Driving controller capable of dynamically adjusting voltage at control terminal of transistor

A driving controller for driving a transistor, includes an operation unit, a first adjustment unit, a second adjustment unit, a first comparator, a comparison unit. A first terminal of the transistor receives an operation voltage. The operation unit is coupled to a control terminal of the transistor. The first adjustment unit is used to increase a voltage of the control terminal of the transistor. The second adjustment unit is used to decrease the voltage of the control terminal of the transistor. The first comparator and the comparison unit are coupled to the first terminal of the transistor and used to compare the operation voltage with a first reference voltage to a third reference voltage respectively so that the transistor may be controlled accordingly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates to a driving controller, and more particularly, a driving controller used for dynamically adjusting a voltage at a control terminal of a transistor so as to reduce conduction loss of a power switch.

2. Description of the Prior Art

In an electrical power conversion driving controller (e.g. a flyback circuit), a diode can be used as a rectification component. For example, a Schottky diode can be used because it has a lower forward voltage. However, power loss may be an issue. For example, when a voltage across a diode is 0.5 volts, and a root mean square of a current flowing through the diode is 10 amps, the power loss would be a product of the current and the voltage, which is 5 watts.

For reducing the power loss, a transistor may be used to replace a diode. For example, two terminals (e.g. a drain terminal and a source terminal) of a metal-oxide-semiconductor field-effect transistor (MOSFET) can be used to replace an anode and a cathode of a diode. After replacing the diode, if resistance of an enabled transistor is 10 mΩ, and a current flowing through the transistor is still 10 amps, the power loss would be a product of the resistance and the square of the current, which is 1 watt. The abovementioned values are merely examples. In this example, power loss may be reduced from 5 watts to 1 watt, so the power loss would be decreased using a transistor instead of a diode to be a rectification component in an electrical power conversion driving controller.

However, when the voltage across a transistor is converted to a forward voltage, the current may flow through a parasitic body diode within the transistor. A forward voltage across the body diode is larger than a forward voltage of the foresaid diode and is as high as 0.7 volts. This further increases the power loss. Hence, if the turning on and off of the transistor cannot be controlled properly, the power loss is increased further. Because of this, when the voltage across the transistor is close to 0 volts, the transistor can be turned off to reduce the conduction of the body diode so as to reduce the power loss. However, if the transistor is turned off too early, the transistor cannot properly reduce power loss.

For reducing the power loss, a transistor with a lower on-resistance can be intuitively selected, but it is difficult to improve the effect without adjusting the operation method.FIG. 1illustrates a waveform diagram of a driving controller according to prior art. InFIG. 1, the operation current ID is a current flowing through a transistor. The operation VDS is a voltage across the transistor. The voltage Vdrv is a voltage at the control terminal of the transistor. The curve181corresponds to a transistor with a higher on-resistance, and the curve182corresponds to a transistor with a lower on-resistance. The voltage Voff is a threshold to be compared with the operation voltage VDS to accordingly turn off the transistor. As shown inFIG. 1, when using a transistor with a lower on-resistance, the curve of the operation voltage VDS will change from the curve181to the curve182corresponding to the same operation current ID. Hence, the time point of turning off the transistor can be changed from the time point t1to the time point t2. Since the transistor is turned off earlier, the effect of reducing the power loss is worsened.

According toFIG. 1, when turning off the transistor, the voltage Vdrv at the control terminal of the transistor is pulled down from a maximum voltage, so it is difficult to shorten the turn-off delay time, and the operation may slow down the turning off of the circuit.

SUMMARY OF THE INVENTION

An embodiment discloses a driving controller for driving a transistor. The transistor includes a first terminal for receiving an operation voltage, a second terminal and a control terminal. The driving controller includes a first operation unit, a first adjustment unit, a second adjustment unit, a first comparator and a comparison unit. The first operation unit includes a first terminal for receiving a first voltage, a control terminal, and a second terminal coupled to the control terminal of the transistor. The first adjustment unit is coupled to the control terminal of the transistor and used to increase a voltage at the control terminal of the transistor. The second adjustment unit is coupled to the control terminal of the transistor and used to decrease the voltage at the control terminal of the transistor. The first comparator includes a first terminal coupled to the first terminal of the transistor, a second terminal for receiving a first reference voltage, and an output terminal for outputting a first comparison signal when the operation voltage is equal to the first reference voltage. The comparison unit includes a first terminal coupled to the first terminal of the transistor to receive the operation voltage, and a set of output terminals. The comparison unit is used to compare the operation voltage and a second reference voltage and compare the operation voltage and a third reference voltage. The set of output terminals outputs a second comparison signal when the operation voltage is equal to the second reference voltage. The set of output terminals outputs a third comparison signal when the operation voltage is equal to the third reference voltage.

