Power-Supply Circuit For An Electrical Appliance Having A Battery And A DC-TO-DC Converter

Abstract

A power supply circuit for a small electrical appliance is disclosed. The power supply circuit includes a battery; a first load with a relatively high power consumption; a controllable switch; at least a second load with a low power consumption; and a DC-to-DC converter. The first load is connected to the battery via the controllable switch and the DC-to-DC controller supplies power from the battery to the second load, such that the controllable switch supplies to the first load a pulsed voltage having a pulse-pause ratio. The DC-to-DC converter powers the second load at least during the pauses.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of European Patent Convention Application No. 11007660.1, filed Sep. 16, 2011 and European Patent Convention Application No. 12004883.0, filed Jun. 29, 2012, the substance of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present disclosure is directed to a power-supply circuit for a battery-powered small electrical appliance which includes a first load with a relatively high power consumption, a controllable switch, at least a second load with a relatively low power consumption and a DC-to-DC converter. The present disclosure is further directed to a power supply method for such a small electrical appliance.

BACKGROUND OF THE INVENTION

WO 02/15374 A1 describes a power supply circuit for electromotive small electrical appliances that are battery-powered and controlled by means of a microcontroller. The power supply circuit comprises a DC-to-DC converter that increases the voltage of the battery to a level that is sufficient for the microcontroller. The DC-to-DC converter is a step-up converter whose choke coil is formed by the electric motor. The electric motor is controlled by the microcontroller with a pulse width modulated voltage in order to, on the one hand, enable the motor to run at the desired speed and, on the other hand, enable the step-up converter to provide sufficient voltage. However, the power supply circuit has the disadvantage that the step-up converter does not supply voltage when the speed of the electric motor is reduced—for instance when switching off the motor.

EP 0 875 978 B1 describes a power supply circuit for electromotive small electrical appliances which are powered by an accumulator and controlled by means of a microcontroller. The power supply circuit comprises a DC-to-DC converter that increases the voltage of the accumulator to a level that is sufficient for the microcontroller. If the accumulator is sufficiently charged, the microcontroller is powered by the DC-to-DC converter and the accumulator. If the accumulator is not sufficiently charged, the microcontroller is powered via a capacitor while charging the accumulator by means of a charger, whereas the charging process of the accumulator is intermittently interrupted for short periods of time in order to recharge the capacitor.

Typical DC-to-DC converters contain an internal circuit that deactivates the DC-to-DC converter whenever the supply voltage drops below a minimum voltage of e.g. 0.95 V. If the DC-to-DC converter powers a control circuit of a small electrical appliance containing a battery with only one cell (e.g. a NiMH battery with a nominal voltage of 1.2 V) and an electric motor, the starting current (e.g. 7 A) of the electric motor might lead at least temporarily to a drop in battery voltage sufficient for the DC-to-DC converter to deactivate and stop supplying power to the control circuit, even with a fully-charged battery. This might occur in an old battery with a relatively high internal resistance (e.g. 50 mΩ).

There exists a need for a simple circuit and a method of power supply to a small electrical appliance as described above that better exploits any charge still left in the battery. This need may be met by means of a power supply circuit in which the load with the relatively high power consumption is powered by a pulsed voltage having a pulse-pause ratio, and in which the DC-to-DC converter powers the load with the relatively low power consumption at least during the pauses.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiment set forth in the drawing is illustrative in nature and not intended to limit the invention defined by the claims The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawing, where like structure is indicated with like reference numerals and in which:

FIG. 1 is a drawing of a power supply circuit according to one embodiment.

SUMMARY OF THE INVENTION

In one embodiment, a power supply circuit for a small electrical appliance is provided. The power supply circuit includes a battery; a first load with a relatively high power consumption; a controllable switch; at least a second load with a low power consumption; and a DC-to-DC converter. The first load is connected to the battery via the controllable switch and the DC-to-DC controller supplies power from the battery to the second load, such that the controllable switch supplies to the first load a pulsed voltage having a pulse-pause ratio. The DC-to-DC converter powers the second load at least during the pauses.

These and other features, aspects and advantages of specific embodiments will become evident to those skilled in the art from a reading of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The following text sets forth a broad description of numerous different embodiments of the present disclosure. The description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. It will be understood that any feature, characteristic, component, composition, ingredient, product, step or methodology described herein can be deleted, combined with or substituted for, in whole or part, any other feature, characteristic, component, composition, ingredient, product, step or methodology described herein. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims. All publications and patents cited herein are incorporated herein by reference.

