Power supply device

Abstract

To reduce a power threshold value of overload protection when an output voltage is switched to a lower voltage, in an AC DC power supply which switches over its output voltage by switching a reference voltage on the secondary side.SOLUTION: In a conventional power supply device, Vcc for a control IC was generated from auxiliary winding on the primary side, and an output voltage on the secondary side was estimated from a Vcc voltage. A threshold value for overload protection was able to be switched over based on the estimated voltage. However, if a changeover ratio of the output voltage is large, it is necessary to provide a regulator for the Vcc, and the output voltage cannot be estimated from the Vcc. Therefore, a method for detecting "overload at a low-voltage condition" from transformer current Ip and a feedback signal FB from the secondary side is proposed. Using means for determining a continuous mode from the Ip, means for storing an FB value at the start timing of the power supply to the secondary side, means for generating a threshold value from Ip information, and the stored FB value, the "overload at the low-voltage condition" can be detected from the threshold value and the FB value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a flyback switching power supply with an output voltage switching function in a single converter for converting commercial AC to DC.

Background Art

[0002] A flyback type AC-DC power supply is often used as a power supply for devices such as inkjet printers. Among flyback methods, the current mode PWM method is often used for AC-DC power supplies of several W to about 100 W.

[0003] Patent Document 1 describes a power supply of a current mode flyback type having an output voltage switching function in a single converter.

[0004] FIG. 8 of Patent Document 1 describes a configuration for performing voltage switching with a switch 25.

[0005] Not only inkjet printers, but many devices that require mechanism driving are often equipped with a voltage switching function. The reason for voltage switching is to reduce power consumption during standby.

[0006] Generally, a high voltage (32V) is required to drive a printing motor, and 3.3V is required to drive a control circuit.

[0007] During printer operation, 32V is output from the AC-DC power supply and used to drive the motor.

[0008] Also, part of the power is converted from 32V to 3.3V by a DC-DC converter on the control circuit board and used as the power supply for the control circuit.

[0009] During standby, it is desired to reduce power consumption as much as possible. Therefore, for example, 8.8V is output from the AC-DC power supply and converted to 3.3V for the control circuit.

[0010] At this time, by reducing the input voltage of the DCDC converter, the conversion efficiency of the DCDC converter is improved and the standby power is reduced. Thus, a voltage switching function is provided to reduce power consumption.

[0011] A general current-mode flyback power supply is equipped with an overload protection function.

[0012] For example, if the maximum power consumption during motor drive is 70W, overload protection operates at an output of about 80W and is designed to shut down (stop the output).

[0013] In the normal mode of the ACDC power supply during printer operation, since the output voltage is 32V, it will shut down when the load current exceeds 2.5A.

[0014] However, when outputting 8.8V in the standby mode, it will shut down when the load current is 9.1A or more. The standby mode should consume less power, so 9.1A is abnormal. That is, it is desirable to shut down when the load current is about 2 - 3A.

[0015] In Patent Document 1, to address this issue, the output power is restricted in the standby mode. If an overload occurs with the output power restricted in the standby mode, the output voltage will drop and stop.

[0016] Figure 8 of Patent Document 1 is a general current-mode flyback power supply.

[0017] The primary-side control IC controls the overload protection.

[0018] The secondary-side Vout changes depending on whether it is the normal mode or the standby mode (mode switching is performed by switch 25).

[0019] In this configuration, on the primary side, the secondary-side voltage Vout cannot be directly known. Information from the secondary side is only the FB signal from the photocoupler 21, and the FB signal indicates the excess or deficiency of voltage and does not indicate the absolute value of Vout.

[0020] Then, how does one determine the mode on the primary side?

[0021] Therefore, the output voltage is known from the Vcc voltage of the control IC, and the mode is determined. The Vcc voltage is approximately equal to the AUX voltage, and the AUX voltage is proportional to the output voltage. Therefore, the mode is determined by comparing the Vcc voltage with an appropriate predetermined value.

