HK1124968A - Electronic circuit for a small electric appliance - Google Patents

Description

Circuit for small electrical equipment

Technical Field

The invention relates to an electronic circuit for a small electrical appliance which is driven by a battery, for example an electric toothbrush or an electric shaver, the battery of which can be charged inductively by a charger and which preferably has a display device for displaying the charging process and/or the charging state of the battery.

Background

EP 0875978 discloses a device which is driven by a battery and which has an electronic circuit and a battery which can be charged by a charging device. In this case, it may happen that, in the case of a discharged battery, the voltage supplied by the charging device is disconnected and the electronic circuit no longer operates. In order to avoid this, the electronic circuit is supplied with a sufficiently high voltage during the charging of the battery from a capacitor which is charged by the charging device by means of a diode. The charging of the capacitor is effected in that the electronic switch interrupts the charging process of the accumulator for a short time, continuously and repeatedly, whereby the load is removed from the charging device and the voltage of the charging device will rise to such an extent that the capacitor can be charged via the diode. During the charging of the accumulator, the capacitor then supplies the electronic circuit. The parameters of the capacitor are selected such that during its discharge (i.e. during the charging of the battery) its voltage drops only within a permissible range.

Disclosure of Invention

The object of the invention is to provide an electronic circuit for a small electrical device which is driven by a rechargeable battery, which has as few components as possible, thus having a low space requirement and is inexpensive.

The electronic circuit according to the invention is envisaged for a small electrical appliance driven by a battery, for example for an electric toothbrush or an electric shaver, which has two different operating states, namely a first state in which the small electrical appliance is operated by a user and a second state in which the small electrical appliance is inductively connected to a charging station. The display device can signal the charging process when the storage battery is charged; and/or signaling the charging state of the storage battery after the charging is finished.

The light-emitting diode is designed as a display device for displaying the charging process and/or the charging state of the rechargeable battery, wherein the electronic circuit has the important advantage that: a light emitting diode with a forward voltage greater than the battery voltage can be used. In this way, for example, the charging process and/or the charging state can be represented by a blue light-emitting diode, although the small electrical device is operated with a battery having only one battery cell. In addition, the circuit is designed such that the light-emitting diode is not subjected to a reverse voltage.

The electronic circuit according to the invention comprises a series circuit known per se comprising a battery, a rectifier diode and a charging coil. If the charging coil is coupled to a charger, the charging coil supplies an alternating current, which is rectified by a rectifier diode and charges the battery. Depending on the polarity of the battery or the type of electronic component used (for example, npn transistors instead of pnp transistors), the ends of the charging coils are connected either to the anode of the rectifier diode and to the cathode of the light-emitting diode or to the cathode of the rectifier diode and to the anode of the light-emitting diode. The electronic circuit also comprises a control circuit for controlling the light-emitting diodes, for controlling the charging process of the battery, and for controlling a load, which in the case of an electric toothbrush or an electric shaver consists, for example, of an electric motor. The control circuit is supplied with current from the battery. The basic advantage of this electronic circuit is that the battery can be charged even in the case of deep discharge of the battery (which also means when the control circuit is not operating). When the battery voltage is sufficiently high, the control circuit operates and, if necessary, terminates the charging of the battery, which is achieved by the control circuit controlling a controllable switch which somewhat short-circuits the alternating current supplied by the charging coil, which means that the charging current can no longer flow into the battery, but only through the controllable switch, the rectifier diode and, if necessary, the light-emitting diode. The light emitting diode can be switched on and off by the control circuit via a further controllable switch. The stopping of the charging process will be effected in connection with the decision conditions known per se, such as the battery voltage, the charging and/or discharging time, the charging and/or discharging current, and/or the battery temperature, etc.

Drawings

The electronic circuit according to the invention shown in the drawings will be elucidated with reference to an embodiment in which like components are indicated with like reference numerals. Other configurations will be described in the specification.

In the drawings:

fig. 1 shows a first electronic circuit;

FIG. 2 shows a second electronic circuit;

fig. 3 shows a third electronic circuit.

