Handheld device and power supply circuit thereof

1. Technical Field

The present disclosure relates to handheld devices, and particularly to a handheld device with a power supply circuit.

2. Description of Related Art

Most handheld devices, such as mobile phones, are powered by power management units (PMUs), which can meet power demand of a handheld device after the handheld device is booted up. However, if the PMU is the power supply for the handheld device, when the handheld device is being booted-up, the PMU may fail to power up the handheld device because a backlight driving unit of the handheld device takes a high current when the handheld device is booted-up. If the high current taken is over the maximum current of the PMU, the PMU enters an under-voltage protection mode. Therefore, a PMU with a greater maximum current can be employed, but the greater the maximum current, the more expensive the PMU.

Many aspects of the present disclosure can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments.

The FIGURE is a circuit diagram of a handheld device in accordance with an embodiment of the present disclosure.

The disclosure, including the accompanying drawing, is illustrated by way of example and not by way of limitation. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references can mean “at least one.”

The figure shows an embodiment of a handheld device 100 . The handheld device 100 comprises a power supply circuit 10 , a backlight driving unit 20 , and a charging unit 30 which is connected to commercial power supply (not shown). The backlight driving unit 20 is powered by the power supply circuit 10 . The power supply circuit 10 is powered by the charging unit 30 . The backlight driving unit 20 drives a display (not shown) of the handheld device 100 . In one embodiment, the handheld device 100 may be a mobile phone or a personal digital assistant, the power supply circuit 10 may also power other elements of the handheld device 100 , to enable the handheld device 100 to operate normally.

The power supply circuit 10 comprises a power management unit (PMU) 12 , a first electronic switch Q 1 , a second electronic switch Q 2 , a control unit 14 , a voltage multiplying unit 16 , and a rechargeable battery BAT. The PMU 12 comprises a first input pin I 1 , a second input pin I 2 , and an output pin IPOUT. The first input pin I 1 is electrically connected to the charging unit 30 . The second input pin I 2 is electrically connected to a positive terminal of the rechargeable battery BAT. A negative terminal of the rechargeable battery BAT is grounded. Each of the first electronic switch Q 1 and the second electronic switch Q 2 comprises a first terminal, a second terminal, and a third terminal The first terminal of the first electronic switch Q 1 is electrically connected to the control unit 14 . The second terminal of the first electronic switch Q 1 is electrically connected to the positive terminal of the rechargeable battery BAT. The third terminal of the first electronic switch Q 1 is electrically connected to the backlight driving unit 20 . The first terminal of the second electronic switch Q 2 is electrically connected to the first terminal of the first electronic switch Q 1 . The second terminal of the second electronic switch Q 2 is electrically connected to the backlight driving unit 20 . The third terminal of the second electronic switch Q 2 is electrically connected to the output pin IPOUT of the PMU 12 . The control unit 14 is electrically connected to the second terminal of the second electronic switch Q 2 and the positive terminal of the rechargeable battery BAT. The voltage multiplying unit 16 is electrically connected to the control unit 14 and the positive terminal of the rechargeable battery BAT. The voltage multiplying unit 16 multiplies voltage of the rechargeable battery BAT into a first voltage, and outputs the first voltage to the control unit. The control unit 14 turns on and turns off the first electronic switch Q 1 and the second electronic switch Q 2 according to voltage of the second terminal of the second electronic switch Q 2 .

The control unit 14 comprises a third electronic switch Q 3 , a fourth electronic switch Q 4 , and five resistors R 1 -R 5 . Each of the third electronic switch Q 3 and the fourth electronic switch Q 4 comprises a first terminal, a second terminal, and a third terminal The first terminal of the third electronic switch Q 3 is electrically connected to the second terminal of the second electronic switch Q 2 through the resistor R 1 , and grounded through the resistor R 2 . The second terminal of the third electronic switch Q 3 is electrically connected to the positive terminal of the rechargeable battery BAT through the resistor R 3 . The third terminal of the third electronic switch Q 3 is grounded. The first terminal of the fourth electronic switch Q 4 is electrically connected to the second terminal of the third electronic switch Q 3 through the resistor R 4 . The second terminal of the fourth electronic switch Q 4 is electrically connected to the voltage multiplying unit 16 through the resistor R 5 , to receive the first voltage. The third terminal of the fourth electronic switch Q 4 is grounded. In one embodiment, a turn-on voltage of the electronic switch Q 3 functions as a reference voltage of the control unit 14 .

