The voltage controller 250 is electrically connected to the voltage output terminal Vout, the output terminal of driver 220, and an input terminal of driver 220, for providing a feedback voltage Vfbk. The over-current protection circuit 240 is electrically connected to the output terminal of driver 220 and the linear regulator 210. The over-current protection circuit 240 detects the output voltage of the driver 220 for comparing with a comparison voltage, and if the output voltage of the driver 220 is larger than the comparison voltage, the over-current protection circuit 240 controls the driver 220 to turn off the converter 230.
In an embodiment of the invention, the driver 220, the over-current protection circuit 240, and the voltage controller 250 ate integrated in a single IC. Thus, in case the load current of the voltage regulator circuit has changed, the voltage regulator circuit can be compensated by simply replacing the converter 230 with one having corresponding load current capacity, giving great flexibility of circuit design. That is, during the design of voltage regulator circuit with over-current protection, a simple replacement of the converter 230 is sufficient to adapt for different current loads, as compared to the traditional approach in which both the linear regulator and the over-current protection circuit needs to be replaced and thus gives rise to costs.
The first operational amplifier 221 has a first input terminal (+) and a second input terminal (−). The first input terminal (+) of the first operational amplifier 221 is used for receiving a reference voltage (Vref). The second input terminal (−) of the first operational amplifier 221 is electrically connected to the voltage controller 250.
In this embodiment, the voltage controller 250 is a passive network, having a first input connected to the output terminal of the first operational amplifier 221, and a second input terminal connected to the output terminal of the converter 230. Thus the voltage controller 250 can generate a feedback voltage Vfbk based on the voltage at the output terminal of the first operational amplifier 221 and the voltage at the output terminal of the converter 220.
The over-current protection circuit 240 includes a second operational amplifier 241 having a first input terminal (+) and a second input terminal (−), a current source 242, a reference resistor 243, and a buffer 244. The first input terminal (+) of the second operational amplifier 241 is electrically connected to the output terminal of first operational amplifier 221 via the buffer 244. The second input terminal (−) of the second operational amplifier 241 is electrically connected to the current source 242. In other embodiments, the first input terminal (+) of the second operational amplifier 241 can also be electrically connected to the output terminal of the first operational amplifier 221 directly.
The second input terminal (−) of the second operational amplifier 241 is electrically connected to one terminal of the reference resistor 243. The other terminal of the reference resistor 243 is connected to a low voltage, and is preferably of zero volts. Through such, the current provided by the current source 242 can flow through the reference resistor 243 and provide a comparison voltage at the second input terminal (−) of the second operational amplifier 241.
The first operational amplifier 221 further has a first power supply terminal 2211. The second operational amplifier 241 further has an output terminal electrically connected to the first power supply terminal 2211 of the first operational amplifier 221 via the first transistor 222.
When the output voltage of the first operational amplifier 221 is larger than the comparison voltage, the second operational amplifier 241 generates a high voltage and outputs the high voltage to the first transistor 222 through the output terminal of the second operational amplifier 241. Since the first transistor 222 is a P-Channel MOSFET transistor, the high voltage generated by the second operational amplifier 241 causes the first transistor 222 to be turned off. The turn-off of the first transistor 222 stops voltage Vcc from being supplied to the first operational amplifier 221. The first operational amplifier 221 thus ceases to operate, thereby also turning off the converter 230.
In this embodiment, the converter 230 is an active switch, such as a field-effect transistor. For instance, the converter 230 in this embodiment is preferably a N-Channel MOSFET. In other embodiments, the converter 230 may be a BJT (bi-polar junction transistor), or other types of transistors with different electrical connections, which are known to a person skilled in the art, and hence the descriptions of which are hereby omitted.
In view of the foregoing, the voltage regulator circuit with over-current protection in accordance with a preferred embodiment of the invention is able to provide over-current protection by detecting the output voltage of the driver, and comparing the detected output voltage with the reference voltage, thereby successfully eliminating the power loss problem associated with prior art when sense resistor R3 is used, and increasing the efficiency of the linear regulator.
Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.
Number | Date | Country | Kind |
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095118385 | May 2006 | TW | national |