Background Art All systems including electronic appliances basically have a microcomputer and a separate power supply device, i. e. , regulator, for operating the microcomputer.

Conventional regulators for a microcomputer are classified into two types: One adopts a transformer and the other adopts a capacitive divided circuit.

The regulator adopting the transformer regulates a rated voltage inputted from a power supply unit to a specified DC voltage using a transformer and provides the regulated DC voltage to a microcomputer. However, this type of regulator has the drawbacks in that its size becomes large with a large power consumption and high manufacturing cost.

The regulator adopting the capacitive divided circuit has widely been used since it does not require the transformer and thus its circuit construction is simplified with a reduced manufacturing cost.

FIG. 1 is a circuit diagram illustrating the construction of a conventional regulator for a microcomputer adopting the capacitive divided circuit.

Referring to FIG. 1, the regulator 100 for a microcomputer includes a first capacitor Cl one terminal of which is connected to an input terminal of a commercial AC power supply, a first diode D1 the anode of which is connected to the other terminal of the first capacitor C1, a second capacitor C2 one terminal of which is connected to a cathode of the first diode D1 and the other terminal of which is grounded, a second diode D2 a cathode of which is connected to the anode of the first diode D1, a third capacitor C3 one terminal of which is connected to an anode of the second diode D2 and the other terminal of which is grounded, and a first resistor R1 connected in parallel to the third capacitor C3.

Here, the microcomputer 1 is connected in parallel to the second capacitor C2 and receives a voltage VO applied on both terminals of the second capacitor C2 as its driving voltage. In this case, the driving voltage is determined by the ratio of the capacitance of the first capacitor Cl to the capacitance of the second capacitor C2, and it is general that the power consumption of the regulator 100 itself exceeds 100mW under the commercial AC power supply of 220V.

Since the regulator 100 is composed of a plurality of capacitors, it has the drawback in that the phase difference between the voltage and current supplied to the microcomputer 1 becomes great.

Brief Description of the Drawings The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment (s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: FIG. 1 is a circuit diagram illustrating the construction of a conventional regulator for a microcomputer adopting the capacitive divided circuit; FIG. 2 is a block diagram illustrating the construction of a regulator for a microcomputer according to an embodiment of the present invention; FIG. 3 is a detailed circuit diagram of the regulator of FIG. 2; FIGs. 4A and 4B are graphs showing results of simulation performed based on the construction of FIG. 3 ; and FIG. 5 is a table showing calculated power factors of the regulator for a microcomputer according to the present invention and the conventional regulator for a microcomputer.

Disclosure of the Invention The present invention is directed to a regulator for a microcomputer that substantially obviates one or more problems due to limitations and disadvantages of the related art.

It is an object of the present invention to provide a regulator for a microcomputer which has a low power

consumption and an improved power factor of the power applied to the microcomputer..

To achieve this object and other advantages in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a regulator for a microcomputer comprising a rectifying unit for rectifying a commercial AC input voltage and outputting a rectified voltage, a switching unit for intermittently switching an output voltage of the rectifying unit at predetermined intervals, a smoothing unit for smoothing an AC voltage outputted from the switching unit into a DC voltage and outputting the DC voltage to the microcomputer, and a pulse width modulation (PWM) signal generating unit for outputting a PWM signal for intermittently turning on/off the switching unit under the control of the microcomputer.

Preferably, the regulator according to the present invention further comprises a serial regulator for receiving and converting the output voltage of the rectifying unit into a proper size to output the converted voltage to the smoothing unit and being inactivated by a control signal transmitted from the microcomputer after a predetermined time elapses.

Preferably, the smoothing unit comprises a capacitor, and the predetermined time refers to a time point where the capacitor is charged.

Best Mode for Carrying Out the Invention

Reference will now be made in detail to the preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts.

FIG. 2 is a block diagram illustrating the construction of a regulator for a microcomputer according to an embodiment of the present invention, and FIG. 3 is a detailed circuit diagram of the regulator of FIG. 2.

Referring to FIG. 2, the regulator 200 for a microcomputer includes a diode D the anode of which is connected to an input terminal of the commercial AC power supply, a switching unit 10 one terminal of which is connected to the cathode of the diode D, a PWM controller 14, connected to the other terminal of the switching unit 10, for supplying a PWM signal to the switching unit 10, a serial regulator 12, connected to the cathode of the diode D, for providing a driving power to the microcomputer 16 when the regulator is initially operated, and a capacitor C one terminal of which is commonly connected to the switching unit 10 and the serial regulator 12 and the other terminal of which is grounded. Here, a voltage of a node (hereinafter referred to as an"output node") commonly connected to the switching unit 10, the serial regulator 12 and the capacitor C is supplied to the microcomputer 16 as its driving voltage.

The diode D half-wave-rectifies the AC voltage inputted from the commercial AC power supply and supplies the rectified voltage to the switching unit 10 and the serial regulator 12.

The serial regulator 12 receives the half-wave- rectified voltage from the diode D and provides the driving voltage to the microcomputer 16. After a predetermined time elapses, the serial regulator 12 is inactivated by a specified control signal transmitted from the microcomputer 16.

