Regulating system having overvoltage protection circuit and current protection circuit

A regulating system includes an input port having a first input terminal and a second input terminal, an output port having a first output terminal and a second output terminal, a regulating circuit, an over-current protection circuit, and an overvoltage protection circuit. The overvoltage protection circuit includes a regulating diode, a first bipolar transistor and a second bipolar transistor. The first output terminal is connected to the base of the first bipolar transistor via the regulating diode and grounded via first bipolar transistor. A base of the second bipolar transistor connects to the collector of the first bipolar transistor. The second output terminal is grounded via the second transistor. When an output voltage of the first output terminal increases over a predetermined voltage, an electrical connection between the second output terminal and ground is cut off to stop providing output voltage from the output port.

BACKGROUND

1. Technical Field

The present disclosure relates to a regulating system, and more particularly, to a regulating system having an overvoltage protection circuit and a current protection circuit.

2. Description of Related Art

Power circuits are widely used in various electronic products such as computers notebooks, and LCD monitors. Normally, power circuits include a regulating system for regulating output voltage of the power circuits. However, the configuration of a typical regulating system is normally complicated.

Therefore, a new regulating system is desired to overcome the above-described shortcoming.

DETAILED DESCRIPTION

Reference will now be made to the drawings to describe various inventive embodiments of the present disclosure in detail, wherein like numerals refer to like units throughout.

The FIGURE shows a regulating system10according to one embodiment of the present disclosure. The regulating system10includes an input port12and an output port14. The input port12includes a first input terminal12aand a grounded second input terminal12b. The output port14includes a first output terminal14aand a second output terminal14b.

The regulating system10further includes a regulating circuit120, an over-current protection circuit140, and an overvoltage protection circuit160. As shown inFIG. 1, the input port12is connected in series to the output port14via the regulating circuit120, the over-current protection circuit140, and the overvoltage protection circuit160.

The regulating circuit120includes a metal oxide semiconductor (MOS) transistor Q1, a first resistor R1, a second resistor R2, a third resistor R3, and a regulating unit Q2. The MOS transistor Q1includes a drain electrode124, a gate electrode125, and a source electrode126. The regulating unit Q2includes an anode121, a cathode122, and a reference terminal123. The regulating unit Q2can automatically adjust a voltage of the cathode122according to a voltage of the reference terminal123. In one embodiment, the voltage of the cathode122increases following a voltage decrease of the reference terminal123and the voltage of the cathode122decreases following a voltage increase of the reference terminal123. In one embodiment, the regulating unit Q2is a three-terminal adjustable voltage regulator.

The drain electrode124of the MOS transistor Q1connects to the first input terminal12aof the input port12. The gate electrode125of the MOS transistor Q1connects to the cathode122of the regulating unit Q2and connects to the first input terminal12avia the third resistor R3.

The first resistor R1and the second resistor R2connects in series between the first output terminal14aand ground. The cathode122of the regulating unit Q2connects to the first input terminal12avia the third resistor R3. The anode121of the regulating unit Q2is grounded. The reference terminal123of the regulating unit Q2connects to a node “a” between the first resistor R1and the second resistor R2.

The over-current protection circuit140includes a first bipolar transistor Q3and a fourth resistor R4. An emitter of the first bipolar transistor Q3connects to the first output terminal14a. A collector of the first bipolar transistor Q3connects to the gate electrode125of the MOS transistor Q1. A base of the first bipolar transistor Q3connects to the source electrode126of the MOS transistor Q1and connects to the first output terminal14avia the fourth resistor R4. In one embodiment, the first bipolar transistor Q3is an npn bipolar transistor.

The overvoltage protection circuit160includes a regulating diode Q4, a fifth resistor R5, a sixth resistor R6, a second bipolar transistor Q5, and a third bipolar transistor Q6. The regulating diode Q4includes a cathode161and an anode162. The cathode161of the regulating diode Q4connects to the first output terminal14a. The anode162of the regulating diode Q4connects to the base of the second bipolar transistor Q5via the fifth resistor R5. A collector of the second bipolar transistor Q5connects to the first output terminal14avia the sixth resistor R6. An emitter of the second bipolar transistor Q5is grounded. A base of the third bipolar transistor Q6connects to the collector of the second bipolar transistor Q5. An emitter of the third bipolar transistor Q6is grounded. A collector of the third bipolar transistor Q6connects to the second output terminal14b. In one embodiment, the second and the third bipolar transistors Q5and Q6are npn bipolar transistors.

The node “a” between the first resistor R1and the second resistor R2is defined to be a first reference point. A node “b” between the MOS transistor Q1and the regulating unit Q2is defined to be a second reference point.

In operation, the input port12receives a power supply from an external circuit (not shown). The regulating system10generates an output voltage and outputs it from the output port14.

If the output voltage of the first output terminal14adecreases, a first reference voltage of the first reference point, which is a divided voltage of the output voltage, is correspondingly decreased. Since the reference terminal123of the regulating unit Q2connects to the first reference point, the voltage of the cathode122of the regulating unit Q2increases following a voltage decrease of the reference terminal123. Therefore, a voltage of the source electrode of the MOS transistor Q1correspondingly increases based on the characteristic of the MOS transistor Q1to compensate the voltage decrease of first output terminal14a. On the contrary, if the output voltage of the first output terminal14aincreases, the first reference voltage of the first reference point is correspondingly increased. The voltage of the cathode122of regulating unit Q2correspondingly decreases and the voltage of the source electrode of the MOS transistor Q1correspondingly decreases to compensate the voltage increase of first output terminal14a. In one alternative embodiment, a bipolar transistor can be used to replace the MOS transistor Q1.

Because an electrically conductive voltage between the base and the emitter of the first bipolar transistor Q3is approximately equal to 0.7V, the first bipolar transistor Q3turns on when the current flowing through the fourth resistor R4increases to reach 0.7V divided by a resistance “r4” of the fourth resistor R4, namely 0.7V/r4. That is, the maximum voltage across the fourth resistor R4is limited to be 0.7V by the first bipolar transistor Q3, a maximum current flowing through the fourth resistor R4is approximately equal to 0.7V/r4. Therefore, the maximum current output from the output port14is also limited to 0.7V/r4to achieve over-current protection function.

When the output voltage of the first output terminal14aincreases over a predetermined voltage, the regulating diode Q4is reversed biased to turn on the second bipolar transistor Q5. The base of the third bipolar transistor Q6is connected to ground via the activated third bipolar transistor Q6. Thus, the third bipolar transistor Q6turns off to cut off the electrical connection between the second output terminal14band ground. Therefore, the output port14stops providing output voltage and the overvoltage protection circuit160performs an overvoltage protection function.

As described above, both the configuration and the principle of the regulating system10is simple.