Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-07-02
2004-01-06
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S076000
Reexamination Certificate
active
06674243
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an EL driving circuit, a control method and an apparatus more particularly to those having an electroluminescent element.
2. Description of the Prior Art
FIG. 6
is a circuit diagram of a conventional EL driving circuit. The EL driving circuit is arranged that an IC chip
40
applies voltage, which is supplied through a coil L and a resister R
3
by a control signal Hon from a microcomputer to be not shown, to an EL element
50
to drive (Refer to U.S. Pat. No. 4,527,096).
In the IC chip
40
, main circuits such as an oscillating circuit OSC, flip-flops FF
1
and FF
2
as a dividing circuit and a switched H-bridge circuit are provided. Terminals (PAD) of PIN
1
to
8
connecting to each circuit are also provided in the IC chip
40
.
The oscillating circuit OSC is connected to a capacitor C
3
through the PIN
7
and PIN
8
, and connected to the flip-flop FF
1
in the IC chip
40
. The oscillating circuit OSC generates a high frequency clock and outputs the clock to the flip-flop FF
1
.
The flip-flop FF
1
outputs its output to the flip-flop FF
2
and one of input terminals of an AND circuit
1
described below (hereinafter referred to as “AND
1
”).
The flip-flop FF
2
generates a low frequency clock of which the clock outputted from the flip-flop FF
1
is divided byl
6
. The flip-flop FF
2
outputs its output, as two low frequency clocks in reversal phase each other to output them to one of input terminals of an AND circuit
2
described below (hereinafter referred to as “AND
2
”) and one of input terminals of an AND circuit
3
described below (hereinafter referred to as “AND
3
”) respectively.
The switched H-bridge circuit is constituted by main elements such as ANDs
1
,
2
and
3
, transistors Tr
1
,
2
and
3
, diodes
1
to
4
and thyristors SCR
1
and
2
, and those elements are connected as described below.
Each one of input terminals of the ANDs
1
,
2
and
3
is connected to the PIN
1
respectively. The control signal Hon from the microcomputer not to be shown is connected to the PIN
1
The PIN
6
is a power supply terminal Vdd of the IC chip
40
and connected to a positive electrode vdd of a power supply such as a battery and the like. The PIN
2
is a power supply terminal GND of the IC chip
40
and connected to a negative electrode of the power supply such as the battery and the like. The PIN
2
and PIN
6
are connected to Vdd and GND in an inner circuit of the IC to supply electric power respectively. A capacitor C
2
is located outside the IC and connected to the PIN
2
and PIN
6
to operate as an electrolytic compensating capacitor.
Wiring between the other input terminals of ANDs
1
,
2
, and
3
and the PIN
1
is connected to a pull-down resister R
1
connected to the GND. An output of the AND
1
is connected to a base of the transistor Tr
1
through a capacitor C
1
and a resistor R
2
which are connected in parallel. An output of the AND
2
is connected to a base of the transistor Tr
2
, and an output of the AND
3
is connected to a base of the transistor Tr
3
.
A collector of the transistor Tr
1
is connected to the PIN
3
. Between the PIN
3
and the positive electrode Vdd of the power supply, the voltage set-up coil outside the IC is connected, strictly the resister R
3
and the coil L are connected in series. Anodes of the diodes D
1
and D
3
are connected to wiring between the transistor Tr
1
and the PIN
3
.
A cathode of the diode D
1
is connected to an anode of the thyristor SCR
1
. An gate of the thyristor SCR
1
is connected to a collector of the transistor Tr
2
. A cathode of the thyristor SCR
1
is connected to the PIN
4
and an anode of the diode D
2
. A cathode of the diode D
2
, like the gate of the thyristor SCR
1
, is connected to the collector of the transistor Tr
2
.
