DC power supply circuit

Abstract

To simply and certainly detect a short circuit state immediately after starting energization to prevent breakage of a device.SOLUTION: A DC power supply device 10 comprises: a variable DC voltage source 11; an inverter 12; a resonance circuit 13 provided on an output end of the inverter; a transformer 14 provided on an output end of the resonance circuit; a rectification circuit 15 which rectifies output of the transformer; a capacitor C3 connected between a pair of external output terminals; an output voltage detection circuit 17 which detects voltage of the capacitor; an output current detection circuit 18 which detects output current; and a control circuit 19 comprising a load resistance calculation unit which calculates a load resistance value between the external output terminals on the basis of the detected voltage and current, a short circuit determination unit which determines a short circuit state when the load resistance value is a predetermined threshold or less, and an output voltage control unit which performs control so that the output voltage becomes a predetermined voltage value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a DC power supply circuit.

Background Art

[0002] A DC power supply device using a series resonance converter method is known. A DC power supply device using the series resonance converter method can output a large amount of power.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a DC power supply device using a series resonance converter method, in order to detect a surge current at the time of a sudden load change including arc discharge or the like during voltage application and stop power supply, a short-circuit detection mechanism using a current transformer or the like is mounted. However, since the short-circuit detection mechanism is configured to detect a sudden change in current, it does not operate under conditions where no sudden change in current occurs, for example, when starting energization with a load short-circuited from the beginning. For this reason, an unintended large current is applied inside the inverter, leading to problems such as a risk of device damage and restrictions on the circuit configuration.

[0005] The present invention has been made in view of the above, and provides a DC power supply circuit that can simply and surely detect and determine a short-circuit state immediately after starting energization, and prevent damage to the device.

Means for Solving the Problems

[0006] In order to solve the above-described problems and achieve the object, a DC power supply circuit according to the present invention is a DC power supply circuit that converts the voltage value of an input DC voltage into a predetermined voltage value and outputs it toward a load, and includes a DC voltage source that outputs a DC voltage, an inverter that converts the DC voltage into an AC voltage, a resonance circuit provided at an output end of the inverter, a transformer provided at an output end of the resonance circuit, a rectifier circuit that rectifies the output of the transformer into DC power, a capacitor connected between a pair of external output terminals, an output voltage detection circuit that detects the voltage of the capacitor, an output current detection circuit that detects the output current of the DC power supply circuit, a load resistance calculation unit that calculates a load resistance value between the external output terminals based on the detected output voltage and the output current, a short-circuit determination unit that determines that a short-circuit state exists when the load resistance value is equal to or less than a predetermined threshold resistance value, and an output voltage control unit that controls the voltage of the detected capacitor to be a predetermined voltage value. The output voltage control unit performs output voltage control to increase the target value of the output voltage with the passage of time from a predetermined voltage value at the start of output to a predetermined voltage value when the DC power supply circuit starts output, and stops the output of the DC power supply circuit when the short-circuit determination unit determines that a short-circuit state exists.

Effect of the Invention

[0007] According to the present invention, it is possible to easily detect and determine a short-circuit state immediately after energization starts, and prevent damage to the device.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0009] FIG. 1 is a schematic configuration diagram of a DC power supply device according to the embodiment. The DC power supply device 10 outputs a DC output voltage VOUT (= output voltage value Vo) obtained by boosting the input DC voltage between a first output terminal T1 and a second output terminal T2. For example, the DC power supply device 10 is used as an internal DC power supply of a pulse voltage generator that generates a pulse voltage supplied to a plasma generator.

[0010] The DC power supply device 10 includes a variable DC voltage source 11, an inverter 12, a resonance circuit 13, a transformer 14, a rectifier circuit 15, a smoothing circuit 16, a voltage detection circuit 17, a current detection circuit 18, and a control circuit 19.

[0011] The variable DC voltage source 11 generates a DC voltage having a corresponding voltage Vdc based on a voltage control signal VC. In this embodiment, the value of the generated voltage of the variable DC voltage source 11 is configured to be controlled by the control circuit 19. More specifically, at the time of power-on, the generated voltage is gradually increased under the control of the control circuit 19 and reaches a predetermined voltage after a predetermined time, so that even if there is a short-circuit state at the time of power-on, the inrush current (overcurrent) can be suppressed from flowing into the subsequent circuit including the inverter 12, and the subsequent circuit can be protected.