[0022] Specifically, at time a in FIG. 6 of Patent Document 1, the switching to the standby mode is performed, and when Vcc falls below Vthvcc_l, it is determined that the standby mode is entered. At this timing, the upper limit of the switching frequency is lowered (switched to fswmax_l), and at the same time, the current limit of the FET is lowered (switched to Vthocp_l).

Prior Art Documents

Patent Documents

[0023]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0024] However, this method has a problem in that it cannot be applied to a power supply with a large switching voltage ratio (such as a power supply for an inkjet printer).

[0025] In Patent Document 1, Vout switches between 20V and 10V, with a voltage ratio of 2 times. However, in an inkjet printer or the like, for example, when it is 32V and 8.8V, it is necessary to switch with a voltage ratio of 3.6 times. On the other hand, for the power supply voltage Vcc of the IC, a voltage capable of driving the switching element FET17 is required, and about 13V is desirable. Therefore, Standby mode: 8.8V output, Vcc = 13V Normal mode: 32V output (3.6 times that of the standby mode), Vcc = 46.8V (3.6 times that of the standby mode) Although such a design is desired, in this design, it is necessary to use a high breakdown voltage specification for the Vcc terminal of the IC, resulting in an expensive design.

[0026] Therefore, in a conventional power supply for an inkjet printer, a linear regulator is inserted between the AUX voltage and Vcc to keep the Vcc voltage constant regardless of the AUX voltage, that is, regardless of the voltage switching state. For example, it is set to 15V. That is, there is a problem that the mode cannot be determined from the Vcc voltage as in Patent Document 1.

[0027] An object of the present invention is to provide a power supply device capable of determining an overload state in the standby mode from the FB signal and the Vcs signal and shutting down.

Means for Solving the Problems

[0028] A method for detecting on the primary side that VM is 8.8V and overloaded from the Vcs signal and the FB signal in a configuration where the VM voltage cannot be determined from Vcc is proposed.

[0029] That is, the ACDC power supply of the present invention is characterized by means for determining that it is in the continuous mode from the Vcs signal, means for storing the FB value at the timing of starting power supply to the secondary side, means for generating a threshold value from the Vcs information, means for determining the mode (high or low) of the output voltage from the stored FB value and the previous threshold value, and determining that it is in an overloaded state when it is determined that the output voltage is in a low mode and in the continuous mode.

Effects of the Invention

[0030] It is possible to determine the overload state in the standby mode from the FB signal and the Vcs signal, and shut down can be performed.

Brief Explanation of Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Modes for Carrying Out the Invention

Examples

[0032] Figure 2 is a perspective view showing the mechanism of the printer.

[0033] 108 is a recording head that ejects ink according to the inkjet method to perform recording. A plurality of ink tanks 123 are mounted on the head 108, and the head 108 is further mounted on the carriage 119.

[0034] The driving force generated by the CR motor 114 is transmitted to the carriage 119 by the transmission mechanism 120, and the carriage 119 reciprocates in the direction of arrow A.

[0035] At the time of recording, the paper P is fed by the paper feeding mechanism 121 and conveyed to the recording position.

[0036] At the recording position, the head 108 is scanned, and recording is performed by ejecting ink from the head 108 onto the paper P.

[0037] 122 is a conveyance roller that conveys the paper P and is driven by the paper conveyance motor 116. The paper P is conveyed between the scans of the head 108.

[0038] The CR motor 114 and the paper conveyance motor 116 are DC motors and require a large current during acceleration. Also, in order to improve the printing throughput, the two motors may be simultaneously driven for acceleration. At this time, the power consumption of the device becomes maximum.

[0039] The control of this motor drive is executed by the control of the CPU 203 described later.

[0040] Figure 3 is a block diagram of the electrical system of the printer to which the present case is applied.

[0041] 201 is an ACDC power supply for converting commercial AC to DC and supplying it to the inside of the device.

[0042] In this embodiment, the supply destinations of the VM are the DCDC converter 218, the inkjet head 214, and the motor driver 216.

[0043] The DCDC converter 218 supplies 3.3V, 1.1V, etc. to the block 219 that operates at a low voltage.

[0044] The following is an explanation of each part.

