Resistance determining system and method for circuit protection

1. Technical Field

The present disclosure relates to a resistance determining systems and methods, and particularly to a resistance determining system and method for determining resistances for circuit protection.

2. Description of Related Art

Power circuits for various electronic devices usually have protection circuits, such as an under voltage protection (UVP) circuit. When an input voltage is at an under voltage state, the UVP circuit controls the power circuits to turn off, and when an input voltage is at a recovered state, the power circuits can turn on. The UVP circuit needs resistors, usually called input resistors and responsive resistors, to support the its work at the under voltage state and at the voltage recovered state, respectively.

The resistances of the input resistor and the responsive resistor have to be determined in designing the UVP circuit. Typical methods usually manually change out different resistors in the UVP circuit to determine the proper resistors for the UVP circuit at the under voltage state and at the voltage recovered state, respectively; this method is inefficient.

What is needed, therefore, is a resistance determining system and method, which can overcome the above shortcomings.

Many aspects of the present disclosure 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 disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a circuit diagram showing one embodiment of a resistance determining system.

FIG. 2 is a circuit diagram of one embodiment of an under voltage protection (UVP) circuit of a power circuit.

FIGS. 3 and 4 are flowcharts of a method for determining resistances for the UVP circuit of FIG. 2 .

Embodiments of the present resistance determining system and method will now be described in detail below and with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of a resistance determining system 300 . The system 300 is configured to determine workable resistances for an under voltage protection (UVP) circuit 200 of a power circuit 100 (shown in FIG. 2 ). The workable resistances include a resistance of an input resistor 201 of the UVP circuit 200 at an under voltage state, and a resistance of a responsive resistor 202 of the UVP circuit 200 at a voltage recovered state.

Referring to FIG. 2 , the UVP circuit 200 of the power circuit 100 includes a first voltage input end 211 connected to an external voltage Vin, a second voltage input end 212 connected to a reference voltage Vref. The UVP circuit 200 is configured to interconnect a first terminal B 1 and a second terminal B 2 nearest to the input resistor 201 , a third terminal B 3 and a fourth terminal B 4 nearest to the responsive resistor 202 , a PWM controller 213 , a comparator U 1 , a bipolar junction transistor (BJT) Q 1 , a first resistor R 1 , a second resistor R 2 , a third resistor R 3 , a fourth resistor R 4 , a first capacitor C 1 and a second capacitor C 2 . The PWM controller 213 is configured to control the power circuit 100 to turn on or turn off. In particular, the PWM controller 213 has a COMP leading pin 213 a , when the COMP leading pin 213 a is at a high voltage level, the PWM controller 213 controls the power circuit 100 to turn on, and when the COMP leading pin 213 a is at a low voltage level, the PWM controller 213 controls the power circuit 100 to turn off. In the present embodiment, the reference voltage Vref is provided by a voltage stabilizing device in order to ensure the reference voltage Vref is a stabilized voltage.

The first input end 211 is electrically connected to an inverting input of the comparator U 1 via the first resistor R 1 , and the second input end 212 is electrically connected to a positive input of the comparator U 1 via the second resistor R 2 . A voltage input of the comparator U 1 is connected to a 12V power supply. A base electrode of the BJT Q 1 is connected to an output of the comparator U 1 via the third resistor R 3 , an emitter electrode of the BJT Q 1 is grounded, and a collector electrode of the BJT Q 1 is connected to the COMP leading pin 213 a . The base electrode and the emitter electrode of the BJT Q 1 are interconnected by the fourth resistor R 4 . One end of the first capacitor C 1 is electrically connected to the inverting input node of the comparator U 1 , and another end of the first capacitor C 1 is connected to the ground. One end of the second capacitor C 2 is electrically connected to the voltage input of the comparator U 1 , and the other end of the second capacitor C 2 is connected to ground. The first terminal B 1 is connected to the first resistor R 1 and the inverting input of the comparator U 1 , and the second terminal B 2 is connected to ground. The third terminal B 3 is connected to the second resistor R 2 and the positive input of the comparator U 1 , and the fourth terminal B 4 is connected to the output of the comparator U 1 .

The UVP circuit workable resistor determining system 300 includes a resistance determining unit 31 and a display unit 32 .

The resistance determining unit 31 includes a microcontroller 310 and a digital resistor 311 . The microcontroller 310 includes a number of input/output terminals RB 2 -RB 7 , RA 1 -RA 5 and RC 0 -RC 4 . In the present embodiment, the microcontroller 310 can be a PIC16F73 microcontroller. The microcontroller 310 has a first setting voltage and a second setting voltage. The first and second setting voltages are receivable voltages for the microcontroller 310 which correspond to an under voltage threshold at which the PWM controller 213 of the UVP circuit 200 should control the power circuit 100 to turn off. In addition, a recovered voltage threshold at which the PWM controller 213 of the UVP circuit 200 would control the power circuit 100 to turn on, respectively. The terminal RA 1 of the microcontroller 310 is configured to receive the external voltage Vin and convert the external voltage Vin to be a first converted voltage and a second converted voltage applicable for the microcontroller 310 , thereby preventing a too high external voltage Vin from directly inputting to the microcontroller 310 .

The digital resistor 311 includes a first variable resistor, a second variable resistor, a number of input terminals A 0 -A 3 , clock terminal SCL and data terminal SDA. The first variable resistor has two terminals VW 0 and VL 0 , the second variable resistor has two terminals VW 1 and VL 1 . The terminals A 0 -A 3 of the digital resistor 311 are connected to the terminals RB 7 -RB 4 of the microcontroller 310 , respectively. The clock terminal SCL of the digital resistor 311 is connected to the terminal RB 3 of the microcontroller 310 . The data terminal SDA is connected to the terminal RB 2 of the microcontroller 310 . The two terminals VW 0 , VL 0 of the first variable resistor are connected to the first terminal B 1 and the second B 2 . The two terminals VW 1 and VL 1 of the second variable resistor are connected to the third terminal B 3 and the fourth terminal B 4 . In the present embodiment, the digital resistor 311 is X9241 digital resistor.