[0012] And since the output voltage when the DC power supply device 10 starts output increases with the passage of time, for example, even when starting energization with a load short-circuited from the beginning, even under conditions where there is no sudden change in current, it is possible to stop the output of the DC power supply device 10 at a stage where the output voltage value of the DC power circuit is low by determining whether or not there is a short-circuit state at an early stage. If the output voltage value of the DC power supply device 10 is low, it means that the voltage value of the internal circuit (for example, the resonance circuit) of the DC power supply device is also low. Also, it means that the current value flowing inside the DC power supply device 10 is small. Therefore, the risk of damage inside the DC power supply device 10 can be reduced.

[0013] Incidentally, from the perspective of conversion efficiency, the input voltage of the inverter 12, and thus the output voltage, was changed using the variable DC voltage source 11. However, it is also possible to configure the inverter 12 by setting the output voltage of the DC voltage source to a constant voltage and performing a so-called phase shift to adjust the phase difference of the switching operations of the two bridges that make up the inverter 12 to control the output voltage of the inverter 12.

[0014] The inverter 12 includes an N-channel MOS transistor Q1 whose drain terminal is connected to the high-potential side terminal of the variable DC voltage source 11, an N-channel MOS transistor Q2 whose drain terminal is connected to the source terminal of the N-channel MOS transistor Q1 and whose source terminal is connected to the low-potential side terminal of the variable DC voltage source 11, an N-channel MOS transistor Q3 whose drain terminal is connected to the other end of the coil L1 of the first output chopper 14, and an N-channel MOS transistor Q4 whose drain terminal is connected to the source terminal of the N-channel MOS transistor Q5 and whose source terminal is connected to the low-potential side terminal of the variable DC voltage source 11.

[0015] The resonance circuit 13 includes a coil Lr whose one end is connected to the source terminal of the N-channel MOS transistor Q1 of the inverter 12 and a capacitor Cr whose one end is connected to the other end of the coil Lr. The resonance circuit 13 has an impedance at a predetermined resonance frequency. For example, it has a resonance frequency that resonates at the frequency at which the N-channel MOS transistors Q1 to Q4 that make up the inverter 12 and function as switches are switched.

[0016] The transformer 14 has one terminal on the primary side connected to the other end of the capacitor Cr of the resonance circuit 13, and the other terminal on the primary side connected to the source terminal of the N-channel MOS transistor Q3 and the drain terminal of the N-channel MOS transistor Q4 of the inverter 12.

[0017] The rectifier circuit 15 includes a diode D1 whose anode terminal is connected to one terminal on the secondary side of the transformer 14, a smoothing capacitor C1 whose one terminal is connected to the cathode terminal of the diode D1 and the other terminal is connected to the other terminal on the secondary side of the transformer 14, a diode D2 whose cathode terminal is connected to one terminal on the secondary side of the transformer 14, and a smoothing capacitor C2 whose one terminal is connected to the other terminal on the secondary side of the transformer 14 and the other terminal is connected to the anode terminal of the diode D2.

[0018] The smoothing circuit 16 includes a coil L1 as an inductor whose one terminal is connected to the cathode terminal of the diode D1 and the other terminal is connected to the first output terminal T1, and a capacitor C3 that functions as a smoothing capacitor with one end connected to the other end of the coil L1 and the other end connected to the anode terminal of the diode D2 of the rectifier circuit 15. As a result, since the smoothing circuit 16 functions as a low-pass filter, pulsating current can be reduced.

[0019] The voltage detection circuit 17 detects the voltage across the terminals of the capacitor C3 (the voltage corresponding to the output voltage VOUT) that constitutes the smoothing circuit 16, and outputs it to the control circuit 19 as an output voltage detection signal Vout. The current detection circuit 18 detects the current flowing through the load LD via the first output terminal T1 and the second output terminal T2, and outputs it to the control circuit 19 as an output current detection signal Iout.

[0020] The control circuit 19 controls the inverter 12 based on the output voltage detection signal Vout and the output current detection signal Iout.

[0021] Figure 2 is a functional block diagram of the control circuit. The control circuit 19 includes a load resistance calculation unit 19A, a short-circuit determination unit 19B, and an output voltage control unit 19C.

[0022] Based on the output voltage corresponding to the output voltage detection signal Vout output by the voltage detection circuit 17 and the output current corresponding to the output current detection signal Iout output by the current detection circuit 18, the load resistance calculation unit 19A calculates the load resistance value Rload, which is the resistance value of the load LD between the pair of external output terminals T1 and T2.

