Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2001-08-13
2003-06-10
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S551000, C327S514000
Reexamination Certificate
active
06576885
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a charging/discharging circuit with fast operation, especially to a charging/discharging circuit using a negative reference voltage to speed up operation.
BACKGROUND OF THE INVENTION
The conventional charging/discharging circuit can be implemented by semiconductor switching elements. For example, the U.S. Pat. No. 4,754,175 “Solid state relay having a thyristor discharge circuit” by Kobayashi et al. discloses a charging/discharging circuit composed of a plurality of diodes and resistor. The resistor with larger resistance can suppress leakage current during charging operation. However, the response time of discharging operation is degraded due to reduction of discharging current. On the contrary, the resistor with smaller resistance can accelerate discharging operation, while the charging operation is degraded due to large leakage current. Therefore, the resistance is a trade off factor in charging/discharging circuit design.
Moreover, the charging/discharging circuit disclosed in above-mentioned patent comprises undue number of electronic elements; the process thereof is cumbersome. The conventional charging/discharging circuit generally uses ground level as lowest reference level for discharging operation. The response time of the discharging operation thereof is not satisfactory.
As shown in
FIG. 1
, another prior art charging/discharging circuit is the U.S. Pat. No. 4,931,656 “Means to dynamically discharge a capacitively charged electrical device” by Ehalt et al. This patent discloses a charging/discharging circuit composed of a resistor
40
, an NPN transistor
44
and a photodiode
42
. The photodiode
42
is used as switch element of the NPN transistor
44
for charging/discharging operation.
When the LED array
20
is driven to emit light, the photodiode array
30
receives the light and conducts a charging current flowing to an energy-storing element (a FET shown in this figure)
50
along a path C
1
indicated by a dashed arrow shown at top of this figure. Most of the charging current then flows to the energy-storing element
50
along a path C
2
due to the isolation provided by the resistive circuit
40
. At the same time, the photodiode
42
also generates a photo current in response to the light of the LED array
20
. The photo current of the photodiode
42
flows the emitter E of the NPN transistor
44
along a path C
3
. The NPN transistor
44
is cut off whereby the charging current is not leaked through the NPN transistor
44
and can rapidly charge the energy-storing element
50
.
During the discharging stage of this charging/discharging circuit, the photodiode
42
does not receive light sufficient to conduct a photo current, part of the discharging current from the energy-storing element
50
flows to the base B of the NPN transistor
44
through a resistor
46
and along the path D
3
. Therefore, the NPN transistor
44
is turned on or saturated to conduct most of discharging current along paths D
1
and D
2
.
However, in above-mentioned charging/discharging circuit, a resistive element
46
is still present, which imposes a dilemma to circuit design. Moreover, the above-mentioned charging/discharging circuit also uses ground level as lowest reference level for discharging operation. The response time of the discharging operation thereof is not satisfactory.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a charging/discharging circuit with fast operation
In one aspect of the present invention, the charging/discharging circuit has an energy-storing element such as a capacitor on a discharging path thereof. During the charging stage, the capacitor is charged by a photodiode and establishes a negative reference voltage. The negative reference voltage can speed up discharging operation.
In one aspect of the present invention, the charging/discharging circuit uses transistors and diodes to replace resistive elements and the drawbacks caused by the resistive elements can be prevented.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which:
REFERENCES:
patent: 4754175 (1988-06-01), Kobayashi et al.
patent: 4931656 (1990-06-01), Ehalt et al.
Allen Stephone B.
Opto Tech Corporation
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