JP7488111B2 - Power supplies and how to configure power supply thresholds - Google Patents

Description

The present invention relates to a power supply device and a method for setting a threshold for the power supply device.

In recent years, there has been an increase in switching power supplies with full digital control using microcomputers. With full digital control, analog information such as the power supply's output voltage, output current, and temperature is converted to digital values using an A/D converter and then input into a microcomputer, which then performs various controls based on this data and operates the switching power supply in optimal conditions. In addition, because various sequence operations can be set using firmware, it is possible to reduce the number of parts and make the system more compact.

When performing full digital control in a switching power supply, a threshold consisting of a digital value corresponding to the overcurrent is used to detect overcurrent flowing through the load device. However, with digital control, current detection is performed at a specific timing per clock cycle, so the detected current tends to be lower than with analog control. Also, because the peak current changes due to variations in the capacitance of the capacitors that make up the power supply, there are individual differences in the detected current for each device.

The object of the present invention is to provide a power supply device that sets a threshold value for determining overcurrent for each device and uses it to actually determine overcurrent.

<First aspect of the present invention>
In order to achieve the above-mentioned object, a first aspect of the present invention is a power supply device that supplies power to a load device, comprising: a current detection unit that detects an output current flowing through the load device; a first input unit to which the detected output current is input; and a second input unit to which a threshold value for determining whether or not an overcurrent has occurred is input; a comparator that compares the detected output current with the threshold value to determine whether an overcurrent has occurred; and a control unit that controls the output current to be equal to or less than a maximum allowable current of the load device, wherein when a reference current that is 1/n (n is a number greater than or equal to 2) of the maximum allowable current is flowing through the load device as the output current, a digital value that changes monotonically and discretely over time in response to the current is input to the second input unit instead of the threshold value, and the digital value when the output of the comparator switches by comparing the reference current with the digital value is multiplied by n to set the threshold value.

With the above configuration, the comparator compares a constant reference current that is 1/n of the maximum allowable current flowing through the load device with a digital value corresponding to the current, and this digital value is changed monotonically and discretely over time to observe the output change from the comparator. The digital value at the time when the output change occurs is made to correspond to the reference current. The new digital value obtained by multiplying this digital value corresponding to the reference current by n is set as the threshold value for determining whether an overcurrent exists. While the power supply device is operating, the set threshold value is input to the second input section of the comparator to determine whether an overcurrent exists in the load device.

<Second aspect of the present invention>
A second aspect of the present invention is a power supply device comprising a current detection unit that detects an output current flowing through a load device, a first input unit to which the detected output current is input, and a second input unit to which a threshold value for determining whether an overcurrent exists or not is input, a comparator that compares the detected output current with the threshold value to determine whether an overcurrent has occurred, and a control unit that controls the output current to be equal to or less than a maximum allowable current of the load device, and a method for setting the threshold value in the power supply device that supplies power to the load device, the method comprising the steps of: flowing a reference current that is 1/n (n is a number equal to or greater than 2) of the maximum allowable current to the load device as the output current; inputting, into the second input unit, instead of the threshold value, a digital value that changes monotonically and discretely over time in response to the current while the reference current is flowing through the load device; and setting, as the threshold value, a value obtained by multiplying n by the digital value when the output of the comparator switches by comparing the reference current with the digital value;
The present invention is characterized in that it has the following features:

According to the present invention, a threshold value for determining an overcurrent in a load device can be set for each individual power supply device and used for actual overcurrent determination. This improves the accuracy of overcurrent detection in the load device. In addition, in order to set the threshold value, a current that is 1/n of the maximum allowable current is passed through the load device, instead of the maximum allowable current, so that the burden on the electrical components that make up the power supply device and the load device can be reduced.

1 shows a circuit diagram of a DC/DC converter according to an embodiment; 11 is a graph illustrating a method for setting a threshold value by passing a current that is 1/n of the maximum allowable current. 13 is a graph illustrating a method for setting a threshold value by passing a current that is half the maximum allowable current. 4 is a flowchart showing an operation of the DC/DC converter.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a power supply device according to one embodiment. It goes without saying that the present invention is not limited to the embodiment described below, and various modifications are possible within the scope of the invention described in the claims.