[0023] The short-circuit determination unit 19B determines whether the load resistance value Rload is less than or equal to a predetermined threshold resistance value Rth. When the load resistance value Rload is less than or equal to the predetermined threshold resistance value Rth, it determines that it is in a short-circuit state and outputs a short-circuit determination result signal DS.

[0024] In this way, the short-circuit determination unit 19B determines whether or not it is in a short-circuit state based on the load resistance value Rload. That is, as the short-circuit determination unit 19B, it is possible to determine whether or not it is in a short-circuit state by a simple determination method. Also, since a special detection circuit or the like is not required, it can be realized with a simple configuration.

[0025] The output voltage control unit 19C controls the detected output voltage VOUT to a predetermined voltage value, and when a short-circuit is detected in the short-circuit determination unit 19B, it performs a short-circuit protection operation described later.

[0026] Here, the output voltage control unit 19C performs output voltage control to increase the target value of the output voltage VOUT of the DC power supply device 10 from a predetermined voltage value at the start of output to a predetermined voltage value as time passes. More specifically, based on the output voltage detection signal Vout corresponding to the output voltage VOUT, the DC output voltage VOUT is fed back, and the output voltage of the variable DC voltage source 11 is changed so that the DC output voltage VOUT becomes the target voltage corresponding to the control command value Vref. In this case, for a predetermined time (e.g., 120 ms) from the start of output, the target voltage corresponding to the control command value Vref changes the DC output voltage VOUT by increasing the target voltage corresponding to the control command value Vref in a ramp function manner. Then, after a predetermined time has elapsed from the start of output, the target voltage corresponding to the control command value Vref is set to a constant value.

[0027] Also, when the short - circuit determination result signal DS indicating a short - circuit state is output by the short - circuit determination unit 19B, the output voltage control unit 19C stops the output of the DC power supply device 10 by setting the inverter 12 to the conversion stop state.

[0028] In this case, the conversion stop state of the inverter 12 means, for example, turning all of the N - channel MOS transistors Q1 to Q4 off. As a result, it is possible to avoid the inrush current (overcurrent) and overvoltage being supplied to the subsequent - stage circuit of the inverter 12 and the variable DC voltage source 11 including the inverter 12, and it is possible to protect the entire DC power supply device 10 including the internal circuits of the DC power supply device 10.

[0029] Next, the operation of the embodiment will be described. First, the general operation in the normal state will be described. In the DC power supply device 10, corresponding switching control signals among the switching control signals SQ1 to SQ4 are input from the control circuit 19 to the gate terminals of the N - channel MOS transistors Q1 to Q4. At this time, the N - channel MOS transistor Q1 and the N - channel MOS transistor Q4 are turned on / off simultaneously by the switching control signals SQ1 and SQ4.

[0030] Similarly, the N - channel MOS transistor Q2 and the N - channel MOS transistor Q3 are turned on / off simultaneously by the switching control signals SQ2 and SQ3 in an exclusive manner and with a predetermined interval with respect to the N - channel MOS transistor Q1 and the N - channel MOS transistor Q4.

[0031] More specifically, for example, at a certain point in time, when the N-channel MOS transistors Q1 and Q4 are in the on state, the N-channel MOS transistors Q2 and Q3 are in the off state.

[0032] After that, after the N-channel MOS transistors Q1 and Q4 transition to the off state and after a predetermined time interval has elapsed, the N-channel MOS transistors Q2 and Q3 transition to the on state. As a result, all of the N-channel MOS transistors Q1 to Q4 do not turn on simultaneously and enter a short-circuit state.

[0033] The resonance circuit 13 is connected between the connection point of the N-channel MOS transistor Q1 and the N-channel MOS transistor Q2 and one terminal of the primary coil of the transformer 14. The resonance circuit 13 has an impedance at a predetermined resonance frequency. For example, the resonance circuit 13 includes an LC circuit having a resonance frequency that resonates at the frequency at which the first switch 24 and the second switch 26 are switched. For example, the resonance circuit 13 includes a coil (inductor) Lr and a capacitor Cr connected in series. The resonance circuit 13 can pass a large current at the resonance frequency.

