JP4161551B2 - High voltage power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digitally controlled high-voltage power supply apparatus that outputs a DC voltage by driving a step-up transformer by turning on / off a switching element.
[0002]
[Prior art]
An electrophotographic printer is provided with a high-voltage power supply device. The high-voltage power supply device provided in the printer detects the output voltage and controls the duty ratio and frequency when the CPU turns on and off the switching element so that the detected output voltage becomes a predetermined voltage. Therefore, a digital control system that outputs a predetermined DC voltage is common.
[0003]
Such digital control high-voltage power supply devices include a forward method and a flyback method. FIG. 20 shows a high-voltage power supply device 200 as an example using the flyback method. In this high-voltage power supply device 200, the switching element 204 is turned on by a switching signal output from the CPU 202, whereby a predetermined voltage Vin is applied from the DC power source to the primary winding 206 </ b> A of the step-up transformer 206 and power is stored in the step-up transformer 106. Is done.
[0004]
By turning off the switching element 204, the electric power stored in the step-up transformer 206 is supplied from the secondary winding 206B to the load while being converted into a DC voltage (output voltage Vout) through the smoothing circuit.
[0005]
At this time, the CPU 202 monitors the output voltage Vout to the load by the output voltage detection circuit 208 and the A / D conversion unit 210, and controls the on-time and switching cycle of the switching element 204, so that the output voltage Vout becomes the target. The PWM control of the switching element 204 is performed so as to be a voltage.
[0006]
By the way, a printer or the like requires a high-voltage power supply device that can obtain a highly accurate output voltage. Further, the impedance of a transfer roller or the like that uses a voltage output from a high voltage device changes according to environmental conditions such as humidity and temperature. For this reason, in a printer or the like, the load capacity connected to the high voltage device changes greatly.
[0007]
On the other hand, in a high voltage power supply device using a digital control system, for example, if the load is constant, the output voltage is set according to the on-duty (on time) of the switching element by appropriately setting the circuit constant according to the load. The monotonously increasing characteristic increases, and the stabilization control for controlling the output voltage to become the target voltage is extremely easy.
[0008]
However, in reality, the load often fluctuates, and monotonically increasing characteristics are rarely obtained in the entire load fluctuation range and output voltage control range. In color printers and the like, the output voltage is increased. A high-voltage power supply controlled with precision is required.
[0009]
For this reason, Japanese Patent Laid-Open No. 2000-102249 proposes to control the duty ratio based on environmental conditions that affect the impedance of the load such as temperature and humidity. However, even if the on-duty is controlled based on the environmental condition of the load, the output voltage cannot always be a monotonously increasing characteristic.
[0010]
In the above proposal, complicated calculation processing must be performed and a high-performance CPU is required, which hinders cost reduction. Furthermore, since the tandem method requires four times as many power supply circuits, the CPU also requires four times the performance.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described facts, and an object of the present invention is to propose a high-voltage power supply apparatus capable of high-precision output voltage control at low cost regardless of a change in load capacity or the like.
[0012]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides a step-up transformer, a DC power source that is connected to one terminal of a primary winding of the step-up transformer and supplies a DC voltage to the step-up transformer, and one of the step-up transformers.Next volumeA switching element connected to the other terminal of the line to turn on / off voltage supply from the DC power supply to the step-up transformer, and boosted to the secondary winding of the step-up transformer by turning on / off the switching element Smoothing means for smoothing the voltage and outputting it to the load, and a PWM control unit for controlling the ON time of the switching element based on the output voltage to the load and performing PWM control of the switching element so that the output voltage becomes the target voltage A voltage detecting means for detecting a voltage between the other terminal of the primary winding of the step-up transformer and the ground as a terminal voltage, and detecting an output voltage output to the load. A reference voltage setting means for setting a reference voltage based on the detected output voltage;Comparing means for comparing the terminal voltage detected by the voltage detecting means with the reference voltage;in frontRecordingThe on-timing of the switching elementThe switching element is turned on after it is determined from the comparison result of the comparison means that the terminal voltage has decreased to the reference voltage.Setting means for setting, and driving means for driving the switching element based on the ON timing set by the setting means with an ON time based on the output voltage.Mu
[0013]
  According to the present invention, the ON time is set based on the output voltage, and the output voltage is controlled to be the target voltage by the PWM control that drives the switching element based on the set ON time. At this time, a change in the terminal voltage on the primary winding side of the step-up transformer is detected, and the timing for turning on the switching element is set based on the change in the terminal voltage.
  Further, the reference voltage setting means sets the reference voltage based on the output voltage,Terminal voltage isThis reference voltage(After the terminal voltage has fallen below the reference voltage)Switching elementTo turn onBy setting the ON timing of the switching element, the switching element can be driven at an appropriate timing even when the amplitude of the terminal voltage changes according to the output voltage.
[0014]
As a result, the switching element can be turned on at a fixed timing with respect to the terminal voltage that changes according to the output voltage and the load capacitance, and the output voltage can be monotonously increased according to the ON time of the switching element.
[0015]
Therefore, it is not necessary to perform complicated PWM control, and high-precision control of the output voltage is possible at low cost.
[0021]
  like thisThe present inventionsoMore preferably, a mask time for stopping reading of the comparison result of the comparison means for a predetermined time after the switching element is turned off is set.
