Circuit for a small electric appliance with an accumulator and method for measuring a charging current

• US 9,124,118 B2
• Filed: 09/13/2012
• Issued: 09/01/2015
• Est. Priority Date: 09/16/2011
• Status: Active Grant

• Current Assignee: Braun GmbH (The Procter & Gamble Company)
• Original Assignee: Braun GmbH (The Procter & Gamble Company)
• Inventors: Klemm, Torsten, Faranda, Leo, Kchler, Kervin Heinrich
• Primary Examiner(s): Ro, Bentsu
• Assistant Examiner(s): DINH, THAI T
• Application Number:
  US13/612,977
• Publication Number:
  US 20130069565A1
• Time in Patent Office: 1,083 Days
• Field of Search: 318/139, 318/494, 318/501, 318/504, 320/125, 320/127, 320/136, 320/148, 320/162, 320/165
• US Class Current: 1/1
• CPC Class Codes: H02J 2207/10 Control circuit supply, e.g. means for supplying power to the control circuit
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/0068 Battery or charger load switching, e.g. concurrent charging and load supply H02J7/0013 takes precedence
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters

Abstract

A circuit for a small electric appliance is disclosed. The circuit includes a battery (B); a control circuit (uC) for measuring the charging current of the battery (B); a DC-DC converter (DC/DC) which supplies the control circuit (uC) from the battery; and a current sensing resistor (R1), whose one end lies at a reference potential and whose other end is connected to the battery (B). The control circuit (uC) has a terminal which is at reference potential, and a measurement input which is related to the reference potential.

Claims

1. A circuit for a small electric appliance, comprising:

a battery having a negative terminal and a positive terminal;

a current-sensing resistor sensing a charging current;

a control circuit measuring the charging current of the battery;

a DC-DC converter directly connected to the battery such that the DC-DC converter is directly connected to both the negative terminal of the battery and the positive terminal of the battery, wherein the DC-DC converter supplies power to the control circuit from the battery; and

wherein the control circuit has a measurement input (ADC) which is related to a reference potential, wherein the reference potential is connected via the current-sensing resistor (R1) to the negative terminal of the battery.

2. The circuit according to claim 1, wherein the measuring input of the control circuit (uC) is connected to the other end of the current sensing resistor (R1) via a low pass filter (R2, C2).

3. The circuit according to claim 1, wherein at least one further load is provided which is connected to reference potential, which is controllable by the control circuit (uC), and which is powered by the DC-DC converter (DC/DC).

4. The circuit according to claim 3, wherein the control circuit (uC) measures the charging current only when the at least one further load is switched off.

5. The circuit according to claim 3, wherein the control circuit (uC) provides the measured charging current with at least one correction value when the at least one further load is not switched off.

6. A small electrical appliance comprising the circuit according to claim 1.

7. The small electric appliance according to claim 6, further comprising an electric motor (M) which is connected to the battery (B) via a controllable switch (S2) controlled by the control circuit (uC).

8. A method for measuring a charging current of a battery having a positive terminal and a negative terminal, the method comprising:

providing a current-sensing resistor and a control circuit;

providing a DC-DC converter directly connected to the battery such that the DC-DC converter is directly connected to both the negative terminal of the battery and the positive terminal of the battery, the converter supplying power to the control circuit from the battery;

supplying power to the control circuit from the DC-DC converter and at least one further load from the battery, wherein the control circuit has a measurement input to a reference potential that is connected via the current-sensing resistor to the negative terminal of the battery.

9. A circuit for a small electric appliance, comprising:

a battery having a negative terminal and a positive terminal;

a current-sensing resistor sensing a charging current;

a control circuit measuring the charging current of the battery;

a DC-DC converter directly connected to the battery, wherein the DC-DC converter supplies power to the control circuit from the battery in series with the battery and the current-sensing resistor; and

wherein the control circuit has a measurement input (ADC) which is related to a reference potential, wherein the reference potential is connected via the current-sensing resistor (R1) to the negative terminal of the battery, and wherein neither the motor current nor the current of the DC-DC converter flows through the current-sensing resistor R1.

10. The circuit according to claim 9, wherein the DC-DC converter is directly connected to both the negative terminal of the battery and the positive terminal of the battery.