Power supply device

Abstract

To achieve a power supply device that can obtain stable output voltage even with a small load on the power supply device, without increasing power from a power supply to be wasted.SOLUTION: A power supply device has first control means. In a switching power supply that detects an auxiliary winding voltage that is on a primary side in a period when a secondary-side rectifier diode is electrically conducted after the drive of a main switching element in the switching power supply is turned off, and controls the drive of the main switching element according to the value to maintain secondary-side voltage constant, the drive of the main switching element is performed multiple times as a set. The auxiliary winding voltage is detected immediately after only a single drive in the set. The auxiliary winding voltage is not detected immediately after the drive for the other drives in the set. A time width of the drive when detecting the auxiliary winding voltage immediately after the drive is made longer than a time width of the drive when not detecting the auxiliary winding voltage immediately after the drive.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a technique for improving the output voltage accuracy of a primary-side controlled power supply during light load operation.

Background Art

[0002] Power supply devices are used in all electrical products. Inkjet recording devices, which are widely used in general households and small offices, require not only functional design but also environmentally considerate design, and designs that meet these requirements are sought.

[0003] One aspect of environmentally considerate design is to achieve a configuration with fewer components or a configuration with lower power consumption.

[0004] In a power supply device, in order to keep the output voltage constant, usually the output voltage on the secondary side is detected and transmitted to the primary side in an insulated state to control the output voltage. As a specific example, on the secondary side, an error between the output voltage and the reference voltage is amplified using a shunt regulator, and this is transmitted in an insulated state via a photocoupler. On the primary side, the on-time of a switch such as a MOSFET connected to the primary winding is controlled using this information, thereby controlling the current flowing through the primary winding of the transformer and controlling the amount of magnetic energy transmitted to the secondary side.

[0005] On the other hand, there is a primary-side controlled power supply as a power supply with a configuration having fewer components. By adopting a configuration in which the output voltage on the secondary side is detected on the primary side, components such as a shunt regulator and a photocoupler on the secondary side can be eliminated, and a simple configuration with fewer components can be achieved. The details are as follows.

[0006] The voltages of the windings of a transformer that magnetically couples the primary side and the secondary side each generate a voltage proportional to the number of turns of the winding. A specific example will be given for explanation. For example, let Ns be the number of turns of the transformer winding that generates the output voltage Vout on the secondary side, and Na be the number of turns of the winding for generating the power supply of the control circuit on the primary side. Let Vs be the voltage between the terminals of the secondary-side winding, Na be the number of turns of the transformer winding for generating the power supply of the primary-side control circuit, and Va be the voltage between the terminals. Then, during the period when current flows through the secondary-side winding, the following relationship holds.

[0007] [Number]

[0008] Also, when the forward voltage of the secondary-side rectifying diode is VF, the relationship between the secondary-side output voltage Vout and the voltage Vs between the terminals of the secondary-side winding is as follows.

[0009] [Number]

[0010] Therefore, in order to accurately detect the secondary-side output voltage Vout from the primary-side Va, it is necessary to detect Va at the timing when VF is zero, that is, at the moment when the secondary-side winding current becomes zero. For this, it is necessary to detect the voltage at the moment when the switching waveform Va transitions from a positive voltage to a negative voltage. However, it can be detected by detecting that the waveform has changed steeply and reading the voltage immediately before that.

[0011] By adopting the above configuration, it is possible to stabilize the output voltage even in a configuration that eliminates components such as a shunt regulator and a photocoupler on the secondary side.

[0012] However, in this configuration, waveform quality becomes an issue in detecting the timing at which Va, which is a switching waveform, transitions from a positive voltage to a negative voltage. As described above, since Va is a switching waveform, when Va is in the on state, that is, when it transitions from a negative voltage to a positive voltage, a surge voltage is generated due to the leakage inductance of the transformer and the capacitance of the snubber circuit, etc., and the oscillation continues. In the Va waveform during the oscillation period, Vout cannot be accurately detected. Therefore, assuming the time width for the oscillation to subside, control is performed such that the on-time of the Va waveform is equal to or greater than this time width. To increase the on-time of the Va waveform, the on-time of the Vs waveform that supplies power to the secondary side needs to be increased, so surplus power is supplied to the secondary side. In this state, the secondary side voltage increases, so a dummy resistor is required to consume this surplus power. That is, excessive power is generated and consumed by the dummy resistor, leading to a deterioration in the efficiency of the power supply device, particularly the efficiency at light loads with low output power.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

[0014] Capture the second peak of the ringing waveform at the first turn-on of the auxiliary winding and the second peak value of the ringing waveform at the second turn-on, and control the drive according to these values. Since the ringing waveform decays, the second ringing of the ringing waveform has fewer error components than the first ringing waveform, so more accurate voltage detection can be performed.