[0022]
When the switching element is turned off from on, ringing or the like may occur. However, by setting the mask time, it is possible to reliably prevent the occurrence of malfunction due to ringing.
[0023]
The present invention preferably includes start means for forcibly driving the switching element at intervals within a predetermined time at the start of driving of the switching element, whereby the switching element is switched based on the terminal voltage of the primary winding. When this is done, reliable driving is possible.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a high-voltage power supply device 10 according to the present embodiment.
[0025]
The high-voltage power supply device 10 includes a DC power supply 12 that outputs a predetermined voltage Vin, and a booster unit 14 that outputs an output voltage Vout obtained by boosting a voltage input from the DC power supply 12, and is output from the booster unit 14. Is supplied to the load 16. When this high-voltage power supply device 10 is used in a printer such as a color printer using an electrophotographic process, a transfer roller or the like is connected as the load 16, but not limited to this, on the output side of the high-voltage power supply unit 14. Any load 16 can be connected as long as it uses DC power.
[0026]
The step-up transformer 14 is provided with a step-up transformer 18. A snubber circuit 20 is provided on the primary winding 18A side of the step-up transformer 18, and DC power of voltage Vin is input from the DC power supply 12 to one terminal 32A of the primary winding 18A. Further, a smoothing circuit 22 is provided on the secondary winding 18B side of the step-up transformer 18, and a DC voltage of a predetermined output voltage Vout is output through the smoothing circuit 22.
[0027]
On the other hand, the boosting unit 14 is provided with a switching element 24. The switching element 24 is connected in series to the other terminal 32B of the primary winding 18A of the step-up transformer 18. Further, the booster unit 14 is provided with a PWM control unit 26. The switching element 24 is driven on / off according to the switching signal st output from the PWM control unit 26.
[0028]
The switching element 24 is turned on / off by a switching signal st, and energizes and interrupts the primary winding 18A of the step-up transformer 18 from the DC power supply 12. As the switching element 24 at this time, a known semiconductor element such as a bipolar transistor, a power transistor, a MOS field effect transistor (MOSFET), a power MOSFET, or an IGBT (Insulated Gate Bipolar Transistor) can be applied.
[0029]
This high-voltage power supply device 10 uses a flyback system, and power is supplied from the DC power supply 12 to the primary winding 18A side of the step-up transformer 18 while the switching element 24 is on, and power is supplied to the step-up transformer 18. accumulate. Thereafter, when the switching element 24 is turned off and the power supply from the DC power supply 12 is cut off, the power stored in the step-up transformer 18 is converted into a DC voltage via the smoothing circuit 22 and is supplied to the load 16. Supply. That is, the time during which the switching element 24 is off is the flyback time.
[0030]
The booster 14 is provided with an output voltage detector 28. The output voltage detection unit 28 outputs a voltage corresponding to the output voltage Vout output to the load 16 to the PWM control unit 26.
[0031]
Based on the voltage detected from the output voltage detector 28, the PWM controller 26 sets an ON time when the switching element 24 is turned on so that the output voltage Vout becomes a preset target voltage. That is, the high-voltage power supply device 10 performs PWM control of the switching element 24 so that the output voltage Vout becomes the target voltage.
[0032]
  Incidentally, the voltage booster 14 is provided with a voltage detector 30, and this voltage detector 30 is connected to the PWM controller 26. The voltage detection unit 30 includes a terminal 32B of the primary winding 18A of the step-up transformer 18.Terminal that is the voltage between and groundVoltage V₀A signal (for example, a voltage) corresponding to is output to the PWM control unit 26. That is, the voltage detection unit 30 is connected to the primary winding 18A.Between windings between terminal 32A and terminal 32BVoltage V₁Of the terminal 32B which changes according toTerminal voltageV₀Output a signal according to. Thereby, in the PWM control unit 26, the voltage V of the primary winding 18 </ b> A according to the on / off of the switching element 24.₁Changes can be detected.
[0033]
The PWM control unit 26 detects the voltage V detected via the voltage detection unit 30.₀Based on the above, the switching element 24 is turned on. That is, the PWM control unit 26 determines the voltage V of the primary winding 18A of the step-up transformer 18.₁Based on the above, the switching element 24 is turned on.
[0034]
In the step-up unit 14, the voltage V of the primary winding 18 </ b> A of the step-up transformer 18 is turned on when the switching element 24 is turned on.₀When the switching element 24 is turned off from the on state, the voltage V on the secondary winding 18B side is reduced.₂Depending on the voltage V₁Changes. This voltage V₁The time constant when changes mainly depends on the power consumption such as the circuit constant on the secondary winding 18B side and the impedance of the load.
[0035]
At this time, the PWM control unit 26 determines the terminal voltage V of the primary winding 18A.₀When the voltage reaches a predetermined value set in advance, the output voltage Vout is changed in accordance with the change in the ON time of the switching signal regardless of the size of the load 16 by turning on the switching element 24. To be able to. That is, it is possible to achieve a monotonically increasing characteristic in which the output voltage Vout increases when the ON time is increased (longer).
[0036]
Below, the specific example of the high voltage power supply device 10 is demonstrated, referring drawings.