The voltage multiplying unit 16 comprises a Schmitt trigger U, a first diode D 1 , a second diode D 2 , three capacitors C 1 -C 3 , and two resistors R 6 and R 7 . The Schmitt trigger U comprises an input terminal and an output terminal Each of the first diode D 1 and the second diode D 2 comprises an anode and a cathode. The input terminal of the Schmitt trigger U is grounded through the capacitor C 1 . The output terminal of the Schmitt trigger U is electrically connected to the input terminal of the Schmitt trigger U through the resistor R 6 , and is electrically connected to the anode of the first diode D 1 and the cathode of the second diode D 2 through the capacitor C 2 . The cathode of the first diode D 1 is grounded through the capacitor C 3 and grounded through the resistor R 7 . The anode of the second diode D 2 is electrically connected to the positive terminal of rechargeable battery BAT. A node between the cathode of the first diode D 1 and the resistor R 7 functioning as the output terminal of the voltage multiplying unit 16 , is electrically connected to the control unit 14 to output the first voltage to the control unit 14 .

The operating principle of the voltage multiplying unit 16 will be described as follows.

When the handheld device 100 is not turned on, the Schmitt trigger U is not powered on, the output terminal of the Schmitt trigger U maintains a low level, such as logic 0, and the second diode D 2 is turned on. A voltage difference between two ends of the capacitor C 2 is approximately equal to the voltage of rechargeable battery BAT minus a voltage of the second diode D 2 . When the handheld device 100 is turned on, the Schmitt trigger U is powered on and operates. The input terminal of the Schmitt trigger U receives a low level signal, such as logic 0, and the output terminal of the Schmitt trigger U outputs a high level signal, such as logic 1. A voltage of the anode of the first diode D 1 is pulled up and the capacitor C 3 is charged, because the voltage difference between two ends of the capacitor C 2 is maintained to be the same by the capacitor C 2 . When the output terminal of the Schmitt trigger U outputs the high level signal, the capacitor C 1 is charged by the output terminal of the Schmitt trigger U through the resistor R 6 . Therefore, a voltage at the input terminal of the Schmitt trigger U increases. When the voltage of the input terminal of the Schmitt trigger U is equal to or more than a positive threshold voltage of the Schmitt trigger U, the output terminal of the Schmitt trigger U outputs a low level signal. The voltage of the anode of the first diode D 1 is pulled down, and the capacitor C 3 is discharged. When the output terminal of the Schmitt trigger U outputs the low level signal, the capacitor C 1 is discharged, and the voltage at the input terminal of the Schmitt trigger U decreases. When the voltage of the input terminal of the Schmitt trigger U is equal to or less than a negative threshold voltage of the Schmitt trigger U, the output terminal of the Schmitt trigger U outputs the high level signal. The voltage of the anode of the first diode D 1 is pulled up, and the capacitor C 3 is charged. The output terminal of the voltage multiplying unit 16 can then output the first voltage. The first voltage is used for turning on the second electronic switch Q 2 when the fourth electronic switch Q 4 is turned off

When the first input pin I 1 of the PMU 12 is not connected to the charging unit 30 , the PMU 12 supplies power taken from the rechargeable battery BAT, to the handheld device 100 . When the first input pin I 1 of the PMU 12 is electrically connected to the charging unit 30 , the PMU 12 supplies power taken from the charging unit 30 to the handheld device 100 and to the rechargeable battery BAT by way of recharging the rechargeable battery BAT.