Summary of the Invention

Problems to be Solved by the Invention

[0015] In the prior art, when the load is light, the on-width becomes short and only ringing occurs in the auxiliary winding voltage waveform, resulting in inaccurate control of the output voltage. Focusing on the fact that the error is less in the second peak than in the first peak of ringing, the driving is controlled by the second peak voltage. However, in the case of no load, since the power released to the secondary side is small, the on-time of the auxiliary winding becomes short and may turn off before the second peak occurs. Also, ringing depends more on the inductance of the transformer, the capacitance of the circuit, and the input voltage than on the state of the secondary side, and does not accurately reflect the secondary side voltage. Therefore, the improvement in the accuracy of controlling the secondary side voltage is only slight.

[0016] Therefore, the following problems are presented.

[0017] · It is difficult for the primary side control power supply to stabilize the output voltage during light load, and it is necessary to waste power with a dummy resistor or the like to stabilize the output voltage.

[0018] · In the prior art, due to the configuration of controlling by the peak value of ringing, accurate voltage control is difficult.

[0019] The present invention has been made in view of the above problems, and aims to realize a power supply device that can obtain a stable output voltage even during light load without increasing the wasted power of the power supply.

Means for Solving the Problems

[0020] In order to achieve the above object, the power supply device of the present invention detects the voltage of the auxiliary winding on the primary side during the period when the rectifying diode on the secondary side is conducting after the driving of the main switching element in the switching power supply is turned off, and controls the driving of the main switching element according to this value to keep the secondary side voltage constant. In the switching power supply, the driving of the main switching element is performed as a set of multiple drives, and the voltage of the auxiliary winding is detected only once immediately after the drive within the set. In other drives within the set, the voltage of the auxiliary winding is not detected immediately after the drive. The control means has a driving time width when detecting the voltage of the auxiliary winding immediately after the drive longer than the driving time width when not detecting the voltage of the auxiliary winding immediately after the drive.

Advantages of the Invention

[0021] According to the present invention, the following effects can be obtained.

[0022] · In the control by the voltage of the auxiliary winding, the secondary side voltage can be accurately detected even under light load, and the stability of the secondary side voltage can be improved.

[0023] · The dummy resistor provided to stabilize the output voltage under light load becomes unnecessary, and the power supply efficiency under light load can be improved.

[0024] · Since the stability of the output voltage can be improved in the entire load region, it can contribute to the deletion and cost reduction of the feedback circuit (coupler, shunt regulator).

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

MODE FOR CARRYING OUT THE INVENTION

[0026] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the configurations described in this embodiment are merely examples, and are not intended to limit the scope of the present invention thereto.

[0027] Prior to the description of this embodiment, an inkjet recording apparatus to which the power supply device described later is applied will be described. FIG. 1 is a perspective view of the inkjet recording apparatus. The inkjet recording apparatus 101 (hereinafter referred to as the recording apparatus) mounts a recording head 103 that discharges ink according to the inkjet method on a carriage 102. A driving force generated by a carriage motor 108 is transmitted to the carriage 102 through a transmission mechanism 104, and the carriage 102 is reciprocated in the direction of arrow A. At the time of recording, for example, a recording medium (for example, recording paper) P is fed by a paper feeding mechanism 105 and conveyed to a recording position. At the recording position, the recording head 103 is scanned, and recording is performed by discharging ink from the recording head 103 onto the recording medium P. 107 is a conveyance roller that conveys the recording medium P and is driven by a conveyance motor 109. The recording medium P is conveyed between the scans of the recording head 106.

[0028] In the power supply used for such a recording apparatus 101, it is necessary to be configured to supply a large amount of power such as when a plurality of motors included in the recording apparatus are started simultaneously. At the same time, even when the power required by the device to which the power supply is connected is small during standby or the like, high power efficiency and output voltage stability are required.