Another embodiment discloses a control method for a driving controller. The driving controller is used to drive a transistor. The transistor includes a first terminal for receiving an operation voltage. The driving controller includes a first operation unit coupled between a control terminal of the transistor and a first voltage terminal providing a first voltage, a first adjustment unit coupled to the control terminal of the transistor, and a second adjustment unit coupled to the control terminal of the transistor. The control method includes turning on the first operation unit to increase a voltage at the control terminal of the transistor to turn on the transistor when the operation voltage decreases to a first reference voltage; turning off the first operation unit and turning on the second adjustment unit for the second adjustment unit to decrease the voltage at the control terminal of the transistor when the operation voltage increases to a second reference voltage; and turning off the second adjustment unit and turning on the first adjustment unit for the first adjustment unit to increase the voltage at the control terminal of the transistor when the operation voltage decreases to a third reference voltage. The first adjustment unit and the second adjustment unit are not turned on concurrently, the first reference voltage is lower than the third reference voltage, and the third reference voltage is lower than the second reference voltage.

DETAILED DESCRIPTION

FIG. 2illustrates a driving controller100according to an embodiment. The driving controller100may be used to drive a transistor100. The driving controller100may include a first operation unit SW1, a second operation unit SW2, a first adjustment unit C1, a second adjustment unit C2, a first comparator comp1, a comparison unit CU, and a fourth comparator comp4. The transistor110may include a first terminal, a second terminal and a control terminal. For example, the transistor110may be a power switch. For example, if the transistor110is an N-type MOSFET, the first terminal may be a drain terminal, the second terminal may be a source terminal, and the control terminal may be a gate terminal. The first terminal of the transistor110may be used to receive an operation voltage VD, and a current flowing through the transistor110may be an operation current ID. If setting a voltage at the second terminal of the transistor110as a baseline, the operation voltage VD may be a voltage across the first terminal and the second terminal of the transistor110. The first operation unit SW1may include a first terminal coupled to a first voltage terminal for receiving a first voltage VDD, a control terminal, and a second terminal coupled to the control terminal of the transistor110. The second operation unit SW2may include a first terminal coupled to the control terminal of the transistor, a control terminal, and a second terminal coupled to a second voltage terminal for receiving a second voltage VLL. The second voltage VLL may be lower than the first voltage VDD. The first voltage terminal may be a high voltage terminal, and the second voltage terminal may be a ground terminal. The first operation unit SW1and the second operation unit SW2may be a first switch and a second switch respectively, or other controllable operation units. The first adjustment unit C1may be coupled to the control terminal of the transistor110and used to increase a voltage at the control terminal of the transistor110. For example, as shown inFIG. 2, the first adjustment unit C1may be a current source used to adjust and increase the voltage at the control terminal of the transistor110. The second adjustment unit C2may be coupled to the control terminal of the transistor110and used to decrease the voltage at the control terminal of the transistor110. For example, as shown inFIG. 2, the second adjustment unit C2may be another current source. The first adjustment unit C1and the second adjustment unit C2being current sources as shown inFIG. 2is merely an example. According to other embodiments, each of the first adjustment unit C1and the second adjustment unit C2may be a controllable circuit unit formed with a set of resistors and/or transistors.

The first comparator comp1may include a first terminal coupled to the first terminal of the transistor110for receiving the operation voltage VD, a second terminal for receiving a first reference voltage Vref1, and an output terminal for outputting a first comparison signal S1when the operation voltage VD is equal to the first reference voltage Vref1. The comparison unit CU may include a first terminal coupled to the first terminal of the transistor for receiving the operation voltage VD, and a set of output terminals including one output terminal or a plurality of output terminals. The comparison unit CU may be used to compare the operation voltage VD and a second reference voltage Vref2and compare the operation voltage VD and a third reference voltage Vref3. The set of output terminals of the comparison unit CU may output a second comparison signal S2when the operation voltage VD is equal to the second reference voltage Vref2. The set of output terminals of the comparison unit CU may output a third comparison signal S3when the operation voltage VD is equal to the third reference voltage Vref3.

