Power transistor chip with built-in junction field effect transistor and application circuit thereof

A power transistor chip and an application circuit thereof have a junction field effect transistor to act as a start-up circuit of an AC/DC voltage converter. The start-up circuit can be turned off after the PWM circuit of the AC/DC voltage converter operates normally to conserve the consumption of the power. Besides, the junction field effect transistor is built in the power transistor chip. Because the junction field effect transistor is fabricated with the same manufacturing process as the power transistor, it is capable of simplifying the entire process and lowering the production cost due to no additional mask and manufacturing process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a voltage regulator circuit and particularly to a power transistor chip with a function field effect transistor (JEFT) built therein and an AC/DC voltage converter using the power transistor chip.

2. Brief Description of the Related Art

Due to the semiconductor technology being developed progressively, the digital products such as the computer and the peripherals thereof are capable of being upgraded continuously. The fast change of the manufacturing process for the semiconductor results in a variety of demands for the power source of the integrated circuit (IC) employed in the computer and the peripherals thereof. Hence, various combinations of voltage regulators using such as the boost converter and the buck converter to meet the need of different power sources of the integrated circuit become one of the most important factors to offer versatile digital products. The AC/DC voltage converter is widely taken as the primary stage circuit of the voltage regulator circuit because it is capable of converting the AC power input to the needed steady direct power output.

Referring toFIG. 1, a circuit diagram of the conventional AC/DC voltage converter is illustrated. The AC/DC voltage converter10includes a bridge type rectifying circuit11, a power transistor chip12, a pulse width modulation (PWM) circuit13, a start-up circuit14, a transformer circuit15, a filtering and feedback circuit16and a working power circuit17. The pulse width modulation circuit13produces the modulated PWM signal to control and output the direct power output Voaccording to the magnitude of the feedback voltage of the direct power output Vo. However, the pulse width modulation circuit13usually is driven by a low voltage direct power and there is no direct power available for operating the pulse width modulation circuit13at the time of the AC/DC voltage converter10initiating the work thereof. Therefore, it is necessary to use the start-up circuit14and the working power circuit17to supply the successive power needed by the pulse width modulation circuit13.

When the AC/DC voltage converter10initiates the work thereof, the output terminal of the bridge type rectifying circuit11outputs a rippling direct power to the pulse width modulation circuit13via the resistance in the start-up circuit14for operating the pulse width modulation circuit13. Then, the pulse width modulation circuit13performs the normal job thereof afterward according to the magnitude of the feedback voltage of the output direct power Voand produces the modulated PWM signal such that the time duration of ON and OFF of the power transistor can be controlled for outputting a steady direct power Vo. The working power circuit17, which is connected to the transformer circuit15, supplies more steady working power for the pulse width modulation circuit13performs the job thereof much steadily after the AC/DC voltage converter10is started up and outputs the steady direct power Vo.

Although the preceding way allows the AC/DC voltage converter to work normally, the start-up circuit14keeps in a state of supplying the power to the pulse width modulation circuit13unnecessarily. In order to improve the deficiency, the depletion metal oxide semiconductor field effect transistors (Depletion MOSFET)221,331are employed instead to output a start-up signal st via the pulse width modulation circuit23or33to turn off the operation of the depletion metal oxide semiconductor field effect transistors221,331respectively for conserving the power consumption.

The difference betweenFIG. 2andFIG. 3is in that the depletion metal oxide semiconductor field effect transistors221,331are integrated in the power transistor chip22and the pulse width modulation circuit33respectively for starting up the AC/DC voltage converter. However, the manufacturing process of the chip becomes more complicated due to the additional process of the channel (N channel or P channel) of the depletion metal oxide semiconductor field effect transistors221,331.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a power transistor chip and an AC/DC voltage converter using the power transistor chip, which has a junction field effect transistor built in the power transistor chip to act as a start-up circuit such that not only the power consumption is conserved but also no additional mask and process are involved for simplifying the manufacturing process and lowering the production cost.