[0034] For the transformer 14, one terminal of the primary coil is connected to the resonance circuit 13, the other terminal of the primary coil is connected to the connection point of the N-channel MOS transistor Q3 and the N-channel MOS transistor Q4, and an AC voltage whose amplitude is a predetermined multiple of the AC voltage applied to the primary coil is generated from the secondary coil. For example, if the turns ratio of the primary coil to the secondary coil is 1:8, an AC voltage with an amplitude eight times that of the input is generated from the secondary coil.

[0035] The rectifier circuit 15 outputs a rectified voltage obtained by full-wave rectifying the AC voltage generated in the secondary coil of the transformer 14. The smoothing circuit 16 smoothes the rectified voltage output from the rectifier circuit 15 and outputs a DC output voltage obtained by smoothing the rectified voltage between the first output terminal T1 and the second output terminal T2. As a result, according to the DC power supply device 10 of the embodiment, DC power having a predetermined voltage is supplied to the load resistor LD.

[0036] Next, the operation of the DC power supply device of the embodiment at the time of power-on will be described more specifically using circuit simulation. In the circuit simulation used below, the control of the output voltage VOUT is performed by varying the voltage of the variable DC voltage source 11 based on the input (set) control command value Vref.

[0037] More specifically, in the simulation, the output voltage VOUT is controlled by varying the output voltage Vdc of the variable DC voltage source 11 in the range of 0V to 500V. Also, the rate of change per unit time of the control command value Vref for controlling the output voltage VOUT is set to 5V / msec.

[0038] Furthermore, the current flowing through the coil Lr (resonance current) is denoted as Ires, and the voltage applied to the capacitor Cr (resonance voltage) is denoted as VCres. Furthermore, as an example, Lr = 4.2 μH, Cr = 210 nF, Cs = 1 nF, C1 = C2 = 0.2 μF, the turns ratio of the transformer = 1:8, and the switching frequency of the transistors Q1 to Q4 = 175 kHz.

[0039] First, the results of the circuit simulation at the rated load will be described. FIG. 3 is an explanatory diagram of the circuit simulation results at the rated load. FIG. 3(A) is an explanatory diagram of the control command value Vref and the output voltage VOUT. In FIG. 3(A), the vertical axis represents the voltage value and the unit is V. Also, the horizontal axis represents time and the unit is s (seconds). Figure 3(B) is an explanatory diagram of the output current IOUT. In Figure 3(B), the vertical axis represents current with the unit of A, and the horizontal axis represents time with the unit of s (seconds). Figure 3(C) is an explanatory diagram of the voltage Vdc of the variable DC voltage source 11. In Figure 3(C), the vertical axis represents the voltage value with the unit of V, and the horizontal axis represents time with the unit of s (seconds). Figure 3(D) is an explanatory diagram of the resonance current Ires. In Figure 3(D), the vertical axis represents the current value with the unit of A, and the horizontal axis represents time with the unit of s (seconds). Figure 3(E) is an explanatory diagram of the resonance voltage VCres. In Figure 3(E), the vertical axis represents the voltage value with the unit of V, and the horizontal axis represents time with the unit of s (seconds).

[0040] In the following description, it is assumed that the final output voltage VOUT = 6000V and the output current Iout = 6A. At this time, the output of the final variable DC voltage source 11 is a voltage Vdc = 400V and a current of 90A.

[0041] As shown in Figure 3(A), the control command value Vref is increased from 0V with a change rate of 5V / msec. Therefore, as shown in Figure 3(C), the voltage Vdc of the variable DC voltage source 11 is gradually increased from 0V, and considering the power conversion loss, a simulation is performed such that the voltage Vdc of the variable DC voltage source 11 becomes 400V at the time when 120ms has elapsed from the operation start timing (= 0s). As a result, after a predetermined time lag with respect to the change in the control command value Vref, as shown in Figure 3(A), the output voltage VOUT becomes 6000V corresponding to the control command value Vref = 6000V. In this case, since the load resistance = 1000Ω, the output current Iout becomes 6A (= 6000 / 1000).

[0042] Figure 4 is a partial enlarged view of Figure 3. Figures 4(A) to 4(E) respectively correspond to the portions from time = 0 to time = 20ms of Figures 3(A) to 3(E), and the scale of the vertical axis is enlarged for each. As shown in the waveform of the resonance current Ires in FIG. 4(D) and the resonance voltage VCres in FIG. 4(E), since the control command value Vref is changed at a predetermined rate of change, although some waveform variations can be seen, it can be understood that no inrush current flows into the resonance circuit 13.

