Electric lamp and discharge devices: systems – Condenser in the supply circuit – Condenser in shunt to the load device and the supply
Reexamination Certificate
2001-04-24
2003-01-21
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Condenser in the supply circuit
Condenser in shunt to the load device and the supply
C315S24100S, C396S206000
Reexamination Certificate
active
06509695
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flash apparatus for photography or the like, and to a camera having the flash apparatus.
2. Description of Related Art
A conventional flash apparatus will be schematically explained as to its arrangement and operation with reference to
FIGS. 4 and 5
.
FIG. 4
is a circuit diagram showing the arrangement of the conventional flash apparatus.
FIG. 5
is a flowchart showing the operation of the conventional flash apparatus in a flash mode.
First, a control circuit (not shown) operates a charge inhibition timer for interrupting an operation for charging a main capacitor
21
(step S
401
). Next, the control circuit applies an H level signal through a terminal a to start oscillation and further applies an L level signal (pulse signal) to a terminal b (step S
402
).
The H level signal applied to the terminal a acts as the base current of a transistor
9
through a resistor
6
, which makes the transistor
9
conductive. As a result, one input terminal of a NOR circuit
12
, which has been pulled up by an auxiliary power source Vcc
23
through a resistor
7
, becomes an L level. In contrast, since the terminal b is momentarily set to an L level, the other end of the NOR circuit
12
also becomes an L level. With this operation, the output of the NOR circuit
12
becomes an H level, and potential is applied to a resistor
15
.
Since this potential is connected to the gate terminal of an FET
14
, the FET
14
is conducted by receiving a gate driving voltage. The conduction of the FET
14
causes a current to flow from a battery
1
to the primary winding P of an oscillation transformer
13
. Thus, an electromotive force is induced in the secondary winding S of the oscillation transformer
13
so that a current flows through a loop composed of a high voltage rectifying diode
17
, a main capacitor
21
, and a rectifying element
16
.
Since the cathode potential of the rectifying element
16
is lower than the anode potential thereof by about 0.7 V, a current flows from the auxiliary power source Vcc
23
through resistors
10
and
11
. With this operation, since potential connected to a midpoint between the resistors
10
and
11
becomes an L level, the L level can be maintained even after the terminal b momentarily becomes the L level.
When the conduction of the FET
14
is continued and the magnetic flux of the core of the oscillation transformer
13
is saturated, a counter electromotive force is generated and the current charged in the main capacitor
21
is exhausted as well as no current flows from the auxiliary power source Vcc
23
to the resistors
10
and
11
, which sets one input terminal of the NOR circuit
12
to an H level so that the output from the NOR circuit
12
becomes an L level.
When the output from the NOR circuit
12
becomes the L level, the gate charge of the FET
14
becomes an L level, which makes the FET
14
non-conductive momentarily. While the counter electromotive force is generated by receiving a reverse bias due to the capacitance of the high voltage rectifying diode
17
, potential higher than that of the auxiliary power source Vcc
23
is generated to the cathode of the rectifying element
16
.
When the magnetic flux of the core is reduced and the counter electromotive force is reversed to a forward oscillation voltage, the rectifying element
16
receives a bias voltage again and the cathode potential thereof is reduced, whereby a current flows from the auxiliary power source
23
to the resistor
11
through the resistor
10
and the input terminal of the NOR circuit
12
becomes an L level, which conducts the FET
14
again.
Oscillation is executed by repeating the above actions so that the voltage charged in the main capacitor
21
is increased.
While the main capacitor
21
is charged, the control circuit causes a voltage detecting circuit
18
to output the information of the voltage charged in the main capacitor
21
through a terminal d and determines whether or not the charged voltage has reached a predetermined charge completion voltage (step S
403
).
When the voltage charged in the main capacitor
21
has reached the predetermined charge completion voltage, the control circuit interrupts the charging operation of the main capacitor
21
by stopping the H level signal outputted through the terminal a (step S
405
). Next, the control circuit completes the charging operation by setting a charge completion flag (step S
406
).
Otherwise, when the voltage charged in the main capacitor
21
has not reached the charge completion voltage, the control circuit determines whether or not the above-mentioned charge inhibition timer has reached a predetermined count completion value (step S
404
). When the charge inhibition timer has not reached the predetermined charge completion value, the control circuit returns to step S
403
, whereas when the charge inhibition timer has reached the predetermined charge completion value, the control circuit interrupts the charging operation of the main capacitor
21
by stopping the H level signal outputted through the terminal a (step S
407
). Next, the control circuit completes the charging operation by setting a charge NG flag indicating the charge NG (step S
408
).
However, as the voltage of the battery drops, a power source voltage compensating circuit temporarily stops the oscillating operation of an oscillation circuit temporarily. As a result, a secondary current is reduced. Further, when the power source voltage compensating circuit stops the oscillating operation just before the oscillation transformer is saturated, the secondary current is more reduced. As a result, there is a possibility that the oscillating operation of the voltage boosting circuit is perfectly stopped.
Further, the conventional flash apparatus measures the voltage charged in the main capacitor every time a predetermined time passes and detects a problem in an charging operation from a result of the measurement. However, the conventional flash apparatus cannot detect abnormal states, for example, discharge of a large current due to short-circuit of the main capacitor, breakage of a charged voltage detection wiring, a voltage excessively charged in the main capacitor, and the like at an early time.
An object according to a first aspect of the invention is to provide a flash apparatus capable of detecting the operating state of a voltage boosting circuit at an early time and controlling the operation of the voltage boosting circuit according to the operating state and to provide a camera having the flash apparatus.
Further, the conventional flash apparatus ordinarily emits a discharge tube to illuminate, for example, a subject in such a manner that the voltage of a battery is increased using a bipolar transistor as an oscillation transistor, a charge having an increased voltage is accumulated in a main capacitor and discharged through the discharge tube.
Since the bipolar transistor has a low operating voltage and a present DC/DC converter is of a current feedback type, it is possible to flow the current charged in the main capacitor through a loop between the base and emitter of the oscillation transistor. Thus, there is an advantage that the number of parts can be considerably reduced.
However, as the sizes of cameras become smaller, the number of batteries used thereby is reduced, and, at present, cameras employ 3 V power sources in many cases, while they conventionally employed 6 V power sources.
Further, recent compact cameras are required to have large guide numbers to be provided with a zoom function and to expand a photographing region.
Therefore, bipolar transistors used for oscillation are required to have such a performance that they have higher hEF, a lower saturated voltage VCE (sat) between an emitter and a collector and further a larger current-carrying capacity. Accordingly, at present, bipolar transistors, which can satisfy these requirements, are limited.
In contrast with these bipolar transistors, FETs acting as insulated gat
Ichimasa Shoji
Odaka Yukio
Canon Kabushiki Kaisha
Robin Blecker & Daley
Vu David
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