[0045] 202 is a System on Chip (SOC) that integrates on one chip the logic circuit, external I / F, etc. necessary for controlling each part of the device.

[0046] Inside 202, there are a CPU 203 that controls each part, 207, 209, 210, 217 which are I / Fs with external devices, a GPIO (General Purpose I / O) 208 that controls external ports, a data processing block 205 that performs image processing, etc., an external I / F 206 that receives print data from an external device, a clock generator 204 that supplies clocks to each part, etc. Each block is connected by an internal bus.

[0047] A PW_CONT signal is output from the GPIO 208 and input to the ACDC power supply 201. The PW_CONT signal is a signal that switches the output voltage of the ACDC power supply 201.

[0048] 202 requires a 3.3V power supply for I / O and a 1.1V power supply for internal logic.

[0049] 211 is a ROM that stores the control program of the CPU 203.

[0050] 212 is a RAM used as a work area and data buffer for program execution.

[0051] 214 is an inkjet head that ejects ink droplets by heating the heater provided for each nozzle.

[0052] 216 is a motor driver that drives the motors 114 and 116.

[0053] Figure 1 is a first embodiment of the ACDC power supply 201 to which the present invention is applied.

[0054] The operation of the AC-DC power supply 201 will be described below.

[0055] The part inside the dashed line is the control IC.

[0056] The voltage from the commercial power supply is rectified by the bridge diode BD1 and charges C1. This voltage is switched at several tens of kHz by the switching of Q1 under the control of the PWM control block PWM1 inside the control IC.

[0057] P1 is the primary winding of the transformer TR1, S1 is the secondary winding, and A1 is the auxiliary winding that generates the power supply voltage Vcc of the control IC.

[0058] During the period when Q1 is on, energy is accumulated in the transformer from the primary winding P1, and during the off period, energy is released to the secondary winding S1 and the auxiliary winding A1. By controlling the on-time duty, this accumulation amount can be controlled, and the output voltage is stabilized by supplying energy according to the load.

[0059] Here, the basic operation of the current-mode flyback power supply will be described.

[0060] First, the primary side will be described.

[0061] During the period when Q1 is on, the current flowing through P1 increases linearly, and its current value is converted into voltage information by Rcs to become the voltage Vcs. Vcs is compared with the voltage FB by the comparator CMP1. FB is the voltage of the feedback information obtained from the secondary side, which is high when the secondary side voltage is insufficient and low when the secondary side voltage is excessive. Then, when Vcs linearly rises and becomes equal to FB, the comparator CMP1 detects the coincidence, and the PWM control unit PWM1 controls the gate voltage of Q1 to turn Q1 off. At this time, the magnetic field energy accumulated in the core of the transformer is proportional to the square of the P1 current. This energy is released to the secondary side S1 (and also to A1) during the off period of Q1.

[0062] That is, when the secondary-side voltage is insufficient (lower than a predetermined value), FB increases, the energy stored in the transformer increases, the energy supply to the secondary side increases, and as a result, the secondary-side voltage is stabilized. When the secondary-side voltage is excessive, the reverse movement occurs and the secondary-side voltage is also stabilized.

[0063] Next, the operation of the secondary side will be described.

[0064] The current Is output to the secondary side is smoothed by a diode and a capacitor to become the output voltage VM.

[0065] AMP1 is an error amplifier (actually a shunt regulator) that compares VM with the reference voltage. The reference voltage is 32V or 8.8V.

[0066] Here, for example, when VM rises above the reference voltage, the following events occur sequentially.

[0067] The VM voltage rises, the difference from the reference voltage increases, the LED light amount of PC1 (photo coupler) increases, the collector current of the photo transistor of PC1 increases, FB decreases, the peak of the P1 current decreases, the energy supply amount to the secondary side decreases, and the VM voltage drops. That is, the voltage is stabilized.

[0068] Such a feedback operation for stabilizing the secondary-side voltage occurs.

[0069] The above is the basic operation of the current-mode flyback power supply.

[0070] The reference voltage is selected as 32V or 8.8V. The selection is made by switching SW1 according to the PW_CONT signal output from SOC202.