[0029] FIG. 2 is a diagram showing an example of the power supply configuration of the recording apparatus 100 in the prior art. FIG. 3 is a diagram for explaining the control unit in FIG. 2. The operation of the conventional primary-side controlled power supply will be described with reference to FIGS. 2 and 3.

[0030] FIG. 2(a) is a diagram showing the configuration of the entire power supply.

[0031] In FIG. 2(a), the commercial power supply 201 is rectified by the diode bridge 202 and the input capacitor 203, and reaches the ground via the switching element 206 and the current detection resistor 207 through the transformer 204. Np, Ns, and Na shown in the transformer 204 are the number of turns of the primary winding, the number of turns of the secondary winding, and the number of turns of the auxiliary winding, respectively. The power supply voltage Vcc for the control unit 205 rectifies the output of the auxiliary winding of the transformer 204 with the diode 208 and the capacitor 209, and further stabilizes and supplies the fluctuation of the auxiliary winding voltage by the transistor 210, the Zener diode 212 provided at the base of the transistor 210, and the resistor 211. 213 is the Vcc capacitor for the control unit 205. The control unit 205 periodically turns on the VDRV signal for driving the switching element 206, compares the voltage obtained by converting the voltage obtained by dividing the auxiliary winding voltage by a method described later with the voltage Vcs of the current detection resistor 207 inside the control unit, and turns off the VDRV signal if the voltage Vcs of the current detection resistor 207 reaches the level obtained by converting the auxiliary winding voltage.

[0032] The diode 216 and the capacitor 217 rectify the secondary-side output of the transformer 204 to generate the output Vout.

[0033] FIG. 2(b) is a diagram showing the internal configuration of the control unit 205. The operation for stabilizing the output Vout will be described with reference to this figure.

[0034] 230 in FIG. 2(b) is means for estimating the secondary-side voltage from the voltage obtained by dividing the auxiliary winding voltage by the resistors 214 and 215. Details will be described with reference to FIG. 3.

[0035] As described above, within the control unit 205, a VDRV signal for driving the switching element 206 is generated. A timing signal Fsw periodically supplied from the oscillator 234 is connected to the set terminal of the flip-flop 236 via the edge generation element 235. To the reset terminal of the flip-flop 236, the voltage of the AUX terminal is converted in the manner described with reference to FIG. 3, inverted and appropriately level-changed with respect to the voltage Vref by the inverting amplification means 231 to generate a level signal Ltd_AUX, which is connected to the negative electrode of the comparator 232. To the positive electrode of the comparator 232, the voltage Vcs of the current detection resistor 207 is connected. The output of the comparator 232 is connected to the reset terminal of the flip-flop 236 via the edge generation element 233. With this configuration, the VDRV signal is periodically turned on.

[0036] Also, as the current flowing through the switching element 206 increases, Vcs also rises, and when this reaches the voltage of the negative electrode of the comparator 232, it is turned off. When the secondary load is large, the discharge of the secondary capacitor 217 is steep, so the ripple of the output voltage drops significantly, and the level signal Ltd_AUX becomes high. Therefore, Vcs when the switching element 206 is turned off becomes high, and more power is sent to the secondary side. When the secondary load is small, the discharge of the secondary capacitor 217 is gentle, so the drop in the ripple of the output voltage is small, and the level signal Ltd_AUX becomes low. Therefore, Vcs when the switching element 206 is turned off becomes low, and the power supplied to the secondary side decreases.

[0037] FIG. 3 shows means for detecting the auxiliary winding voltage during the off period of the switching element 206.

[0038] Fig. 3(a) shows the configuration of the voltage detector 230 in the control unit 205. The auxiliary winding voltage divided by resistors 214 and 215 is connected to the voltage detector 230 via the AUX terminal of the control unit 205. Resistor 301 and capacitor 302 in the voltage detector 230 are filters, and the signal V1 passing through them is connected to the positive terminal of the first comparator 305. Also, the signal V1 is connected to the analog latch 303 that is periodically updated by the timer 304, and the output signal V2 of this is connected to the negative terminal of the comparator 305 and the second analog latch 307. The second analog latch 307 is periodically updated by the output of the AND element 306 to which the timer 304 and the comparator 305 are connected.

[0039] The operation will be described with reference to Figs. 3(b) and (c).

[0040] Fig. 3(b) shows the waveform of the signal V1.

