Voltage converting device

The disclosure relates to a voltage converting device, and more particularly to a voltage converting device adapted for converting an AC input voltage into a DC output voltage for use by a light emitting diode (LED) unit.

Referring to FIG. 1 , a conventional voltage converting device for a light emitting device (e.g., an LED device) includes a frontend boost-type AC-DC converter 4 with power factor correction, and a backend half-bridge LLC resonant DC-DC converter 5 . Since each of the frontend stage and the backend stage of such a conventional voltage converting device requires a dedicated controller, the entire voltage converting device may include at least three power switches, which results in relatively high circuit complexity due to the number of circuit components, resulting in high costs.

Therefore, an object of the disclosure is to provide a voltage converting device that may have a relatively simple circuit structure and low costs.

According to the disclosure, the voltage converting device includes an input circuit, a voltage converter, a switch, an inductor, a capacitor, a first discharging diode, a second discharging diode, and an output circuit.

The input circuit is configured to receive and rectify an alternating current (AC) input voltage, and to generate a rectified voltage. The voltage converter is coupled to the input circuit for receiving the rectified voltage therefrom, and includes a primary-side winding and a secondary-side winding, each of which has a first terminal and a second terminal. The switch has a first terminal coupled to the second terminal of the primary-side winding, and a second terminal. The inductor has a first terminal coupled to the second terminal of the switch, and a second terminal coupled to the input circuit. The capacitor has a first terminal, and a second terminal coupled to the second terminal of the switch. The first discharging diode has an anode coupled to the second terminal of the inductor, and a cathode coupled to the first terminal of the capacitor. The second discharging diode has an anode coupled to the first terminal of the capacitor, and a cathode coupled to the first terminal of the primary-side winding. The output circuit is coupled to the secondary-side winding in parallel, and is configured to generate a direct current (DC) output voltage.

Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiments with reference to the accompanying drawings, of which:

FIG. 1 is a block diagram illustrating a conventional voltage converting device for an LED device;

FIG. 2 is a schematic circuit diagram illustrating an embodiment of the voltage converting device according to this disclosure;

FIG. 3 is a waveform diagram illustrating operations of the embodiment;

FIG. 4 is a schematic circuit diagram illustrating operation of the embodiment in a first duration;

FIG. 5 is a schematic circuit diagram illustrating operation of the embodiment in a second duration; and

FIG. 6 is a schematic circuit diagram illustrating operation of the embodiment in a third duration.

Before the disclosure is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure.

Referring to FIG. 2 , the embodiment of the voltage converting device according to this disclosure is adapted for converting an AC (alternating current) input voltage (V AC ) into a DC (direct current) output voltage (VO) for use by an LED (light emitting diode) unit 9 , and includes an input circuit 1 , a voltage converter 2 , a switch (S), an inductor (L), a capacitor (C), a first discharging diode (D5), a second discharging diode (D6) and an output circuit 3 .

The input circuit 1 is coupled to an AC power source 6 for receiving the input voltage (V AC ), filters out noises from and rectifies the input voltage (V AC ), and generates a rectified voltage (V REC (t)). In detail, the input circuit 1 includes a filter circuit 11 and a rectifier circuit 12 . The filter circuit 11 is coupled to the power source 6 for receiving the input voltage (V AC ), and filters out the noises from the input voltage (V AC ) to obtain a filtered voltage (not shown). The rectifier circuit 12 is coupled to the filter circuit 11 for receiving the filtered voltage therefrom, and rectifies the filtered voltage to obtain the pulsating DC rectified voltage (V REC (t)).

In this embodiment, the filter circuit 11 includes: a resonant inductor (Lf) having a first terminal coupled to the power source 6 , and a second terminal; and a resonant capacitor (Cr) having a first terminal coupled to the second terminal of the resonant inductor (Lf), and a second terminal. The rectifier circuit 12 includes: a first rectifying diode (D1) having an anode coupled to the first terminal of the resonant capacitor (Cr), and a cathode; a second rectifying diode (D2) having a cathode coupled to the anode of the first rectifying diode (D1), and an anode; a third rectifying diode (D3) having a cathode coupled to the cathode of the first rectifying diode (D1), and an anode coupled to the second terminal of the resonant capacitor (Cr); and a fourth rectifying diode (D4) having a cathode coupled to the second terminal of the resonant capacitor (Cr), and an anode coupled to the anode of the second rectifying diode (D2).

The voltage converter 2 is coupled to the input circuit 1 for receiving the rectified voltage (V REC (t)), and includes a primary-side winding (n p ) and a secondary-side winding (n s ), each of which has a polarity first terminal, and a non-polarity second terminal.