<Power supply configuration>
1 shows a DC/DC converter 1 according to one embodiment of the present invention. The DC/DC converter 1 includes a switching circuit 10 and a control circuit 20 that controls the switching circuit 10.

The switching circuit 10 is a step-down chopper type, and has a first capacitor 13, a switching element 14, a diode 15, an inductor 16, and a second capacitor 17 between the input section 11 and the output section 12. The input section 11 has a pair of input terminals 11A, 11B, and is connected to a DC power source 2. The output section 12 has a pair of output terminals 12A, 12B, and is connected to a load device 3. In this embodiment, the maximum allowable current that can be passed through the load device 3 is 12A.

The switching circuit 10 includes a first line L1 on the high potential side that electrically connects the input section 11 and the output section 12, and a second line L2 on the low potential side. A switching element 14 and an inductor 16 are connected in series to the first line L1 from the input terminal 11A to the output terminal 12A.

The switching element 14 is an N-channel MOSFET, with its drain connected to the input terminal 11A and its source connected to the inductor 16. A control signal from the control unit, which will be described later, is input to the gate of the MOSFET. One end of the inductor 16 is connected to the switching element 14, and the other end is connected to the output terminal 12A.

The first capacitor 13 is an electrolytic capacitor that is connected between the first line L1 and the second line L2 on the input terminal 11A side of the switching element 14, and smoothes the input voltage input to the input section 11.

The diode 15 is connected between a node N1 between the switching element 14 and the inductor 16 in the first line L1 and a node N2 in the second line L2. The anode of the diode 15 is connected to the node N2, and the cathode is connected to the node N1.

The second capacitor 17 is an electrolytic capacitor that is connected between the first line L1 and the second line L2 on the output side of the inductor 16 to smooth the output voltage from the inductor 16.

A resistor R is connected to the second line L2 to detect the output current output from the switching circuit 10 and flowing through the load device 3.

The control circuit 20 has a voltage detection unit 21, a current detection unit 22, an analog comparator 23, a control unit 24, and a memory 25, and controls the output voltage and output current applied from the output unit 12 to the load device 3. In particular, the control circuit 20 controls the output current to be equal to or less than the maximum allowable current. If the output current exceeds the maximum allowable current, the control circuit 20 determines that an overcurrent is flowing in the load device 3, switches off the switching element 14, and cuts off the output of power to the load device 3.

The voltage detection unit 21 detects the output voltage of the switching circuit 10. The current detection unit 22 detects the output current. The analog comparator 23 has first and second input units and one output unit, and as a comparator, compares the output current input to the first input unit with a threshold value input to the second input unit to determine whether the output current is an overcurrent. If the output current is greater than the threshold value, the analog comparator 23 outputs an overcurrent detection signal to the control unit 24.

The control unit 24 is made up of a microcomputer, and performs PWM control by sending a control signal to the switching element 14 based on the output voltage of the switching circuit 10. Furthermore, when the control unit 24 determines that the output current exceeds a threshold based on the output of the analog comparator 23, it determines that an overcurrent in the load device 3 has been detected, and sends an overcurrent detection signal. In response to the overcurrent detection signal, the control unit 24 turns off the switching element 14 to cut off the power output.

Memory 25 consists of flash memory and stores the threshold value for determining overcurrent.

In addition, since the control circuit 20 performs full digital control, a table in which each current value flowing through the switching circuit 10 corresponds to a digitally converted AD value is stored in the memory 25. In this embodiment, the AD value is an example of a "digital value" and is a 12-bit binary number, but is expressed in decimal. Therefore, the maximum value that can be expressed as a 12-bit binary number corresponds to the decimal number "4095".

<Operation of DC/DC Converter as Power Supply Device>
The operation of the DC/DC converter 1 will be described. When power is input from the DC power source 2 to the input unit 11, the control circuit 20 is started, and the control unit 24 performs PWM control on the switching element 14. The switching element 14 is turned on and off in response to a control signal based on the output from the voltage detection unit 21, and when it is on, it supplies the input power to the inductor 16, and when it is off, it cuts off the supply of the input power to the inductor 16. Therefore, the input power from the DC power source 2 is smoothed by the first capacitor 13, and the power is adjusted by the PWM control of the switching element 14. Next, the power is supplied to the inductor 16, smoothed by the second capacitor 17, and output from the output unit 12 as power having a desired output voltage.

