MAGNAFON 24" BELVIS 2 CONTACTLESS TOUCH SENSOR PROGRAM CHANGE KEYBOARD
CIRCUIT ARRANGEMENT FOR ESTABLISHING A CONSTANT POTENTIAL OF THE
CHASSIS OF AN ELECTRICAL DEVICE WITH RELATION TO GROUND :TV PROGRAM SENSOR BUTTON CHANGE.
Circuit
arrangement for establishing a reference potential of a chassis
of an electrical device such as a radio and/or TV receiver, such
device being provided with at least one contactless touching switch
operating under the AC voltage principle. The device is switched
by touching a unipole touching field in a contactless manner so as
to establish connection to a grounded network pole. The circuit
arrangement includes in combination an electronic blocking switch
and a unidirectional rectifier which separates such switch from the
network during the blocking phase.
1.
A circuit arrangement for establishing, at the chassis of an
electrical device powered by a grounded AC supply network, a reference
potential with relation to ground, said device having at least one
contactless touching switch operating on the AC voltage
principle, the switch being operated by touching a unipole
touching field in a contactless manner, said arrangement
comprising an electronic switch for selectively blocking the
circuit of the device from the supply network, a half-wave
rectifier including a pair of diodes individually connected in
series-aiding relation between the terminals of the supply network
and the terminals of the device for separating the electronic
blocking switch from the supply network during a blocking phase
defined by a prescribed half period of the AC cycle, and a pair of
condensers individually connected in parallel with the respective
diodes. 2. A circuit
arrangement according to claim 1, wherein the capacitances of the
two condensers are of equal magnitude.
Description:
This
invention relates to a circuit arrangement for establishing a
constant reference potential on the chassis of an electrical
instrument such as a radio and/or a TV receiver. Such instrument
includes at least one contactless touching switch operating under
the AC voltage principle, whereby by touching a single pole
touching field the contactless switch is operated.
In
electronic devices, for example TV and radio receivers, there are
used in ever increasing numbers electronic touching switches for
switching and adjusting the functions of the device. In one known
embodiment of this type of touching switch, which operates on a DC
voltage principle, the function of the electronic device, is
contactlessly switched by touching a unipole touching field, the
switching being carried out by means of an alternating current
voltage. When using such a unipole touching electrode, one takes
advantage of the fact that the AC current circuit is generally
unipolarly grounded. In order to close the circuit by touching the
touching surface via the body of the operator to ground, it is
necessary to provide an AC voltage on the touching field. In one
special known embodiment there is employed a known bridge current
rectifier for the current supply. This type of arrangement has the
drawback that the chassis of the device changes its polarity
relative to the grounded network pole with the network frequency.
With such construction considerable difficulties appear when
connecting measuring instruments to the device, such difficulties
possibly eventually leading to the destruction of individual parts
of the electronic device.
In order to avoid these
drawbacks, the present invention provides a normal combination of a
unidirectional rectifier with an electronic blocking switch that
separates the chassis of the electronic device from the network
during the blocking phase. In accordance with the present
invention, the polarity of the chassis of the electronic device
does not periodically change, because the electronic device is
practically separated from the network during the blocking phase
of the unidirectional rectifier by means of the electronic
blocking switch.
In a further embodiment of the
invention a further rectifier is connected in series with the
unidirectional rectifier in the connection between the circuit and
the negative pole of the chassis. Such further rectifier is
preferably a diode which is switched in the transfer direction of
the unidirectional rectifier. According to another feature of the
invention there are provided condensers, a respective condenser
being connected parallel with each of the rectifiers. Preferably
the two condensers have equal capacitances. Because of the use of
such condensers, which are required because of high frequency
reasons, during the blocking phase there is conducted to the
chassis of the electronic device an AC voltage proportional to the
order of capacitances of the condensers. Thus there is placed
upon the touching field in a desired manner an AC voltage, and
there is thereby assured a secure functioning of the adjustment of
the device when such touching occurs.
I
n
the embodiment of the invention employing two rectifiers there is
the further advantage that over a bridging over of the minus
conduit of the rectifier that is connected between the network and
the negative pole of the chassis connection, no injuries can be
caused by a measuring instrument in the electronic device itself
and in the circuit arrangement connected thereto.
In the accompanying drawing:
The sole FIGURE of the drawing is a circuit diagram of a preferred embodiment of the invention.