Detailed Description

The first electronic circuit shown in fig. 1 comprises a full-wave rectifier with a first diode D1, a second diode D2 and a charging coil with a center tap, which thus comprises a first partial winding L1 and a second partial winding L2. The center tap of the charging coil is connected to the anode of another diode D3, and the cathode of diode D3 is connected to the anode of battery a. The negative pole of the battery a is connected to the anode of the first diode D1 and the anode of the second diode D2 and to the center tap of the charging coil via the first transistor T1. The cathode of the first diode D1 is connected to the first partial winding L1, and the cathode of the second diode D2 is connected to the second partial winding L2 and to the anode of the light-emitting diode LED. The cathode of the light-emitting diode LED is connected via a resistor R and a controllable switch S (e.g. a transistor) to the negative pole of the battery a. A series circuit composed of the second transistor T2 and the electric motor M is connected to the battery a. Of course, other loads may be connected to battery a via an electronic switch. The controllable switch S and the first transistor T1 and the second transistor T2 are controlled by a control circuit uC supplied with current by the battery a. The control circuit uC is also connected to the center tap of the charging coil to detect the presence or absence of a charging voltage.

The operation of the electronic circuit will be explained below. If the charging coil is inductively coupled to a charger (not shown), the full-wave rectifier provides a pulsed dc voltage at its center tap, and the corresponding pulsed dc current flows via a further diode D3 into the battery a, which is charged thereby. If the battery a is already deeply discharged at the beginning of charging, the voltage across the battery is so low that the control circuit uC cannot operate. If, after a short charging time, the battery voltage rises to such an extent that the control circuit uC "wakes up", the control circuit uC detects the presence of a pulsed direct voltage and switches on the light-emitting diode LED via the controllable switch S, which visually shows the charging of the battery a. Furthermore, the control circuit uC continuously compares the potential of the battery voltage with a reference value corresponding to a fully charged battery voltage. If the control circuit uC finds that the battery a is fully charged, it shorts the charging current to some extent by means of the first transistor T1, which means that the center tap of the charging coil is connected to the anode of the first diode D1 and to the anode of the second diode D2. When the first transistor T1 is gated on, the additional diode D3 prevents the battery a from also being short-circuited.

If the charging coil is still inductively connected to the charger, a half-wave of the pulsed dc current can still flow through the first diode D1, the first partial winding L1, the second partial winding T2 and the light-emitting diode LED as long as the controllable switch S is switched on. Preferably, the control circuit uC now controls the controllable switch S in such a way that the light-emitting diode LED blinks and thus indicates the fully charged state of the battery a. The other half-wave of the pulsed direct current now flows only through the second diode D2, the second partial winding L2 and the first transistor T1. If the charging coil is disconnected from the charger, the pulsed DC current no longer flows and the LED goes off.

If the control circuit uC gates the first transistor T1, the control circuit uC switches the electric motor M on or off by means of the second transistor T2, since the further diode D3 decouples the battery a from the full-wave rectifier, which battery a also supplies the control circuit uC and the electric motor M.

In a variant of the above-described electronic circuit, the controllable switch S may be replaced by a jumper. In this case, if the charging coil is coupled with the charger, the light emitting diode LED is always lit; the user is therefore unable to distinguish: whether battery a is still charging or has been fully charged.

In another variant of the electronic circuit described above, which is shown in fig. 2, the first diode D1 and the first partial winding L1 are absent and the first transistor T1 is replaced by an n-channel MOSFET. Such a transistor has a protective diode in a known manner. If the control circuit uC gates the first transistor T1 in order to terminate the charging of the battery a, the light-emitting diode LED indicates the fully charged state of the battery a, wherein the current required for this purpose (i.e. one half-wave of the pulsed direct current) flows through the charging coil L2, the protective diode, the controllable switch S switched on by the control circuit uC and the resistor R. The other half-wave of the pulsed dc current will flow through the charging coil L2, the second diode D2 and the first transistor T1.

The third electronic circuit shown in fig. 3 comprises the same full-wave rectifier as in the electronic circuit shown in fig. 1, with a first diode D1, a second diode D2 and a charging coil with a center tap, which thus comprises a first partial winding L1 and a second partial winding L2. The cathode of the first diode D1 is connected to the first partial winding L1, and the cathode of the second diode D2 is connected to the second partial winding L2 and to the anode of the light-emitting diode LED. The cathode of the light-emitting diode LED is connected via a resistor R and a controllable switch S (e.g. a transistor) to the cathode of the battery a and to the anode of the first diode D1 and to the anode of the second diode D2. The control circuit uC controls the controllable switch S, and the battery a supplies current to the control circuit uC. The control circuit uC is also connected to the center tap of the charging coil to detect the presence or absence of a charging voltage.