[First embodiment]
FIG. 2 shows a high-voltage power supply device 10A applied to the first embodiment. The power supply device 10A is provided with a snubber circuit 20 in which a capacitor 40 and a resistor 42 are connected in series, and a smoothing circuit 22 that is half-wave rectified by a diode 44, smoothed by a capacitor 46, and output. .
[0037]
On the other hand, the PWM control unit 26 </ b> A provided as the PWM control unit 26 is formed by the CPU 48. Further, the output voltage detection unit 28 divides the output voltage Vout by the resistors 50A and 50B and outputs it as a monitor voltage Vout-mon of the output voltage Vout. The CPU 48 is provided with an A / D conversion unit 52, and the CPU 48 performs A / D conversion and reads the monitor voltage Vout-mon input from the output voltage detection circuit 28.
[0038]
The switching element 24 uses a power MOSFET as an example, and is turned on / off based on a change in voltage input as a switching signal from the CPU 48.
[0039]
Incidentally, a voltage detection circuit 56 including a buffer 54 is provided as the voltage detection unit 30 in the boosting unit 14A of the high-voltage power supply device 10A. In the voltage detection circuit 56, the voltage divided by the resistors 58 </ b> A and 58 </ b> B is output to the A / D conversion unit 60 provided in the CPU 48 via the buffer 54. Thereby, the CPU 48 determines the voltage V at the terminal 32B of the primary winding 18A of the step-up transformer 18.₀Can be read and monitored after A / D conversion (hereinafter referred to as “monitor voltage Vmon”).
[0040]
On the other hand, in the CPU 48, the on-time t of the switching element 24 is set so that the output voltage Vout becomes the target voltage based on the monitor voltage Vout-mon of the output voltage Vout._ONSet. That is, the monitor voltage Vout-mon when the output voltage Vout becomes the target voltage is set as the target reference voltage, the monitor voltage Vout-mon is compared with the target reference voltage, and when the monitor voltage Vout-mon is higher than the target reference voltage, ON time t of the switching element 24_ONIs shortened by one step, and conversely when the monitor voltage Vout-mon is low, it is lengthened by one step.
[0041]
In the boosting unit 14A, the ON time t of the switching element 24 is thus obtained._ONBy performing this feedback control, the output voltage Vout is made to coincide with the target voltage. The on-time t of the switching element 24_ONA general configuration can be applied to this setting, and detailed description thereof is omitted in this embodiment.
[0042]
In the CPU 48, the terminal voltage V input from the voltage detection circuit 56.₀The timing for turning on the switching element 24 is set from the monitor voltage Vmon. That is, the CPU 48 compares the reference voltage Vs set in advance with the monitor voltage Vmon. When the monitor voltage Vmon falls to the reference voltage Vs, the CPU 48 outputs the switching signal st and turns on the switching element 24.
[0043]
The reference voltage Vs at this time is the voltage V V when the energy release is almost finished when the switching element 24 is turned off and the energy stored in the step-up transformer 18 is released.₀Has been applied. Thereby, in the high voltage power supply device 10A, the accumulation of new energy is started at the timing when the release of the energy accumulated in the step-up transformer 18 is completed.
[0044]
Here, an outline of the operation of the high-voltage power supply apparatus 10A will be described with reference to FIGS. FIG. 3 shows an outline of switching processing in which the CPU 48 outputs a switching signal. This flowchart is executed when the high voltage power supply apparatus 10A outputs a predetermined high voltage to the load 16. Further, in the CPU 48, in parallel with this switching process, the on-time t based on the monitor voltage Vout-mon of the output voltage Vout._ONPerform the setting process.
[0045]
In this flowchart, the switching signal st is output in the first step 100, and in step 102, the time after the switching signal st is output is a separately set on time t._ONIn order to confirm whether or not the value has reached, an affirmative determination is made in step 102, the process proceeds to step 104, and the output of the switching signal st is stopped. That is, from step 100 to step 104, the ON time t set based on the monitor voltage Vout-mon_ONBased on the above, the switching element 24 is turned on.
[0046]
Terminal voltage V of the step-up transformer 18₀Becomes a predetermined voltage when the switching element 24 is turned on. This voltage is the voltage V between the drain and source of the switching element 24 when the switching element 24 is on._DSAs shown in FIG. 4, the monitor voltage Vmon is equal to this voltage V_DSVoltage V according to_{ds (ON)}It becomes.
[0047]
On the other hand, in the flowchart of FIG. 3, when the switching signal st is turned off, the routine proceeds to step 106 where the monitor voltage Vmon is read and it is confirmed whether or not the monitor voltage Vmon is higher than the reference voltage Vs (step 108). ) If the monitor voltage Vmon is higher than the reference voltage Vs (Yes in step 108), the process proceeds to step 110, and the monitor voltage Vmon is read. Thereafter, in step 112, it is confirmed whether or not the monitor voltage Vmon has decreased to the reference voltage Vs (Vmon ≦ Vs).
[0048]
That is, as shown in FIG. 4, when the switching element 24 is turned off, the flyback is started and the discharge of the energy accumulated in the step-up transformer 18 is started, and accordingly, the terminal voltage V₀At the same time, the monitor voltage Vmon rises and then gradually decreases with time (also indicated by a two-dot chain line in FIG. 4).