[0071] In the normal operating state, 32V is selected, and in the power-saving standby state, 8.8V is selected.

[0072] Next, the current waveform on the primary side will be described with reference to Fig. 4 for the normal mode and Fig. 5 for the power-saving mode. The figures show the waveforms for three cycles each.

[0073] The solid line is the current Ip flowing through P1, Q1, and Rcs, which is the current flowing when Q1 is ON.

[0074] The dashed line is the current waveform output on the secondary side converted to the primary side by the turns ratio of the transformer. The secondary current flows when Q1 is OFF.

[0075] Magnetic energy is accumulated in the core of the transformer during the period when Q1 is ON, and the energy accumulated on the secondary side is released during the period when Q1 is OFF. Energy is transmitted from the primary side to the secondary side in the form of a so-called bucket relay.

[0076] The three waveforms are the waveforms when the voltage HV of C1 is 90V, 120V, and 230V respectively.

[0077] The solid line in Fig. 4 is the current waveform of Ip, and the conditions are an output voltage of 32V, a primary inductance of the transformer of 390 μH, a switching frequency of 65 KHz, and a load of 50W. The peak of Ip is controlled to be about 2A by feedback from the secondary side.

[0078] When a voltage is applied to an inductor (in this case, the transformer), the current increases linearly while energy is accumulated. Since the rate of increase is proportional to the applied voltage, if HV is high, it rises steeply as shown in the figure, and if HV is low, it rises gently.

[0079] The dashed line is the secondary current Is converted to the primary side by the turns ratio of the primary:secondary of the transformer.

[0080] Hereafter, for the sake of simplicity, this dashed line will be referred to as the waveform of the "secondary side current".

[0081] The slope of this secondary side current is proportional to the output voltage, but since it is fixed at 32V, it always decreases at a constant slope regardless of HV.

[0082] When HV = 230 and HV = 120, Is reaches zero every cycle, and such a state is called the discontinuous mode. On the other hand, when HV = 90V, the next cycle starts before reaching zero. (Point B). Such a state is called the continuous mode.

[0083] Figure 5 shows the waveforms with an output voltage of 8.8V, a switching frequency of 65KHz, and a load of 3W assuming a power-saving standby state.

[0084] Due to the low peak current, it enters the discontinuous mode.

[0085] Comparing Figure 4 and Figure 5 here, it can be seen that there is a difference in the slope of the secondary-side current (dashed line). As already described, since the slope of this straight line is proportional to the output voltage, it is gentler at the 8.8V output.

[0086] If the slope of this secondary-side current can be detected on the primary side, it is possible to determine whether the output voltage is 32V or 8.8V. And to detect the slope, it is necessary to know the start point and the end point of the straight line. In the waveform of Figure 5, the start point is point A and its current value can be known on the primary side. However, the end point C, the timing when the current becomes zero, cannot be known on the primary side. That is, the position of point C cannot be specified. Therefore, in the case of Figure 5, the slope cannot be detected.

[0087] However, there is a case where this slope can be detected on the primary side. The case is shown in Figure 6.

[0088] Figure 6 shows the Ip current waveforms at an 8.8V output, HV = 90V, and loads of 3W, 6W, and 12W. When the load is 12W, it is in the continuous mode. At this time, the slope of the straight line (dashed line) of the secondary-side current can be detected on the primary side. That is, the slope can be detected by knowing the start point at point A and the current value at the end point at point B.

[0089] Then, what is the relationship between point A and point B? It is shown in Figure 7.

[0090] For example, looking at the case where point B is 0.2 A in continuous mode, in the power-saving mode (8.8 V output), point A is around 1 A and is almost constant regardless of HV. The waveform in the power-saving mode is shown in Fig. 8. In normal mode, point A changes depending on HV. The waveform in normal mode is shown in Fig. 9.

[0091] It can be seen from Fig. 7 that the plot areas of the power-saving mode and the normal mode do not overlap and are distinguishable.

[0092] Returning to Fig. 7, a method for determining overload during the power-saving mode, which is the object of the present application, will be described.

