Charging circuit for a vehicle charger

A charging circuit for a vehicle charger includes a front high-voltage protective circuit, a rear high-voltage protective circuit, a first filtering circuit, an over-voltage protective circuit, a high frequency step-down switching regulator, a second filtering circuit, a frequency modulation circuit, a reference voltage input circuit, a sampling circuit, a short-circuit protective circuit and two charging interfaces. The front high-voltage protective circuit connects to a vehicle DC power, the first filtering circuit connects the front high-voltage protective circuit to the switching regulator, the second filtering circuit connects to an output point of the switching regulator to the rear high-voltage protection circuit, the frequency modulation circuit connects to a second input point of the switching regulator, the third input point of the switching regulator connects to the reference voltage input circuit, the short-circuit protective circuit connects the second filtering circuit to the fourth input point of the switching regulator, the sampling circuit connects the second filtering circuit to the fifth input point of the switching regulator, the rear high-voltage protection circuit connects to the two charging interfaces. For the unique design, the charging circuit for a vehicle charger has a short-circuit protective function and provides two charging interfaces.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This present invention relates to a charging circuit, and more specifically to a charging circuit for a vehicle charger.

2. The Related Art

Since portable electric devices, cameras, mobiles, MP3, etc. are popular today, the battery is designed to be as small as possible. In this case, the battery is needed to be charged rapidly.

A conventional vehicle charger can provide power to charge the battery of the electric device. However, each charger is dedicated to charge only one kind of electric device. In order to charge different electric devices, different chargers must be carried in the vehicle. In this case, it would occupy much space of the vehicle, which is inconvenient to the user.

SUMMARY OF THE INVENTION

An object of the invention is to provide a charging circuit for a vehicle charger comprising a front high-voltage protective circuit, a rear high-voltage protective circuit, a first filtering circuit, an over-voltage protective circuit, a high frequency step-down switching regulator, a second filtering circuit, a frequency modulation circuit, a reference voltage input circuit, a sampling circuit, a short-circuit protective circuit, a first charging interface and a second charging interface.

The front high-voltage protective circuit connects to the output point of a vehicle DC power. The first filtering circuit connects the high-voltage protective circuit to the first input point of the high frequency step-down switching regulator. The input point of the second filtering circuit connects to the output point of the switching regulator. The second input point of the high frequency step-down switching regulator connects to the frequency modulation circuit. The third input point of the high frequency step-down switching regulator connects to the reference voltage input circuit. The short-circuit protective circuit connects the output point of the second filtering circuit to the fourth input point of the high frequency step-down switching regulator. The sampling circuit connects the output point of the second filtering circuit to the fifth input point of the switching regulator to adjust the output voltage from the output point of the switching regulator. The over-voltage protective circuit connects the output point of the second filtering circuit to the high frequency step-down switching regulator. The rear high-voltage protective circuit connects the output point of the second filtering circuit to the first and second charging interfaces.

For the first charging interface and the second charging interface designed in this invention, the charging circuit for a vehicle charger can provide two interfaces, and for the front high-voltage protective circuit, the rear high-voltage protective circuit, the short-circuit protective circuit and the over-voltage protective circuit, the charging circuit for a vehicle charger is not destroyed by short of the first and second charging interfaces.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

First referring toFIG. 1, a charging circuit for a vehicle charger according to the invention is shown. The charging circuit for a vehicle charger includes a high frequency step-down switching regulator10, a front high-voltage protective circuit111, a rear high-voltage protective circuit112, a first filtering circuit12, an over-voltage protective circuit13, a second filtering circuit14, a frequency modulation circuit15, a reference voltage input circuit16, a sampling circuit17, a short-circuit protective circuit18, a first charging interface19and a second charging interface20.

An input point of the front high-voltage protective circuit111connects to an output point of a vehicle DC power100. The first filtering circuit12connects an output point of the front high-voltage protective circuit111to a first input point I1of the switching regulator10. An input point of the second filtering circuit14connects to an output point O1of the switching regulator10, and is used to filter the interfering signal from the switching regulator10. An second input point I2of the switching regulator10connects to the frequency modulation circuit15, while the parameter of the frequency modulation circuit15is adjusted, the output power of the switching regulator10will charge at the same time, so the interfering signal from the outside will not effect the switching regulator10. A third input point I3of the switching regulator10connects to the reference voltage input circuit16, the reference voltage input circuit16provides a reference voltage to the switching regulator10, the switching regulator10compares the reference voltage with the DC voltage in the inner of the switching regulator10to adjust the conduction time of the switching circuit in the inner of the switching regulator10, and then, the switching regulator10will output steady current. The short-circuit protective circuit18connects an output point of the second filtering circuit14to a fourth input point I4of the switching regulator10. The sampling circuit17and the over-voltage protective circuit13connect the output point of the second filtering circuit14to a fifth input point I5of the switching regulator10to adjust the output voltage from the output point O1of the switching regulator10. The rear high-voltage protective circuit112connects the output point of the second filtering circuit14to the first charging interface19and the second charging interface20.

Please refer toFIGS. 1 and 2, in this embodiment, the switching regulator10is a MP4459 chip. Pins8and9of the chip are regarded as the first input point I1of the switching regulator10, and connect to a supply voltage Vin of the charging circuit for a vehicle charger. Pin7, pin2, pin3, pin5and pin1of the chip are regarded as the second input point I2, the third input point I3, the fourth input point I4, the fifth input point I5and the output point O1of the switching regulator10respectively, pin6connects to GND of the charging circuit for a vehicle charger.

