Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2000-12-07
2002-08-20
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S244000, C315S276000
Reexamination Certificate
active
06437521
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an electronic control circuit for adjusting the control voltage of a device to be controlled, the control circuit comprising a primary coil, a control bus comprising a first secondary coil, a first control diode, a first capacitor and means for adjusting the control voltage, the means being parallel-connected with the first capacitor, the parallel connection being further series-connected with the first secondary coil and the first control diode, and a control voltage supply circuit comprising a series-connected second secondary coil, a second control diode and a second capacitor.
In the present specification, the term diode refers to any electronic component conducting current in one direction only and providing a diode-like effect. It is obvious to a person skilled in the art that this can be implemented by a transistor, for example. In the same way, in the present specification, the term capacitor refers to any capacitive element which is electrically chargeable in the same way as a capacitor.
BACKGROUND OF THE INVENTION
Electronic control loops and circuits commonly employ a separate control unit which often requires galvanic separation from the equipment to be controlled. Galvanic separation enables a sufficient electric separation between different electronic circuits and yet at the same time transmits a voltage signal from one electronic circuit to another. Galvanic separation is implemented by either optical or magnetic components.
The use of a 1 to 10 volt direct-current voltage as the control voltage has become more common in many electronic control circuits, particularly in lighting control systems. In this case a 10 V control voltage creates a maximum light level and a 1 V control voltage a minimum light level. Minimum and maximum light levels can preferably be freely selected and adjusting the control voltage allows the light level to be changed steplessly between minimum and maximum values. Usually the operating voltage of a control unit is directly supplied from the power source of the device to be controlled, the power source supplying current to the control unit via a control bus. This solution enables a simple implementation for a control unit, whereby the control unit does not necessarily require external operating voltage. Such a control principle is commonly used for example in adjusting electronic connectors in fluorescent lamps, phase angle controllers and electronic halogen and neon lamp transformers.
A control circuit is often implemented by the connection shown in FIG.
1
. The connection comprises a control transformer T
1
having three coils N
1
, N
2
and N
3
. N
1
is the primary coil of the transformer, N
2
the secondary coil of a control bus
1
and N
3
the secondary coil of a device to be controlled. The control bus
1
further comprises a diode D
1
, a adjustable zener diode Z
1
and a capacitor C
1
. The diode D
1
is series-connected with the secondary coil N
2
of the control bus
1
. The zener diode Z
1
and the capacitor C
1
are parallel-connected, the paralleling, in turn, being series-connected with the secondary coil N
2
of the control bus
1
and the diode D
1
. In a control voltage supply circuit
2
, the secondary coil N
3
of the device to be controlled is series-connected with the diode D
2
and the capacitor C
2
. A switch K
1
is coupled to the primary coil N
1
of the transformer, and opened and closed under the control of a control block A. The operation of the control block A is known per se to a person skilled in the art, and does not need to be discussed in any greater detail herein.
The connection of the control circuit is what is known as a forced flyback connection. As the control block A closes the switch K
1
, a magnetization current starts to flow in the primary coil N
1
of the transformer T
1
. The magnitude of the magnetization current varies substantially between 5 and 100 mA. The operating current of the control block A is typically between 3 and 5 mA. The coiling directions of the coils in the transformer T
1
are so selected that the ends of the secondary coils N
2
and N
3
on the side of the diodes D
1
and D
2
are negative when the magnetization current is flowing, whereby no current flows in the secondary coils N
2
and N
3
. The level of the control voltage is controlled by an adjustable zener diode Z
1
. When the control block A opens the switch K
1
, the magnetization energy stored in the ferrite of the transformer T
1
causes a current in the secondary coils N
2
and N
3
charging the capacitors C
1
and C
2
. The magnitude of the voltage U
c
over the capacitor C
1
is adjusted by the zener diode Z
1
. In this case, provided the secondary coils N
2
and N
3
have an identical number of turns, the control voltage U
e
of the device to be controlled is equal to the voltage U
c
, i.e. U
e
=U
c
. This way the voltage level, adjusted by the zener diode Z
1
, for controlling the light level, has been transmitted magnetically.
In accordance with prior art, the control circuit connection can be also implemented by a connection according to FIG.
2
. The connection in
FIG. 2
is what is known as a blocking oscillator, in which the control block A and the switch K
1
have been replaced by a transistor V
1
, resistors R
1
, R
2
and R
3
and a capacitor C
3
as compared with the connection in FIG.
1
. Together with a coil N
1
, these form an oscillation circuit in such a way that the coil N
1
is connected to the emitter of the transistor V
1
, the resistors R
1
and R
2
, the coil N
3
and the resistor R
3
are parallel-connected with these to the operating voltage, and the capacitor C
3
is parallel-connected with the resistors R
1
and R
2
and the coil N
3
. The filtering capacitor C
2
is prevented from being charged by connecting it with a reverse-biased diode D
2
between the transistor V
1
and the coil N
1
. The base current of the transistor can be taken preferably from between the resistors R
1
and R
2
, for example.
The base current of the transistor V
1
flows via the resistor R
2
, the coil N
3
and the resistor R
3
and brings the transistor V
1
to a saturation state, whereby the operation of the transistor V
1
corresponds to a closed switch, and as a result the coil N
1
is coupled via the transistor V
1
to the operating voltage V
cc
. The current passing through the coil N
1
makes the coil N
1
operate as a primary coil with respect to N
3
, whereby an increasing voltage in N
3
controls more strongly the transistor V
1
to a saturation state. When the current passing through the coil N
1
increases so high that the base current is no longer sufficient to keep the transistor V
1
in a saturation state, the direction of the current passing through the transistor V
1
turns in an opposite direction. As the voltage over the coil N
1
decreases, the base current also decreases, making the transistor V
1
an opened switch. An opposite current direction opens the diode D
2
, whereby a negative control voltage U
e
charges over the capacitor C
2
and has a magnitude which is determined by the relation between the number of turns of the coils N
1
and N
2
, i.e. U
e
=(−N
1
/N
2
)*U
c
.
In other words, in prior art solutions, the magnetization current of the primary coil is taken from the operating voltage of the control electronics of the device to be controlled, the voltage being typically between 10 and 15 V. In this case, if the control current is 1 mA, a typical value for the control current, the output level is correspondingly (10-15 V)*1 mA=10 to 15 mW. The efficiency of the connection in
FIG. 1
is about 0.5 and that of the connection in
FIG. 2
about 0.2. In this case the power consumption of the connections is 2 mA and 5 mA, respectively. in addition, in the connection according to
FIG. 1
, the control block A typically consumes between 3 and 5 mA of current.
However, prior art solutions show clear drawbacks. In both of the above connections the power source of the device to be controlled also operates as
Innoware Oy
Lee Wilson
Leydig , Voit & Mayer, Ltd.
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