Load-testing circuit for USB ports

1. Technical Field

The present disclosure relates to load-testing circuits, and particularly to a load-testing circuit for USB ports.

2. Description of Related Art

USB ports include four different types, such as type 1.0, type 1.1, type 2.0, and type 3.0. The maximum standard load currents of the USB ports respectively are 100 mA, 150 mA, 500 mA, and 900 mA. Typically, one load-testing circuit can simulate only one maximum standard load current. As a result, different load-testing circuits must be designed for different types of USB ports, which is inconvenient and costly.

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 load-testing circuit 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 load-testing circuit 10 used for simulating maximum standard load currents for different types of USB ports 20 when the USB ports 20 are under test. The load-testing circuit 10 comprises a first electronic switch Q 1 , a second electronic switch Q 2 , a current selection module 100 , and three resistors R 1 -R 3 .

Each USB port 20 comprises a power terminal VCC. 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 power terminal VCC through the resistor R 1 . The second terminal of the first electronic switch Q 1 is electrically connected to the power terminal VCC. The third terminal of the first electronic switch Q 1 is electrically connected to the current selection module 100 . The first terminal of the second electronic switch Q 2 is electrically connected to the current selection module 100 through the resistor R 3 . The second terminal of the second electronic switch Q 2 is electrically connected to the first terminal of the first electronic switch Q 1 through the resistor R 2 . In one embodiment, the power terminal VCC of the USB port 20 supplies a 5 volts voltage to the first the terminal of the first electronic switch Q 1 and the first electronic switch Q is maintained in the turned on state.

The current selection module 100 comprises a first current branch circuit 110 , a second current branch circuit 120 , a third current branch circuit 130 , and a fourth current branch circuit 140 . Each current branch circuit comprises a relay 112 , a first switch K 1 , a first diode D 1 , and a resistor R 4 . The relay 112 comprises a coil J and a second switch K 2 . A first terminal of the coil J is electrically connected to the third terminal of the first electronic switch Q 1 . A second terminal of the coil J is electrically connected to a first terminal of the first switch K 1 . A second terminal of the first switch K 1 is electrically connected to the first terminal of the second electronic switch Q 2 through the resistor R 3 . A first terminal of the second switch K 2 is electrically connected to the third terminal of the first electronic switch Q 1 . A second terminal of the second switch K 2 is grounded through the resistor R 4 . An anode of the first diode D 1 is electrically connected to the second terminal of the coil J. A cathode of the first diode D 1 is electrically connected to the third terminal of the first terminal of the coil J. In one embodiment, the first diode D 1 is used for discharging electrical energy stored in the coil J. A resistance of the resistor R 4 of each current branch circuit is different.

The second current branch circuit 120 further comprises a second diode D 2 . An anode of the second diode D 2 is electrically connected to the second terminal of the first switch K 21 of the second current branch circuit 120 . A cathode of the second diode D 2 is electrically connected to the first terminal of the second electronic switch Q 2 though the resistor R 3 . The third current branch circuit 130 further comprises a third diode D 3 and a fourth diode D 4 . An anode of the third diode D 3 is electrically connected to the second terminal of the first switch K 31 of the third current branch circuit 130 . A cathode of the third diode D 3 is electrically connected to an anode of the fourth diode D 4 . A cathode of the fourth diode D 4 is electrically connected to the first terminal of the second electronic switch Q 2 though the resistor R 3 . The fourth current branch circuit 140 further comprises a fifth diode D 5 , a sixth diode D 6 , and a seventh diode D 7 . An anode of the fifth diode D 5 is electrically connected to the second terminal of the first switch K 41 of the fourth current branch circuit 140 . A cathode of the fifth diode D 5 is electrically connected to an anode of the sixth diode D 6 . A cathode of the sixth diode D 6 is electrically connected to an anode of the seventh diode D 7 . A cathode of the seventh diode D 7 is electrically connected to the first terminal of the second electronic switch Q 2 though the resistor R 3 .

When the first switch K 1 of the first current branch circuit 110 is turned on, the first current branch circuit 110 is activated. In the relay 112 of the first current branch circuit 110 , a current passes through the coil J, and thus the second switch K 2 is turned on. A voltage at the third terminal of the first electronic switch Q 1 is supplied to the first terminal of the second electronic switch Q 2 through the coil J, the first switch K 1 , and the resistor R 3 in that order. The second electronic switch Q 2 is turned on. A voltage of the resistor R 4 of the first current branch circuit 110 is approximately equal to a sum of a voltage at the first terminal of the second electronic switch Q 2 and a voltage of the resistor R 3 . A current of the resistor R 4 of the first current branch circuit 110 is equal to the voltage of the resistor R 4 of the first current branch circuit 110 divided by a resistance of the resistor R 4 of the first current branch circuit 110 . In one embodiment, when the second electronic switch Q 2 is turned on, the voltage at the first terminal of the second electronic switch is approximately equal to 0.7V. A resistance of the resistor R 3 is very large, and thus a current of the resistor R 3 is small and can be negligible. In this state, a current of the third terminal of the first electronic switch Q 1 is approximately equal to the current of the resistor R 4 of the first current branch circuit 110 .

