Power supply module providing feedback voltage stabilization to eliminate inductor spike

1. Technical Field

The disclosed embodiments relate to power supply modules, and more particularly to a power supply module with a feedback circuit.

2. Description of Related Art

Electronic devices powered by a power supply module correspond to various rated voltages. The power supply module receives and processes an input alternating current (AC) voltage from an external power source, and generates a first direct current (DC) voltage to power the electronic device.

Generally, the power supply module includes an AC/DC converter, a voltage transforming circuit, an inductor, and a feedback circuit. The AC/DC converter is used for converting the input AC voltage to a primary DC voltage. The voltage transforming circuit is used for transforming the primary DC voltage to the first DC voltage. The feedback circuit is used for generating a feedback signal according to the first DC voltage. The voltage transforming circuit adjusts the first DC voltage according to the feedback signal, so as to maintain the first DC voltage to a first predetermined value.

However, the voltage transforming circuit is coupled to the electronic device via the inductor, one end of the feedback circuit is coupled between the inductor and the electronic device. When the power supply module is powered on, the first DC voltage is usually larger, and a current flowing through the inductor spikes. Accordingly, the first DC voltage is likely to be above the first predetermined value and may damage the electronic device.

What is needed, therefore, is a power supply module for overcoming the above described limitation.

Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a block diagram of a power supply module in accordance with an exemplary embodiment.

FIG. 2 is a circuit diagram of the power supply module of FIG. 1 in accordance with an exemplary embodiment.

Referring to FIG. 1 , a power supply module 100 in accordance with an exemplary embodiment is illustrated. The power supply module 100 is used for converting an input alternating current (AC) voltage from an external power source 200 to a first direct current (DC) voltage, and applying the first DC voltage to a load 300 . The power supply module 100 includes an AC/DC converter 10 , a voltage transforming circuit 20 , a feedback circuit 30 , and a detecting circuit 40 .

The AC/DC converter 10 is coupled to the external power source 200 . The AC/DC converter 10 is used for converting the input AC voltage to a primary DC voltage, and providing the primary DC voltage to the voltage transforming circuit 20 .

The voltage transforming circuit 20 is coupled to the AC/DC converter 10 . The voltage transforming circuit 20 is used for transforming the primary DC voltage to the first DC voltage and a second DC voltage. The first DC voltage is used to power the load 300 . The second DC voltage is used to power the feedback circuit 30 . In detail, the voltage transforming circuit 20 includes a transformer T 1 , a rectifying-filtering circuit 22 , and an inductor L 1 . The transformer T 1 is coupled to the AC/DC converter 10 , the rectifying-filtering circuit 22 is coupled to the transformer T 1 , and the inductor L 1 is coupled between the rectifying-filtering circuit 22 and the load 300 .

The feedback circuit 30 is used for sampling the first DC voltage to generate a first voltage and a second voltage. A feedback voltage is defined by subtracting the second voltage from the first voltage. The feedback circuit 30 is further used for generating a feedback signal according to the feedback voltage. The voltage transforming circuit 20 maintains the first DC voltage at a first predetermined value according to the feedback signal.

The detecting circuit 40 is coupled to the feedback circuit 30 . The detecting circuit 40 is used for detecting whether the power supply module 100 is powered on, and generating a third voltage when detecting that the power supply module 100 is powered on. A difference voltage is defined by subtracting the third voltage from the second voltage. When the difference voltage reaches a second predetermined value, the second voltage is reduced, and the feedback voltage is increased. The feedback circuit 30 increases the magnitude of the feedback signal according to the increased feedback voltage. Therefore, when the power supply module 100 is powered on, the voltage transforming circuit 20 still can maintain the first DC voltage at the first predetermined value according to the increased feedback signal.

