GB2293098A

GB2293098A - Hair drier

Info

Publication number: GB2293098A
Application number: GB9418604A
Authority: GB
Inventors: Chun Yiu Lok; Tim Yuen Leung
Original assignee: Kenford Industrial Co Ltd
Current assignee: Kenford Industrial Co Ltd
Priority date: 1994-09-15
Filing date: 1994-09-15
Publication date: 1996-03-20
Anticipated expiration: 2014-09-15
Also published as: CN1128121A; GB2293098B; GB9418604D0; CN1078061C; HK1010319A1; DE19534105A1

Description

is HAI TLtEATMENT DEVICE 2293098 The present invention relates to a

hand-held hair treatment device which is switchable to operate on at least two different mains Supply AC voltages and also capable of operating in hot as well as cool (room temperature) mode.

According to the invention, there is provided a hair treatment device which comprises a body, having an air duct, a DC motor and a fan or propeller to be driven by the motor for driving air through the air duct, a plurality of heating elements provided in the air duct, and an electrical circuit provided inside the body for controlling the operation of the motor and the heating elements, which electrical circuit comprises a first electrical switch for selecting the operating voltage of the hair treatment device between at least two supply voltage levels by rearranging the connection of at least one of the heating elements in order to maintain the power rating of the heating elements regardless of the selected operating voltage, a second electrical switch for selecting the power rating of the heating elements between at least hot and cool modes, a diode rectifier connected with the motor for enabling DC operation of the motor, and a diode-resistor series circuit switchable by the second electrical switch into operation in the cool mode for delivering limited electrical current through the motor and the heating elements.

Preferably, the diode rectifier has diode cathodes connected with one motor terminal to form a circuit node, and the diode-resistor series circui has its cathode end connected to the said circuit node.

In a preferred embodiment# the resistor of the dioderesistor series circuit has a resistance subtantially larger than that of the heating elements.

Specifically, the diode rectifier is formed by two diodes which are separately connected in parallel with the motor to effect full-wave rectification.

Preferably, each diode of the diode rectifier is connected in series with one respective said heating element befor being connected in parallel with the motor.

Advantageously, the first electrical switch has one single switching mechanism.

In a preferred arrangement, the first electrical switch is so connected that it is switchable between a first switching condition in which all the heating elements are effectively connected in series together and a second switching condition in which at least one of the heating elements is effectively connected in parallel with the other heating elements which remain effectively connected in series together.

Preferably, the resistance of said at least one of the heating elements is substantially the same as the sum of the resistance of the other heating elements.

In a specific construction, the electrical circuit has two supply terminals, and the first electrical switch has tour switch terminals, first and second "of which switch terminals are provided in series behind one said supply terminal and the third and fourth switch terminals are connected to opposite ends$ respectively, of said at least one heating element.

is More specifically. the first electrical switch in adapted to have its first and second switch terminals shortcircuited together in the first switching condition and to have its first and second switch terminals short-circuited to the third and fourth switch terminals, respectively, in the second switching condition.

It is preferred that all the heating elements are physically connected in series together.

It is advantageous for the hair treatment device to be switchable by means of the second electrical switch into the cool mode and two different levels of the hot mode.

The invention will now be more particularly described, by way of example only, with reference to the accompanying - 4 drawing which is a schematic circuit diagram of an electrical circuit of an embodiment of a hair treatment device in accordance with the invention.

Referring to the drawing, there is shown an electrical circuit of a hair dryer embodying the invention, which hair dryer comprises a body (not shown) having an internal air duct, a DC motor M and a fan (not shown) to be driven by the motor M for driving air through the air duct. The hair dryer further includes four heating elements R1 to R4 provided in the air duct. In operation, the motor M in energised to drive the fan or a propeller or the like to form a blower for driving air through the heating elements Rl to R4 in the air duct, thereby providing hot air for hair'drying. The electrical circuit is designed to control the operation of the motor M and the heating eleme nts R1 to R4, and is formed by first and second electrical switches SW1 and SW2, four diodes D1 to D4, a resistor RS and a thermostat T.

The motor M incorporates a pair of choke coils Ll and L2 which are connected to opposite terminals of the motor armature, together forming the motor circuitry. A filtering capacitor C is connected in parallel with the motor circuitry. The heating elements R3 and R4 and diodes D2 and D3 are connected in a bridge configuration around the motor M, with the motor circuitry connected diagonally across a circuit node A formed between the cathodes of the is diodes D2 and D3 and another circuit node K formed between the heating elements R3 and R4. It is noted that the diodes D2 and D3 are separately connected in parallel with the motor M to effect full-wave rectification. For DC motor operation, the diodes D2 and D3 constitutes a diode rectifier to deliver alternately, opposite half-cycles of the AC mains supply current to flow through the.motor M in the same direction from the nodes A to K, and the capacitor C maintains the motor current as steady as possible by filtering away the current ripples.

