Power supply unit and image forming apparatus

Abstract

To appropriately protect a power supply device in accordance with an overload state that has occurred.SOLUTION: A switching control unit 400 performs a first process for maintaining a state in which a switching operation is stopped when an overload state is detected from when the switching operation is started to when an output voltage Vout1 becomes a target voltage and performs a second process for stopping the switching operation and restarting the switching operation after a first time has passed when an overload state is detected after the output voltage Vout1 has become the target voltage.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power supply device and an image forming apparatus, and more particularly to control at the time of overload detection in a power supply device having an overload protection function, for example.

Background Art

[0002] Some switching power supplies have a function of determining that an overload state has occurred when detecting overcurrent or overpower, and stopping the switching operation to protect the switching power supply. At this time, for example, Patent Document 1 proposes a configuration for selecting either a restart protection method or a latch protection method. Specifically, in the case of a mild overload, a restart protection method in which the switching operation is started after a predetermined time has elapsed is selected, and in the case of a severe overload, a latch protection method in which the stop state of the switching operation is maintained until the power supply of the control unit becomes below a predetermined voltage is selected.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, protection may be required even when the alternating current (AC) voltage of the AC power supply drops and the current on the primary side increases, resulting in an overload state. At this time, for example, when a severe overload occurs and the latch protection method is selected, the switching stop state is maintained even for a temporary drop in the AC voltage. Therefore, in order to discharge the voltage of the control unit under latch protection, it is necessary for the user to stop the supply of the AC voltage by unplugging the plug from the outlet and wait for a certain period of time. Thus, it is not preferable from the viewpoint of user-friendliness to require the user to take actions such as unplugging the plug every time a temporary drop in the AC voltage occurs.

[0005] Furthermore, when the restart protection method is selected during a minor overload, there is the advantage of being able to automatically recover from a temporary drop in AC voltage. On the other hand, if a minor overload condition occurs continuously, the system will repeatedly automatically recover and then stop switching, which may cause the output voltage to become unstable. In that case, for example, if an image forming machine is equipped with such a power supply, the voltage on the display panel of the image forming machine will become unstable, and the displayed image will also become unstable, which may confuse the user. In addition, repeated overload conditions raise concerns about the deterioration of the power supply's components. For this reason, it is necessary to appropriately protect the power supply according to the type of overload that occurs.

[0006] This invention was made under such circumstances and aims to appropriately protect the power supply device in accordance with the overload conditions that occur. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present invention has the following configuration. (1) A power supply device comprising a transformer having a primary winding, a secondary winding, and an auxiliary winding; a switching element connected to the primary winding and performing a switching operation; and a first control means that operates when a first voltage is supplied and controls the switching operation of the switching element, wherein the power supply device supplies an output voltage corresponding to the voltage induced in the secondary winding, and further comprising a first detection means for detecting an overload condition, wherein if the first detection means detects an overload condition from the start of the switching operation until the output voltage reaches a target voltage, the first control means executes a first process to maintain the state in which the switching operation is stopped; and if the first detection means detects an overload condition after the output voltage has reached the target voltage, the first control means executes a second process to stop the switching operation and restart the switching operation after a first time has elapsed. Then, after the switching operation has started and the soft-start operation has elapsed, the first detection means detects the overload condition. A power supply device characterized by the following features. (2) A power supply device comprising a transformer having a primary winding, a secondary winding and an auxiliary winding, a switching element connected to the primary winding and performing a switching operation, and a first control means that operates when a first voltage is supplied and controls the switching operation of the switching element, wherein the power supply device supplies an output voltage corresponding to a voltage induced in the secondary winding, and further comprising a first detection means for detecting an overload state, wherein the first detection means detects an overload state from the start of the switching operation until the output voltage reaches a target voltage, executes a first process to maintain the state in which the switching operation is stopped, executes a second process to stop the switching operation and restart the switching operation after a first time has elapsed, and after the switching operation has started and the output voltage has become a starting voltage lower than the target voltage, the first detection means detects the overload state. ( 3) A transformer having a primary winding, a secondary winding and an auxiliary winding; a switching element connected to the primary winding and performing a switching operation; a first control means that operates when a first voltage is supplied and controls the switching operation of the switching element; a power supply device that supplies an output voltage corresponding to the voltage induced in the secondary winding; an image forming means that forms an image on a recording material; and a second control means that controls the power supply device and the image forming means. An image forming apparatus comprising the power supply unit having a first detection means for detecting an overload condition, the first control means, if it detects an overload condition by the first detection means from the start of the switching operation until the output voltage reaches the target voltage, executes a first process to maintain the state in which the switching operation is stopped, and if it detects an overload condition by the first detection means after the output voltage reaches the target voltage, executes a second process to stop the switching operation and restart the switching operation after a first time has elapsed. Then, after the switching operation has started and the soft-start operation has elapsed, the first detection means detects the overload condition. An image forming apparatus characterized by the following: (4) An image forming apparatus comprising: a transformer having a primary winding, a secondary winding and an auxiliary winding; a switching element connected to the primary winding and performing a switching operation; a first control means that operates when a first voltage is supplied and controls the switching operation of the switching element; a power supply device that supplies an output voltage corresponding to the voltage induced in the secondary winding; an image forming means that forms an image on a recording material; and a second control means that controls the power supply device and the image forming means, wherein the power supply device has a first detection means for detecting an overload state; the first control means, if it detects an overload state by the first detection means from the start of the switching operation until the output voltage reaches a target voltage, executes a first process to maintain the state in which the switching operation is stopped; if it detects an overload state by the first detection means after the output voltage has reached the target voltage, executes a second process to stop the switching operation and restart the switching operation after a first time has elapsed; and the first detection means detects the overload state after the switching operation has started and the output voltage has become a starting voltage lower than the target voltage. [Effects of the Invention]