The switch (S) has a first terminal coupled to the second terminal of the primary-side winding (n p ), a second terminal, and a control terminal for controlling electrical connection between the first and second terminals thereof. In this embodiment, the switch (S) is an N-type power MOSFET having a drain terminal, a source terminal and a gate terminal to respectively act as the first, second and control terminals of the switch (S).

The inductor (L) has a first terminal coupled to the second terminal of the switch (S), and a second terminal coupled to anode of the fourth rectifying diode (D4) of the input circuit 1 .

The capacitor (C) has a first terminal, and a second terminal coupled to the second terminal of the switch (S).

The first discharging diode (D5) has an anode coupled to the second terminal of the inductor (L), and a cathode coupled to the first terminal of the capacitor (C).

The second discharging diode (D6) has an anode coupled to the first terminal of the capacitor (C), and a cathode coupled to the first terminal of the primary-side winding (n p ).

The output circuit 3 is coupled to the secondary-side winding (n s ) in parallel, and generates the DC output voltage (VO) to drive the LED unit 9 . In this embodiment, the output circuit 3 includes: an output diode (D7) having an anode coupled to the second terminal of the secondary-side winding (n s ), and a cathode; and an output capacitor (CO) having a first terminal coupled to the cathode of the output diode (D7), and a second terminal coupled to the first terminal of the secondary-side winding (n s ). The DC output voltage (VO) is provided at the first terminal of the output capacitor (CO).

Referring to FIG. 3 , V GS represents a voltage between the control terminal and the second terminal of the switch (S), V DS represents a voltage between the first terminal and the second terminal of the switch (S), V L and V Lm respectively represent voltages across the inductor (L) and the primary-side winding (n p ) that has a magnetizing inductance denoted as a magnetizing inductor (Lm) in FIGS. 4 to 6 , i L and i Lm respectively represent currents flowing through the inductor (L) and the magnetizing inductor (Lm), and i D5 , i D6 and i D7 respectively represent currents flowing through the first discharging diode (D5), the second discharging diode (D6) and the output diode (D7). According to switching of the switch (S), operations of this embodiment to drive the LED unit 5 may be divided into three durations. In FIGS. 4-6 , solid lines are used to denote the components that conduct, and dotted lines are used to denote the components that are not conducting. It is noted that, in the following descriptions of the operations, it is assumed that energy has been stored in the output capacitor (CO) and the capacitor (C) during previous operation cycles.

Referring to FIGS. 3 and 4 , in a first duration between t0 to t1, V GS is at a high voltage level and the switch (S) conducts, while the first discharging diode (D5) does not conduct, so that the capacitor (C) provides the current (i D6 ) to charge the magnetizing inductor (Lm) via the second discharging diode (D6), and a current that is associated with the rectified voltage (V REC (t)) flows through the switch (S) to charge the magnetizing inductor (Lm) and the inductor (L). Accordingly, i Lm and i L linearly increase. At this time, a voltage across the secondary-side winding (n s ) is not sufficiently high to cause conduction of the output diode (D7), and the output capacitor (CO) provides the output voltage (VO) to drive the LED unit 9 .

Referring to FIGS. 3 and 5 , in a second duration between t1 to t2, V GS is at a low voltage level and the switch (S) does not conduct, and the second discharging diode (D6) does not conduct either. The inductor (L) provides a current (i D6 ) flowing through the first discharging diode (D5) to charge the capacitor (C). At this time, the magnetizing inductor (Lm) causes generation of the current (i D7 ) flowing to the output capacitor (CO) and the LED unit 9 .

Referring to FIGS. 3 and 6 , in a third duration between t2 to t3, V GS is still at the low voltage level and the switch (S) continues to not conduct, such that the second discharging diode (D6) does not conduct. In this duration, a voltage difference across the capacitor (C) and the inductor (L) is not sufficiently large to cause conduction of the first discharging diode (D5), such that the first discharging diode (D5) transitions to become non-conducting. At this time, since the voltage across the magnetizing inductor (Lm) and the output capacitor (CO) is still sufficiently high to cause conduction of the output diode (D7), the magnetizing inductor (Lm) remains to cause generation of the current (i D7 ) flowing to the output capacitor (CO) and the LED unit 9 , such that the LED unit 9 continues to emit light and the output capacitor (CO) continues to be charged. Then, a cycle of operations in this embodiment completes, and another cycle begins with the first duration.

In summary, via simple operation of the switch (S), the embodiment of this disclosure has the effect similar to that of the conventional AC-DC converter while maintaining a relatively low cost and also having the function of power factor correction (PFC). With the magnetizing inductor (Lm) being designed to operate in a boundary conduction mode, the function of power factor correction is achievable in cooperation with, e.g., a commercially available PFC control IC.

While the disclosure has been described in connection with what is(are) considered the exemplary embodiment(s), it is understood that this disclosure is not limited to the disclosed embodiment(s) but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.