In order to achieve the preceding object, the power transistor chip with a built-in junction field effect transistor according to the present invention is adaptable to the AC/DC voltage converter and comprises a first pin, a second pin, a third pin, a fourth pin, a fifth pin, a power transistor and a junction field effect transistor; wherein, the power transistor acts as a power switch of the AC/DC voltage converter and has a first source/drain, a second source/drain and a power transistor gate with the first source/drain coupling with the first pin, the second source/drain coupling with the second pin and the power transistor gate coupling with the third pin; and the junction field effect transistor acts as the start-up circuit of the AC/DC voltage converter and has a third source/drain, a fourth source/drain and a junction field effect transistor gate with the third source/drain coupling with said first pin, the fourth source/drain coupling with the fourth pin and the junction field effect transistor gate coupling with the fifth pin.

Further, the AC/DC voltage converter according to the present invention is capable of converting the AC power input to the steady DC power output and further comprises a bridge type rectifying circuit, a transformer circuit, a pulse width modulation circuit, a filtering and feedback circuit and a working power circuit in addition to the preceding power transistor chip with the built-in junction field effect transistor.

Wherein, the bridge type rectifying circuit has a power input terminal, which receives the AC power input, and a rectifying output terminal; the transformer circuit has a primary coil, a secondary coil and an auxiliary coil with the primary coil having an terminal coupling with the rectifying output terminal and another terminal coupling with the first pin of the power transistor chip, i.e., coupling with the first source/drain of the power transistor and the third source/drain of the junction field effect transistor.

The pulse width modulation circuit has a start-up power control terminal, a working power terminal, a pulse width modulation signal output terminal and a current sensing terminal with the start-up power control terminal coupling with the fifth pin to control ON and OFF of the junction field effect transistor, the working power terminal coupling with the fourth pin to receive a start-up power from the junction field effect transistor, the pulse width modulation signal output terminal coupling with the third pin to output a pulse width modulation signal according to the magnitude of a feedback voltage for modulating the DC power and the current sensing terminal coupling with the second pin to sense a current passing through the power transistor.

The working power circuit couples with the auxiliary coil and the working power terminal of the pulse width modulation circuit to supply a power needed by the pulse width modulation circuit at the time of the start-up power output by the junction field effect transistor being turned off by the pulse width modulation circuit; and the filtering and feedback circuit couple with the secondary coil to filter and output the steady DC power and supply a feedback voltage needed by the pulse width modulation circuit.

In short, a power transistor chip and an AC/DC voltage converter using the power transistor chip according to the present invention has a junction field effect transistor built in the power transistor chip to act as a start-up circuit of the AC/DC voltage converter. The start-up circuit can be turned off after the PWM circuit of the AC/DC voltage converter operates normally to conserve the consumption of the power. Besides, the junction field effect transistor is fabricated with the power transistor chip with the identical manufacturing process such that it is capable of simplifying the process and lowering the production cost due to no additional mask and manufacturing process.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 4, an AC/DC voltage converter of the preferred embodiment according to the present invention is illustrated. The AC/DC voltage converter40is capable of converting the AC input power Vincoming from the power terminal411to a steady direct output voltage Vo. it can be seen inFIG. 4that the AC/DC voltage converter40includes a bridge type rectifying circuit41, a power transistor chip42, a pulse width modulation circuit43, a transformer circuit45, a filtering and feed back circuit46and a working power circuit47.

The power transistor chip42shown inFIG. 4has a first pin421, a second pin422, a third pin423, a fourth pin244, a fifth pin425, a power transistor426and a junction field effect transistor427. The junction field effect transistor427, which acts as the start-up circuit of the AC/DC voltage converter40, is built in the power transistor chip42to simplify the manufacturing process of the chip arranged in the AC/DC voltage converter40. Although the power transistor426and the junction field effect transistor427are exemplified with N-type metal oxide semiconductor field effect transistor and N-type junction field effect transistor and the resistance428connected to the gate of the power transistor426is built in the power transistor chip42, persons skill in the art realize different type transistors such as the P-type metal oxide semiconductor field effect transistor or P-type junction field effect transistor can be adopted as well. Further, the built-in resistance428can be optionally integrated in a chip with the pulse width modulation circuit43instead of being included in the power transistor chip42.