In this embodiment, the front high-voltage protective circuit111is a stable-voltage diode D1connected between the supply voltage Vin and GND. The first charging interface19is a USB connector, which includes a first VBUS signal pin191, a first D− signal pin192, a first D+ signal pin193and a first ground pin194connecting GND, the second charging interface20is the same as the first charging interface19and includes a second VBUS signal pin201, a second D− signal pin202, a second D+ signal pin203and a second ground pin204connecting GND. The rear high-voltage protective circuit112includes a stable-voltage diode D2connecting the first VBUS signal pin191and the second VBUS signal pin201with GND, and two stable-voltage diodes D3, D4parallel connecting each other which connect the first and second D− signal pins192,202with GND.

The first filtering circuit12is composed by capacitors C1and C2parallel connecting each other. The capacitors C1and C2connect the supply voltage Vin to GND. The first filtering circuit12is used to filter the interface signal from the supply voltage Vin.

The second filtering circuit14is composed by an inductance L1, capacitors C5and C6parallel connect each other. One end of the inductance L1connects to pin1and pin2of the MP4459 chip, the other end of the inductance L1connects to the first and second VBUS signal pins191,201, the capacitors C5and C6connect the first and second VBUS signal pins191,201to GND. A capacitance C4connects the inductance L1to pin10of the MP4459 chip, to provide power for transistors of the MP4459 chip.

The frequency modulation circuit15is composed by a resistance R3. The resistance R3connects pin7of the MP4459 chip to GND. While the resistance R3is adjusted, the operating frequency of the MP4459 will be adjusted to prevent electromagnetic signal interfering.

The reference voltage input circuit16is composed by an unilateral diode D5. The unilateral diode D5connects pin1and pin2of the MP4459 chip to GND. The unilateral diode D5provides a reference voltage to the MP4459 chip, the MP4459 chip compares the reference voltage with the inner voltage of the MP4459 chip to control the conductive time of the inner switching circuit, and then adjusts the MP4459 chip to output steady current.

The sampling circuit17is composed by two resistances R4and R5connecting each other in series. The resistance R4connects the VBUS signal pins191,201of the charging interfaces19,20to pin5of the MP4459 chip. The resistance R5connects pin5of the MP4459 chip to GND.

The short-circuit protective circuit18includes three resistances R11, R12and R13, a first N-channel transistor Q1and a capacitor C9. The resistance R13and the capacitor C9connecting each other in series connects the supply voltage Vin with the resistance R12in series, the resistance R12connects to GND. A base B of the first N-channel transistor Q1connects between the resistance R12and the series of the resistance R13and the capacitor C9, a collector C of the first N-channel transistor Q1connects to the supply voltage Vin, an Emitter E of the first N-channel transistor Q1connects to the pin3of the MP4459 chip. The resistance R11connects the VBUS signal pins191,201of the charging interface19,20to the pin3of the MP4459 chip.

The over-voltage protective circuit13includes a resistance R14, a stable-voltage diode D7and a second N-channel transistor Q2. One end of the resistance R14connects to the VBUS signal pins191,201of the charging interface19,20. A collector C of the second N-channel transistor Q2connects to the pin3of the MP4459 chip, an emitter E of the second N-channel transistor Q2connects to GND, the stable voltage diode D7is connected between a base B of the second N-channel transistor Q2and the other end of the resistance R14.

A controlling circuit21is composed by a resistance R1and a capacitance C8connecting each other in series, which connects the supply voltage Vin to GND.

While the charging circuit for a vehicle charger operating, the current from the supply voltage Vin inputs to pins8and9of the MP4459 chip and then outputs from the pins1,2, and then inputs to the first VBUS pin191of the first charging interface19and the second VBUS pin201of the second charging interface20. If the first VBUS pin191and the first ground pin194of the first charging interface19and/or the second VBUS pin201and the second ground pin204of the second charging interface20make a short circuit, the electric voltage added on the resistance R11equals to pin3of the MP4459 chip and is smaller than the threshold voltage on pin3, so the MP4459 chip stops operating for protecting the MP4459 chip.

A compensation circuit22connects to pin4of the MP4459 chip to compensate the frequency loss of the MP4459 chip. The compensation circuit22is composed by two capacitances C3, C7and a resistance R2. The capacitance C3connects the resistance R2in series, the capacitance C7connects with the capacitance C3and the resistance R2in parallel. The capacitance C7connects pin4of the MP4459 chip to GND, and the resistance R2and the capacitance C3connect the MP4459 chip to GND.

Two resistances R7, R8connecting each other in series and two resistances R9, R10connecting each other in series connects the VBUS signal pins191,201of the charging interface19,20to GND. The first D− signal pin192of the first charging interface19and the second D− signal pin202of the second charging interface20connect between the resistance R7and the resistance R8. The first D+ signal pin193of the first charging interface19and the second D+ signal pin203of the second charging interface20connect between the resistance R9and the resistance R10. While the ratios R7/R8or R9/R10are adjusted, the voltages between the first D− signal pin192and the first D+ signal pin193and/or between the second D− signal pin202and the second D+ signal pin203are charged, so the function of the charging circuit for a vehicle charger is expanded. A resistance R6and an LED D8connecting each other in series connect the VBUS signal pins191,201of the charging interface19,20to GND, while the charging circuit for a vehicle charger operating successfully, the LED D8lighting.

Because the output point of the rear high-voltage protective circuit112connects to the first charging interface19and the second charging interface20synchronously, the charging circuit for a vehicle charger can provide two interfaces, and for the front high-voltage protective circuit111, the rear high-voltage protective circuit112, the short-circuit protective circuit18and the over-voltage protective circuit13, the charging circuit for a vehicle charger can operate steadily.

An above description of the present invention has been discussed in detail. However, this embodiment is merely a specific example for clarifying the technical contents of the present invention and the present invention is not to be construed in a restricted sense as limited to this specific example. Thus, the spirit and scope of the present invention are limited only by the appended claims.