Referring to FIG. 2 , the feedback circuit 30 includes a first resistor R 1 , a second resistor R 2 , a third resistor R 3 , a fourth resistor R 4 , a fifth resistor R 5 , a first capacitor C 1 , a second capacitor C 2 , an optocoupler U 1 , and a triode for alternating current (TRIAC) Q 1 . The optocoupler U 1 includes a first input terminal 11 , a second input terminal 22 , a third input terminal 33 , and an output terminal 44 .

The first resistor R 1 and the second resistor R 2 are coupled in series between the voltage transforming circuit 20 and a cathode of the TRIAC Q 1 . The third resistor R 3 and the fourth resistor R 4 are coupled in series between the voltage transforming circuit 20 and ground. An anode of the TRIAC Q 1 is grounded, a gate of the TRIAC Q 1 is coupled between the third resistor R 3 and the fourth resistor R 4 . The first input terminal 11 is coupled between the first resistor R 1 and the second resistor R 2 . The second input terminal 22 is coupled between the second resistor R 2 and the cathode of the TRIAC Q 1 . The third input terminal 33 and the output terminal 44 are coupled to the voltage transforming circuit 20 . One end of the first capacitor C 1 is coupled to the second input terminal 22 , the other end of the first capacitor C 1 is coupled between the third resistor R 3 and the fourth resistor R 4 . The fifth resistor R 5 and the second capacitor C 2 are coupled between the cathode of the TRIAC Q 1 and the gate of the TRIAC Q 1 .

The detecting circuit 40 includes a diode D 1 , a sixth resistor R 6 , and a third capacitor C 3 . A capacitance of the third capacitor C 3 is very large. One end of the sixth resistor R 6 is coupled between the rectifying-filtering circuit 22 and the inductor L 1 , the other end of the sixth resistor R 6 is grounded through the third capacitor C 3 . An anode of the diode D 1 is coupled to the second input terminal 22 , a cathode of the diode D 1 is coupled between the sixth resistor R 6 and the third capacitor C 3 .

The principal of the power supply module 100 is described as follows. When the power supply module 100 is powered on, the first DC voltage charges up the third capacitor C 3 through the sixth resistor R 6 , thus the third voltage V 3 across the third capacitor C 3 is increased from zero volts. Because the capacitance of the third capacitor C 3 is very large, the third voltage V 3 increases slowly.

The third resistor R 3 and the fourth resistor R 4 divides the first DC voltage to generate a fourth voltage. The fourth voltage is a voltage across the fourth resistor R 4 . The fourth voltage turns on the TRIAC Q 1 , then the first voltage V 1 and the second voltage V 2 are generated. The first voltage V 1 is the voltage of the first input terminal 11 of the optocoupler U 1 . The second voltage V 2 is the voltage of the second input terminal 22 of the optocoupler U 1 . The feedback voltage V 4 is the voltage across the second resistor R 2 . The feedback voltage V 4 is defined by subtracting the second voltage from the first voltage, the difference voltage is defined by subtracting the third voltage from the second voltage. Because the third voltage V 3 is increased slowly, therefore the difference voltage reaches a bias voltage of the diode D 1 , the diode D 1 is turned on. The second voltage V 2 is reduced, and the feedback voltage V 4 is increased.

Because the feedback voltage V 4 is increased, thus the magnitude of the feedback signal is increased, and the voltage transforming circuit 20 can maintain the first DC voltage at the first predetermined value according to the increased feedback signal.

A charge time τ of the third capacitor C 3 is calculated by the following formula:

τ= R 6* C 3

After the charge time τ, the third voltage V 3 is equal to the first DC voltage. The second voltage V 2 is smaller than the third voltage V 3 . Because the difference voltage is defined by subtracting the third voltage from the second voltage, the difference voltage is smaller than the bias voltage of the diode D 1 , the diode D 1 is turned off. Therefore, the second voltage V 2 becomes stable, and the feedback voltage V 4 becomes stable, the power supply module 100 is working normally.

Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from the spirit and scope. Accordingly, the present invention should be deemed not to be limited to the above detailed description, but rather by the claims that follow.