Wherein, the power transistor426, which is a power switch of the AC/DC voltage converter40, has the first source/drain coupling with the first pin421, the second source/drain coupling with the second pin422and the gate coupling with the third pin423. The junction field effect transistor427has the third source/drain D coupling with the first pin421, the fourth source/drain S coupling with the fourth pin424and the gate G coupling with the fifth pin425.

When the AC/DC voltage converter40is initiated to work, the bridge type rectifying circuit41receives the AC power input Vinfrom the power source terminal411and rectifying the full wave of the AC power input Vinsuch that a rippling direct power is output to the first pin421via a primary coil of the transformer circuit451, which has an terminal coupling with the rectifying output terminal412of the rectifying circuit41and another terminal thereof coupling with the first pin421of the power transistor chip42.

In order to supply the power to operate the pulse width modulation circuit43, the working power terminal432of the pulse width modulation circuit43couples with the fourth pin424of the power transistor chip42, i.e., the fourth source/drain S of the junction field effect transistor427. Meanwhile, the start-up signal st output by the pulse width modulation circuit43is a low reference level signal and the built-in transistor436is still in a state of OFF such that the working power terminal432and the start-up power control terminal431of the pulse width modulation circuit43have the same potential as the VCC.

Besides, the start-up power control terminal431couples with the fifth pin425of the power transistor chip42, i.e., the gate G of the junction field effect transistor427. The working power terminal432couples with the fourth pin424of the power transistor chip42, i.e. the fourth source/drain S of the junction field effect transistor427. Hence, the fourth source/drain S of the junction field effect transistor427and the gate G of the junction field effect transistor427have the same potential as the VCC and are in a state of ON (SeeFIG. 5) such that the rippling direct power output by the bridge type rectifying circuit41can be transmitted to the fourth source/drain S of the junction field effect transistor427.

Meanwhile, the pulse width modulation circuit43obtains the power for initiating the operation and starting up the work thereof. In addition, the pulse width modulation circuit43produces the modulated PWM signal in accordance with the magnitude of the feedback voltage of the direct power Vooutput by the AC/DC voltage converter40and the current of the power transistor chip42, which is sensed from the current sensing terminal434. Then, the modulated PWM signal is sent to the PWM signal output terminal433and transmitted to the gate of the power transistor of the power transistor chip42via the third pin423and the resistance428to control the time duration of ON and OFF of the power transistor426such that the AC/DC voltage converter40is capable of outputting a steady direct power Vo.

When the pulse width modulation circuit43initiates to work, the secondary coil452is induced a voltage, and then the voltage is filtered by the filtering and feedback circuit46, which couples with the secondary coil452, to output the steady direct power Vc. The reference feedback voltage needed by the pulse width modulation circuit43is obtained by means of the isolated detection of a light emitting diode461and an optical transistor435in the filtering and feedback circuit46.

In addition, an auxiliary coil453of the transformer circuit45produces an induced voltage simultaneously and the induced voltage is filtered and transmitted to the working power terminal432by the working power circuit47, which couples with the auxiliary coil453. Under this circumstance, the steady working power supplied by the working power circuit47has been capable of meeting the need of much steadiness of the pulse width modulation such that the pulse width modulation circuit43raises the start-up signal st to a high reference level to activate the built-in transistor436for lowering the potential of the start-up control terminal431to the GND ground potential. In this way, it creates a reverse bias voltage between the fourth source/drain S and the gate G of the junction field effect transistor427to cause pinch-off as shown inFIG. 6such that the start-up power output by the junction field effect transistor427is turned off after the steady working power supplied by the working power circuit47is capable of constantly offering the power required by the pulse width modulation circuit43. In this way, the power consumption of the AC/DC voltage converter40is conserved significantly.

Referring toFIGS. 5 and 6, the power transistor chip42according to the preferred embodiment of the present invention provides the built-in junction field effect transistor427and the junction field effect transistor427has the similar doped structure as the power transistor426such that the identical manufacturing process is capable of being performed for fabricating both the power transistor426and the junction field effect transistor427with no additional mask and process. Therefore, the whole process is simplified and the production cost is lowered advantageously.

While the invention has been described with referencing to a preferred embodiment thereof, it is to be understood that modifications or variations may be easily made without departing from the spirit of this invention, which is defined by the appended claims.