[0049]
Thereby, when the release of the energy accumulated in the step-up transformer 18 is almost finished and the monitor voltage Vmon reaches the reference voltage Vs, in the flowchart shown in FIG. The output of the switching signal st is started. That is, the switching element 24 is turned on, and accumulation of new energy is started on the secondary winding 18B side of the step-up transformer 18 (see FIG. 4).
[0050]
Thus, the frequency of the switching signal st (period T_F) Is fixed, and the off time t of the switching element 24 is adjusted in accordance with the release of energy from the step-up transformer 18._OFFIn order to set the flyback time, the switching element 24 can be switched so as to achieve an optimum flyback time according to the capacity of the load.
[0051]
Therefore, the on-time t of the switching element 24 regardless of the change in the capacity of the load._ONThe output voltage Vout can be monotonously increased, and the output voltage Vout can be stabilized with high accuracy without performing complicated PWM control.
[0052]
In addition, since the switching element 24 can be switched at an appropriate timing in accordance with the release of the energy accumulated in the step-up transformer 18, efficient step-up is possible.
[Second Embodiment]
Next, a second embodiment will be described. In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
[0053]
FIG. 5 shows an outline of a high-voltage power supply device 10B applied to the second embodiment. In this high voltage power supply device 10B, a PWM control unit 26B configured by a CPU 48A and a switching control circuit 62 is provided in the boosting unit 14B as the PWM control unit 26.
[0054]
Further, the voltage booster 14B is provided with a voltage detection circuit 68 including a comparator 64 and a reference power supply 66 for inputting the reference voltage Vs to the comparator 64 as the voltage detector 30.
[0055]
The CPU 48A determines the on-time t of the switching signal st based on the monitor voltage Vout-mon of the output voltage Vout._ONTo set this on time t_ONIs output to the switching control circuit 62. Further, the CPU 48A outputs a start signal start for starting switching control.
[0056]
The voltage detection circuit 68 is connected to the terminal voltage V of the step-up transformer 18.₀Exceeds the reference voltage Vs, the comparison signal C output from the comparator 64 is turned on, and the terminal voltage V₀Is lowered to the reference voltage Vs, the comparison signal C is turned off.
[0057]
The switching control circuit 62 has an on-time t set by the CPU 48A._ONIs output to the switching element 24 in accordance with the comparison signal C.
[0058]
At this time, as shown in FIG. 6, when the comparison signal C input from the voltage detection circuit 68 is turned off, the switching control circuit 62 turns on the switching signal st and drives the switching element 24. Note that a delay time α occurs between the time when the comparison signal C is turned off and the time when the switching signal st is turned on. For this reason, the reference voltage Vs may be set in consideration of the delay time α.
[0059]
As described above, also in the high-voltage power supply device 10B configured as described above, the off-time t of the switching element 24 is adjusted in accordance with the release of energy from the step-up transformer 18 without fixing the frequency (period) of the switching signal st._OFFIn order to set the flyback time, the switching element 24 can be switched so as to achieve an optimum flyback time according to the capacity of the load.
[0060]
Therefore, the on-time t of the switching element 24 regardless of the change in the capacity of the load._ONThe output voltage Vout can be monotonously increased, and the output voltage Vout can be stabilized with high accuracy without performing complicated PWM control. In addition, since the switching element 24 can be switched at an appropriate timing in accordance with the release of the energy accumulated in the step-up transformer 18, efficient step-up is possible.
[0061]
At the same time, since the switching signal st is output using the switching control circuit 62 provided separately from the CPU 48A, the burden on the CPU 48A can be reduced. Therefore, it is not necessary to use an expensive CPU 48A with high processing capability in order to perform PWM control, and the cost can be reduced.
[Third embodiment]
Next, a third embodiment will be described. In the third embodiment, parts that are the same as those in the first or second embodiment are given the same reference numerals, and descriptions thereof are omitted.
[0062]
FIG. 7 shows a schematic configuration of a high-voltage power supply device 10C according to the third embodiment. In the boosting unit 14C of the high-voltage power supply device 10C, the terminal voltage V₀Is set to a delay time Δt when the switching signal st is output. That is, the CPU 48B of the switching control unit 26C sets the on time t of the switching signal st._ONAt the same time, the delay time Δt is output to the switching control circuit 62A.
[0063]
When the switching element 24 is turned on based on the comparison signal C, the switching control circuit 62A delays this delay time Δt.
[0064]
As shown in FIGS. 8A to 8C, during flyback, the terminal voltage V₀However, it oscillates damped around the voltage Vin of the DC power supply 12. At this time, as shown in FIGS. 8A and 8B, when the output voltage Vout is low or not relatively high, the voltage V of the primary winding 18A₁However, the voltage Vin of the DC power supply 12 is not exceeded. Terminal voltage V during flyback in this state₀Is the voltage V when the switching element 24 is on._{DS (ON)}Never reach.
[0065]
On the other hand, as shown in FIG. 8C, when the output voltage Vout is high, the voltage V of the primary winding 18A₁Exceeds the voltage Vin, so that the terminal voltage V₀Is the voltage V when the switching element 24 is on._{DS (ON)}May be lower. 8A to 8C show a state in which the flyback time is extended by stopping the switching after outputting the switching signal st.
