, the resultant structure is covered with a molded layer
110
made of a light-shielding resin such as an epoxy resin, in order to reflect an optical signal from the light emitting element
101
and/or block interfering stray light from outside.
FIG. 12
is a schematic circuit diagram of the photocoupler device including the light emitting element
101
, the output photodetector
105
, and the monitor photodetector
107
, which are electrically isolated from one another. Between the light emitting element
101
and the photodetector
105
, and between the light emitting element
101
and the photodetector
107
, only optical signals are transmitted.
In such a structure, upon receiving an electric signal through the lead frame
103
for connecting a line, the light emitting element
101
photoelectrically converts the electric signal to an optical signal, and emits the optical signal. The optical signal travels through the light-transmissive resin layer
109
and is reflected by the interface between the light-transmissive resin layer
109
and the molded layer
110
. The reflected optical signal reaches the output photodetector
105
and the monitor photodetector
107
. The output photodetector
105
converts the optical signal to an electric signal, and outputs the electric signal. Likewise, the monitor photodetector
107
converts the optical signal to an electric signal, and outputs the electric signal. The electric signal from the monitor photodetector
107
is fed back in order to control an emitting operation of the light emitting element
101
.
Next, prior art directed to a lead frame for a photocoupler device is described.
FIG. 17
is a circuit diagram showing a configuration example of a high-linearity analogue photocoupler device (hereinafter, simply referred to as a “linear photocoupler”). Although not shown, two devices are required for the substitution of pulse transes. Thus, a majority of linear photocoupler devices include two channels of devices in one package.
A typical linear photocoupler includes a light emitting element (LED)
202
and a monitor output element (photodiode)
203
on a primary side, and an output element (photodiode)
204
on a secondary side. In the case where a current flowing through the light emitting element
202
on the primary side is represented by IF, and photoelectric currents flowing through the monitor output element
203
and the output element
204
are represented by IPD
1
and IPD
2
, respectively, the relationships between IF, IPD
1
and IPD
2
are as follows:
IPD
1
=
IF×K
1
,
IPD
2
=
IF×K
2
.
If K
3
=K
2
/K
1
, IPD
2
=IPD
1
×K
3
. It is desirable that K
3
is as close to 1 as possible. “K3=1” is most desirable for facilitating the design of the peripheral circuits. That is, it is required to adjust the photoelectric currents flowing through the monitor output element
203
and the output element
204
to the same or substantially identical value (i.e., it is required that the elements
203
and
204
receives light from the light emitting element
202
at the same level). Furthermore, electrical insulation between the primary and secondary sides are required, which is an essential characteristic of the photocoupler device.
As described above, a typical photocoupler includes the light emitting element
202
, the monitor photodetector
203
, which is used for stabilizing the emission of the light emitting element
202
, on the primary side and the output photodetector
204
on the secondary side. In such a device, it is required that the same level of light from the light emitting element
202
is incident on each of the two photodetectors
203
and
204
, and that the primary side and the secondary side are electrically isolated from each other.
Hereinafter, an exemplary structure of the conventional linear photocoupler and an exemplary fabrication method thereof will be described with reference to
FIGS. 18A
, and
18
B,
19
, and
20
.
Referring to
FIGS. 18A
(plan view) and
18
B (cross-sectional view), a light emitting element
202
, a monitor output photodetector
203
, and an output photodetector
204
are die-bonded (adhered) onto a flat lead frame
201
. After the elements are connected to the outer leads by gold wires
205
, the elements are covered with a transparent silicone resin
206
or the like, and then transfer-molded with an epoxy resin
207
.
FIG. 19
(an example of the structure of the lead frames) and
FIG. 20
(a cross sectional view of an example of a photocoupler) show another example. In this example, lead frames
201
and
201
′ are used. A tip of the lead frame
201
is raised upward and provided with only the light emitting element
202
adhered and mounted thereon, while a tip of the lead frame
201
′ is lowered and provided with a photodetector
203
for monitoring and a photodetector
204
for output adhered and mounted thereon. Each element is wire bonded to the outer leads, respectively, as shown in the drawings. The light emitting element
202
is precoated with a transparent silicone resin
208
for relieving the stress thereof, and then positioned over the photodetector
203
for monitoring and the photodetector for output
204
so as to face the photodetectors
203
and
204
.
Thereafter, the first transfer molding process is performed with a light-transmissive epoxy resin
209
and, in addition, the second transfer molding process is performed with a light-shielding
Hasegawa Yasushi
Kusuda Kazuo
Takakura Hideya
Le Que T.
Luu Thanh X.
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