A cathode of the diode D
3
is connected to an anode of the thyristor SCR
2
. A gate of the thyristor SCR
2
is connected to a collector side of the transistor Tr
3
. A cathode of the thyristor SCR
2
is connected to the PIN
5
and an anode of the diode D
4
. A cathode of the diode D
4
, like the gate of the thyristor SCR
2
, is connected to the collector of the transistor Tr
3
.
Emitters of the transistors Tr
1
, Tr
2
and Tr
3
are connected to the GND respectively. The PIN
4
and PIN
5
are connected to a capacitor C
4
which is an equivalent circuit of the EL element
50
.
Operation of above described configuration of the EL driving circuit is explained below. When the EL turns on, the microcomputer not to be shown switches the signal Hon from a low state to a high state. The signal is inputted to one of inputs of the AND
1
, AND
2
and AND
3
through the PIN
1
respectively.
At this point, when the higher frequency clock signal generated by the oscillating circuit OSC is inputted to the other input terminal of the AND
1
through the flip-flop FF
1
, the transistor Tr
1
performs switching operation responsive to the clock. The transistor Tr
1
applies pulsating voltage to the diodes D
1
and D
3
through the coil L and the resister R
3
by the switching operation.
On the other hand, inputting the lower frequency clock from the flip-flop FF
2
causes the AND
2
and AND
3
to output the high state alternately, which causes the transistors Tr
2
and Tr
3
to perform the switching operation alternately.
When output from the AND
2
exists in the base of the transistor Tr
2
, the transistor Tr
2
turns on, the thyristor SCR
1
turns off, and the PIN
4
becomes almost equivalent electric potential as the GND through the diode D
2
. At this point, the transistor Tr
3
is turned off. Electric charge is being accumulated in the capacitor C
4
through the diode D
3
and the thyristor SCR
2
by the pulsating voltage. In this way, voltage generating in the capacitor C
4
is gradually approaching a saturation state.
When output from the flip-flop FF
2
is inversed, the transistor Tr
2
turns off and the transistor Tr
3
turns on. At this point, the thyristor SCR
2
turns off, and the PIN
5
becomes almost equivalent electric potential as the GND through the diode D
4
. The electric charge is being accumulated in the capacitor C
4
through the diode Dl and the thyristor SCR
1
by the pulsating voltage. The voltage generating in the capacitor C
4
is gradually approaching a saturation state.
As described above, polarity of voltage applied to the capacitor C
4
is switched alternately and the voltage is continuously supplied to the capacitor C
4
, which permits high voltage to be supplied to the EL element
50
.
FIG. 7
is a timing chart of an EL driving circuit. The timing chart shows timing of relationship between voltage and time. When the signal Hon inputted from the PIN
1
to the IC chip
40
is turned on, the timing chart shows appearance that, in case that the clock (CLOCK) outputted from the oscillating circuit OSC to the flip-flop FF
1
is supplied to the switched H-bridge circuit, responsive to the clock from the flip-flop FF
2
not to be shown in
FIG. 7
, voltage (EL
1
) of the PIN
5
and voltage (EL
2
) of the PIN
4
are alternately set-upped to be supplied to the capacitor C
4
.
However, in the above described conventional EL driving circuit, when the EL element is turned off, the microcomputer switches the signal Hon from a high state to a low state at the timing (duration X shown in
FIG. 7
) when the polarity of the voltage applied to the capacitor of the EL device is reversed, which causes the transistor (Tr
1
) to be turned off, thus creating the counter electromotive force Vcoil
1
in the PIN
3
. A problem is that, when the Vcoil
1
exceeds a rating Vces of the transistor (Tr
1
), the transistor (Tr
1
) to be turned off turns on, which causes noise such as power supply fluctuation and the like to be created.
Particularly, the noise is created from the coil as electromagnetic wave, the microcomputer is sometimes reset by error due to the electromagnetic wave, consequently there exerts a problem that the noise causes operation of the microcomputer to be unstable. For example, t
A Minh D
Adams & Wilks
Seiko Instruments Inc.
Wong Don
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