When the first converted voltage is substantially equal to the first setting voltage, the microcontroller 310 adjusts a resistance of the first variable resistor to be a first threshold resistance. At this time, the UVP circuit 200 controls the power circuit 100 to turn off. When the second converted voltage is substantially equal to the second setting voltage, the microcontroller 310 adjusts a resistance of the second variable resistor to be a second threshold resistance. At this time, the UVP circuit 200 controls the power circuit 100 to turn on.

The display unit 32 is configured to receive and display the first threshold resistance and the second threshold resistance obtained from the microcontroller 310 . In the present embodiment, the display unit 32 includes input terminals SDA, SCK, CS, RST and A 0 -A 2 . In particular, the input terminal SDA is connected to the terminal RC 3 of the microcontroller 310 , the input terminal SCK is connected to the terminal RC 4 of the microcontroller 310 , the input terminal CS is connected to the terminal RA 2 of the microcontroller 310 , the input terminal RST is connected to the terminal RA 3 of the microcontroller 310 , the input terminal A 0 is connected to the terminal RC 0 of the microcontroller 310 , the input terminal A 1 is connected to the terminal RA 5 of the microcontroller 310 , and the input terminal A 2 is connected to the terminal RA 4 of the microcontroller 310 .

In the UVP circuit 200 , when the voltage of the inverting input of the comparator U 1 is less the voltage of the positive input of the comparator U 1 , the BJT Q 1 is turned on, and the COMP leading pin 213 a is connected to the ground, the PWM controller 213 controls the power circuit 100 to turn off. When the voltage of the inverting input of the comparator U 1 is greater than the voltage of the positive input of the comparator U 1 , the BJT Q 1 is turned off, the COMP leading pin 213 a remains at a high voltage level, the PWM controller 213 controls the power circuit 100 to turn on.

In application of the UVP circuit workable resistance determining system 300 , when an under voltage is input as the external voltage Vin, the terminal RA 1 of the microcontroller 310 receives and converts the external voltage Vin to be the first converted voltage. Then the first converted voltage is compared with the first setting voltage in the microcontroller 310 , and if the first converted voltage is substantially equal to the first setting voltage, the microcontroller 310 adjusts the resistance of the first variable resistor to make sure the voltage of the inverting input node of the comparator U 1 is less than the voltage of the positive input node of the comparator U 1 , such that the PWM controller 213 controls the power circuit 100 to turn off. At this time, the resistance of the first variable resistor is the first threshold resistance, the microcontroller 310 obtains the first threshold resistance, and the display unit 32 displays the first threshold resistance.

When a recovered voltage is input as the external voltage Vin, the terminal RA 1 of the microcontroller 310 receives and converts the external voltage Vin to be the second converted voltage. Then the second converted voltage is compared with the second setting voltage in the microcontroller 310 , and if the second converted voltage is substantially equal to the second setting voltage, the microcontroller 310 adjusts the resistance of the second variable resistor to make sure the voltage of the positive input node of the comparator U 1 is less than the voltage of the inverting input node of the comparator U 1 , such that the PWM controller 213 controls the power circuit 100 to turn on. At this time, the resistance of the second variable resistor is the second threshold resistance, the microcontroller 310 obtains the second threshold resistance, and the display unit 32 displays the second threshold resistance.

FIGS. 3 and 4 are flowcharts of a method for determining resistances for the UVP circuit 200 of FIG. 2 . The resistances to be determined includes a resistance of an input resistor 201 of the UVP circuit 200 at a under voltage state, and a resistance of a responsive resistor 202 of the UVP circuit 200 at a voltage recovered state. The method includes the following steps.

In step S 14 : two terminals VW 0 and VL 0 of the first variable resistor are connected to the first terminal B 1 and the second terminal B 2 .

In step S 16 : at an under voltage state, the microcontroller 310 receives and converts a first external voltage Vin to a first converted voltage.

In step S 18 : the microcontroller 310 compares the first converted voltage with the first setting voltage.

In step S 20 : if the first converted voltage is substantially equal to the first setting voltage, the microcontroller 310 adjusts the resistance of the first variable resistor to be a first threshold resistance, and the digital resistor 311 gives the first threshold resistance.

If the first converted voltage is not substantially equal to the first setting voltage, it can go back to step S 16 .

In step S 22 : the resistance of the input resistor 201 is determined to be substantially equal to the first threshold resistance.

In step S 24 : two terminals VW 1 and VL 1 are connected to the third terminal B 3 and the fourth terminal B 4 .

In step S 26 : at a voltage recovered state, the microcontroller 310 receives and converts a second external voltage Vin to be a second converted voltage.

In step S 28 : the microcontroller 310 compares the second converted voltage with the second setting voltage.

In step S 30 : if the second converted voltage is substantially equal to the second setting voltage, the microcontroller 310 adjusts the resistance of the second variable resistor to a second threshold resistance, and the digital resistor 311 shows the second threshold resistance.

If the second converted voltage is not substantially equal to the second setting voltage, it can go back to step S 26 .

In step S 32 : the resistance of the responsive resistor 202 is determined to be substantially equal to the second threshold resistance.

It is understood that once the first and second setting voltages are reset, the resistance determining system and method are also applicable in determining resistances for other protection circuits, such as over voltage protection.

It is understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments and methods without departing from the spirit of the disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.