[0093] All the points plotted in Fig. 7 are the relationships between point A and point B in continuous mode. Looking at the data at the left end here, when point B is 0.2 A in the power-saving mode, the supply power is 11 - 14 W, and it is already in an overload state as the power-saving mode.

[0094] That is, if it is in continuous mode and power-saving mode, it can be judged as overload.

[0095] The fact that it is in continuous mode can be known from the current value of point B.

[0096] And the fact that it is in the power-saving mode can be judged by the slope of the secondary-side current at the time of point B.

[0097] The overload protection operation in the power-saving mode of the present invention will be described below with reference to Fig. 1.

[0098] Since the explanation of the main part of Fig. 1 has already been made, the explanation of the remaining part will be given here.

[0099] It has been explained that for CMP1, Ip is controlled by the over-voltage / under-voltage information (FB signal) from the secondary side to achieve stabilization. CMP2 is provided to limit the maximum value of Ip on the primary side. Even if the FB voltage becomes abnormally large due to a fault or the like, the maximum value of Ip can be controlled. In this embodiment, the maximum value of Ip is set to 3A. When Vcs reaches FB or equivalent to 3A, a high level is output from OR1, and Q1 is controlled to be OFF by PWM1 (as a result, the output waveforms of CMP1 and CMP2 become pulses).

[0100] Here, AND1 blocks the transmission of the output of OR1 to PWM1 while the blanking signal is high. The blanking signal is output from PWM1, and its waveform becomes high for a predetermined period from the start of Q1 driving as shown in FIG. 10. Noise occurs in the Vcs waveform for a certain period from the ON of Q1. During that time, CMP1 or CMP2 may react due to the noise, and AND1 blocks it so that it is not transmitted to PWM1 during the blanking period.

[0101] Next, the inside of the dashed line is the additional part according to the present invention.

[0102] It stores the current value at point A and determines whether it is in the power-saving mode and the continuous mode at the time of point B.

[0103] The determination is made by evaluating the output of a circuit composed of S&H, CMP3, CMP4, AND2, etc. at the timing of point B. However, as shown in FIG. 10, noise is present in the Vcs signal at point B. Therefore, the determination is made at the falling edge of the blanking signal without noise. That is, the falling edge of the blanking signal is used as the CLK of DFF1, and the output of AND2 at that timing is used as the determination result for that cycle.

[0104] The connection of the determination circuit will be described.

[0105] S&H is a sample & hold circuit provided for the FB signal. While Q1 is ON, it samples the voltage of FB and holds the FB voltage at the moment when Q1 is turned OFF. Since FB and Vcs match at the moment when Q1 is turned OFF, it holds (stores) the Vcs voltage corresponding to the current value at point A. The output of S&H is connected to one side of CMP3 through a level shift (voltage down) circuit corresponding to 1.4A. The other side of CMP3 is connected with a threshold value which is Vcs multiplied by the gain G. In this embodiment, G = 1 is set.

[0106] The concept of making a determination at the timing of point B is shown in Fig. 11.

[0107] So far, it has been stated that "detecting the slope" is sufficient. However, in this embodiment, instead of directly grasping the slope as a quantity, it makes a determination by utilizing the fact that the difference in slope appears as the current value at point A.

[0108] For example, when explaining the case where point B is 0.8A, in the normal mode, since the slope of the secondary - side current is large, point A is 2.5A and it decreases to 0.8A at point B. In the power - saving mode, since the slope of the secondary - side current is small, what was around 1.5A at point A decreases to 0.8A at point B.

[0109] That is, since the magnitude of the slope appears as the magnitude of the current value at point A, by comparing the current value at point A with the threshold value, it is possible to determine the magnitude of the slope, that is, to determine the mode.

[0110] Specifically, since the current value (voltage corresponding thereto) at point A is stored in S&H at the timing of point B, this voltage at point A is decreased by an amount corresponding to 1.4A and further compared with an appropriate threshold value. If it is higher than the threshold value, it can be determined that it is the normal mode; if it is lower, it is the power - saving mode.