When the handheld device 100 is booted-up, the output pin IPOUT of the PMU 12 supplies power to the backlight driving unit 20 through the second electronic switch Q 2 . When the backlight driving unit 20 is being powered on, a spike current will be drawn by the backlight driving unit 20 and flow from the PMU 12 through the second electronic switch Q 2 . When the spike current does not reach its peak and is less than the maximum current of the PMU 12 , the PMU 12 does not enter into an under-voltage protection mode.

The PMU 12 has a small resistance, and the voltage of the rechargeable battery BAT is divided by the PMU 12 and the backlight driving unit 20 connected in series. When the spike current is small, a voltage of the PMU 12 is negligible, and the voltage of the backlight driving unit 20 is approximately equal to the voltage of the rechargeable battery BAT. When the spike current is high, the voltage of the PMU 12 will be greater, and the voltage of the backlight driving unit 20 will be less. In this state, a voltage of the second terminal of the second electronic switch Q 2 is less than the reference voltage of the control unit 14 , a voltage received by the first terminal of the third electronic switch Q 3 is less than the turn-on voltage of the electronic switch Q 3 , the third electronic switch Q 3 is turned off, and the fourth electronic switch Q 4 is turned on. The second terminal of the fourth electronic switch Q 4 outputs a low level signal, such as logic 0, to the first terminals of the first electronic switch Q 1 and the second electronic switch Q 2 . The first electronic switch Q 1 is turned on, the second electronic switch Q 2 is turned off, and the rechargeable battery BAT is then supplying power to the backlight driving unit 20 through the first electronic switch Q 1 .

When the backlight driving unit 20 is powered by the rechargeable battery BAT through the first electronic switch Q 1 , the voltage of the backlight driving unit 20 is approximately equal to the voltage of the rechargeable battery BAT, which is more than the reference voltage of the control unit 14 . The voltage received by the first terminal of the third electronic switch Q 3 is more than the turn-on voltage of the electronic switch Q 3 , the third electronic switch Q 3 is turned on, and the fourth electronic switch Q 4 is turned off The output terminal of the voltage multiplying unit 16 outputs the first voltage to the first terminals of the first electronic switch Q 1 and the second electronic switch Q 2 through the resistor R 5 . The first electronic switch Q 1 is turned off, the second electronic switch Q 2 is turned on. The output pin IPOUT of the PMU 12 supplies power to the backlight driving unit 20 through the second electronic switch Q 2 . Because the spike current is only transitory, when the second electronic switch Q 2 goes to a turned on state from a turned off state, the spike current goes away. The second electronic switch Q 2 is then maintained in the turned on state, and the output pin IPOUT of the PMU 12 supplies power to the backlight driving unit 20 through the second electronic switch Q 2 .

In one embodiment, the first electronic switch Q 1 is a p-channel metal-oxide semiconductor field-effect transistor (PMOSFET), and the first terminal, the second terminal, and the third terminal of the first electronic switch Q 1 are respectively corresponding to a gate, a drain, and a source of the PMOSFET. The second electronic switch Q 2 is an n-channel metal-oxide semiconductor field-effect transistor (NMOSFET), and the first terminal, the second terminal, and the third terminal of the second electronic switch Q 2 are respectively corresponding to a gate, a drain, and a source of the NMOSFET. Each of the third electronic switch Q 3 and the fourth electronic switch Q 4 is an npn-type bipolar junction transistor (BJT), and the first terminal, the second terminal, and the third terminal of each of the third electronic switch Q 3 and the fourth electronic switch Q 4 respectively corresponding to a base, a collector, and an emitter of the npn-type BJT. In other embodiments, the first electronic switch Q 1 may be a pnp-type bipolar junction transistor, or other switch having similar functions. The second electronic switch Q 2 may be an npn-type bipolar junction transistor, or other switch having similar functions. Each of the third electronic switch Q 3 and the fourth electronic switch Q 4 may be an NMOSFET, or other switch having similar functions.

Even though numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.