Note: Descriptions are shown in the official language in which they were submitted.
~` 1113S39
- TO~CH C_NTROL SWITCH
The invention relates to a touch control switch suit-
able for connection between a lamp load and a supply circuit
- in a lighting installation for alternating current and com-
prising a semiconductor switching element with a gate
electrode, a counting circuit with a forward stepping input
and a digital control output connected to the gate electrode
of the semiconductor switching element via a trigger pulse
. generating circuit for controlling the conduction of the
.semiconductor switching element in dependence on the condition
of activation of the digital control output, and a control
pulse shaping circuit having.an output connected to the forward
.stepping input of the counting.circuit and a first and second .
input terminal for connection to a first and second,
respectively terminal of the supply circuit via a touch . .-
sensitive impedance. --
. A touch control switch of the type defined above is
described in the U.S. Patent No. 3,811,054. A large scale
use of that touch control switch is complicated thereby that
20 it has a high non-load power dissipation, that it cannot cope .-
with reactive loads such as fluorescent lamps, and that many
of its components are not possible to integrate in a
monolithic form.
.. The present invention is characterized in that the
trigger pulse generating circuit comprises an edge-triggered
. mono-pulse generating-circuit that has a first input for
leading edge triggering and a second input for trailing edge
. triggering jointly connected to the supply circuit.
. . ~ . . ~
3S39
The touch control switch according to the invention has a very low
non-load power dissipation. It can cope with reactive loads and is
possible to integrate in a monolithic form with the exception of
only a few components.
rrhe invention, the characteristics of which appear from the appended
claims, will now be explained more in detail with reference made to
the accompanying ~rawing wherein Fig. 1 is a block diagram of a pre-
ferred embodiment of the touch control switch according to the in-
vention and Fig. 2 is a circuit diagram of a touch detecting clipper
stage included in the block diagram in Yig. 1.
Fig. 1 shows a touch control switch the principal function of which
is with the exception of the improvements accoding to the invention
to be described below explained in detail in the U.S. Patent No~
3,811,084 and which is interconnected between a lamp load 1 and a
supply circuit 2 in a lighting installation for alternating current
and comprises a semiconductor switching element 3 with a gate elect-
rode. The touch control switch comprises further a counting circuit 4
with a forward stepping input and a digital control output connected
to the gate electrode of the semiconductor switching element 3 via a
triyger pulse generating circuit 5 for controlling the conduction of
the semiconductor switching element 3 in dependence on the condition
of activation of the digital control output, and a control pulse shap-
ing circuit 6 having an output connected to the forward stepping input
of the counting circuit 4 and a first and second input terminal with
a connection to a first terminal 7 and to a second terminal 8, re-
spectively of the supply circuit 2 via a touch sensitive external
capacitative reactance.
The control pulse shaping circuit 6 comprises a touch detecting clip-
per stage 9 in which, a~ it will be described later on in connection
with Fig. 2, a peak value detector and an adding circuit are included
with a respective input connected to the input of the control pulse
shaping circuit 6, a second input of the adding circuit being connect-
ed to the output of the peak value detector.
The output of the control pulse shaping circuit 6 is connected to the
output of the clipper stage 9 via a pulse counting circuit 10 and an
~D-circuit 11 with an inhibiting input connected to the supply cir-
cuit 2 via a second clipper stage 12 given the same internal structure
~ :lil3~;~9
as the clipper stage 9 and having the purpose to inhibit a malfunction
caused by false control pulses occurring as a consequence of a voltage
rise on the supply circuit 2 upon, for example, a disconnection of
electric ovens.
In the preferred embodiment of the invention, the touch control switch
has the trigger pulse generating circuit 5 arranged to comprise a
mono-stable flip-flop 13 with a first input for leading edge trigger-
ing and a second input for trailing edge triggering jointly connected
to the supply circuit 2 in shunt with the semiconductor switching ele-
/O ment 3 and in series with the lamp load 1 in order to be controlledby the current through the latter that can be an incandescent lamp or
a fluorescent lamp with a phase compensating capacitor. The connect-
tion of the trailing edge triggering input of the mono-stable flip-
flop 13 to the supply circuit 2 is arranged via a resistive voltage
divider in which a shunt link is connected to a biasing potential in
order to provide a symmetrical triggering for the positive and nega-
tive half periods of the alternating current through the lamp load 1.
According to the example, the mono-stable flip-flop is of the C-MOS
type, the biasing potential is the supply voltage VDD -~ the flip-
ao flop and the resistance of the shunt link is substantially half the
value of the resistance of the series lin~ in the voltage divider.
The trigger pulse generating circuit 5 comprises further an AND-cir-
cuit 14 that has a first input connected to the output of the mono-
stable flip-flop 13 and a second input connected to the digital con-
trol output of the counting circuit 4 and that has an output connected
to the gate electrode of the semiconductor element 3 via a driver
stage 15. The latter supplies a trigger pulse when a predetermined
voltage has been built up over the semiconductor element 3 that accord-
ing to the example is a TRIAC. The duration of the trigger pulse can
~a be very short as compared with the duration of the half period of the
alternating current, for example 100 /us and 10 ms, respectively, im-
plying that the non-load power dissipation of the touch control switch
can be brought down to a very low value since the demand on its supply
of current to the control circuitry pertaining to the semiconductor
element 3 will be modest.