The output current flowing through the load device 3 is detected by the current detection unit 22 and input to the first input unit of the analog comparator 23. The analog comparator 23 compares the output current with a threshold value. If the output current is smaller than the threshold value, the control unit 24 continues PWM control of the switching element 14 to continue supplying power to the load device 3. On the other hand, if the output current is larger than the threshold value, the analog comparator 23 sends an overcurrent detection signal to the control unit 24. In response to the input of the overcurrent detection signal, the control unit 24 turns off the switching element 14 and cuts off the power supply.

<How to set the threshold>
Next, a method for setting a threshold value for determining whether an overcurrent occurs in the load device 3 will be described below with reference to FIG.

The DC/DC converter 1 is operated to pass an output current toward the load device 3. The maximum allowable current of the load device 3, 12A, is made to correspond to the maximum AD value Tmax shown in FIG. 2. Then, the control unit 24 performs PWM control on the switching element 14 so that the output current is 1/n of the maximum allowable current (n is a number equal to or greater than 2). This output current is detected by the current detection unit 22 as a reference current, and is input to the first input unit of the analog comparator 23.

On the other hand, the AD values are read out from the table stored in the memory 25 in order from the maximum value and input to the second input section of the analog comparator 23. Then, the AD values input to the analog comparator 23 are monotonically and discretely decreased one by one as time passes. At time _t1 when the AD value Tcal is input to the second input section, the output of the analog comparator 23 is switched, for example, from LOW to HIGH (or from HIGH to LOW). At this time, the control circuit 20 determines that the reference current corresponds to the AD value "Tcal". That is, the control circuit 20 recognizes that a current 1/n of the maximum allowable current of 12A is detected by the AD value "Tcal". Next, the control circuit 20 utilizes the proportional relationship between the current and the AD value to store the AD value "n·Tcal", which is n times the AD value "Tcal", in the memory 25 as a threshold value for determining an overcurrent of 12A.

After that, when the DC/DC converter 1 is actually operated, the AD value "n·Tcal" stored in the memory 25 is read out and input to the second input section of the analog comparator 23, and is used as a threshold value for determining whether an overcurrent has occurred in the load device 3.

In this way, a threshold value is set for each DC/DC converter 1 and stored in memory 25.

In addition, since the threshold value is obtained by passing a current that is 1/n of the maximum allowable current through the DC/DC converter 1, the burden on the electrical components that make up the DC/DC converter 1 and the load device 3 can be reduced compared to when the maximum allowable current is passed through the DC/DC converter 1 to obtain the threshold value.

Next, we will explain how to set the threshold when n=2 with reference to Figure 3.

The DC/DC converter 1 is started by starting the power supply from the DC power source 2 to the DC/DC converter 1. Since the maximum allowable current that can be passed through the load device 3 is 12 A (4095 in 12-bit binary), the control circuit 20 uses PWM control of the switching element 14 to pass a current of 6 A, which is half the maximum allowable current, through the switching circuit 10 as a reference current. This reference current of 6 A is detected by the current detection unit 22 and input to the first input unit of the analog comparator 23.

On the other hand, when a reference current of 6A is continuously flowing through the switching circuit 10, the maximum value "4095" is read from the table stored in the memory 25 and input to the second input section of the analog comparator 23, and the AD value is monotonically decreased by one as time passes. At time _t2 when the AD value "2000" is input to the second input section, the output of the analog comparator 23 is switched, for example, from LOW to HIGH (or from HIGH to LOW). At this time, the control circuit 20 recognizes that the reference current of 6A corresponds to the AD value "2000". Next, the control circuit 20 stores the AD value "4000", which is twice the AD value "2000", in the memory 25 as a threshold value for determining an overcurrent of 12A.

Next, when the DC/DC converter 1 is operated, the AD value "2000" stored in the memory 25 is read out as a threshold value. "2000" is input to the second input section of the analog comparator 23 and compared with the input current input to the first input section to determine whether or not an overcurrent is flowing through the load device 3.

