In the past, a range of different battery types have been developed to power portable electronic devices. Specific types or chemistries include Nickel Cadmium (Ni-Cad), Nickel Metal Hydride (Ni-MH) and Lithium-Ion (Li-Ion). Of these, Li-Ion batteries are increasingly popular due to their high output voltage and power density. This makes Li-Ion batteries ideal for a wide range of application including cellular telephones, personal music players and laptop computers.
Numerous charging circuits have been developed to support the rechargeable batteries used in portable electronic devices. The basic function of these circuits is to provide power at the correct current and voltage to match battery requirements. Often this is done in multiple stages.
For example, for Li-Ion rechargeable batteries, a battery condition mode or tickle charge stage is introduced first, followed by a rapid charge stage when constant current at a high rate is applied until the battery voltage reaches a predefined threshold. Next, a constant voltage stage is applied until the charger current drops below a lower threshold at which point the charging cycle terminates. Ni-Cad and Ni-MH batteries, on the other hand, use an initial activation stage in which a low level current is supplied to the battery. The activation stage is followed by a rapid charge stage where the battery is charged at a relatively high rate. A trickle stage may then be used to top off the voltage of charged batteries.
In practice, charging circuits generally monitor a number of parameters such as battery voltage and the current flowing to the battery. Other parameters may have to be monitored as well. For example, U.S. Pat. Nos. 6,507,172 and 6,148,652 (both incorporated in this document by reference) both disclose chargers that allow portable devices to be recharged using power drawn from a USB (universal serial bus) connection. For chargers of this type, it is generally necessary to monitor the load applied by the charger to the USB bus. This prevents overloading of the USB bus which can result in data lose or other failures.
To save cost, battery charging circuits are typically implemented as stand alone integrated circuits. For the typical case, where the charger controls its output using a linear regulator, this means that the integrated circuit includes a power control transistor. The power control transistor generates heat which increases the temperature of the integrated circuit in which it is included. For this reason, it becomes necessary to monitor temperature and reduce output to prevent thermal overloading. For example, U.S. Pat. No. 6,507,172 (incorporated previously) discloses a temperature feedback that uses a linear regulator to reduce output current and maintain operating temperature within a predetermined range.
A temperature control circuit for a battery charger includes a digital to analog converter connected to receive the value stored in an up/down counter. The digital to analog converter generates a control output signal based on the counter value. The control output signal is used to regulate the output current of the battery charger.
A first comparator increments or decrements the counter based on the difference between the temperature of the charger and a desired temperature. The value in the counter is increased during each clock cycle when the temperature of the circuit is below the desired temperature. The value in the counter is decreased during each clock cycle when the temperature of the circuit is above the desired temperature.
A reset circuit zeros the counter when the temperature of the charger has exceeded an upper threshold and subsequently maintains the counter at zero until the temperature of the charger has fallen below a lower threshold. The reset circuit includes a second comparator and a multiplexer. One input of the second comparator monitors the temperature of the charger. The second is selects between two voltages representing the high and the low thresholds. When the battery charger temp exceeds the high threshold, the second comparator resets the counter and switches the multiplexer. As a result, the second comparator continues to monitor and reset the counter until the temperature of the charger has fallen below the low threshold.
The present invention includes a temperature control loop (and associated method) for battery charging and other circuits. As show in
The output VT forms the input of a first comparator. The second input to the first comparator is a voltage V1. V1 corresponds to the desired temperature (or target temperature) for the semiconductor that includes the temperature control loop. This means that VT is equal to V1 when the semiconductor is operating at the target temperature.
The output of the first comparator controls up and down operation of a shifter. The shifter also receives a clock input from a clock generator. The result is that, on a clock by clock basis, the count in the shifter increases when VT is less that V1 and decreases when VT is greater than V1. The n-bit output of the shifter is converted by a digital to a control output signal. In turn, this means that the control output signal decreases during each clock cycle where VT is greater V1 and increases when VT is less than V1.
As shown in
During operation, temperatures in excess of T2 cause the second comparator to reset the shifter. This causes the control output signal to drop to its minimum level. At the same time, the output of the multiplexer is switched from V2 to V3. This is shown as the reset phase in
This application is a continuation in part of U.S. patent application Ser. No. 11/023,017 filed Dec. 23, 2004.
Number | Date | Country | |
---|---|---|---|
Parent | 11023017 | Dec 2004 | US |
Child | 11835840 | Aug 2007 | US |