GB2267151A - Capacitative switching apparatus - Google Patents

Abstract

The apparatus comprises oscillator 11, which is turned off by the presence of external capacitance at touch plate 12, amplifier 13 and inverter 14 with parallel capacitor CA, the output of inverter 14 controlling switching means 21. The frequency of the oscillator is adjustable by capacitor CV. In operation the oscillator output is amplified and rectified at 13 and charges capacitor CA holding the output of inverter 14 low and triac switch 21 off. When the touch plate is touched, body capacitance shows the output capacitance of the oscillator, reducing its output, to zero. Capacitor CA discharges and the output of inverter 14 goes high switching triac 21 and load 20 on. The apparatus may be used on a hair dryer, curling tongs or electrically powered hair brush with the sensor plate on the handle thereof. <IMAGE>

Description

A Switching Apparatus This invention relates to a switching apparatus, in particular but not exclusively for use in devices such as hair dryers, curling tongs and electrically powered hair brushes.

It is known in electrical technology to employ touch sensors, which rely on a capacitance change when contacted by hand, to initiate a switching function.

According to the invention, there is provided a switching apparatus comprising: an oscillator; first means, connected in parallel with said oscillator, permitting the selective connection in parallel with said oscillator of an external capacitance; amplifier means connected to said oscillator and said first means; inverter means connected to the output of said amplifier means, said inverter means being operatively connectable to the power supply and to current switching means of a load device; and capacitance means operatively connected in parallel with said inverter means, whereby in the absence of an external capacitance the capacitance means is charged and the output of the inverter means is such as to maintain any current switching means to which the switching apparatus is connected in an off condition, and when an external capacitance is connected to said first means the capacitance means discharges, thereby causing the output of the invert Or means to maintain any such current switching means in an on condition.

An advantage of this arrangement is that it is adequately simple and its power consumption characteristics are suitably low for it to be readily included in, for example, a hair dryer, curling tongs or an electrically powered hairbrush.

Preferably the first means is a touch sensor. Thus, the switching apparatus can be used to provide instantaneous operation of devices such as hair dryers on manual picking up of such devices for use.

It is preferable that the oscillator is tuneable. Thus, the oscillator may be adjusted so that the switching apparatus is reliably actuated.

In a preferred embodiment of the apparatus, in which the oscillator may be tuneable, the values of the components of the switching apparatus are selected such that the capacitance of at least part of the human body is suitable as the external capacitance to cause the output of the inverter means to maintain the current switching means in an on condition.

The invention also relates to a switching apparatus as defined above, in combination with a load device including a current switching means. In a preferred embodiment, the current switching means is a triac.

According to a third aspect of the invention, there is provided a hair dryer including a switching apparatus as defined above.

According to a fourth aspect of the invention, there is provided a set of electric hair curling tongs including a switching apparatus as defined above.

According to a fifth aspect of the invention, there is provided an electrically powered hairbrush including a switching apparatus as defined above.

There now follows a description of a preferred embodiment of the invention, by way of example, with reference being made to the accompanying drawings in which: Figure 1 is a schematic block diagram illustrating the operation of the switching apparatus; and Figure 2 is a circuit diagram of the components constituting the apparatus of Figure 1.

Referring to Figure 1, there is shown schematically a switching apparatus 10 for apparatus 20 such as an electric hair dryer, electrically powered curling tongs, an electrically powered hairbrush or other, similar apparatus. The apparatus 20 constitutes a current load, operation of which is to be controlled by the switching apparatus. The switching apparatus 10 is operatively connected to a switching means 21 for the apparatus 20.

Switching means 21 in the embodiment shown is constituted as a triac. Current for apparatus 20 is provided by AC source 22, which is operatively connected to triac 21. AC source 22 also provides alternating current for an oscillator forming part of the switching apparatus 10, and to be described below.

Switching apparatus 10 includes an oscillator 11, a wave form shaping circuit and signal amplifier 13, and an inverter 14 connected in series, the output of the inverter being connected to the control input of triac 21. The AC source 22 is connected to drive these three components.

A touch sensor plate 12 is connected in parallel with the oscillator 11.

The principle of the operation of the switching apparatus is as follows: When the AC power source 22 is energised and no external capacitance is in contact with the touch sensor 12, the oscillator 11 is caused to oscillate.

The output signal of the oscillator 11 is shaped and amplified by the components constituting block 13, and input to the inverter 14. The input to inverter 14 is thus a high voltage, and the output of inverter 14 is a low voltage. Since this low voltage is applied directly to the switching input of the triac 21, the triac 21 is maintained in an off state, and the loading represented by block 20 does not operate.