[0066]
For this reason, the terminal voltage V₀In order to detect this change, it is necessary to increase the reference voltage Vs. However, if the output voltage Vout increases while the reference voltage Vs is increased, energy storage in the step-up transformer 18 is started while the energy stored in the step-up transformer 18 is being released. Decreases.
[0067]
Here, in the high voltage power supply apparatus 10C, the reference voltage Vs is set close to the voltage Vin of the DC power supply 12 (Vin> Vs), and the switching signal st is input after the comparison signal C is input based on the output voltage Vout. The delay time Δt until output is set.
[0068]
As the delay time Δt, for example, as shown in FIG. 9A, when the output voltage Vout is low, the terminal voltage Vt₀Reaches the reference voltage Vs and the minimum voltage V_LOWThe time to reach can be set.
[0069]
In this way, the delay time Δt is set, and the on-time t of the switching signal st is determined based on the delay time Δt._ONIs delayed, as shown in FIG. 9A, the output voltage Vout becomes low and the terminal voltage Vout₀When there is little change in the terminal voltage V₀Is the minimum voltage V_LOWThus, it is possible to prevent the switching of the switching element 24 from being started after rising.
[0070]
As shown in FIG. 9B, when the output voltage Vout is high or the load capacity is large, the switching of the switching element 24 can be started before the terminal voltage V0 decreases too much.
[0071]
Thereby, regardless of the output voltage Vout and the load capacity, the switching element 24 can be switched at an appropriate timing when the output voltage Vout has a monotonously increasing characteristic.
[0072]
On the other hand, the delay time Δt may be changed according to the output voltage Vout and the capacity of the load 16. For example, when setting the delay time Δt based on the output voltage Vout, based on the monitor voltage Vout-mon of the output voltage Vout, when the output voltage Vout is high, the delay time Δt is shortened, and when the output voltage Vout is low, The delay time Δt may be lengthened.
[0073]
Here, an outline of setting the delay time Δt based on the output voltage Vout will be described with reference to FIG. Here, the monitor voltage Vout-mon of the output voltage Vout is a low voltage region where the voltage is lower than the voltage Va, a high voltage region where the monitor voltage Vout-mon is higher than the voltage Vb (Va <Vb), and the voltage Va and the voltage Vb (Va ≦ Vout-mon ≦ Vb ) Set the medium pressure range, and set the delay time Δt to Δt in the low pressure range, medium pressure range, and high pressure range.₁, Δt₂, Δt_Three(Δt₁> Δt₂> Δt_Three).
[0074]
In this flowchart, the operation is performed when the high-voltage power supply device 10C starts to operate, and in the first step 120, the delay time Δt is initially set. As an initial value of the delay time Δt, the delay time Δt₂And the shortest delay time Δt_ThreeMay be used.
[0075]
Thereafter, in step 122, the monitor voltage Vout-mon is read. In step 124, it is confirmed whether or not the monitor voltage Vout-mon is lower than the voltage Va. Thus, when the monitor voltage Vout-mon is lower than the voltage Va (Vout-mon <Va), it is determined that the output voltage Vout is in the low voltage range (positive determination in step 124), and the process proceeds to step 126. Delay time Δt is changed to time t₁Set to.
[0076]
When the monitor voltage Vout-mon is higher than the voltage Va (Vout-mon ≧ Va), a negative determination is made at step 124 and the routine proceeds to step 128, where is the monitor voltage Vout-mon higher than the voltage Vb? Confirm whether or not.
[0077]
Thus, when the monitor voltage Vout-mon is higher than the voltage Vb (Vout-mon> Vb), it is determined that the output voltage Vout is in the high voltage range (positive determination in step 128), and the process proceeds to step 130. Delay time Δt is changed to time Δt_ThreeSet to.
[0078]
On the other hand, when the monitor voltage Vout-mon is not less than the voltage Va and not more than the voltage Vb (Va ≦ Vout−mon ≦ Vb, negative determination in steps 124 and 128), it is determined that the output voltage Vout is in the intermediate pressure range. Then, the process proceeds to step 132, and the delay time Δt is changed to the time Δt.₂Set to.
[0079]
In this way, by setting the delay time Δt according to the output voltage Vout, for example, as shown in FIG. 11A, the output voltage Vout− is low and the terminal voltage Vout₀The delay time Δt can be increased in a state in which the amplitude when the value changes is small and the decay period is long. Further, as shown in FIG. 11B, when the output voltage Vout is in the intermediate voltage range, the delay time Δt can be made shorter than when the output voltage Vout is in the low voltage range. Furthermore, when the output voltage Vout is in the high voltage range, the delay time Δt can be minimized.
[0080]
Therefore, regardless of the output voltage Vout, the switching element 24 can be switched at an appropriate timing so that the output voltage Vout has a monotonically increasing characteristic.
[0081]
When the output voltage Vout is constant, an output current that varies depending on the load capacity may be detected, and the delay time Δt may be set based on this output current. The delay time Δt may be set based on the output voltage Vout and the output current, so that the output voltage Vout is monotonically increasing regardless of the capacity of the load 16 or the voltage supplied to the load 16. Can be.