In
the illustrated embodiment the current supply part of the device,
shown at the left, is connected via connecting terminals A and B
to an AC voltage source, the terminal B being grounded at 8. The
current supply part consists of a unidirectional rectifier in the
form of a diode 1 with its anode connected to the terminal I, the
cathode of diode 1 being connected to one input terminal 9 of an
electronic device 2. In the device 2 there is also arranged a sensor
circuit 3, shown here mainly as a block, circuit 3 being shown as
including a pnp input transistor the emitter of which is
connected to an output terminal 11 of the device 2. The collector
of such transistor is connected to the other output terminal 12 of
the device 2. The base of the transistor is connected by a wire
13 to a unipolar touching field 4 which may be in the form of a
simple metal plate instead of the pnp transistor shown, the sensor
circuit itself may consist of a standard integrating circuit which
controls, among other things, the periodic sequential switching
during the touching time of the touching field 4. All of the
circuits of the electronic device 2 are isolated in a known manner
from the chassis potential. Between the network terminal B and the
negative pole 10 of the chassis there is arranged in the direction
opposite that of diode 1 a further diode 5, the anode of diode 5
being connected to the terminal 10, and the cathode of diode 5
being connected to the terminal B of the current supply. To provide
for HF type bridging of the diodes 1 and 5 there are arranged
condensers 6 and 7 respectively, which are connected in parallel
with such diodes.
The invention functions by reason
of the fact that in an AC network separate devices radiate
electromagnetic waves which produce freely traveling fields in the
body of the person who is operating and/or adjusting the device,
thereby producing an alternating current through his body to
ground, as indicated by the - line at the right of the circuit
diagram. If now the person operating the device touches the
switching field 4, then the pnp type input transistor of the sensor
circuit 3, which is placed on a definite reference potential (for
example 12 Volts) and is connected with the negative halfwave of
the AC voltage potential, is made conductive. There is thereby
released a control command in the sequential switching, for
example, for switching the electronic device to the next receiving
channel. It is understood that the most suitable connection is
formed between ground and the touching field 4 by means of a wire.
By the use of such wires it would be assured that in all cases the
base of the transistor in circuit 3 is connected to ground. This
would, however, not permit anyone to operate the switch without the
use of an auxiliary means such as a wire. It will be assumed that
the touching almost always results directly via the almost
isolated human body. For this reason the AC current fields are
necessary, because otherwise there cannot always be provided a
ground contact. Thus this connection is established via the body
resistance of the person carrying out the touching of the switch.
The
positive half wave of the alternating current travels to the
terminal 9 of the electronic device 2 after such current has been
rectified and smoothed by the devices 1, 6. Such positive halfwave
is also conducted to the sensor circuit 3. The thus formed
current circuit is closed by way of the chassis of the electronic
device 3, the diode 5, and the terminal B. When there is a
negative halfwave of the alternating current delivered by the current
supply, both diodes 1 and 5 remain closed so that the chassis of
the device 2 remains separated from the network during the
blocking phase. Nevertheless, by means of condensers 6 and 7 the
chassis is placed in a definite network potential, which depends
on the relationship of the order of magnitude of the two
condensers 6 and 7. When the capacitances of such condensers are
equal, there is placed upon the chassis of the device 2 the
constant reference potential, and simultaneously there is present
via the sensor circuit 3 the required AC voltage at the touching
field 4 for adjusting the function or functions of the device 2 upon
the touching of the touching field 4.
The
reference character 15 indicates a terminal or point at which the
potential of the chassis of the device 2 may be measured. As above
explained, the diode 5 causes the potential of the chassis at 15 to
be separated from the network ground when a negative AC halfwave
arrives. It will be noted that the return conduit of the circuit is
held at a fixed chassis potential. The input transistor of the
sensor circuit 3 remains, however, locked because it is subjected
to a DC current of about 12 volts. If now, by means of touching
the touching field 4, the chassis potential is connected to
ground, then the transistor switches through and releases a
switching function.
If
the connecting terminals AB of the current source are exchanged,
as by changing the plug, then there is still secured the condition
that the chassis of the device is separated from the network
ground via the diode, in this case the diode 1. The reference
potential of the chassis consequently remains constant and the
changing AC fields which are superimposed on the condensers can
produce in the touching human body an AC current voltage due to the
fields which are radiated by the device.
A
suitable sensor which may be employed for the circuit 3 herein may
be a sensor known as the "SAS 560 Tastatur IS," manufactured and
sold by Siemens AG.
It is to be understood that
the present invention is not limited to the illustrated
environment. They can also be used in electronic blocking switch
including a Thyristor circuit, which in the same manner separates
the electronic device during the blocking phase from the network
rectifier. With such Thyristor circuit the drawbacks described in the
introductory portion of the specification of known circuit
arrangements are also avoided.
Although the
invention is illustrated and described with reference to a
plurality of preferred embodiments thereof, it is to be expressly
understood that it is in no way limited to the disclosure of such a
plurality of preferred embodiments, but is capable of numerous
modifications within the scope of the appended claims.
MAGNAFON 24" BELVIS 2 CHASSIS The
tuning circuits has a large knob potentiometers tuning system
which use voltage controlled capacitances such as varactor diodes as
the frequency determining elements.