According to an embodiment, the comparison unit CU may include one comparator or a plurality of comparators for performing comparison with a plurality of reference voltages. The comparison unit CU may compare the operation voltage VD with two reference voltages. When the comparison unit CU includes one single comparator, the comparator may be a Schmitt trigger comparator providing hysteresis so as to perform comparison with two reference voltages. According to another embodiment, as shown inFIG. 2, the comparison unit CU may include a second comparator comp2and a third comparator comp3for performing comparison with two reference voltages. The second comparator comp2may include a first terminal coupled to the first terminal of the transistor110for receiving the operation voltage VD, a second terminal for receiving the second reference voltage Vref2, and an output terminal coupled to at least one output terminal of the set of output terminals of the comparison unit CU for outputting the second comparison signal S2when the operation voltage VD is equal to the second reference voltage Vref2. The third comparator comp3may include a first terminal coupled to the first terminal of the transistor110for receiving the operation voltage VD, a second terminal for receiving the third reference voltage Vref3, and an output terminal coupled to at least one output terminal of the set of output terminals of the comparison unit CU for outputting the third comparison signal S3when the operation voltage is equal to the third reference voltage Vref3. The fourth comparator comp4may include a first terminal coupled to the first terminal of the transistor110for receiving the operation voltage VD, a second terminal for receiving a fourth reference voltage Vref4, and an output terminal for outputting a fourth comparison signal S4when the operation voltage VD is equal to the fourth reference voltage Vref4.

As shown inFIG. 2, the driving controller100may further include a logic control unit150, and the logic control unit150may include a first input terminal in1, a set of functional input terminals, a fourth input terminal in4, and a first output terminal ou1to a fourth output terminal out4. The first input terminal in1may be coupled to the output terminal of the first comparator comp1. The set of functional input terminals may be correspondingly coupled to the set of output terminals of comparison unit CU. In an embodiment of the comparison unit CU having the second comparator comp2and the third comparator comp3, the set of functional input terminals may include a second input terminal in2and a third input terminal in3, where the second input terminal in2is coupled to the output terminal of the second comparator comp2, and the third input terminal in3is coupled to the output terminal of the third comparator comp3. The fourth input terminal in4may be coupled to the output terminal of the fourth comparator comp4. The first output terminal out1may be coupled to the control terminal of the first operation unit SW1for turning on or turning off the first operation unit SW1. The second output terminal out2may be coupled to the control terminal of the second operation unit SW2for turning on or turning off the second operation unit SW2. The third output terminal out3may be coupled to the first adjustment unit C1for controlling the first adjustment unit C1to increase the voltage at the control terminal of the transistor110. The fourth output terminal out4may be coupled to the second adjustment unit C2for controlling the second adjustment unit C2to decrease the voltage at the control terminal of the transistor110. The driving controller100may further include a bias voltage unit185coupled between the logic control unit150and the first voltage terminal providing the first voltage VDD. The first terminal of the transistor110may be coupled to a coil unit195. The coil unit195may include a transformer winding of an electrical power conversion circuit. The driving controller100may be (but not limited to) an integrated circuit (IC) or a part of an IC. Circuit interfaces100a,100band100cmay be interfaces between the driving controller100and the transistor110. For example, the circuit interfaces100a,100band100cmay be pins or circuit nodes of an IC.

FIG. 3illustrates currents and voltages of the driving controller100according to an embodiment. As shown inFIG. 3, the first reference voltage Vref1, the second reference voltage Vref2, the third reference voltage Vref3and the fourth reference voltage Vref4may be negative voltages.

As shown inFIG. 2andFIG. 3, after entering phase PH2from phase PH1, a body diode110dmay switch to be conductive. When the operation voltage VD is decreased to the first reference voltage Vref1(e.g. −150 mV (millivolts)), the first operation unit SW1may be turned on by the first comparison signal S1outputted from the first output terminal out1of the logic control unit150. The voltage Vdrv at the control terminal (e.g. a gate terminal) of the transistor110may increase to further turn on the transistor110. As shown in phase PH2, the voltage Vdrv may increase to a maximum Vdrvmax(e.g. 10 volt) to make the transistor110more conductive. During phase PH3following phase PH2, when the operation current ID decreases, the operation voltage VD may change to 0 volts. Because the operation voltage VD is a negative voltage in this phase, the operation voltage VD may increase.

When the operation voltage VD is increased to the second reference voltage Vref2(e.g. −26 mV), the status may enter phase PH4following phase PH3. The second adjustment unit C2may be turned on by the fourth output terminal out4of the logic control unit150according to the second comparison signal S2, and the second adjustment unit C2may decrease the voltage Vdrv at the control terminal of the transistor110. The conductivity of the transistor110may be reduced, and the on-resistance Rds may be increased. The operation voltage VD may decrease from the second reference voltage Vref2.

When the operation voltage VD is decreased to the third reference voltage Vref3(e.g. −33 mV), the status may enter phase PH5following phase PH4. The first adjustment unit C1may be turned on by the third output terminal out3of the logic control unit150according to the comparison signal S3. The first adjustment unit C1may increase the voltage Vdrv at the control terminal of the transistor110. Because the voltage Vdrv is increased, the on-resistance Rds of the transistor110may decrease, and the operation voltage VD may increase.