According to the present disclosure, a power supply circuit is provided. In one embodiment, the power supply circuit has the advantage that a small electrical appliance can be powered for a relatively long period of time with one single battery charge when the battery presents a high internal (e.g. age-related) resistance. As the load with the relatively high power consumption, e.g. an electric motor, is powered by a pulsed voltage and during the pauses the battery voltage exceeds the voltage present during the pulses, the DC-to-DC converter at least operates during the pauses and charges a capacitor connected in the usual manner at its output terminal, the capacitor powering the load with the relatively low power consumption, for instance a control circuit, which controls the functions of the small electrical appliance. In this manner, the battery charge can be almost completely used—although at a relatively low voltage in older batteries. In one embodiment, the pulsed voltage may have a pulse-pause ratio whose pauses are adjusted in such a way that the DC-to-DC converter can adequately power the second load, even when only operating during the pauses.

In one embodiment, the DC-to-DC converter may exhibit a control port, with the DC-to-DC converter activated when the control port carries sufficient voltage. The control port is connected to the control circuit that can switch the DC-to-DC converter on and off. The power supply circuit may also contain a connection to a charger or a charging coil to charge the accumulator, the former also being connected to the control port of the DC-to-DC converter. The DC-to-DC converter is therefore operating as long as the charger or the charging coil supplies sufficient voltage, or as long as the control circuit keeps the DC-to-DC converter operating. The control circuit can thus prevent the DC-to-DC converter from automatically switching off in the usual manner during periods of low battery voltage. It is advantageous, for instance, for the control circuit to ensure that the DC-to-DC converter remains in operation during the short-term voltage drop that results from switching on the motor. The DC-to-DC converter may still exhibit the usual internal circuitry that switches off the DC-to-DC converter when the supply voltage drops below a minimal voltage, whereby this minimal voltage may be set to a relatively low value, which ensures that the battery will not be deeply discharged by the DC-to-DC converter.

The power supply circuit may be suitable for a battery-powered small electrical appliance, such as an electric toothbrush or shaver, whose batteries only consist of only one cell and whose battery voltages (e.g. 1.2 V) must be increased by a DC-to-DC converter to a voltage (e.g. 3 V) suitable to the control circuit.

In one embodiment, the power supply circuit contains a charging coil L1 connected to a battery B via a diode D1 and a first controllable switch S1, with one end of the charging coil L1 connected to the anode of the diode D1 and the other end of the charging coil L1 to the negative pole of the battery B (reference potential). A first capacitor C1 and a series connection from an electric motor M and a second controllable switch S2 are connected in parallel to the battery B. The battery B is also connected to a DC-to-DC converter DC/DC. The DC-to-DC converter DC/DC further exhibits a control input and an output terminal, to which one end of a second capacitor C3 is connected. The other end of the second capacitor C3 is connected to the negative pole of the battery B. A control circuit uC presents two terminals for its power supply, one of which is connected to the output port of the DC-to-DC connector DC/DC, the other to the reference potential. The control circuit uC further exhibits an input which is connected to the positive pole of the battery B as well as three outputs, one of which is connected to the first controllable switch S1, the second to the second controllable switch S2, and the third to the control input of the DC-to-DC converter DC/DC and to one end of a resistor R4. The other end of the resistor R4 is connected to the cathode of the diode D1, the first controllable switch S1 and one end of a second resistor R3, whose other end is connected to the reference potential. The first controllable switch Si is only represented schematically. It may, for instance, consist of an electronic circuit that will automatically activate when the charging coil applies sufficient voltage in order to charge the battery.

The method according to which this power supply circuit operates is explained hereafter, initially assuming that the DC-to-DC converter DC/DC is not operating. As a consequence, the second capacitor C3 at the output port of the DC-to-DC converter is discharged, thus also rendering the control circuit uC inoperative and leaving both the first Si and the second S2 controllable switch open. If a small electrical appliance with this type of power supply circuit is to be switched on (if, for instance, the motor M is to be put into operation), the small electrical appliance may be connected with a charger not represented in the FIGURE in order for the charging coil L1 to supply voltage via the diode D1 and the resistor R4 to the control input of the DC-to-DC converter. If the voltage at the control input is sufficiently high, the DC-to-DC converter switches on and charges the second capacitor C3 connected to its output (e.g. to a voltage of 3 V). However, the DC-to-DC converter requires a minimum voltage in order to supply power and therefore, despite the sufficiently high voltage at its control input, will not supply power if the voltage at the battery (e.g. a NiMH accumulator with a nominal voltage of 1.2 V) or at the first capacitor C1 is below the minimum voltage.