[Fourth embodiment]
Next, a fourth embodiment will be described. In the fourth embodiment, the same parts as those in the first to third embodiments are denoted by the same reference numerals, and the description thereof is omitted.
[0082]
FIG. 12 shows a schematic configuration of a high-voltage power supply device 10D applied to the fourth embodiment. In the switching control unit 26D provided in the boosting unit 14D of the high-voltage power supply device 10D, a D / A conversion unit 70 is provided in the CPU 48C. The CPU 48C outputs the reference voltage Vs from the D / A conversion unit 70 to the comparator 64 of the voltage detection circuit 68A.
[0083]
On the other hand, the CPU 48C changes the reference voltage Vs according to the output voltage Vout. That is, in the third embodiment, the delay time Δt is changed according to the output voltage Vout. However, in the fourth embodiment, the reference voltage Vs is changed according to the output voltage Vout.
[0084]
Such a reference voltage Vs may be any method that changes according to the output voltage Vout but is set based on the monitor voltage Vout-mon.
[0085]
For example, the voltages Va and Vb (Va <Vb) are used as a reference, and the voltage is divided into a low pressure region, a medium pressure region, and a high pressure region.₁, Vs₂, Vs_Three(However, Vs₁> Vs₂> Vs_Three), The reference voltage Vs is set according to the monitor voltage Vout-mon.
[0086]
Here, an example of setting the reference voltage Vs will be described with reference to FIG. In this flowchart, the initial setting of the reference voltage Vs is performed in the first step 140. At this time, the reference voltage Vs is the highest voltage close to the voltage Vin of the DC power supply (for example, the voltage Vs₁) Is preferable.
[0087]
Thereafter, in step 142, the monitor voltage Vout-mon is read, and in the next step 144, it is confirmed whether or not the monitor voltage Vout-mon is lower than the voltage Va. Thereby, when the monitor voltage Vout-mon is lower than the voltage Va (Vout-mon <Va), it is determined that the output voltage Vout is in the low voltage range (positive determination in step 144), and the process proceeds to step 146. The reference voltage Vs is changed to the voltage Vs.₁Set to.
[0088]
When the monitor voltage Vout-mon is higher than the voltage Va (Vout-mon ≧ Va), a negative determination is made at step 144 and the routine proceeds to step 148, where is the monitor voltage Vout-mon higher than the voltage Vb? Confirm whether or not.
[0089]
Thus, when the monitor voltage Vout-mon is higher than the voltage Vb (Vout-mon> Vb), it is determined that the output voltage Vout is in the high voltage range (positive determination in step 148), and the process proceeds to step 150. Reference voltage Vs to voltage Vs_ThreeSet to.
[0090]
On the other hand, when the monitor voltage Vout-mon is not less than the voltage Va and not more than the voltage Vb (Va ≦ Vout-mon ≦ Vb, negative determination in steps 144 and 148), the output voltage Vout-mon is in the intermediate pressure range. The process proceeds to step 152 and the reference voltage Vs is changed to the voltage Vs.₂Set to.
[0091]
As a result, as shown in FIG. 14A, the output voltage Vout is low and the terminal voltage V₀When the amplitude of the reference voltage Vs is small, the reference voltage Vs is brought close to the voltage Vin of the DC power supply 12, and as shown in FIG. 14B, when the output voltage Vout-mon is relatively high, the reference voltage Vs is separated from the voltage Vin. Can do. Further, as shown in FIG. 14C, when the output voltage Vout-mon is higher and the amplitude of the terminal voltage V0 exceeds twice the voltage Vin, the reference voltage Vs can be greatly reduced.
[0092]
By changing the reference voltage Vs in this way, the output voltage Vout is changed to the on-time t of the switching element 24._ONIt is possible to increase monotonically according to the increase of.
[0093]
In addition, as a high voltage power supply apparatus to which the present invention is applied, the reference voltage Vs may be changed based on the output current and the output voltage Vout-mon.
[Fifth embodiment]
Next, a fifth embodiment will be described. In the fifth embodiment, the same components as those in the first to fourth embodiments are designated by the same reference numerals, and the description thereof is omitted.
[0094]
  In the booster 14E of the high-voltage power supply device 10E applied to the fifth embodiment, the CPU 48D hasTime until the switching element 24 is forcibly turned onWhen the switching signal st is forced onBetweenIs set. Further, when the comparison signal C is switched from OFF to ON, the CPU 48D(When switching signal st switches from on to off)In addition, a mask time tm is set that does not detect switching of the comparison signal C from ON to OFF for a predetermined time.
[0095]
When the switching control circuit 62B starts the switching process, the time until the switching element 24 is forcibly turned on when forced switching is performed from the CPU 48D (hereinafter referred to as “overflow time t”)._OF”). The switching control circuit 62B reads the mask time tm input from the CPU 48D when the masking of the comparison signal C is set.
[0096]
  As a result, the switching control circuit 62B, when switching is started,Switching signal stForced on timeEven afterWhen the comparison signal C does not switch from on to off,Overflow time t _OF Based on the above, the switching element 24 is forcibly turned on. Further, the switching control circuit 62B does not detect switching of the comparison signal C during the mask time tm when the comparison signal C is switched from OFF to ON after the start-up process is completed.