[0043] Next, the operation during a short circuit will be described. In simulation, a short circuit can be regarded as a case where the resistance value of the load (short-circuit load) is approximately 0 Ω and the control command voltage VREF is increased from 0 V to 6000 V.

[0044] FIG. 5 is an explanatory diagram of the simulation results during a short circuit. FIG. 5(A) is an explanatory diagram of the control command value Vref and the output voltage VOUT. In FIG. 5(A), the vertical axis represents the voltage value with the unit of V. Also, the horizontal axis represents time with the unit of s (seconds). FIG. 5(B) is an explanatory diagram of the output current IOUT. In FIG. 5(B), the vertical axis represents the current value with the unit of A. Also, the horizontal axis represents time with the unit of s (seconds). FIG. 5(C) is an explanatory diagram of the voltage Vdc of the DC power supply. In FIG. 5(C), the vertical axis represents the voltage value with the unit of V. Also, the horizontal axis represents time with the unit of s (seconds). FIG. 5(D) is an explanatory diagram of the resonance current Ires. In FIG. 5(D), the vertical axis represents the current value with the unit of A. Also, the horizontal axis represents time with the unit of s (seconds). FIG. 5(E) is an explanatory diagram of the resonance voltage VCres. In FIG. 5(E), the vertical axis represents the voltage value with the unit of V. Also, the horizontal axis represents time with the unit of s (seconds).

[0045] As shown in FIG. 5(A), the control command value Vref is increased from 0 V at a rate of change of 5 V / msec. However, due to the short circuit, the output voltage VOUT remains at 0 V. On the other hand, as shown in FIG. 5(B), the output current IOUT reaches approximately 40 A at the time when 20 ms has elapsed since the start of power supply.

[0046] Also, as shown in FIG. 5(C), the output voltage Vdc of the variable DC voltage source 11 is approximately 150 V at the time 20 ms after the start of power supply. As a result of these, as shown in FIG. 5(D), the resonance current Ires is approximately 600 A at the time 20 ms after the start of power supply.

[0047] Also, as shown in FIG. 5(E), the resonance voltage VCres is approximately 2800 V at the time 20 ms after the start of power supply. Therefore, it can be understood that a current of 6 A or more at rated power is output in the order of ms, and in the resonance circuit 13, an excessive current flows, and there is a high possibility of damaging the resonance circuit 13.

[0048] Particularly for the purpose of increasing the power, in the case of a capacitor provided in series in the current path, in the example of FIG. 1, in the capacitor Cr, the resonance voltage VCres is applied in proportion to the resonance current, and it is expected that the possibility of breakage becomes extremely high.

[0049] However, in the case of short-circuit detection using a current transformer CT as in the conventional case, since the configuration is to detect fluctuations in the output current in ns (nanoseconds) or μs (microseconds), it can be understood that in the situation where the output current Iout is as shown in FIG. 5(B), the short circuit cannot be effectively detected and the resonance circuit 13 cannot be protected.

[0050] Next, the specific protection operation in the case of a short circuit in this embodiment will be described. In the case of the protection operation, it is assumed that a short circuit is detected when all of the following three conditions [1] to [3] are satisfied, and the protection operation is performed. [1] The detected load resistance value Rload is less than or equal to the resistance threshold value Rth. [2] The value of the detected output current Iout is greater than or equal to the current threshold value Ith. [3] The elapsed time from the start of energization exceeds the time threshold value Tth.

[0051] In this case, the condition in [1] is that the value of the resistance threshold Rth is set to a value that should not be detected under normal conditions and can be stably calculated, so that it can be surely set to a value capable of detecting a short-circuit state. The condition in [2] is a value that should not be detected under normal conditions, but is set to shift to a protection operation while the circuit is in a normal state. This is set to avoid malfunction of the short-circuit detection operation because even if the condition in [1] is satisfied, if the value of the detected output current Iout is less than the current threshold Ith, there is no problem without protecting the circuit.

[0052] The condition in [3] is set to ensure the time required for the operation to stabilize and avoid malfunction of the short-circuit detection operation in order to prevent the protection operation from being performed due to detection of a short-circuit state in an unstable operation state at power-on.

[0053] More specifically, the resistance value threshold Rth, the current threshold Ith, and the time threshold Tth can be defined as follows, for example, taking the case where the short-circuit load is ≒ 0Ω and the control command voltage Vref changes from 0V to 6000V as an example as described above. The selected values are just examples.