How AFC Circuit Works in B/W Analog Television Receiver:
Push-Button
tuning on u.h.f. while being very convenient often leaves a margin of
mistuning, especially after some wear and tear has occurred on the
mechanism. Even dial tuning can lead to errors due to the difficulty
many people experience in judging the correct point. Oscillator drift
due to temperature changes can also cause mistuning. Automatic frequency
control (a.f.c.) will correct all these faults. The vision carrier when
the set is correctly tuned on u.h.f. is at 39.5MHz as it passes down
the i.f. strip. Thus if at the end of the i.f. strip a discriminator
tuned circuit is incorporated centred on 39.5MHz the discriminator
output will be zero at 39.5MHz and will move positively' one side of
39.5MHz and negatively the other as the tuning drifts. This response is
shown in Fig. 1.
If the tuning is not correct then the
discriminator output is not zero and if this output is applied to change
the reverse bias on a tuning diode mounted in the oscillator section of
the u.h.f. tuner it will correct most of the error. Tuning, varicap or
varactor diodes-to give them a few of their names-are junction diodes
normally operated with reverse bias but not sufficient to bias them into
the breakdown region in which zener diodes operate. The greater the
reverse bias the lower their capacitance: a typical curve, for the
PHILIPS BB105 or STC BA141 tuning diode, is shown in Fig. 2. All diodes e
xhibit
this basic type of characteristic but special diodes have to be used
for u.h.f. because they must not introduce any excessive loss into the
tuned circuits they control. In other words, just as a coil has to have a
good Q so does a varicap diode. Normally, we don't worry about the Q of
a capacitor as it is usually very good. However, a tuning diode is not a
true capacitor. It has, for example, leakage current so the Q of the
diode is a factor which has to be considered. The diode manufacturer
however will have considered these points and if you buy a diode
specified for u.h.f. use you will have no trouble. These points have
been mentioned to clear up any misunderstandings and to show why any old
diode won't do.
Basic AFC SystemTo return to our TV
set, if the oscillator frequency is too high then the vision carrier
frequency will also be too high and in the simple arrangement shown in
Fig. 3 the discriminator will give a negative signal to decrease the
bias on the tuning diode thus increasing its
capacitance
and in turn reducing the oscillator frequency and correcting the error.
Note that in this diagram the reverse bias on the diode is applied to
its cathode. It is therefore positive with respect to ground so that a
negative signal from the discriminator will reduce the positive voltage
on the diode thus reducing its bias and increasing its capacitance. In
this arrangement the diode is biased somewhere near the mid point of its
characteristic by the positive d.c. bias fed into one side of the
discriminator. The discriminator thus adds to or subtracts from this
d.c. bias.
AFC Loop Gain:The amount by which the error
is reduced depends on the gain of the circuit. An estimate of the gain
required must first be made by guessing how much error is likely to be
given by your push -buttons or hand tuning: 1MHz would be an outside
figure as a tuning error of that magnitude would produce a very bad
picture of low definition in one direction and badly broken up in the
other. This error should be reduced to
about
100kHz to be really unnoticeable, indicating a required gain of ten. In
fitting a.f.c. to an existing set some measure- ments should be done as
an experiment before finally deciding on the circuit gain. The first
thing to do is to add the suggested discriminator to the i.f. strip. As
the circuit (Fig. 4) shows a Foster -Seeley type discriminator is used
and with the coils specified and the driver circuit shown it should give
±4V for 0.5MHz input variation.
EXAMPLE of Circuit Description:The
driver stage Tr1 takes a small sample signal from the i.f. strip but
this should be large enough to drive Tr1 into saturation. That is to say
Tr1 is a limiter stage so that the signal amplitude applied to the
discriminator coil L2 stays constant over the normal range of signal
levels. Trl is biased at approximately 7mA which, according to the
original report ("Simple a.f.c. system for 625 -line TV receivers" by P.
Bissmire, PHILIPS Technical Communications, March, 1970), gives the
best limiting performance. C1, R
14
and R3 damp the stage to prevent oscillation. C2 decouples the power
feed and should be close to the circuit. The coil former and can are the
normal ones used for TV sets and so should be easily obtainable: the
former diameter is 5mm. and length 40mm. and winding details are given
in Fig. 5.
The invention being
thus described, it will be obvious that the same may be varied in many
ways. Such variations are not to be regarded as a departure from the
spirit and scope of the invention, and all such modifications as would
be obvious to one skilled in the art are intended to be included within
the scope of the developed apparates both tubes or transistors.