[0041] First, the relationship between the auxiliary winding voltage and the secondary-side voltage will be described. The auxiliary winding voltage has a rectangular waveform that swings between positive and negative voltages in synchronization with the driving of the switching element 206. During the on period of the switching element 206, the voltage obtained by multiplying the voltage HV rectified by the diode bridge 202 and the capacitor 203 from the commercial power supply 201 by the turns ratio Na / Np of the transformer 204 appears as a negative voltage. During the off period of the switching element 206, when current is flowing through the secondary-side rectifying diode 216, the voltage obtained by multiplying the voltage obtained by adding the forward voltage VF of the secondary-side rectifying diode 216 to the secondary-side terminal voltage of the transformer 204 by the turns ratio Na / Ns of the transformer 204 appears as a positive voltage. Therefore, by detecting the auxiliary winding voltage during the off period of the switching element 206, the secondary-side voltage can be detected. Note that after the current flowing through the secondary-side rectifying diode 216 becomes zero, free oscillation occurs until the switching element 206 turns on.

[0042] The signal V1 is the auxiliary winding voltage described above, which is the auxiliary winding voltage divided by resistors 214 and 215 and passed through a filter composed of resistor 301 and capacitor 302, and is a waveform similar to the auxiliary winding voltage. The positive part of the auxiliary winding voltage is the voltage obtained by multiplying the secondary terminal voltage of the transformer 204 by the turns ratio Na / Ns of the transformer 204. However, since the VF of the rectifier diode 215 is added to the secondary terminal voltage of the transformer 204 in the secondary output voltage, it is desirable to detect the voltage at the position where the forward current of the rectifier diode 215 becomes zero and VF becomes zero, that is, the voltage at the shoulder position indicated by the circled mark in Fig. 3(b) immediately before free oscillation occurs.

[0043] Fig. 3(c) is used to show the procedure for detecting the voltage at the shoulder position indicated by the circled mark in Fig. 3(b). The signal V1 is periodically latched by the timer 304 by the analog latch 303 to output the signal V2. This signal V2 becomes stepped as shown by the dotted line at the uppermost stage of Fig. 3(c) and is connected to the negative terminal of the comparator 305. Since the signal V1 is connected to the positive terminal of the comparator 305, when the shoulder becomes steep and the difference ΔV between V1 and V2 reaches the inversion level of the comparator 305, the output will invert to L. The second analog latch 307 latches the output of the first analog latch 303 and is updated with a time delay for one latch as shown by V2 and V3 in Fig. 3(c). Also, when the output of the comparator 305 inverts to L by the AND element 306, the update of the second analog latch 307 stops, so that the voltage at the shoulder position of the signal V1 can be detected.

[0044] The voltage difference ΔV between the positive and negative input terminals at which the comparator 305 inverts may be set to an appropriate value considering the operation of the entire device. Also, in the discontinuous mode, in the auxiliary winding voltage waveform, an oscillating waveform can be seen during the period from when the current flowing through the rectifier diode 215 becomes zero until the switching element 206 turns on at the next drive timing. In order not to misdetect this part as the shoulder, it may be configured to latch at the first detection and hold until the switching element 206 turns on at the next drive timing.

[0045] As described above, since the secondary-side output voltage can only be detected when the switching element 206 is driven, the minimum value of the driving frequency is determined according to the specifications of the load connected to the power supply device, and it is impossible to drive at a slower speed than this.

[0046] [Embodiment] The configuration diagram of this embodiment is shown in FIG. 4.

[0047] Since the configuration of the 200 series in FIG. 4(a) has been described in FIG. 2, the description thereof is omitted here.

[0048] 401 is a selector that selects the driving signal of the switching element 206 generated by the method described conventionally and the driving signal of the switching element 206 generated in the form of this embodiment. 404 is an SR element that gives a signal for switching the selector 401. The set terminal S of the SR element 404 is connected via the edge element 403 after detecting that the time width of the driving signal VDRV, which is the output of the selector 401 and is the driving signal of the switching element 206, has become equal to or less than the time width predetermined by the timer 402, and is set when the time width of the driving signal VDRV becomes equal to or less than the predetermined time width. The reset terminal R of the SR element 404 is connected via the edge element 406 after detecting by the comparator 405 that the on-level of the auxiliary winding voltage waveform has become equal to or less than the predetermined level, and the SR element 404 is reset when the on-level of the auxiliary winding voltage waveform becomes equal to or less than the predetermined level.