The heating elements R1 and R2 are connected in series to a circuit node Q formed between the heating element R3 and the diode D2. Accordingly, and also an shown, the heating elements R1 to R4 are physically connected In series together. The thermostat T is connected to the far end of the heating element Rl. The resistor RS and diode D4 are connected together to form a series circuit which is connected at its cathode to the node A.

The hair dryer is adjustable by means of the switch SW1 to operate on a mains supply voltage of either 230V/50Kz or IZOV/60Hz. The voltage switch SW1 has one single switching mechanism including four fixed terminals T1 to T4, and is switchable between a first switching condition (terminals MT2) for 230V/50Hz operation in which terminals Tl and T2 are shortcircuited together by a movable bridging contact (shown in dashed line) and a second switching condition is (terminals T1-T3/T2-T4) for 120V/60Hz operation in which terminals T1 and T3 are short-circuited together and terminalz T2 and T4 are short- circuited together by respective movable bridging contacts (shown in dashed line). Terminal T3 is connected to one end of the heating element Rl adjacent the heating element R2, and terminal T4 is connected to the other end of the heating.element Rl adjacent the thermostat T. Terminal TZ is connected to a circuit node J formed between the heating element R4 and the diode D3.

The hair dryer is designed to operate with three different operating temperatures or power levels, namely COOL, HIGH and LOW modes, which are selectable by means of the switch SW2. The temperature switch SW2 has three selectable terminals TV to TV and one common terminal TV. Terminal T11 is connected to the free end of the resistor R6. Terminals TV and TV are both connected to terminal Tl of the voltage switch SW1, directly for terminal TV and indirectly via the diode Dl for terminal TV. Selectable connection of terminal T11, TV or TV to terminal TV determines the COOL, HIGH or LOW modes, respectively. The mains supply voltage is to be applied across the common terminal T4' and the thermostat T, which serve as two supply terminals of the electrical circuit.

The 230V/50Hz operation is firstly referred to. In the HIGH mode, the mains supply current flows through the is heating elements R1, R2, R3 (and the motor M via diode D2) and R4 sequentially for, say, positive half-cycles and flows through the heating elements R4 (and the motor M via diode D3)j R3, R2 and R1 sequentially for negative halfcycles. In the LOW mode, the positive half-cycles of the mains supply current is blocked by the diode Dl, whereby the power rating of the heating elements Rl...to R4 is reduced to about half (from 30OW to 150W) and hence the temperature. The diode DI may be reversed in connection to block, instead, the negative half-cycles of the mains supply current.

In both the HIGH and LOW modes, it should be noted that the beating elements R1 to R4 are effectively connected in series together. In the COOL mode, only the negative halfcycles of the mains supply current can flow through the diode D4.. This mains supply current cannot flow through the diodes D2 and D3 but the motor M and subsequently through the heating elements R3, R2 and R1. Because the resistor R5 has a resistance substantially larger than that of the heating elements R1 to R3, the magnitude of the mains supply current that can flow through is rather limited. resulting in rather limited heating action of the heating elements R1 to R3 (6OW).

The 120V/60Hz operation is now referred to. In the HIGH mode, the flowing paths of the negative half-cycles of the mains supply current are illustrated by current components is Il and 12. Current component Il flows through only the heating element R1, whilst current component 12 flows through the heating elements R2, R3 (and the motor N via diode D2) and R4 sequentially. The flowing paths of the positive half-cycles of the mains supply current are in the reverse direction, but with the reversed current component J2 flowing through the heating elements R4 (and the motor H via diode D3), R3 and R2 sequentially.

The resistance of the heating element Ri is about the same as the sum of the resistance of the heating elements R2, R3 and R4. It should be noted that the beating elements R2 to R4 remain effectively connected in series together, whilst the heating element Ri is now effectively connected in parallel with them. This effective parallel connection of the heating element R1 with the other heating elements R2 to R4 reduces the resultant resistance of all the heating elements R1 to R4 to about half. With the mains supply voltage reduced from 23OV to also about half at 120V, the magnitude of the mains supply current will remain practically the same compared with that in the 230V/50Hz operation, and hence the power rating of the heating elements Rl to R4 remains at about 30OW. Accordingly, at least in the HIGH mode, the performance of the hair dryer is practically not affected by the change in the mains supply voltage between 23OV/50Hz and 12OV/60Hz.

As for 230V/50Hz operation, in the LOW mode of the is 120V/6OHz operation, the Positive half-cycles of the mains supply current is blocked by the diode D1, whereby the power rating of the heating elements Rl to R4 is reduced to about half (from 30OW to 150W) and hence the temperature. Accordingly, the performance of the hair dryer in the LOW mode is also practically not affected by the change in the mains supply voltage. In the COOL mode, the op(ration is not at any rate affected by the change in the mains supply voltage from 230V to 120V because the effective reconnection of the heating element Rl does not come into play. However, as the mains supply voltage is now reduced by about half, the power rating of the heating elements Rl to R3 will also be reduced to half at about 30W.

