Device for reducing the output current of a battery charger
A device for reducing the output current of a primary switched battery charger, which charger includes an input DC power circuit, a high frequency transformer and control unit for modulating the DC input power. The device includes elements for measuring pulse ratio of switch pulses on the output side of the charger, elements for measuring peak value of output voltage, elements for differentially amplifying the signals measured and elements for integrating voltage/current of the differentially amplified signals, wherein the integrated voltage/current is used for modulating the input DC power in order to reduce the output current. The device includes elements for measuring the output effect of the charger, elements for measuring the output voltage of the charger, elements for dividing the signals measured and elements for multiplexing voltage/current of the output from the elements for dividing, wherein the multiplexed voltage/current is used for modulating the input DC power in order to reduce the output current.
1. Device for reducing the output current of a primary switched battery charger, which charger comprises an input DC power circuit, a high frequency transformer and a control unit for modulating the DC input power, said device comprising:
a pulse measuring unit for measuring a pulse ratio of switch pulses on the output side of the charger;
a peak measuring unit for measuring a peak value of an output voltage of the charger;
a differential amplifying unit providing an output signal by differentially amplifying the measured pulse ratio of switch pulses from the pulse measuring unit and the measured peak value of the output voltage from the peak measuring unit; and
an amplifier for adding the output voltage of the charger to the output signal from said differential amplifying unit,
wherein the device is adapted to transmit the output signal from said amplifier to said control unit for use in modulating the input DC power in order to reduce the output current of the charger.
2. Device according to claim 1 , characterised in a switch capable of switching on and off a connection between said amplifying unit and said amplifier.
3. Device according to claim 1 , wherein,
the pulse measuring unit comprises connections for for connection to the output side of the high frequency transformer of the charger, the measured pulse ratio is a ratio between a pulse duration and an interval between two consecutive pulses and is a measure of output effect of the charger at a given output voltage,
the peak measuring unit comprises connections between positive and the negative lines of the charger,
the differential amplifying unit connected to outputs of the pulse measuring unit and the peak measuring unit to receive the measured pulse ratio of switch pulses from the pulse measuring unit and the measured peak value of the output voltage from the peak measuring unit,
the amplifier connected to receive the output signal from the differential amplifying unit and the output voltage of the charger,
an output of the amplifier connected to said control unit by a feedback line, the amplifier transmitting the output signal from the amplifier to said control unit via said feedback line for use in modulating the input DC power in order to reduce the output current of the charger.
4. Method for reducing the output current of a primary switched battery charger, which charger comprises an input DC power circuit, a high frequency transformer and a control unit for modulating the DC input power, the method comprising the steps of:
measuring a pulse ratio of switch pulses on the output side of the charger;
measuring a peak value of an output voltage of the charger;
differentially amplifying the measured pulse ratio of switch pulses and the measured peak value of the output voltage to obtain a differential amplification output signal;
adding the output voltage of the charger to the obtained differential amplification output signal to obtain a control signal; and
transmitting the control signal to the control unit for use in modulating the input DC power in order to reduce the output current of the charger.
5. A combination, comprising:
a primary switched battery charger, said charger comprising an input DC power circuit, a high frequency transformer, and a control unit for modulating the DC input power; and
a device for reducing an output current of the primary switched battery charger, said device comprising
i) a pulse measuring unit connected to the output side of the charger to measure a pulse ratio of switch pulses on the output side of the charger;
ii) a peak measuring unit connected to the output side of the charger to measure a peak value of an output voltage of the charger;
iii) a differential amplifying unit connected to output sides of the pulse measuring unit and peak measuring unit to provide an output signal by differentially amplifying the measured pulse ratio of switch pulses from the pulse measuring unit and the measured peak value of the output voltage from the peak measuring unit; and
iv) an amplifier connected to the output signal of the differential amplifying unit and to the output side of the charger and adding the output voltage of the charger to the output signal from said differential amplifying unit, the amplifier having an output connected to said control unit,
wherein the amplifier transmits the output signal from the amplifier to said control unit, said control unit using the output signal from said amplifier in modulating the input DC power in order to reduce the output current of the charger.