Therefore a stable AFC circuit is developed:
A
superheterodyne receiver having an automatic intermediate
frequency control circuit with means to prevent the faulty
regulation thereof. The receiver has means for receiving a radio
frequency signal and mixing the same with the output of a
superheterodyne oscillator. This produces an intermediate frequency
signal which is coupled to a frequency or phase discriminator to
produce an error signal for controlling the frequency of the
superheterodyne oscillator. A regulation circuit is provided having
an electronic switch to interrupt the feedback circuit when only
unwanted frequencies tend to produce faulty regulation of the
superheterodyne oscillator.
Power supply
is realized with mains transformer and Linear transistorized power
supply stabilizer, A DC power supply apparatus includes a rectifier
circuit which rectifies an input commercial AC voltage. The
rectifier output voltage is smoothed in a smoothing capacitor.
Voltage stabilization is provided in the stabilizing circuits by the
use of Zener diode circuits to provide biasing to control the
collector-emitter paths of respective transistors.A linear regulator
circuit according to an embodiment of the present invention has an
input node receiving an unregulated voltage and an output node
providing a regulated voltage. The linear regulator circuit includes a
voltage regulator, a bias circuit, and a current control device.
In
one embodiment, the current control device is implemented as an
NPN bipolar junction transistor (BJT) having a collector electrode
forming the input node of the linear regulator circuit, an emitter
electrode coupled to the input of the voltage regulator, and a base
electrode coupled to the second terminal of the bias circuit. A
first capacitor may be coupled between the input and reference
terminals of the voltage regulator and a second capacitor may be
coupled between the output and reference terminals of the voltage
regulator. The voltage regulator may be implemented as known to
those skilled in the art, such as an LDO or non-LDO 3-terminal
regulator or the like.
The bias circuit may include a bias
device and a current source. The bias device has a first terminal
coupled to the output terminal of the voltage regulator and a
second terminal coupled to the control electrode of the current
control device. The current source has an input coupled to the first
current electrode of the current control device and an output
coupled to the second terminal of the bias device. A capacitor may
be coupled between the first and second terminals of the bias
device.
In the bias device and current source embodiment, the
bias device may be implemented as a Zener diode, one or more
diodes coupled in series, at least one light emitting diode, or any
other bias device which develops sufficient voltage while
receiving current from the current source. The current source may
be implemented with a PNP BJT having its collector electrode
coupled to the second terminal of the bias device, at least one
first resistor having a first end coupled to the emitter electrode
of the PNP BJT and a second end, a Zener diode and a second resistor.
The Zener diode has an anode coupled to the base electrode of the
PNP BJT and a cathode coupled to the second end of the first
resistor. The second resistor has a first end coupled to the anode
of the Zener diode and a second end coupled to the reference
terminal of the voltage regulator. A second Zener diode may be
included having an anode coupled to the cathode of the first Zener
diode and a cathode coupled to the first current electrode of the
current control device.
A circuit is disclosed for improving
operation of a linear regulator, having an input terminal, an
output terminal, and a reference terminal. The circuit includes an
input node, a transistor, a bias circuit, and first and second
capacitors. The transistor has a first current electrode coupled to
the input node, a second current electrode for coupling to the
input terminal of the linear regulator, and a control electrode. The
bias circuit has a first terminal for coupling to the output
terminal of the linear regulator and a second terminal coupled to
the control electrode of the transistor. The first capacitor is for
coupling between the input and reference terminals of the linear
regulator, and the second capacitor is for coupling between the
output and reference terminals of the linear regulator. The bias
circuit develops a voltage sufficient to drive the control terminal
of the transistor and to operate the linear regulator. The bias
circuit may be a battery, a bias device and a current source, a
floating power supply, a charge pump, or any combination thereof.
The transistor may be implemented as a BJT or FET or any other
suitable current controlled device.
- The EHT Output is realized with a selenium rectifier.
The EHT selenium rectifier which is a Specially designed selenium rectifiers were once widely used as EHT
rectifiers in television sets and photocopiers. A layer of selenium
was applied to a sheet of soft iron foil, and thousands of tiny discs
(typically 2mm diameter) were punched out of this and assembled as
"stacks" inside ceramic tubes. Rectifiers capable of supplying tens of
thousands of volts could be made this way. Their internal resistance was
extremely high, but most EHT applications only required a few hundred
microamps at most, so this was not normally an issue. With the
development of inexpensive high voltage silicon rectifiers, this
technology has fallen into disuse.A selenium rectifier is a type
of metal rectifier, invented in 1933. They were used to replace vacuum
tube rectifiers in power supplies for electronic equipment, and in high
current battery charger applications.
The photoelectric
and rectifying properties of selenium were observed by C. E. Fitts
around 1886 but practical rectifier devices were not manufactured
routinely until the 1930s. Compared with the earlier copper oxide
rectifier, the selenium cell could withstand higher voltage but at a
lower current capacity per unit area.