When an external capacitance (such as the capacitance of the human body when the touch sensor is touched by the hand of an operator of the apparatus 20) is applied, the output capacitance of oscillator 11 is shunted and the oscillator 11 either ceases oscillating entirely or oscillates at a very low frequency.

Thus, the input voltage to the inverter falls to a low state.

Consequently, the output of the inverter is switched to a high state and the triac 21 is switched to an on condition. At this point, the current from AC source 22 is supplied to the apparatus 20 which then operates.

It will be apparent that, if the touch sensor 12 is sited on the surface of the handie of a hair dryer, curling tongs or electric hairbrush, the apparatus will function automatically on manual picking up of the apparatus by means of the handle thereof.

Referring now to Figure 2, the components of the switching arrangement are shown. Oscillator 11 is constituted by amplifier IC 1, resistance R1 and capacitance C1 connected as shown in the conventional manner of an oscillator.

The output frequency of oscillator 11 is tuneable by means of variable capacitance Cv.

As can be seen from Figure 2, the touch sensor plate 12 is connected in parallel with the oscillator 11, so that when the touch sensor plate is touched by the human hand the capacitance of the human body shunts the output capacitance of the oscillator 11 and causes it either to cease oscillating entirely or to oscillate at a frequency which is too low to be passed by capacitance C2, which capacitance forms the input stage of the wave form shaping amplifier 13.

Amplifier 13 is further constituted by DC reference voltage source +v (typically + 5 volts), scaling resistance R2, amplifier IC2, diode D1 and resistance R3 Wave form shaping amplifier 13 configures the output signal (when present) of oscillator 11 to a suitable form for input to inverting amplifier 14. This amplifier includes capacitance CE, inverting amplifier IC3 and output resistance R4 as shown. It will be apparent that when a voltage signal is applied to the input of IC3 (as occurs when no external capacitance is touching touch sensor plate 12), the output of amplifier IC3 will be at a low logic state.Obviously, it is necessary to provide capacitance CE to avoid burning out amplifier IC3. Thus, capacitance CE becomes charged during operation of oscillator 11.

The output of inverting amplifier 14 is applied directly to the control input of triac 21, which in turn switches the supply of AC power from AC source 22 to load 20.

It will be apparent that, on the output of oscillator 11 becoming effectively zero (as occurs when an external capacitance such as that of the human body is applied to touch plate 12) the input to inverting amplifier 14 will be zero and consequently the output of that amplifier will be at a high logic state. Thus, triac 21 is operated to switch on the power supply to the load 20.

On renewal of the external capacitance (as occurs when the apparatus is finished with and put down) a reverse process occurs; oscillation of the oscillator recommences, capacitance Ca is charged and the output of amplifier IC3 reverts to a high state. Thus, the triac returns to an off condition, and current to the load 20 is switched off.

As previously indicated, the switching apparatus of the invention is suitable for automatic switching of, for example, an electric hair dryer, electric hair curling tongs, an electrically powered hairbrush and similar apparatus.

The switching apparatus of the invention may constitute a device as described, in combination with the triac 21 or similar current switching devices (such as a relay).

It is also considered that the invention resides in a hair dryer, curling tongs, hairbrush or similar apparatus including a switching apparatus as specified herein.

Claims (10)

1. A switching apparatus comprising: an oscillator; first means, connected in parallel with said oscillator, permitting the selective connection in parallel with said oscillator of an external capacitance; amplifier means connected to said oscillator and said first means; inverter means connected to the output of said amplifier means, said inverter means being operatively connectable to the power supply and to current switching means of a load device; and capacitance means operatively connected in parallel with said inverter means, whereby in the absence of an external capacitance the capacitance means is charged and the output of the inverter means is such as to maintain any current switching means to which the switching apparatus is connected in an off condition, and when an external capacitance is connected to said first means the capacitance means discharges, thereby causing the output of the inverter means to maintain any such current switching means in an on condition.

2. A switching apparatus according to Claim 1 wherein the first means is a touch sensor.

3. A switching apparatus according to Claim 2, wherein the values of the components thereof are selected such that the capacitance of at least part of the human body is suitable as the external capacitance to cause the output of the inverter means to maintain the current switching means in an on condition.

4. A switching apparatus according to any of Claims 1 to 3 wherein the oscillator is tunable.

5. A switching apparatus according to any preceding claim in combination with a load device including a current switching means.

6. A switching apparatus according to Claim 5 wherein the current switching means is a triac.

7. A hair dryer including a switching apparatus according to any preceding claim.

8. A set of electric hair curling tongs including a switching apparatus according to any of claims 1 to 6.

9. An electrically powered hair brush including a switching apparatus according to any of Claims 1 to 6.

10. A switching apparatus generally as herein described, with reference to or as illustrated in the accompanying drawings.