EP3100329A1

EP3100329A1 - Electrical circuit having precise overcurrent sensing function without additional supply

Info

Publication number: EP3100329A1
Application number: EP14702802.1A
Authority: EP
Inventors: Mucahit Bacaksiz; Ahmet Ihsan Yuce
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2014-01-31
Filing date: 2014-01-31
Publication date: 2016-12-07
Also published as: WO2015113617A1

Abstract

The present invention relates to an overcurrent protection circuit for an electrical household appliance, said overcurrent protection circuit comprising an input stage operable to convert AC voltage to a DC voltage by which AC voltage is rectified and filtered, a voltage generator generating a peak voltage, a reference comparator having a programmable voltage reference (5) comparing said generated voltage with a reference voltage so as to be conducting when a certain voltage level is reached and an isolated signal output.

Description

ELECTRICAL CIRCUIT HAVING PRECISE OVERCURRENT SENSING FUNCTION WITHOUT ADDITIONAL SUPPLY

The present invention relates to an electrical overcurrent protection circuit, more particularly, to a circuit providing overcurrent protection for electrical household appliances.
It is well-known that electrical household appliances such as for instance laundry treatment appliances can draw an excessive amount of electric current due to a variety of reasons. It can be the case that for instance the appliance suffers from manufacturing faults or other external conditions such as temperature and/or moisture can deteriorate the operation of the appliance in time. As such, electrical household appliances necessitate special circuit-level designs for overcurrent protection.
The present invention proposes a circuit design distinguishable in that it provides an overcurrent protection circuit requiring no additional DC terminal for energizing a reference comparator unit such that the circuit is operable to detect overcurrent without an additional supply in order for powering the reference comparator. To this end, the circuit of the invention comprises an input stage, a voltage generator, a reference comparator and an isolated signal output. The advantageous aspect of the circuit of the invention lies in that it affords overcurrent protection without employing an additional power supply for supplying the reference comparator.
Among others, a prior art publication in the technical field of the invention may be referred to as KR 101032045, which discloses a switching mode power supply apparatus having an over voltage protection function, provided to protect a power supply circuit and a load by monitoring the primary side of a transformer. A primary rectifier rectifies an inputted AC power source into DC power. An overvoltage detection unit and an overcurrent detection unit sense the supply of overvoltage and overcurrent to a secondary side of a transformer. A stable operation power source is supplied to a pulse width controller through feedback switching control using a feedback circuit, a pulse width controller, and a power switch.
The present invention provides an overcurrent protection circuit for an electrical household appliance, which is provided by the characterizing features as defined in Claim 1.
Primary object of the present invention is to provide an overcurrent protection circuit for an electrical household appliance without employing an additional power supply for supplying the reference comparator of the overcurrent protection circuit.
The present invention proposes an overcurrent protection circuit for an electrical household appliance. An electrical household appliance having an electrical motor may draw an excessive amount of current under certain conditions. An overcurrent prevention system is hence proposed, by which the voltage applied to the terminals of the electrical equipment (such as for instance the rotary machine) directly supplies power to the overcurrent protection circuit.
The overcurrent protection circuit has an input stage, a peak voltage generator, a reference comparator with a programmable voltage reference, i.e. an adjustable shunt regulator comparing said generated voltage with a reference voltage and conducting when a certain voltage level is reached. Said programmable voltage reference is directly powerable by said generated voltage without any additional power supply.
Said programmable voltage reference’s reference pin is connected to a center point between two resistors such that resistance values of said resistors are selectable to enable the programmable voltage reference to conduct when a certain voltage level is reached at which voltage level a LED is turned on. An optocoupler is used to obtain an isolated signal output.
Accompanying drawings are given solely for the purpose of exemplifying an overcurrent protection circuit for an electrical household appliance, whose advantages over prior art were outlined above and will be explained in brief hereinafter.
The drawings are not meant to delimit the scope of protection as identified in the claims nor should they be referred to alone in an effort to interpret the scope identified in said claims without recourse to the technical disclosure in the description of the present invention.
Fig. 1 demonstrates the circuit diagram of an overcurrent protection circuit for an electrical household appliance according to the present invention.
The following numerals are used in the detailed description:

Overcurrent protection circuit
Input capacitor
Peak detector diode
Peak detector capacitor
Programmable voltage reference
Voltage divider resistance
Voltage divider resistance
LED
Current limiting resistance
Parallel resistance
Photo-transistor
Indication LED