When the first switch K 21 of the second current branch circuit 120 is turned on, the second current branch circuit 120 is activated. In the relay 112 of the second current branch circuit 120 , a current passes through the coil J, and thus the second switch K 2 is turned on. The voltage at the third terminal of the first electronic switch Q 1 is supplied to the first terminal of the second electronic switch Q 2 through the coil J, the first switch K 21 , the second diode D 2 , and the resistor R 3 in that order. The second electronic switch Q 2 is turned on. A voltage of the resistor R 4 of the second current branch circuit 120 is approximately equal to a sum of the voltage at the first terminal of the second electronic switch Q 2 , the voltage of the resistor R 3 , and a voltage of the second diode D 2 . A current of the resistor R 4 of the second current branch circuit 120 is equal to the voltage of the resistor R 4 of the second current branch circuit 120 divided by a resistance of the resistor R 4 of the second current branch circuit 120 . In this state, the current of the third terminal of the first electronic switch Q 1 is approximately equal to the current of the resistor R 4 of the second current branch circuit 120 .

When the first switch K 31 of the third current branch circuit 130 is turned on, the third current branch circuit 130 is activated. In the relay 112 of the third current branch circuit 130 , a current passes through the coil J, and thus the second switch K 2 is turned on. The voltage at the third terminal of the first electronic switch Q 1 is supplied to the first terminal of the second electronic switch Q 2 through the coil J, the first switch K 31 , the third diode D 3 , the fourth diode D 4 , and the resistor R 3 in that order. The second electronic switch Q 2 is turned on. A voltage of the resistor R 4 of the third current branch circuit 130 is approximately equal to a sum of the voltage at the first terminal of the second electronic switch Q 2 , the voltage of the resistor R 3 , a voltage of the third diode D 3 , and a voltage of the fourth diode D 4 . A current of the resistor R 4 of the third current branch circuit 130 is equal to the voltage of the resistor R 4 of the third current branch circuit 130 divided by a resistance of the resistor R 4 of the third current branch circuit 130 . In this state, the current of the third terminal of the first electronic switch Q 1 is approximately equal to the current of the resistor R 4 of the third current branch circuit 130 .

When the first switch K 41 of the fourth current branch circuit 140 is turned on, the fourth current branch circuit 140 is activated. In the relay 112 of the fourth current branch circuit 140 , a current passes through the coil J, and thus the second switch K 2 is turned on. The voltage at the third terminal of the first electronic switch Q 1 is supplied to the first terminal of the second electronic switch Q 2 through the coil J, the first switch K 41 , the fifth diode D 5 , the sixth diode D 6 , the seventh diode D 7 , and the resistor R 3 in that order. The second electronic switch Q 2 is turned on. A voltage of the resistor R 4 of the fourth current branch circuit 140 is approximately equal to a sum of the voltage at the first terminal of the second electronic switch Q 2 , the voltage of the resistor R 3 , a voltage of the fifth diode D 5 , a voltage of the sixth diode D 6 , and a voltage of the seventh diode D 7 . A current of the resistor R 4 of the fourth current branch circuit 140 is equal to the voltage of the resistor R 4 of the fourth current branch circuit 140 divided by a resistance of the resistor R 4 of the fourth current branch circuit 140 . In this state, the current of the third terminal of the first electronic switch Q 1 is approximately equal to the current of the resistor R 4 of fourth current branch circuit 140 .

In one embodiment, when the first current branch circuit 110 is activated, the current of the third terminal of the first electronic switch Q 1 is approximately equal to 100 mA. When the second current branch circuit 120 is activated, the current of the third terminal of the first electronic switch Q 1 is approximately equal to 150 mA. When the third current branch circuit 130 is activated, the current of the third terminal of the first electronic switch Q 1 is approximately equal to 500 mA. When the fourth current branch circuit 140 is activated, the current of the third terminal of the first electronic switch Q 1 is approximately equal to 900 mA.

In one embodiment, each of the first electronic switch Q 1 and the second electronic switch Q 2 is an npn-type bipolar junction transistor (BJT), and the first terminal, the second terminal, and the third terminal of each of the first electronic switch Q 1 and the second electronic switch Q 2 respectively correspond to a base, a collector, and an emitter of the npn-type BJT. Each of the resistors R 1 and R 3 is a current-limiting resistor, and the resistor R 2 is a voltage-dividing resistor. Because a current of the emitter of the npn-type BJT is approximately equal to a sum of a current of the base of the npn-type BJT and a current of the collector of the npn-type BJT according to current characteristics of the npn-type BJT, and a current of the power terminal VCC is approximately equal to a sum of a current of the first of the electronic switch Q 1 and the second terminal of the first electronic switch Q 1 , the current of the power terminal VCC is approximately equal to the current of the third terminal of the first electronic switch Q 1 . In other embodiments, each of the first electronic switch Q 1 and the second electronic switch Q 2 may be an n-channel metal-oxide semiconductor field-effect transistor (NMOSFET), or other switch having similar functions. The number of the current branch circuits of the current selection module 100 and the number of the diodes of each current branch circuit can be adjusted according to actual need.

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.