Cable voltage drop compensation for battery chargers
AssigneeFairchild Semiconductor Corporation
InventorHangseok Choi
Life of this patent
Estimating the term…
Abstract
A battery charger may be configured to charge a battery by way of a charging cable. A DC gain of a voltage control loop of the battery charger may be limited to a predetermined value to compensate for voltage drop on the charging cable. For example, a DC gain of an error amplifier on the voltage control loop may be limited to a predetermined value for cable voltage drop compensation. The error amplifier may use a reference signal that is generated as a function of the error signal. The DC gain of the error amplifier may be limited by connecting a resistor to form an RC circuit on an output node of the error amplifier.
Claims20
A battery charger comprising:
- a transformer having a primary winding and a secondary winding;
- a transistor coupled to the primary winding of the transformer, the transistor being configured to couple the primary winding to ground when the transistor is ON and to decouple the primary winding from ground when the transistor is OFF, the transistor being configured to receive an inductor current through the primary winding when the transistor is ON;
- a comparator having a first input node and a second input node, the first input node of the comparator being coupled to receive a sense signal indicative of the inductor current, the second input node of the comparator being coupled to receive an error signal, the comparator being configured to generate at an output node of the comparator a control signal for controlling switching of the transistor by comparing the sense signal to the error signal;
- and
- an error amplifier having a first input node and a second input node, the first input node of the error amplifier being coupled to receive a reference voltage that changes as a function of the error signal, the second input node of the error amplifier being coupled to receive a sampling of an output voltage generated by the battery charger to charge a battery by way of a charging cable, the error amplifier being configured to generate the error signal at an output node of the error amplifier by comparing the sampling of the output voltage to the reference voltage, the error signal being indicative of a level of the output voltage, the error amplifier being configured to compensate for voltage drop on the charging cable by having a predetermined and limited DC gain.
An electrical circuit for charging a battery, the circuit comprising:
- an error amplifier in a voltage control loop of a battery charger that is configured to charge a battery by way of a charging cable, the error amplifier having a first input node and a second input node, the error amplifier being configured to generate an error signal at an output node of the error amplifier by comparing a sampled output voltage indicative of an output voltage of the battery charger at the first input node of the error amplifier to a reference voltage at the second input node of the error amplifier, a DC gain of the voltage control loop being limited to a predetermined value to compensate for voltage drop on the charging cable and develop a regulated battery voltage to charge the battery;
- a reference voltage generator coupled to the second input node of the error amplifier, the reference voltage generator being configured to generate the reference voltage as a function of the error signal;
- and
- a comparator having a first input node and a second input node, the comparator being configured to generate at an output node of the comparator a control signal to control switching of a transistor and generation of the output voltage by comparing the error signal at the first input node of the comparator to a sense signal at the second input node of the comparator, the sense signal being indicative of inductor current flowing through a primary winding of a transformer of the battery charger.
A method of compensating for voltage drop on a charging cable coupling a battery charger to a rechargeable battery, the method to be performed by an electrical circuit and comprising:
- sensing an output voltage of the battery charger to generate a sampled output voltage;
- comparing the sampled output voltage to a voltage reference to generate an error voltage using an error amplifier, the error amplifier having a limited DC gain;
- adjusting the voltage reference as a function of the error voltage, the error voltage being indicative of a level of the output voltage;
- comparing the error voltage to a sense voltage indicative of inductor current on a primary winding of a transformer to control generation of the output voltage;
- and
- charging the rechargeable battery with a battery voltage presented by the output voltage through the charging cable, the DC gain of the error amplifier being configured to generate the battery voltage to compensate for voltage drop on the charging cable.
Dependencies are inferred from the claim text.