In this way, a threshold value is set for each DC/DC converter 1 and stored in memory 25.

In addition, to set the threshold, a current equal to half the maximum allowable current is passed through the switching circuit 10 instead of the maximum allowable current to determine the threshold. This makes it possible to prevent destruction or damage to the electrical components that make up the DC/DC converter 1, compared to when the maximum allowable current is passed through the switching circuit 10 to determine the threshold.

Next, the operation of the DC/DC converter 1 will be described below with reference to FIG. 4. In step S1, when the DC/DC converter 1 is connected to the power source 2, the control circuit 20 reads the initial setting including the maximum allowable current from the memory 25. In step S2, it is checked whether the threshold has been set. If the threshold has already been set (step S2: YES), in step S3, the control circuit 20 reads the threshold from the memory 25 and inputs it to the second input section of the analog comparator 23. If the threshold has not been set (step S2: NO), in step S4, as described with reference to FIG. 2 or FIG. 3, a reference current is passed through the switching circuit 10 and the load device 3 to set the threshold, and the threshold is input to the second input section of the analog comparator 23. After the threshold has been read or set, in step S5, the control circuit 20 checks whether a start request has been input. If a start request has been input (step S5: YES), the switching circuit 10 is started (step S6). If an overcurrent to the load device 3 is detected while the switching circuit 10 is operating (step S7: YES), the analog comparator 23 outputs an overcurrent detection signal to the control unit 24 to stop the operation of the switching circuit 10 (step S9).

While the switching circuit 10 is operating, the control circuit 20 checks whether a request to stop the DC/DC converter 1 has been input (step S8). If a request to stop the DC/DC converter 1 has been input (step S8: YES), the control circuit 20 stops the operation of the switching circuit 10 and stops the operation of the DC/DC converter 1 (step S9).

In this way, an accurate threshold is set for each DC/DC converter 1, so that overcurrent flowing through the load device 3 can be properly detected and the operation of the DC/DC converter 1 can be stopped.

In the above embodiment, the case where n=2 is described, but any suitable number equal to or greater than 2 can be used for n. As n becomes larger, the reference current flowing to set the threshold can be made smaller than the maximum allowable current, so that the load on the electrical components constituting the DC/DC converter 1 and the load device 3 can be further reduced.

REFERENCE SIGNS LIST 1 DC/DC converter 3 Load device 10 Switching circuit 20 Control circuit 22 Current detection section 23 Analog comparator 24 Control section

Claims (2)

A power supply device that supplies power to a load device,
a current detection unit that detects an output current flowing through the load device;
a comparator including a first input section to which a detected output current is input and a second input section to which a threshold value for determining whether or not an overcurrent exists is input, the comparator comparing the detected output current with the threshold value to determine whether or not an overcurrent exists;
a control unit that controls the output current to be equal to or less than a maximum allowable current of the load device;
Equipped with
A power supply device characterized in that, when a reference current which is 1/n (n is a number equal to or greater than 2) of the maximum allowable current is flowing to the load device as the output current, a digital value which changes monotonically and discretely over time in response to the current is input to the second input section instead of the threshold value, and a value obtained by multiplying the digital value at which the output of the comparator switches by comparing the reference current with the digital value is set to the threshold value. A method for setting the threshold in a power supply device that supplies power to a load device, the power supply device comprising: a current detection unit that detects an output current flowing through a load device; a first input unit to which the detected output current is input; a second input unit to which a threshold for determining whether or not an overcurrent is input; a comparator that compares the detected output current with the threshold to determine whether an overcurrent has occurred; and a control unit that controls the output current to be equal to or less than a maximum allowable current of the load device, the method comprising:
a step of supplying a reference current, which is 1/n (n is a number equal to or greater than 2) of the maximum allowable current, to the load device as the output current;
inputting, instead of the threshold value, a digital value that changes monotonically and discretely over time in response to the current to the second input unit while the reference current is flowing through the load device;
setting, as the threshold value, a value obtained by multiplying the digital value at the time when the output of the comparator is switched by comparing the reference current with the digital value by n;
13. The method of claim 12, further comprising:

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