[0054] Rth = 250Ω: A value that is sufficiently small compared to the rated resistance value (in this case, 1000Ω) and can be stably calculated can be selected. Ith = 6A: For example, the rated current value can be selected. Tth = 4ms: A time can be selected to mask the period during which the voltage and current at startup are unstable.

[0055] Figure 6 is a processing flowchart of the short-circuit detection / protection operation of the control circuit according to the embodiment. The processing shown in Figure 6 is performed as an interrupt process in a subroutine at a predetermined short-circuit detection timing with respect to the normal processing routine. If a short-circuit is not detected, the processing of the normal processing routine is performed until the next short-circuit detection timing. Also, when a short circuit is detected, after the output is stopped, the process will branch from the normal processing routine to the processing routine at the time of short circuit detection, and perform the processing at the time of abnormality detection including abnormality notification.

[0056] The control circuit 19 first detects the output voltage VOUT by the voltage detection circuit 17 (step S11). Subsequently, the control circuit 19 detects the output current Iout by the current detection circuit 18 (step S12).

[0057] The control circuit 19 calculates the load resistance value Rload, which is the resistance value of the load LD, based on the detected output voltage VOUT and output current IOUT (step S13). Specifically, using the output voltage value Vo corresponding to the output voltage VOUT and the output current value Io corresponding to the output current IOUT, the load resistance value Rload is calculated by the following formula. Rload = Vo / Io

[0058] Subsequently, the control circuit 19 determines whether the calculated load resistance value Rload is less than or equal to the resistance threshold value Rth (step S14). In the determination of step S14, when the load resistance value Rload is greater than the resistance threshold value Rth (step S14; No), the control circuit 19 ends the short circuit detection operation assuming that no short circuit has occurred, and returns to the normal processing routine to return to the normal processing routine.

[0059] In the determination of step S14, when the load resistance value Rload is less than or equal to the resistance threshold value Rth (step S14; Yes), the control circuit 19 determines whether the output current value Io corresponding to the output current IOUT is greater than or equal to the current threshold value Ith (step S15).

[0060] In the determination of step S15, when the output current value Io is less than the current threshold value Ith (step S15; No), the control circuit 19 ends the short circuit detection operation assuming that no short circuit has occurred, and returns to the normal processing routine to return to the normal processing routine.

[0061] In the determination of step S15, when the output current value Io is equal to or greater than the current threshold Ith (step S15; Yes), the control circuit 19 determines whether the elapsed time from the start of energization exceeds a predetermined time Tth (step S16).

[0062] In the determination of step S16, when the elapsed time from the start of energization has not yet exceeded the predetermined time Tth (step S16; No), the control circuit 19 assumes that no short circuit has occurred, terminates the short circuit detection operation, and returns to the normal processing routine to return to the normal processing routine.

[0063] In the determination of step S16, when the elapsed time from the start of energization has exceeded the predetermined time Tth (step S; Yes), the control circuit 19 assumes that the short circuit state has been detected because the three conditions [1] to [3] described above are satisfied, and sets it to the output stop state.

[0064] Therefore, before excessive current flows in the resonance circuit 13, the power supply to the resonance circuit 13 can be cut off, and the resonance circuit can be prevented from being damaged.

[0065] FIG. 7 is an explanatory diagram of the timing of the short circuit protection operation. FIG. 7(A) is an explanatory diagram of the output voltage VOUT. In FIG. 7(A), the vertical axis represents the voltage value and the unit is V. The horizontal axis represents time and the unit is s (seconds). FIG. 7(B) is an explanatory diagram of the output current IOUT. In FIG. 7(B), the vertical axis represents the current value and the unit is A. The horizontal axis represents time and the unit is s (seconds). FIG. 7(C) is an explanatory diagram of the calculation result of the load resistance value Rload. In FIG. 7(C), the vertical axis represents the resistance value and the unit is Ω. The horizontal axis represents time and the unit is s (seconds). As shown in FIGS. 7(A) and 7(B), the output voltage VOUT and the output current IOUT gradually increase from the power-on (time = 0 ms). On the one hand, it can be seen that the calculation result of the load resistance value Rload is not stably obtained during the period of time = 0 ms to 0.3 ms due to the initial fluctuations of the output voltage VOUT and the output current IOUT immediately after power-on.