[0049] With this configuration, when the on-level of the auxiliary winding voltage waveform is below a predetermined level, it is controlled by the drive signal VDRV generated by the conventional method. When the on-level of the auxiliary winding voltage waveform is above the predetermined level, it is controlled by the drive signal VDRV generated by the procedure in this embodiment described below. 409 is a means for generating the VDRV signal in this embodiment. According to the on-level of the auxiliary winding voltage waveform detected by 230, one set is selected from a plurality of sets each having a plurality of preset pulse waveforms as a set. In 409, the timing at which one set is selected from a plurality of sets each having a plurality of pulse waveforms as a set is the end of the drive of the selected set of pulse waveforms and the time when the SR element 404 is set.

[0050] Figure 4(b) shows the content of a set of a plurality of pulse waveforms pre-stored in the storage area in 409. The on-time Ton and off-time Toff of each of the first pulse to the nth pulse are stored according to the on-level AUX of the auxiliary winding voltage waveform latched by 230.

[0051] Figure 4(c) shows the configuration and waveform for generating the drive signal VDRV for driving the switching element 206 from the information of the on-time Ton and off-time Toff of each of the first pulse to the nth pulse. The on-time Ton and off-time Toff of each of the first pulse to the nth pulse described above are each connected to a timer. If they match the timer value, the SR element is set or reset. The waveform at this time is shown in the figure taking the case where the on-level of the auxiliary winding voltage waveform is V1 as an example. First, after the SR element becomes on and reaches the on-time Ton11 of the first pulse, the SR element is reset. Next, when the off-time Toff11 of the first pulse is reached, the second pulse is turned on, and thereafter it is repeated in the same manner. Finally, when Toff1n is reached by the drive of the nth pulse, an END signal is generated. As shown in Figure 4(a), this END signal is connected to the latch terminal of 409 via the OR element 408. When the END signal is generated, the on-level of the auxiliary winding voltage waveform is updated in 409.

[0052] According to the configuration described in FIGS. 4(a) to 4(c), the drive signal VDRV1 generated by the conventional method and the drive signal VDRV2 generated by the method described in the embodiment are selected according to the on-level of the auxiliary winding voltage waveform. The drive signal VDRV2 in the embodiment has a set of a plurality of pulses, and the on-time and off-time of each in the set are selected from the storage area according to the on-level of the auxiliary winding voltage waveform.

[0053] Note that the storage area is composed of a plurality of pulses from the first pulse to the nth pulse. If the Ton / Toff of the unnecessary pulses is set to zero, oscillation will not occur. Therefore, for example, if a single pulse is desired, setting the Ton / Toff of pulses other than the first pulse to zero will result in only one drive.

[0054] Using FIG. 5, the auxiliary winding voltage waveform when the load of the power supply device is small will be described.

[0055] Although the ideal auxiliary winding voltage waveform was described in FIG. 3(b), due to the capacitance of the snubber element of the power supply device, the leakage inductance of the transformer, etc., ringing occurs in the actual waveform when the auxiliary winding voltage changes from a negative voltage to a positive voltage as shown in FIG. 5(a). Since this ringing gradually converges, when the load of the power supply device is large enough and the current flowing through the secondary-side rectifying diode continues for a certain period of time, it is possible to detect the voltage at the portion that accurately reflects the secondary-side voltage, that is, the voltage at the shoulder where the auxiliary winding voltage changes from a positive voltage to a negative voltage.

[0056] FIG. 5(b) is the auxiliary winding voltage waveform when the load of the power supply device is small.

[0057] As described above, the ringing when the auxiliary winding voltage changes from a negative voltage to a positive voltage is caused by the capacitance of the snubber element of the power supply device, the leakage inductance of the transformer, etc., and does not change significantly even when the load of the power supply device becomes lighter. When the load is light, the time for power release to the secondary side also becomes shorter, that is, the time during which current flows through the rectifier diode on the secondary side becomes shorter, and free oscillation occurs earlier. As a result, before the ringing of the auxiliary winding voltage waveform converges, a change in the auxiliary winding voltage from a positive voltage to a negative voltage due to free oscillation occurs, and the voltage at the location accurately reflecting the secondary side voltage cannot be accurately detected.

[0058] FIG. 6 is a schematic diagram of the timing for detecting the auxiliary winding voltage during the off period of the switching element 206 in this embodiment.