Referring to FIG. 3, the serial regulator 12 includes first and second resistors R1 and R2 commonly connected to the cathode of the diode D, a first bipolar transistor Ql the collector of which is connected to the other terminal of the first resistor R1, the emitter of which is connected to the output node and the base of which is connected to the other terminal of the second resistor R2, a third resistor R3 one terminal of which is connected to the base of the first bipolar transistor Ql, a second bipolar transistor Q2 the collector of which is connected to the other terminal of the third resistor R3 and the emitter of which is grounded, and a fourth resistor R4 one terminal of which is connected to the base of the bipolar transistor Q2 and the other terminal of which is connected to one output terminal of the microcomputer.

Here, the output voltage of the serial regulator 12 is supplied to the microcomputer 16 through the output node 17 as the driving voltage. Also, the inactive control signal transmitted from the microcomputer 16 is inputted to the base of the second bipolar transistor Q2 through the fourth resistor R4 to turn bff the operation of the serial regulator 12.

Referring again to FIG. 2, the capacitor C performs a smoothing of the AC voltage signal supplied from the switching unit 10 and the serial regulator 12 and supplies the smoothed voltage to the microcomputer 16.

During the initial operation of the regulator 200, the microcomputer 16 receives the driving power from the serial regulator 12, but after the predetermined time elapses, it receives the driving power from the switching unit 10 after it inactivates the serial regulator. Here, it is preferable that the predetermined time refers to a time point where the charging of the capacitor C is completed by the power supplied from the serial regulator 12.

The PWM controller 14 is controlled by the microcomputer 16, and outputs the PWM signal for intermittently turning on/off the switching unit 10.

The switching unit 10 intermittently switches the half-wave-rectified voltage outputted from the diode D and outputs the switched voltage to the capacitor C by being turned on/off in response to the PWM signal inputted from the PWM controller 14.

Referring to FIG. 3, the switching unit 10 includes a MOS transistor M the drain of which is connected to the cathode of the diode D and the gate of which is connected to the output terminal of the PWM controller 14, a fifth resistor R5 one terminal of which is connected to the source of the MOS transistor M and the other terminal of which is connected to the capacitor C, and a sixth resistor R6 one terminal of which is connected to the gate of the MOS transistor M and the other terminal of which is grounded.

Here, the MOS transistor M intermittently switches the half-wave-rectified voltage outputted through its drain and outputs the switched voltage to its source by being turned on/off in response to the variation of the amplitude value of the PWM signal inputted through its gate. This output voltage is dropped for a predetermined value through the fifth resistor R5 and then outputted to the capacitor.

The operation of the regulator for a microcomputer having the above-described construction will now be explained.

During the initial operation of the regulator, the driving voltage outputted from the serial regulator 12 is supplied to the microcomputer 16. This is because the driving voltage is not supplied to the microcomputer during the initial operation of the regulator, and thus the PWM controller 14 and the switching unit 10 that operate under the control of the microcomputer 16 cannot normally operate.

While the driving voltage is supplied from the serial regulator 12, the capacitor 14 is charged, and if this charging operation is completed, the microcomputer 16 inactivates the serial regulator 12. This is because the serial regulator includes a plurality of resistors, and thus has a large power consumption and a lowered efficiency.

Thereafter, the driving voltage outputted from the switching unit 10 is supplied to the microcomputer 16.

FIGs. 4A and 4B are graphs showing results of simulation performed based on the construction of FIG. 3.

In the process of simulation, it is set that R1 = 1MQ, R2 = 50MS2, R3 = 1K2, R4 = 100kas2, R5 = 9. 5K2, R6 = 500K2, C 5LF and AC is 340V, 60Hz.

FIG. 4A shows a waveform of the PWM signal outputted from the PWM controller 14. Referring to FIG. 4A, the PWM signal is a square wave pulse that has an amplitude of 6V and a period of about 0.017s. The PWM signal shows a normal waveform in an area of t 2 0.3s.

FIG. 4B shows a waveform of the output voltage Vo measured at the output node 17. Referring to FIG. 4B, the output voltage Vo gradually increases as it forms a small ripple in an area of Os < t < 0. 3s, while it shows a stable value as it forms a small ripple around 2.5V in an area of t 0. 3s.

Here, the output voltage Vo in the area of Os < t < 0.3s is outputted from the serial regulator 12, and the output voltage Vo in the area of t > 0.3s is outputted from the switching unit 10.

Specifically, the serial regulator 12 is inactivated at t=0.3s, and then the voltage outputted from the switching unit 10 is supplied to the microcomputer 16.

FIG. 5 is a table showing calculated power factors of the regulator for a microcomputer according to the present invention and the conventional regulator for a microcomputer.

For reference, the power factor of the conventional regulator for a microcomputer was calculated based on the circuit of FIG. 1, and it was set that Cl = 0. 025pF, C2 = 5pF, C3 = 5F, R1 = 25KN and AC is 340V, 60Hz.

Referring to FIG. 5, as a result of measurement and calculation, an apparent power, average power and power factor of the conventional regulator were 54mV, 0.6mV, and 0.01, respectively, while those of the regulator according to the present invention were 36mV, 23mV and 0.639, respectively.

Industrial Applicability As described above, according to the present invention, the apparent power is reduced and the power factor is greatly improved in comparison to the related art. This is because the voltage and current of the driving power being supplied to the microcomputer 16 actually have the same phase.

Also, since the voltage inputted from the commercial AC power supply is intermittently supplied through the switching unit and the voltage and current supplied to the microcomputer actually have the same phase, the power factor is greatly improved and thus the power consumption is decreased.

The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.