The supply of current to the control circuitry in the touch control
switch is, according to the example, arranged via a rectifier diode
16, a smoothing capacitor 17, a voltage dropping resistor 18 for the
connection to the supply circuit 2 and a voltage limiting zener diode
113S~9
19. The non-load power dissipation of the touch control switch is
substantlally equal to the power dissipation of the voltage droppinq
resistor 18 and can in the preferred embodiment of the invention be
kept below 1~2 watt at 240 VAC and driving a TRIAC capable of supply-
ing 2.5 A.
Fig. 2 is a circuit diagram over the clipper stage 9 in Fig. 1 in an
embodiment suited for a monolithic integration together with the above
described trigger pulse generatinq circuit 5 and the majority of the
other elements of the touch control switch. Two voltage comparators
/O 20 and 21 have a respective signal input jointly connected to a con-
trol input 22 of the clipper stage 9 via a protection circuit consist-
ing of a resistor 23 and a capacitor 24. They have further a respect-
ive reference input jointly connected to the output of the one compa-
rator 20 via a peak value detector consisting of a rectifier diode 25,
a capacitor 26, a charge resistor 27 and a discharge resistor 28 keyed
by a switching diode 29 as it will be explained more in detail below,
the connection of the s$gnal input of the other comparator 21 to the
control input 22 being arranged via a resistive voltage divider con-
sisting of a series resistor 30 and a shunt resistor 31. The voltage
O comparator 21 constitutes the above-mentioned adding circult and ha~
an output 32 with a current-feeding resistor 33 connected to the output
of the clipper stage.
The sensitivity of the touch detecting clipper stage 9 is inversely
proportional to the attenuation in the above-mentiomed resistive volt-
aqe divider which can with a maintained margin to a generation of
false control pulses be reduced in an inverse proportion to an in-
crease of the time constants for charge and discharge in the above-
mentioned peak value detector. In the latter, the charge time constant
must in any case be considerably greater than the period time of the
~k~ alternating current in the supply circuit 2. The resistance of the
discharge resistor 28 can, however, be considerably smaller than the
resistance of the charge resistor 27 thanks to the fact that the form-
er resistor 28 ls keyed by the switching diode 29 that is arranged to
conduct only during a very short time interval of the period of the
alternating current in the supply circuit 2 corresponding to the dura-
tion of the trigger pulse for the negative half period applied to the
semiconductor element 3. This is accomplished thereby that the switch-
ing diode 29 is connected to the output of an AND-circuit 34 which has
a signal input 35 arranged to be connected to the output of the mono-
3r~ 3
stable flip-flop 13 in Fig. 1 and an inhibiting input 36 arranged to
be connected to the tralllng edge trlggerinq lnput of the fllp-flop 13.
The clrcuit structure of the clipper stage in Fig. 2 can be modlfied
thereby that the rectifier diode 25 and the switching dlode 29 are re-
placed by analog MOS-gates with low leakage currents. In addition, the
series resistor 30 can possibly be replaced by a direct wire connect-
ion and a negative biasing of thè signal input of the voltage compara-
tor 21 relatively its reference input.
The function of the clipper stage in Fig. 2 corresponds to the function
1~ of a clipper stage described in the above-mentloned U.S. Patent No.
3~811,054 but works with a lower signal volta~e and with larger tole-
rances in the circuit resistors, which makes it suited for a monollthic
ntegration. It is essential that variations in the external capacit-
ance on the input of the touch detecting clipper stage 9 influences
the phase position of the control pulses supplied from this only to a
small extent in order to insure a correct signal processing in the AND-
circuit 11 and in the pulse counting stage 10. This is accomplished
by selecting the resistance of all the resistors 23, 30 and 31 con-
siderably lower than the reactance of the capacitor 24 the capacitance
of which in its turn is selected substantially equal to the maximum
external capacitance, according to the example 500 pF. In addition,
the input of the clipper stage 9 can be provided with a shunt circuit
with a variable attenuation produced, for example, by means of a field
effect transistor controlled by the voltage over the capacitor 26 of
the peak value detector in a known manner described in Electronics,
Vol. 50, No. 7, pp. 107. A constant ratio between a varying external
series reactance and a shunt resistance varying proportionally there-
to in the input circuitry of the clipper stage is then obtained and
results in that the phase position of the control pulses supplied from
~k~ this is malntained constant relatively the phase of the alternating
current in the supply current 2 which makes it possible for the AND-
circuit 11 andthe clipper stage 12 to increase the margin in inhibit-
ing false control pulses produced as a consequence of voltage transi-
ents in the supply circuit 2.