[0008] According to the present invention, the power supply device can be appropriately protected according to the overload condition that occurs. [Brief explanation of the drawing]

[0009] [Figure 1] Diagram showing the image forming apparatus of Example 1 [Figure 2] Circuit diagram showing the power supply unit of Example 1 [Figure 3] Internal block diagram of the switching control unit of Example 1 [Figure 4] Flowchart showing the control of Example 1 [Figure 5] Flowchart showing the control in Example 2 [Figure 6] Diagram showing the monitor circuit and the transmission circuit of Example 2. [Figure 7] Circuit diagram showing the power supply unit of Example 3 [Figure 8] Internal block diagram of the switching control unit in Example 3 [Modes for carrying out the invention]

[0010] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings using examples. [Examples]

[0011] [Image forming apparatus] The present invention will now describe the case in which the power supply unit 100 is applied to an image forming apparatus. Figure 1 shows an overall view of a laser beam printer 700 as an example of an image forming apparatus. The laser beam printer 700 (hereinafter referred to as the printer 700) includes a photosensitive drum 701 which is an image carrier on which an electrostatic latent image is formed, a charging unit 702 which uniformly charges the photosensitive drum 701, and a developing unit 703 which develops the electrostatic latent image formed on the photosensitive drum 701 with toner. The toner image developed on the photosensitive drum 701 is transferred to a sheet P, which is a recording material supplied from a cassette 704, by a transfer unit 705, the toner image transferred to the sheet P is fixed by a fuser 706 heated by a heater 117, and discharged to an output tray 707. The printer 700 also includes a power supply unit 100 which supplies power to a drive unit (not shown) such as a motor and a control unit 501 which has a CPU 500 as a second control means. The control unit 501 and CPU 500 control the image forming operation by the image forming unit, the transport operation of the sheet P, the temperature of the heater 117, etc. The image forming unit, which is the image forming means, includes at least a photosensitive drum 701, a developing unit 703, and a transfer unit 705.

[0012] [Power supply] FIG. 2 is a circuit block diagram showing the power supply device 100 of Example 1. In FIG. 2(a), the case where the power supply device 100 is a flyback type switching power supply will be described. An AC voltage is supplied to the power supply device 100 from an AC power supply 101 (commercial power supply). The AC voltage supplied to the power supply device 100 is supplied to a diode bridge 103 via a fuse 102. When the AC voltage is rectified by the diode bridge 103, a pulsating DC waveform with one side being positive is obtained. The AC voltage having the pulsating DC waveform is smoothed into a substantially DC voltage by the action of a primary electrolytic capacitor 104. Here, the substantially DC voltage is not limited to the case where it is strictly DC. The voltage across both ends of this primary electrolytic capacitor 104 (hereinafter referred to as the voltage across both ends) is defined as Vdc, and the potential of the minus terminal of the primary electrolytic capacitor 104 is defined as DCL.