[0097]
FIG. 16 shows an outline of the starting process. This flowchart is executed when a start signal start for starting switching is input from the CPU 48D. In the first step 160, the ON time t of the switching signal st is set._ONInitial value and overflow time t_OFIs read.
[0098]
Thereafter, in step 162, the switching signal st is turned on at a predetermined timing, and the driving of the switching element 24 is started.
[0099]
Here, at the start of switching activation, when the switching element 24 is turned off from on, the routine proceeds to step 164 where a timer (not shown) is reset / started and the switching element 24 is turned off (off time t_OFFIn step 166, the comparison signal C is read, and it is confirmed whether or not the comparison signal C has been switched from on to off (step 168).
[0100]
At this time, when the comparison signal C is not switched from ON to OFF and a negative determination is made in step 168, the process proceeds to step 170 and the OFF time t measured by the timer._OFFIs the overflow time t_OFCheck whether or not.
[0101]
Thus, the off time t before the comparison signal C switches from on to off._OFFIs the overflow time t_OF(T_OFF≧ t_OF) If the determination in step 170 is affirmative, the routine proceeds to step 162 where the switching signal st is turned on and the switching element 24 is forcibly driven again.
[0102]
In this way, the overflow time t_OFThe output voltage Vout gradually rises by forcibly turning on the switching element 24 at intervals of the terminal voltage V₀The amplitude of becomes larger. As a result, the terminal voltage V₀Is lower than the reference voltage Vs, the comparison signal C output from the comparator 64 is switched from on to off.
[0103]
As a result, when an affirmative determination is made in step 168, the process proceeds to step 172, where the starting process is terminated, and the normal control for driving the switching element 24 by outputting the switching signal st at the timing based on the comparison signal C is performed. Transition.
[0104]
That is, as shown in FIG. 17, when the switching of the switching element 24 is started (start-up is started), the output voltage Vout does not increase, so the terminal voltage V₀Terminal voltage V₀Alternatively, the monitor voltage Vmon may not fall below the reference voltage Vs. For this reason, the comparison signal C is not output, and the switching of the switching element 24 is stopped. At this time, if the reference voltage Vs is brought close to the voltage Vin of the DC power supply 12, it causes malfunction.
Here, in the high voltage power supply device 10E, the terminal voltage V₀However, by forcibly driving the switching element 24, the terminal voltage V₀When switching is performed based on the above, it is possible to start the start accurately.
[0105]
Such activation processing can be applied to any of the first to fourth embodiments described above.
[0106]
On the other hand, the switching control circuit 62B of the boosting unit 14 reads the mask time tm together with the delay time Δt from the CPU 48D when the activation process is completed, and detects the comparison signal C used for the mask time tm.
[0107]
Here, the flow of the switching process using the mask time tm will be described with reference to FIG. In this flowchart, when the switching element 24 is switched based on the predetermined on-time tON in Step 100 to Step 104, a timer (not shown) is reset / started in Step 180 to start time measurement. In Step 182, It is confirmed whether or not the measurement time has reached the mask time tm.
[0108]
Thereby, when the elapsed time after turning off the switching element 24 reaches the mask time tm and an affirmative determination is made in step 182, the process proceeds to step 184, where the comparison signal C is read and the comparison signal C is turned on. It is confirmed whether or not it has been switched off (step 186). That is, after the switching element 24 is turned off (the switching signal st is turned off), the comparison signal C is read after the mask time tm has elapsed.
[0109]
As a result, when the comparison signal C is switched from on to off and an affirmative determination is made in step 186, the process proceeds to step 188, where the measurement of the delay time Δt is started by resetting / starting a timer (not shown). When the delay time Δt has elapsed and an affirmative determination is made in step 190, the process proceeds to step 100 to perform the next switching.
[0110]
That is, when the switching element 24 is turned off from the on state, the terminal voltage V₀At this time, ringing may occur depending on the characteristics of the step-up transformer 18 and the circuit connected to the primary winding 18A and the secondary winding 18B of the step-up transformer 18.
[0111]
As a result, as shown in FIG.₀Once becomes lower than the reference voltage Vs, and the comparison signal C is turned off. When the switching element 24 is turned on at this timing, energy accumulation is started in the middle of the energy release from the secondary winding 18B of the step-up transformer 18, and an appropriate output voltage Vout cannot be obtained.
[0112]
At this time, by providing the mask time tm, it is possible to prevent malfunction due to ringing and obtain an appropriate output voltage Vout.
[0113]
The startup process and the mask process may be configured by hardware in the switching control circuit 62B. When the switching control circuit 62B is provided with a CPU for generating a switching signal, the CPU performs the process. It may be.
[0114]
The present embodiment described above shows an example of the present invention and does not limit the configuration of the present invention. For example, when the capacity (impedance, etc.) of the load 16 is affected by environmental conditions such as temperature and humidity, such as a transfer roller, environmental condition detecting means for detecting environmental conditions such as temperature and humidity is provided. The reference voltage Vs and the delay time Δt may be corrected based on the detection result of the condition detection unit. This makes it possible to control the output voltage Vout more appropriately.