[0066] And it can be seen that the calculation result of the load resistance value Rload becomes stable after the time of 0.3 ms. Therefore, in this embodiment, until a predetermined time Th = 4 ms has elapsed, the control circuit is not allowed to perform a short-circuit determination. After the time of 0.3 ms, the load resistance value Rload = 0 Ω, which is below the resistance threshold value Rth. After the predetermined time Th = 4 ms has elapsed, the load resistance value Rload still remains 0 Ω. Therefore, the control circuit can surely perform a short-circuit determination.

[0067] And when it comes to around the time of 7 ms, the output current value Io corresponding to the output current IOUT exceeds the current threshold value Ith = 6 A, and it becomes the cutoff timing Tbr at which all the above-mentioned conditions [1] to [3] are satisfied. Therefore, assuming that a short circuit is detected, the control device 19 executes a short-circuit protection operation. More specifically, as a short-circuit protection operation, the control circuit 19 outputs the cutoff control signals SCBU and SCBL to the wiring cut-off devices 20U and 20L, and sets the wiring cut-off devices 20U and 20L to the cut-off state to cut off the power supply from the variable DC voltage source 11.

[0068] Furthermore, as a short-circuit protection operation, the control circuit 19 sets all the channel MOS transistors Q1 to the N-channel MOS transistor Q4 to the off state by the switching control signals SQ1 to SQ4 to set the inverter 12 to the conversion stop state. Therefore, no inrush current (overcurrent) flows into the resonance circuit 13.

[0069] As a result, immediately after the energization starts, it is possible to simply and surely detect and determine a short-circuit state, and prevent damage to the device.

[0070] The embodiments of the present invention have been described above. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. The embodiments can be modified in various ways.

Description of Reference Numerals

[0071] 10 DC power supply device, 11 variable DC voltage source, 12 inverter, 13 resonance circuit, 14 transformer, 15 rectifier circuit, 16 smoothing circuit, 17 voltage detection circuit, 18 current detection circuit (output current detection circuit), 19 control circuit, 20U, 20L wiring circuit breakers, C3 capacitor (smoothing capacitor, low-pass filter), Cr capacitor, L1 coil (inductor, low-pass filter), Lr coil, Q1 to Q4 N-channel MOS transistors.

Claims

1. A DC power supply circuit that converts the voltage value of an input DC voltage into a predetermined voltage value and outputs it to a load, comprising: A DC voltage source that outputs a DC voltage; An inverter that converts the DC voltage into an AC voltage; A resonance circuit provided at the output terminal of the inverter; A transformer provided at the output terminal of the resonance circuit; A rectifier circuit that rectifies the output of the transformer into DC power; A capacitor connected between a pair of external output terminals; An output voltage detection circuit that detects the voltage of the capacitor; An output current detection circuit that detects the output current of the DC power supply circuit; A load resistance calculation unit that calculates the load resistance value between the external output terminals based on the detected voltage of the capacitor and the output current; A short-circuit determination unit that determines that a short-circuit state exists when the load resistance value is equal to or less than a predetermined threshold resistance value; An output voltage control unit that controls the output voltage so that the detected output voltage becomes a predetermined voltage value; The DC power supply circuit further comprises: When the DC power supply circuit starts output, the output voltage control unit performs output voltage control to increase the target value of the output voltage from a predetermined start-up voltage value to a predetermined voltage value as time elapses. When the short-circuit determination unit determines that a short-circuit state exists, the output of the DC power supply circuit is stopped. DC power supply circuit.

2. The short-circuit determination unit determines that a short-circuit state exists when the load resistance value is equal to or less than a predetermined threshold resistance value and the output current is equal to or greater than a predetermined threshold current value. The DC power supply circuit according to claim 1.

3. The short-circuit determination unit determines that a short-circuit state exists when the load resistance value is equal to or less than a predetermined threshold resistance value and a predetermined time has elapsed since the start of energization. The DC power supply circuit according to claim 1.

4. An inductor is provided between the rectifier circuit and the capacitor. The capacitor functions as a low-pass filter circuit in cooperation with the inductor. The DC power supply circuit according to claim 1.

5. The output voltage of the DC voltage source is adjustable. The output voltage control unit controls the output voltage of the DC voltage source so that the detected output voltage value becomes the target value of the output voltage. The DC power supply circuit according to any one of claims 1 to 4.

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