The electronic circuit shown in fig. 3 differs from the electronic circuit shown in fig. 1 in that: the center tap of the charging coil is connected to the transverse branch of a bridge circuit having four transistors T1, T2, T3, T4, and the electric motor M or other load is arranged in the transverse branch of the bridge circuit. The four transistors T1, T2, T3, T4 are MOSFETs, which are controlled by a control circuit uC and each have a protective diode in a known manner. The first transistor T1 and the second transistor T2 are n-channel MOSFETs, the source terminals of which are connected to the negative pole of the battery a; the third transistor T3 and the fourth transistor T4 are p-channel MOSFETs, and their source terminals are connected to the positive electrode of the secondary battery a. The drain terminals of the first and third MOSFETs T1 and T3 are connected to a center tap of the full wave rectifier and one end of the motor M, while the drain terminals of the second and fourth MOSFETs T2 and T4 are connected to the other end of the motor M.

In contrast to the circuit shown in fig. 1, the protective diode of the transistor T3 takes over the function of the further diode D3, i.e. in this circuit, in the presence of a pulsed direct current at the center tap of the charging coil, the battery a is charged, without the control circuit uC having to be operated. The function of the first transistor T1 of the circuit shown in fig. 1 (i.e. to switch off the charging of the battery a) is likewise taken over in the circuit shown in fig. 3 by the first transistor T1. When the first transistor T1 is gated on, the control circuit uC serves to turn off the third transistor T3, whereby the battery a is not short-circuited.

In a variant of the electronic circuit shown in fig. 3, the first diode D1 and the first partial winding L1 are absent. The operation of the electronic circuit is similar to the circuit shown in fig. 2 or 3.

Claims (8)

1. Electronic circuit for a small electrical appliance driven by a battery, said small electrical appliance being inductively powered by an external power supply, said electronic circuit comprising:

a charging circuit for charging a battery (A), having a charging coil (L2) and a diode (D2), wherein the battery (A) is connected in series with the diode (D2) and the charging coil (L2);

a Light Emitting Diode (LED) as a display device for displaying a charging process and/or a charging state of the storage battery (A);

wherein an end of the charging coil (L2) is connected to either an anode of the diode (D2) and a cathode of the Light Emitting Diode (LED), or a cathode of the diode (D2) and an anode of the Light Emitting Diode (LED).

2. The electronic circuit of claim 1, wherein:

the electronic circuit has a controllable switch (S) which can be controlled by a control circuit (uC) and by means of which the light-emitting diode (LED) can be switched on and off.

3. The electronic circuit according to claim 1 or 2, wherein:

the electronic circuit has an electronic switch (T1), the electronic switch (T1) being controllable by the control circuit (uC), and the charging process of the battery (A) can be ended by means of the electronic switch (T1).

4. An electronic circuit according to claim 2 or 3, characterized in that:

the control circuit (uC) switches on the light-emitting diode (LED) when the battery (A) is being charged and/or when the charging process of the battery (A) is ended.

5. Electronic circuit according to one of the preceding claims, characterized in that:

the electronic circuit has a further charging coil (L1) and a further diode (D1), which together with the diode (D2) and the charging coil (L2) form a full-wave rectifier.

6. Electronic circuit for a small electrical appliance driven by a rechargeable battery, having a load (M) and a charging coil (L2) for generating an alternating current, the load (M) being connected in a bridge circuit with a plurality of electronic switches (T1, T2, T3, T4), wherein at least one electronic switch (T3) is connected in parallel with a protection diode, in particular according to one of the preceding claims, characterized in that:

the battery (A) is connected in series with the protection diode and the charging coil (L2) in such a way that a charging current provided by the charging coil (L2) flows through the protection diode when the battery (A) is charged.

7. The electronic circuit of claim 6, wherein:

the electronic switches (T1, T2, T3, T4) are formed by MOSFETs with built-in protection diodes.

8. The electronic circuit according to one of claims 3 to 7, characterized in that:

the electronic switch by which the charging process of the battery (A) can be terminated is formed by one of the electronic switches (T1) of the bridge circuit.