[0059] Conventionally, the level of the auxiliary winding voltage has been detected at all drive timings when the auxiliary winding voltage is on, but in this embodiment, the level of the auxiliary winding voltage is detected at a drive timing once every several times. For the drive for detecting the level of the auxiliary winding voltage, the on-time of the switching element 206 is set so that the on-time of the auxiliary winding voltage is sufficient time for detection. This on-time does not need to be used for controlling the output voltage on the secondary side, and it is sufficient to obtain the time required for detecting the level of the auxiliary winding voltage. The energy generated by this drive is transmitted to the secondary side, but since the output voltage on the secondary side is not the control target, it becomes excess power and the output voltage on the secondary side exceeds the set value. Therefore, the drive following the drive for detecting the level of the auxiliary winding voltage does not perform level detection, that is, since the on-time of the auxiliary winding voltage can be short, the on-time of the switching element 206 can be set short, and it can be set so that the excess power in the previous drive is consumed.

[0060] The effect of this embodiment will be described with reference to FIG. 7 in comparison with the prior art.

[0061] FIG. 7(a) shows the drive in the conventional technology. The upper diagram of FIG. 7(a) shows the drive under no load. Conventionally, the auxiliary winding voltage level is detected in all drives, so even under no load, it is necessary to extend the on-time of the switching element 206 in order to secure the on-time width of the auxiliary winding waveform, resulting in a state in which excess power is supplied. If the peak current of the switching element 206 at the VDRV width required to measure the on-time of the auxiliary winding voltage is I, the power input to the secondary side is as follows. Note that here, 10 drives are used as an example, but the specific cycle is set to a time short enough to follow the changes in the load of the power supply device.

[0062]

number

[0063] This power is 5LI even when the power supply is unloaded. 2 Since the secondary side voltage continues to rise, a dummy resistor is provided on the secondary side to dissipate the excess power. Even when there is a load, the power dissipated by the dummy resistor is 5LI. 2 Since the load power Wout of the power supply and the load power 5LI due to the dummy resistor are added, the VDRV width is widened. 2 Combined power [Wout+5LI 2 This results in a decrease in the efficiency of the power supply. This is shown in the lower diagram of Figure 7(a).

[0064] Fig. 7(b) shows the driving in this embodiment. The upper figure in Fig. 7(b) is the driving under no load. In the embodiment, since the frequency of the driving for detecting the auxiliary winding voltage level is low, the dummy load can be made smaller than in the prior art, so the decrease in the output voltage Vout becomes gentler than in the case of the prior art. After driving at the minimum ON width for detecting the level of the auxiliary winding voltage, for example, when there is no load, by setting the driving width to zero, the surplus power due to this driving can be suppressed to a small value. Therefore, when the VDRV width of the driving without measuring the ON time of the auxiliary winding voltage is set to zero and there is no dummy resistor on the secondary side and the discharge is gentle, as an example, if the number of drivings is set to 1 / 4, the surplus power is as follows.

[0065] [Number] Therefore, by performing the control of the embodiment, the following power consumption becomes unnecessary.

[0066] [Number]

[0067] The lower figure in Fig. 7(b) is the driving when there is a load Wout. The ON width of the driving at the timing when the level detection of the auxiliary winding voltage is not performed is set to a width determined in advance according to the level of the auxiliary winding voltage. Thereby, a rapid increase in the secondary-side voltage Vout after driving can be suppressed. Note that since the degree of decrease in the output voltage Vout is faster than when there is no load, driving is performed at a time interval short enough to follow the change in the load of the power supply device as in the prior art. At this time, the driving width may be a driving width that can maintain the secondary-side voltage Vout at the minimum voltage required by the load of the power supply device until the driving with the driving width for detecting the next auxiliary winding voltage level is performed. Therefore, the total power supplied to the secondary side by the driving with the driving width for detecting the level of the auxiliary winding voltage and the subsequent driving with the driving width without detecting the level of the auxiliary winding voltage is [Wout + 1.25LI 2 , and by suppressing the surplus power to a low level, the efficiency of the power supply device can be improved.

[0068] The control flow will be described using the flowchart of Fig. 8.