If the voltage at the second capacitor C3 is sufficiently high, the control circuit uC switches on and takes control of the small electrical appliance including the motor M (via the controllable switch S2), the DC-to-DC converter DC/DC and the battery charging process (in particular the termination of the charging process by opening the controllable switch S1 when the battery reaches full charge condition) as well as additional loads, where required, not described in the FIGURE, such as a display. The control of the small electrical appliance depends on the battery voltage or the voltage at the first capacitor C1, which is continuously monitored by the control circuit. It is particularly advantageous if the control circuit keeps the DC-to-DC converter in operating condition during the start-up of the motor by applying a respective signal to the control input of the DC-to-DC converter. Should the voltage at the first capacitor C1 temporarily drop below the minimum voltage of the DC-to-DC converter, due to the signal applied to the control input the DC-to-DC converter will immediately resume power supplying as soon as the minimum voltage is reached again.

In one embodiment, the control circuit uC powers the motor M with a pulsed voltage, which may exhibit a fixed frequency (fixed cycle duration) and a fixed pulse-pause ratio. The control circuit controls the second controllable switch S2, for example, in such a way that it will be switched on during 95-99% of the cycle and is only inactive during 1-5% of the cycle. In one embodiment, the control circuit may be operational at a frequency of about 250 Hz and is switched on during approximately 98% of the cycle time, while the motor M is running The length of the pauses of the pulsed voltage, the properties of the DC-to-DC converter, the size of the second capacitor C3 (e.g. 10 μF), and the power consumption of the control circuit uC (e.g. TI MSP 430) are optimally coordinated in order for the control circuit to receive a sufficient power supply, even when the DC-to-DC converter is charging the second capacitor C3 only during the pauses. This might occur when the battery voltage is relatively low, that is, the battery is almost empty, and/or the motor M has a particularly high power requirement—for instance during start-up. If the battery voltage is relatively high, the DC-to-DC converter may be operating during the whole cycle length and supplying sufficient current to not only power the control circuit uC, but the other loads as well. With medium battery voltage and a running motor M, the situation can arise that the voltage at the first capacitor C1 drops below the minimum voltage of the DC-to-DC converter after half a cycle and thus will stop supplying power. The control circuit will then temporarily switch off the other loads and will draw power from the second capacitor C3 during the remaining cycle time, while the DC-to-DC converter will recharge the second capacitor C3 during the pause (if the DC-to-DC converter's minimum voltage has been reached again after switching off of the motor).

The above-described power supply circuit of a small electrical appliance hence operates according to a method wherein the load with a relatively high power consumption is powered by a pulsed voltage having a pulse-pause ratio and the load with a relatively low power consumption is powered by the DC-to-DC converter, at least during the pauses. In one embodiment, the pauses may be adjusted such that the load with the relatively low power consumption will receive sufficient power even with the DC-to-DC converter merely operating during the pauses. If the battery voltage is higher than a determined minimum voltage, the DC-to-DC converter will power the second and further loads even during the pulses. The control circuit furthermore provides continuous monitoring of the battery voltage and switches the small electrical appliance off whenever necessary. If, for instance, the battery voltage is lower than a first threshold value directly after switching off the motor, or the battery voltage is lower than a second threshold value during operation of the motor, the control circuit may first disconnect the motor, then the other loads, and lastly the DC-to-DC converter. As soon as the voltage at the second capacitor C3 has dropped accordingly, the control circuit uC will also disconnect. In this manner, a deep discharge of the battery can be avoided. Then the small electrical appliance can only be put back into operation by charging the battery B.

In one embodiment, the control circuit uC may be implemented in a microcontroller.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

1. A power supply circuit for a small electrical appliance, comprising:

a battery;

a first load with a relatively high power consumption;

a controllable switch;

at least a second load with a low power consumption; and

a DC-to-DC converter;

wherein the first load is connected to the battery via the controllable switch and the DC-to-DC controller supplies power from the battery to the second load, such that the controllable switch supplies to the first load a pulsed voltage having a pulse-pause ratio, and wherein the DC-to-DC converter powers the second load at least during the pauses.

2. A power supply circuit according to claim 1, wherein the first load is an electric motor and the second load is a control circuit.

3. A power supply circuit according to claim 1, wherein the pulsed voltage has a pulse-pause ratio whose pause is adjusted in such a way that the DC-to-DC converter can sufficiently power the second load even when only operating during the pauses.

4. A power supply circuit according to claim 1, wherein the DC-to-DC converter exhibits a control input and can be switched on and off by applying the appropriate voltages to the control input.

5. A power supply circuit according to claim 4, further comprising a charging coil, and wherein the DC-to-DC converter can be activated by the charging coil by applying a voltage to the control input.

6. A power supply circuit according to claim 4, wherein the control input of the DC-to-DC converter is connected to the control circuit.

7. A small electrical appliance with a power supply circuit according to claim 1.