[0115]
【The invention's effect】
  As described above, according to the present invention,A reference voltage is set based on the output voltage.By turning on / off the switching element based on the voltage change on the primary winding side of the step-up transformer, the output voltage can be monotonously increased according to the increase of the ON time of the switching element, so that complicated PWM control can be performed. Even without this, the output voltage can be controlled with high accuracy and the burden on the CPU can be reduced.High pressureAn excellent effect of providing a power supply device can be obtained.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a schematic configuration of a high-voltage power supply device applied to the present embodiment.
FIG. 2 is a schematic configuration diagram of a high-voltage power supply device applied to the first embodiment.
FIG. 3 is a flowchart showing an outline of a switching process in the first embodiment.
FIG. 4 is a timing chart showing an outline of changes in the monitor voltage of the terminal voltage and on / off of the switching signal in the first embodiment.
FIG. 5 is a schematic configuration diagram of a high-voltage power supply device applied to a second embodiment.
FIG. 6 is a timing chart showing an outline of terminal voltage change, comparison signal change, and switching signal on / off in the second embodiment.
FIG. 7 is a schematic configuration diagram of a high-voltage power supply device applied to a third embodiment.
FIGS. 8A to 8C are timing charts showing outlines of changes in the terminal voltage and comparison signal after the switching signal is turned off, respectively, and FIG. 8A shows a low voltage range where the output voltage is low. (C) shows the change in the medium voltage range of the output voltage, and (C) shows an example of the change in the high voltage range where the output voltage is high.
FIGS. 9A and 9B are timing charts showing a change in terminal voltage, a change in comparison signal, and a switching signal on / off according to a delay time based on the terminal voltage when the output voltage is low (A). ) Indicates the low and medium voltage range of the output voltage, and (B) indicates the high voltage range of the output voltage.
FIG. 10 is a flowchart showing an outline of setting a delay time based on an output voltage.
FIGS. 11A to 11C are timing charts showing an outline of a change in terminal voltage, a change in a comparison signal, and an on / off state of a switching signal based on a delay time set from the output voltage, and FIG. The output voltage is in the low voltage range, (B) shows the output voltage in the medium voltage range, and (C) shows the output voltage in the high voltage range.
FIG. 12 is a schematic configuration diagram of a high-voltage power supply device applied to a fourth embodiment.
FIG. 13 is a flowchart showing an outline of setting a reference voltage based on an output voltage.
FIGS. 14A to 14C are timing charts schematically showing changes in terminal voltage, comparison signal, and switching signal on / off based on a reference voltage set from an output voltage. FIGS. The output voltage is in the low voltage range, (B) shows the output voltage in the medium voltage range, and (C) shows the output voltage in the high voltage range.
FIG. 15 is a schematic configuration diagram of a high-voltage power supply device applied to a fifth embodiment.
FIG. 16 is a flowchart showing an outline of start-up processing when switching is started based on a terminal voltage.
FIG. 17 is a timing chart showing an outline of a change in terminal voltage, a change in comparison signal, and on / off of a switching signal at start-up.
FIG. 18 is a flowchart showing an outline of switching processing using a mask time of a comparison signal.
FIG. 19 is a timing chart schematically showing on / off of a switching signal using a change in terminal voltage, a change in a comparison signal, and a mask time in which ringing has occurred.
FIG. 20 is a schematic configuration diagram showing an example of a conventional high-voltage power supply device.
[Explanation of symbols]
10 (10A-10E) High voltage power supply
12 DC power supply
14 (14A-14E) Booster
16 Load
18 Step-up transformer
18A primary winding
18B secondary winding
22 Smoothing circuit
24 Switching element
26 (26A-26E) PWM controller
28 Output voltage detector
30 Voltage detector
48, 48A, 48B, 48C, 48D CPU
56, 68 Voltage detection circuit
62, 62A, 62B switching control circuit
64 comparator
66 Reference power supply

Claims (3)

A step-up transformer,
A DC power source connected to one terminal of the primary winding of the step-up transformer and supplying a DC voltage to the step-up transformer;
A switching element connected to the other terminal of the primary winding of the step-up transformer to turn on / off the voltage supply from the DC power source to the step-up transformer;
Smoothing means for smoothing a voltage generated by boosting the secondary winding of the step-up transformer by turning on / off the switching element and outputting the smoothed voltage to a load;
A PWM control unit for controlling the ON time of the switching element based on the output voltage to the load and performing PWM control of the switching element so that the output voltage becomes a target voltage;
A high-voltage power supply including
Voltage detecting means for detecting a voltage between the other terminal of the primary winding of the step-up transformer and the ground as a terminal voltage;
A reference voltage setting means for detecting an output voltage output to the load and setting a reference voltage based on the detected output voltage;
Comparing means for comparing the terminal voltage detected by the voltage detecting means with the reference voltage;
The on-timing before kissing switching element, a setting unit which the terminal voltage from the comparison result of said comparing means is set to turn on the switching element after it is determined that the decreases to the reference voltage,
Driving means for driving the switching element based on an on timing set by the setting means with an on time based on the output voltage;
The including high-voltage power equipment. 2. The high voltage power supply apparatus according to claim 1 , wherein a mask time for stopping reading of the comparison result of the comparison means for a predetermined time after the switching element is turned off is set . 3. The high-voltage power supply device according to claim 1 , further comprising an activation unit that forcibly drives the switching element at an interval within a predetermined time at the start of driving of the switching element .

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