[0013] The smoothed AC voltage (hereinafter referred to as the AC voltage Vdc) is input to the primary winding Np of a transformer 108. Thereafter, the AC voltage Vdc is fed back from the minus terminal of the primary electrolytic capacitor 104 and the bridge diode 103 to the AC power supply 101 via a field effect transistor (hereinafter referred to as FET) 107 which is a switching element. The on / off timing of the FET 107 is controlled by a switching control unit 400.

[0014] The switching control unit 400, which is the first control means, has an ST terminal, a SW terminal, a FB terminal, an IS terminal, a Vss terminal, a Vcc terminal, an SS terminal, and a Lat terminal. An AC voltage Vdc is connected to the ST terminal via a resistor 105 to supply the power for the operation of the switching control unit 400. The SW terminal is connected to the gate terminal of the FET 107 via a resistor 106, and a voltage of high level (about 10V) or low level (about 0V) is supplied as a signal (hereinafter referred to as a drive signal) for driving (switching) the FET 107 from the SW terminal. The FET 107 turns on (conducts) when the drive signal is at a high level and turns off (non-conducts) when it is at a low level. After the switching of the FET 107 starts, the voltage induced in the auxiliary winding Nb of the transformer 108 is rectified by the diode 109 and the electrolytic capacitor 110 into a substantially DC voltage and supplied to the Vcc terminal. Thereby, the power supply device 100 continuously performs a switching operation. The Vss terminal of the switching control unit 400 is a ground terminal and is connected to DCL.

[0015] The voltage induced in the primary winding Np of the transformer 108 by the switching of the FET 107 is voltage-converted to the secondary winding Ns, and its power is rectified and smoothed by the rectifier diode 151 and the electrolytic capacitor 152, so that the output voltage Vout1 becomes a predetermined DC voltage. The output voltage Vout1 is output to a load 158 outside the power supply device 100. The load 158 has, for example, a drive unit such as the motor of the printer 700 in FIG. 1. The output voltage Vout1 is connected to the voltage feedback unit 150. The voltage feedback unit 150 outputs information indicating whether the output voltage Vout1 is a predetermined voltage to the switching control unit 400.

[0016] Specifically, the voltage obtained by dividing the output voltage Vout1 by resistors 156 and 157 is input to the REF terminal of shunt regulator 155. The shunt regulator 155 has a photodiode 154d of photocoupler 154 connected to its K terminal, and its A terminal is grounded (GND). When the output voltage Vout1 is lower than a preset target voltage (hereinafter referred to as the target voltage) for the output voltage Vout1, the shunt regulator 155 lights the photodiode 154d of the photocoupler 154 via resistor 153. At this time, the phototransistor 154t of the photocoupler 154 turns on, and the primary capacitor 111 connected to the FB terminal of the switching control unit 400 discharges.

[0017] As a result, a voltage can be output as an electrical signal between the FB terminal and the Vss terminal of the switching control unit 400 (hereinafter referred to as between FB-Vss). The switching control unit 400 determines the on / off timing of FET107 based on the voltage value between FB-Vss and the voltage value of resistor 112 (hereinafter referred to as the IS terminal voltage), which is a second detection means for detecting the current flowing through FET107. Thereby, the switching control unit 400 controls so that the output voltage Vout1 becomes a predetermined voltage value (in other words, the target voltage). The SS terminal and the Lat terminal of the switching control unit 400 will be described later.

[0018] Also, as shown in FIG. 2(b), there is a DCDC converter 165 that generates a predetermined voltage lower than the output voltage Vout1 with the output voltage Vout1 as an input. The DCDC converter 165 supplies an output voltage Vout2 (about 3.3V) to the load 164 (Vout2 < Vout1). The load 164 includes, for example, a CPU 500 provided in the control unit 501 and a sensor (not shown) for detecting the state of the printer 700. The DCDC converter 165 has a VIN terminal, a GND terminal, and an OUT terminal. The output voltage Vout1 is input to the VIN terminal, and the output voltage Vout2 is output from the VOUT terminal. The GND terminal is grounded.

[0019] The switching control unit 400 detects an overload condition based on the current detection result from the resistor 112. In other words, the switching control unit 400 detects an overload condition based on the IS terminal voltage. Therefore, the switching control unit 400 also functions as a first detection means for detecting an overload condition.

[0020] [Switching Control Unit] Figure 3 is an internal block diagram of the switching control unit 400. Figure 4 is a flowchart showing the switching control of the switching control unit 400 under overload conditions. Using Figures 3 and 4, we will explain how the switching control unit 400 of Embodiment 1 performs switching control. The switching control method will be explained using a fixed frequency on-width control method as an example. The switching frequency will be 100 kHz.