[0111] This mode determination can be achieved by CMP3 in Fig. 1. If the output of CMP3 is High, it indicates the power - saving mode; if it is Low, it indicates the normal mode.

[0112] When the current at point B is greater than zero, it is determined to be in the continuous mode. However, when the current at point B is close to zero, it may be misjudged due to the influence of noise. Therefore, when the current at point B is equal to or greater than a predetermined value (0.2 A or more in this embodiment), it is desired to be determined to be in the continuous mode. For this purpose, Vcs is connected to one side of CMP4 in FIG. 1 and compared with the voltage corresponding to 0.2 A. If CMP4 outputs High, it means that Ip (Vcs) is equal to or greater than the predetermined value, and it is possible to determine that it is in the continuous mode without being affected by noise.

[0113] Therefore, if CMP3 outputs High and CMP4 outputs High at the timing of point B, the output of AND2 will be High. The result evaluated at the timing of point B (the end timing of the blanking period) is output from DFF1. Although the output of DFF1 is updated every cycle, if it remains High continuously for a predetermined period, it is determined to be an overload state in the power-saving mode, and the power supply is shut down.

[0114] Since it is common to stop when an abnormal state is detected for a predetermined time, the explanation of the method is omitted.

[0115] As described above, it is possible to determine the power-saving mode from the slope of the secondary-side current, that is, the current values at point A and point B on the primary side, and to determine that it is in an overload state when it is in the continuous mode.

[0116] In this embodiment, it is possible to determine an overload when the load is about 13 W or more (about 1.5 A in terms of current) in the power-saving mode with an AC230V input.

Embodiment

[0117] FIG. 12 shows a second embodiment of the present invention.

[0118] The concept is the same as that of the second embodiment, but the difference is that a discharge circuit is provided instead of a level shift circuit for the output of the S&H. The S&H stores the voltage at point A in an internal capacitor. During the period when Q1 is off, this capacitor is discharged by a constant current circuit to lower the voltage. Thereby, the same effect as lowering the current value information at point A by a level shift circuit can be obtained.

[0119] The same result as that of the first embodiment can be obtained with this configuration.

Industrial Applicability

[0120] An AC-DC power supply that reduces the output voltage in a power-saving mode (standby) in a flyback power supply such as a printer.

Explanation of Reference Numerals

[0121] BD1 Diode bridge C1 Capacitor Q1 Switching FET Rcs Current detection resistor P1 Primary winding S1 Secondary winding PC1 Photo coupler AMP1 Error amplifier (shunt regulator) Reg Series regulator SW1 Switch PWM1 PWM control unit OSC1 Oscillator OR1 OR circuit AND1, AND2 AND circuits S&H Sample & Hold circuit DFF1 D-Flip Flop 108 Recording head 114 CR motor 116 Paper transport motor 119 Carriage 120 Transmission mechanism 121 Paper feeding mechanism 122 Conveyor roller 123 Ink tank P Paper 201 AC / DC Power Supply 202 SOC 203 CPU 204 Clock Generator 205 Data Processing Block 206 External Interface 207, 209, 210, 217 Interface Block 208 GPIO 211 ROM 212 RAM 214 Inkjet Head 216 Motor Driver 218 DCDC Converter 219 Block Operable at Low Voltage

Claims

1. A flyback type AC-DC power supply capable of switching the output voltage by switching the reference voltage on the secondary side, means for detecting the current Ip of the primary side transformer, means for detecting the over / under voltage information FB of the voltage from the secondary side, comprising: means for determining that it is in the continuous mode from Ip, means for storing the FB value at the power supply start timing to the secondary side, means for generating a threshold value from the Ip information, means for determining the mode (high / low) of the output voltage from the stored FB value and the previous threshold value, An AC-DC power supply characterized in that it is determined that the output voltage is in a low mode and that it is overloaded when it is in the continuous mode.

2. The AC-DC power supply according to claim 1, characterized in that the stored FB value is reduced (level-shifted) by a predetermined value and compared with the threshold value.

3. The AC-DC power supply according to claim 1, characterized in that the stored FB value is compared with the threshold value after discharging the stored capacitor with a constant current.

Images