When the operation voltage VD is increased to the second reference voltage Vref2, the status may enter phase PH6following phase PH5. The operation in phase PH6may be similar to the operation in phase PH4. The second adjustment unit C2may be turned on by the logic control unit150. The second adjustment unit C2may decrease the voltage Vdrv at the control terminal of the transistor110, and the operation voltage VD may decrease.

When the operation voltage VD is decreased to the third reference voltage Vref3, the status may enter phase PH7following phase PH6. The operation in phase PH7may be similar to the operation in phase PH5. The first adjustment unit C1may be turned on by the logic control unit150. The first adjustment unit C1may increase the voltage Vdrv at the control terminal of the transistor110, so the operation voltage VD may increase.

When the operation voltage VD is increased to the second reference voltage Vref2, the status may enter phase PH8following phase PH7. The operation in phase PH8may be similar to the operation in phase PH6, so it is not repeated herein. As shown inFIG. 3, by comparing the operation voltage VD with the second reference voltage Vref2and the third reference voltage Vref3, the voltage Vdrv at the control terminal of the transistor110may be dynamically adjusted so as to keep the operation voltage VD between the second reference voltage Vref2and the third reference voltage Vref3. As shown inFIG. 3, during phases PH4to PH8, the number of times of adjusting the operation voltage VD is merely an example. The number of times of adjusting the operation voltage VD may vary according to different embodiments, but the goal is to keep the operation voltage VD between the second reference voltage Vref2and the third reference voltage Vref3.

During phase PH9following phase PH8, the operation current ID may decrease and approach to 0 amps, and the operation voltage VD may increase. When the operation voltage VD increases to the fourth reference voltage Vref4(e.g. −5 mV), the status may enter phase PH10following phase PH9. During phase PH10, the operation voltage VD may not be kept between the second reference voltage Vref2and the third reference voltage Vref3. The second operation unit SW2may be turned on by the second output terminal out2of the logic control unit150according to the fourth comparison signal S4for the control terminal of the transistor110to receive the second voltage VLL. Since the voltage Vdrv is pulled down to the second voltage VLL, the transistor110may be turned off. The duration of phase PH10may be the time for turning off the transistor110. The voltage of the control terminal of the transistor is pulled down from a maximum voltage according to prior art. However, the voltage Vdrv may be pulled down from a level lower than half the maximum voltage (e.g. 5 volt) during phase PH10ofFIG. 3, and the time for turning off the transistor110may be reduced to speed up the operation of the circuit.

According to an embodiment, the first adjustment unit C1and the second adjustment unit C2may not be turned on at the same time substantially. In addition, the first operation unit SW1and the second operation unit SW2may not be turned on at the same time substantially. The first reference voltage Vref1to the fourth reference voltage Vref4may be negative voltage. The first reference voltage Vref1may be lower than the third reference voltage Vref3. The third reference voltage Vref3may be lower than the second reference voltage Vref2. The second reference voltage Vref2may be lower than the fourth reference voltage Vref4. For example, the first reference voltage Vref1, the second reference voltage Vref2, the third reference voltage Vref3and the fourth reference voltage Vref4may be (but not limited to) −150 mV, −26 mV, −33 mV and −5 mV respectively.

FIG. 4illustrates a control method400for the driving controller100according to an embodiment. As shown inFIG. 2,FIG. 3andFIG. 4, the control method400may include following steps.

Step410: turn on the first operation unit SW1to increase the voltage Vdrv at the control terminal of the transistor110to turn on the transistor110when the operation voltage VD is decreased to a first reference voltage Vref1;

Step420: turn off the first operation unit SW1and turn on the second adjustment unit C2for the second adjustment unit C2to decrease the voltage Vdrv at the control terminal of the transistor110when the operation voltage VD is increased to the second reference voltage Vref2;

Step430: turn off the second adjustment unit C2and turn on the first adjustment unit C1for the first adjustment unit C1to increase the voltage Vdrv at the control terminal of the transistor110when the operation voltage VD is decreased to the third reference voltage Vref3;

Step440: determine whether the operation voltage VD is increased to the fourth reference voltage Vref4? If so, enter Step450; else enter Step420; and

Step450: turn on the second operation unit SW2for the control terminal of the transistor to receive the second voltage VLL to turn off the transistor110when the operation voltage VD is increased to the fourth reference voltage Vref4.

In summary, by means of the driving controller100and the control method400, the voltage Vdrv at the control terminal of the transistor110may be dynamically adjusted before the operation current ID decreases to 0 amps. According to embodiments, the time for turning off the transistor may be reduced. Hence, the effect and the operation speed of the circuit may be improved.