The present invention proposes an overcurrent protection circuit for an electrical household appliance, the circuit being designated generally by the numeral 1.
The electrical household appliances may for instance incorporate an electrical motor as shown in the accompanied drawings. The circuit will perform overcurrent detection in the event excessive current is drawn, for instance if overloading or locked rotor condition is present, and will then generate a respective indication signal in this effect.
According to the present invention, the AC power can be rectified by a half-wave rectifier, i.e. a diode (not shown) and filtered into a DC voltage by an input capacitor (2). A voltage generator can incorporate a diode and a capacitor, a peak detector diode (3) charging a peak detector capacitor (4) up to the peak voltage at its input. Once the peak detector capacitor (4) is charged up to the peak voltage, the peak detector diode (3) conducts to keep the latter charged, prevents the same from draining. The peak detector diode (3) can be any low voltage diode with stable forward voltage drop (such as for instance SB160).
The present invention further features a reference comparator having a programmable voltage reference (5), which can be realized by commercially available TL431 or TS431 regulators, such regulators constituting an appropriate replacement for a zener diode.
The output voltage of the programmable voltage reference (5) can be set to any value within a predefined range (typically between 2,5V and 36V for TL431). In use, the resistances R₁₁ and R₁₅ (6, 7) acting as a voltage divider, are selected such that said programmable voltage reference (5) will begin conducting only when a certain voltage level is reached; a center point between said resistors R₁₁ and R₁₅ (6, 7) is connected to the reference pin of the programmable voltage reference (5). The upper voltage limit can typically be calculated in accordance with the following expression while V_ref is a fixed value (approximately 2,5V):
V_ref(1 + R₁₁/R₁₅)
Since the voltage at which a LED (8) is turned on is determined by the resistances R₁₁ and R₁₅ (6, 7) acting as a voltage divider, they can accordingly be selected to provide the upper voltage limit that determines the voltage level at which the programmable voltage reference (5) will begin conducting.
The R₄ resistance is a current limiting resistance (9) protecting the LED (8) from excessive current being connected in series therewith. Further, a parallel resistance R₉ (10), in parallel with the LED (8) is effective in that the LED (8) is prevented from conducting if no overcurrent situation is in question. To provide an isolated signal to the overcurrent prevention system, an optocoupler is conventionally used, in which, current from the source signal emits an infra-red light, intensity of which is proportional to the electrical signal. The photo-transistor is then switched on by the light falling upon its base.
According to the present invention, a source signal is then generated to detect presence of overcurrent conditions without using an additional power supply. The photo-transistor (11) functions as a normal bipolar junction transistor (BJT) and its collector current drives another BJT (Q₁) being a PNP transistor, whose collector current in turn turns an indication LED (12) on through a capacitor and another switching element (Q₂). To this end, while the indication LED (12) itself can let end-users reach authorized maintenance and service staff, a respective circuit in the form of an overcurrent prevention system can disconnect the appliance from the mains upon receiving a respective signal.
In a nutshell, the present invention proposes an overcurrent protection circuit for an electrical household appliance, said overcurrent protection circuit comprising an input stage operable to convert AC voltage to a DC voltage by which AC voltage is rectified and filtered, a voltage generator generating a peak voltage, a reference comparator having a programmable voltage reference (5) comparing said generated voltage with a reference voltage so as to be conducting when a certain voltage level is reached and an isolated signal output. Said programmable voltage reference (5) is directly powerable by the generated voltage.
According to an embodiment of the invention, the input stage comprises a half-wave rectifier and a filtering input capacitor (2). The voltage generator comprises a peak detector diode (3) and a peak detector capacitor (4).
According to an embodiment of the invention, the programmable voltage reference (5) is a TL431 or TS431 regulator. The programmable voltage reference’s (5) reference pin is connected to a center point between two resistances R₁₁ and R₁₅ (6, 7) and the resistances R₁₁ and R₁₅ (6, 7) are selected such that the programmable voltage reference (5) conducts when a certain voltage level is reached at which voltage level a LED (8) is turned on.
In a further embodiment of the invention, said LED (8) is electrically in series with a current limiting resistance R₄ (9) protecting the latter from excessive current and a parallel resistance R₉ (10) is provided in parallel with the LED (8). An optocoupler is used to provide an isolated signal to an overcurrent prevention system, the system in turn turning an indication LED (12) on or disconnecting the electrical household appliance from the mains.
The present invention ensures that an overcurrent protection circuit for an electrical household appliance is obtained without having an additional power supply for supplying the reference comparator of the overcurrent protection circuit. In other words, the voltage applied to the terminals of the electrical equipment (such as for instance the rotary machine) in the appliance also supplies the overcurrent protection circuit’s reference comparator in the manner to be directly powerable by the voltage generated by the voltage generator of the overcurrent protection circuit.

Claims

An overcurrent protection circuit for an electrical household appliance, said overcurrent protection circuit comprising an input stage operable to convert AC voltage to a DC voltage by which AC voltage is rectified and filtered, a voltage generator generating a peak voltage, a reference comparator having a programmable voltage reference (5) comparing said generated voltage with a reference voltage so as to be conducting when a certain voltage level is reached and an isolated signal output characterized in that;

said programmable voltage reference (5) is directly powerable by said generated voltage.
An overcurrent protection circuit as in Claim 1, characterized in that the input stage comprises a half-wave rectifier and a filtering input capacitor (2).
An overcurrent protection circuit as in Claim 1, characterized in that the voltage generator comprises a peak detector diode (3) and a peak detector capacitor (4).
An overcurrent protection circuit as in Claim 1, characterized in that the programmable voltage reference (5) is a TL431 or TS431 regulator.
An overcurrent protection circuit as in Claim 1 and 4, characterized in that the programmable voltage reference’s (5) reference pin is connected to a center point between two resistances R₁₁ and R₁₅ (6, 7).
An overcurrent protection circuit as in Claim 5, characterized in that said resistances R₁₁ and R₁₅ (6, 7) are selected such that the programmable voltage reference (5) conducts when a certain voltage level is reached at which voltage level a LED (8) is turned on.
An overcurrent protection circuit as in Claim 6, characterized in that the LED (8) is electrically in series with a current limiting resistance R₄ (9) protecting the latter from excessive current.
An overcurrent protection circuit as in Claim 6 or 7, characterized in that a parallel resistance R₉ (10), is provided in parallel with the LED (8).
An overcurrent protection circuit as in Claim 6 or 7, characterized in that an optocoupler is used to provide an isolated signal to a overcurrent prevention system, said system in turn turning an indication LED (12) on or disconnecting said electrical household appliance from the mains.