[0069] First, the procedure for switching from the conventional primary-side control to the control of the embodiment will be described with reference to Fig. 8(a). First, in order to determine whether the width during AUX on is equal to or greater than the time width for measuring the level of the width during AUX on, the on-time Ton of the switching element 206, which is in a proportional relationship with the energy sent to the secondary side, is measured (800). It is determined whether the on-time Ton of the switching element 206 is equal to or greater than the reference on-time TonRef, which is the criterion for determining whether the width during AUX on is equal to or greater than the time width for measuring the level of the width during AUX on (801). If it is equal to or greater than TonRef, the process returns to 800 to continue measuring the time width of Ton. If the on-time Ton is less than TonRef in 801, it is determined that the width during AUX on cannot accurately detect the level during AUX on, and the selector 401 is switched to IN2 to which the drive signal VDRV of the switching element 206 generated in the embodiment is connected (801). The generation of the drive signal VDRV in the embodiment updates the level during AUX on (803) and is generated according to the procedure described in Figs. 4 to 7 according to the level during AUX on (804). Thereafter, 803 and 804 are repeated until the selector 401 is switched to IN1 in the procedure described later with reference to Fig. 8(b).

[0070] Next, the procedure for switching from the control of the conventional primary-side control to the control of the embodiment using FIG. 8(b) will be described. During the control of the embodiment, the level at the time of AUX on is updated (810), and the level at the time of AUX on and the reference voltage Vref are compared by the comparator 405 (811). When the level at the time of AUX on is higher than the reference voltage Vref, since the voltage drop on the secondary side is small, the load on the power supply is small and the time width of the drive signal VDRV is narrow, it is determined that a sufficient width at the time of AUX on for measuring the level at the time of AUX on cannot be obtained, and the selector 401 continues the control in the embodiment while selecting IN2 (811). If the level at the time of AUX on becomes lower than the reference voltage Vref, since the voltage drop on the secondary side is large, the load on the power supply is large and the time width of the drive signal VDRV is wide, it is determined that a sufficient width at the time of AUX on for measuring the level at the time of AUX on can be obtained, and this is detected by the comparator 405 (811). By resetting the SR element 404, the selector 401 switches to IN1 to which VDRV1 generated by the conventional primary-side control is connected (812).

[0071] With the above configuration, in the control by the voltage of the auxiliary winding, even at light load, even if the power consumption due to the dummy resistor for stabilizing the output voltage is low, the secondary-side voltage can be accurately detected, so the stability of the secondary-side voltage can be improved, and the power efficiency at light load can be improved. Also, since the stability of the output voltage can be improved in the entire load range, the application range of the primary-side control type power supply is expanded, contributing to the deletion and cost reduction of the feedback circuit (coupler, shunt regulator).

[0072] In this embodiment, the drive signal VDRV of the switching element 206 is generated by discrete components 409 with information of a plurality of pulses whose on-time and off-time are set in advance, but the same applies if it is generated by calculation using the level at the time of AUX on.

Description of Reference Numerals

[0073] 101 Inkjet recording apparatus 102 Carriage 103 Recording head 107 Conveyor roller 108 carriage motor 109 conveyance motor 201 commercial power supply 202 diode bridge 203 input capacitor 204 transformer 205 control unit

Claims

1. In a switching power supply that maintains a constant secondary-side voltage by detecting an auxiliary winding voltage on the primary side during a period when a rectifying diode on the secondary side conducts after the driving of a main switching element in the switching power supply is turned off, and controlling the driving of the main switching element according to this value, the driving of the main switching element is performed as a set of multiple drives, and the auxiliary winding voltage is detected only once immediately after driving within the set. In other drives within the set, the auxiliary winding voltage is not detected immediately after driving. A first control means is provided such that the time width of the drive when the auxiliary winding voltage is detected immediately after driving is longer than the time width of the drive when the auxiliary winding voltage is not detected immediately after driving. A power supply device characterized by this is provided.

2. In Claim 1 above, a second control means is provided that detects the auxiliary winding voltage on the primary side every time the driving of the main switching element in the switching power supply is turned off, and maintains a constant secondary-side voltage by controlling the driving of the main switching element according to the detected auxiliary winding voltage. The transition from the second control means to the first control means described in Claim 1 above is made when the on-width of the driving of the main switching element becomes equal to or less than a predetermined time width, and the transition from the first control means described in Claim 1 above to the second control means is made when the detection level of the auxiliary winding becomes equal to or less than a predetermined level. A power supply device characterized by this is provided.

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