It should be noted that the motor M draws a very small current compared with the heating elements Rl to R4, and therefore its presence will not substantially affect the analysis of the mains supply current given above. With the change of the mains supply voltage from 230V to 120V, whether in the HIGH or LOW mode, the overall magnitude of the mains supply current remains substantially unchanged and so does the motor current. Accordingly, the speed of the motor M will remain substantially the same. The motor speed is critical only when the heating elements R1 to R4 are performing air-heating action, because this affects the air blowing rate and hence the temperature of the hot air output. In the COOL mode, the motor speed is therefore relatively much less critical.

Although diodes only allow electric current to flow through in one direction, a whole group of related diodes may be re-connected in the reversed direction without affecting the general operation of the relevant circuitry in AC operation. Accordingly, in a slightly different embodiment, the diodes D2, D3 and D4 are all connected in the reversed direction, namely having the anpdes of the diodes D2 and D3 connected with the anode of the diode D4 to form the circuit node A leading to one terminal of the motor M# and this will not affect the general operation of the &fore-described hair dryer electrical circuit.

It is envisaged that the hair treatment device of thia invention way take a different form other than a hair dryet, such as a hair curler, a hair styler or an air brush.

The invention has been given by way of example only, and various modifications of and/or alterations to the described embodiment may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.

Claims

1. A hair treatment device comprising a body having an air duct, a DC motor and a fan or propeller to be driven by the motor for driving air through the air duct, a plurality of heating elements provided in the air duct, and an electrical circuit provided inside the body for.co.ntrolling the operation of the motor and the heating elements, which electrical circuit comprises a first electrical switch for selecting the operating voltage of the hair treatment device between at least two supply voltage levels by rearranging the connection of at least one of the heating elements in order to maintain the power rating of the heating elements regardless of the selected operating voltage, a second electrical switch for selecting the power rating of the heating elements between at least hot and cool modes, a diode rectifier connected with the motor for enabling DC operation of the motor, and a diode-resistor series circuit switchable by the second electrical switch into operation in the cool mode for delivering limited electrical current through the motor and the heating elements.

2. A hair treatment device as claimed in claim 1, wherein the diode rectifier has diode cathodes connected with one motor terminal to form a circuit node, and the dioderesistor series circuit has its cathode end connected to the said circuit node.

is

3. A hair treatment device as claimed in claim 1, wherein the diode rectifier has diode anodes connected with one motor terminal to form a circuit node, and the dioderesistor series circuit has its anode end connected to the said circuit node.

4. A hair treatment device as claimed In 4ny one of claims 1 to 3, wherein the resistor of the diode-resistor series circuit has a resistance substantially larger than that of the heating elements.

5. A hair treatment device an claimed in any one of claims 1 to 4, wherein the diode rectifier is formed by two diodes which are separately connected in parallel with the motot to effect full-wave rectification.

6. A hair treatment device as claimed in claim 6, wherein each diode of the diode rectifier is connected in series with one respective said heating element before being connected in parallel with the motor.

7. A hair treatment device as claimed in any one of the preceding claims, wherein the first electrical switch has one single switching mechanism.

8. A hair treatment device as claimed in any one of the preceding claims, wherein the first electrical switch is so connected that it is switchable between a first switching 16 condition in which all the heating elements are effectively connected in series together and a second switching condition in which at least one of the heating elements is effectively connected in parallel with the other heating elements which remain effectively connected in series together.

9. A hair treatment device as claimed in claim 8, wherein the resistance of said at least one of the heating elements is substantially the same as the sum of the resistance of the other heating elements.

10. A hair treatment device as claimed in claim 8 or claim 9, wherein the electrical circuit has two supply terminals, and the first electrical switch has four switch terminals, first and second of which switch terminals are provided in series behind one said supply terminal and the third and fourth switch terminals are connected to opposite ends, respectively% of said at least one heating element.

11. A hair treatment device as claimed in claim 10, wherein the first electrical switch is adapted to have its first and second switch terminals short-circuited together in the first switching condition and to have its first and second switch terminals short-circuited to the third and fourth switch terminals, respectively, in the second switching condition.

12. A hair treatment device as claimed in any one of claims 8 to 11, wherein all the heating elements are physically connected in series together.

13. A hair treatment device an claimed in any one of the preceding claims, being switchable by means of the second electrical switch into the cool mode end twQ different levels of the hot mode.

14. A hair treatment device as claimed in any one of the preceding claims, being a hair dryer.

15. A hair treatment device substantially as hereinbefore described with reference to the accompanying drawing.