[0021] The configuration and basic operation of the switching control unit 400 will be explained using Figures 3 and 4. When an AC voltage is supplied to the power supply unit 100, the processing from step 1 onwards (hereinafter referred to as S) in Figure 4 begins. When the AC voltage Vdc is applied to the power supply unit 100, in S1, the switching control unit 400 supplies power to the ST terminal. In S2, the switching control unit 400 starts the operation of the startup circuit 401 due to the power supply in S1. The startup circuit 401 charges the Vcc terminal and generates a voltage Vcc for the operation of the FET drive circuit 402 and the regulator 403. The voltage Vcc is approximately 10V (first voltage), which is higher than the gate threshold voltage (3~5V) of the FET 107. Here, the regulator 403 generates a voltage Vreg for the operation of the Logic unit 404, etc. The voltage Vreg is approximately 4V. In S3, the switching control unit 400 determines whether or not the voltage Vreg has been generated (output) by the regulator 403. In S3, if the switching control unit 400 determines that voltage Vreg has not been generated by the regulator 403, it returns to S3; if it determines that voltage Vreg has been generated, it proceeds to S4. Here, "voltage Vreg has been generated" means that voltage Vreg is approximately 4V. In S4, the switching control unit 400 causes the startup circuit 401 to send a high-level EN signal to the logic unit 404 (EN=High). In S5, in response to the high-level (approximately 4V) EN signal being input to the logic unit 404, the switching control unit 400 starts the switching operation of FET 107.

[0022] The switching control unit 400 performs a soft-start operation until the voltage at the FB terminal (hereinafter referred to as the FB terminal voltage) rises. The soft-start operation is performed when the output voltage Vout1 is not outputting and the FB terminal voltage is approximately 0V, and the switching control unit 400 cannot perform feedback control, so it switches at a predetermined frequency and on-duty cycle until the FB terminal voltage is charged. At this time, the logic unit 404 outputs pulse signals to the S terminal and R terminal of the SR-flip-flop 405 at predetermined timings in order to drive the FET 107 at a predetermined on-duty cycle. Then, the SR-flip-flop 405 outputs a pulse signal from the Q terminal to the FET drive circuit 402, and switches the FET 107 at a predetermined frequency and on-duty cycle. Here, the period during which the soft-start operation is performed (hereinafter referred to as the soft-start period) is approximately 10 msec.

[0023] After the soft-start period has elapsed, the on-time is determined by the comparator 406 (Comp). Here, the comparator 406 has the FB terminal voltage input to its - terminal, the IS terminal voltage input to its + terminal, and a voltage source 407 connected to its - terminal. The output terminal of the comparator 406 is connected to the Logic unit 404. In Example 1, a fixed frequency method is used as an example, so once the on-time is determined, the off-time is also determined. For example, if the frequency is 100kHz and the on-time is 3μsec, the off-time will be 7μsec. When the IS terminal voltage matches the FB terminal voltage, the comparator 406 outputs a high-level (approximately 4V) signal to the Logic unit 404, turning off the FET 107. The voltage source 407 is a fixed voltage source and is provided to set an upper limit on the on-time. For example, if the FB terminal has an open fault, the FET 107 will remain on, which could lead to current failure of the FET 107. Therefore, when the IS terminal voltage matches the voltage of the voltage source 407 (which is assumed to be 0.5V in this case), the comparator 406 goes low, and the FET 107 turns off. This prevents the FET 107 from being damaged.

[0024] In S6, the switching control unit 400 determines whether a predetermined time Tst has elapsed, based on the logic unit 404. This is equal to the soft-start period described above (for example, 10 msec), and is provided to determine the overload state excluding transient overload states caused by the soft-start operation. From here on, the logic unit 404 will use the timer 409 to measure the predetermined time. In S6, if the switching control unit 400 determines that the predetermined time Tst has not elapsed, based on the logic unit 404, it returns to processing S6. If it determines that the predetermined time Tst has elapsed, it proceeds to processing S7.

[0025] In S7, the switching control unit 400 determines whether or not an overload condition has been detected by the Logic unit 404 at a predetermined time Tol. The IS terminal is connected to the Logic unit 404. Regarding the determination of an overload condition, the Logic unit 404 determines that an overload condition has occurred if the IS terminal voltage Vis is greater than the first threshold Vth1. In other words, an overload condition is determined when Vis > Vth1. In S7, if the state of Vis > Vth1 continues for the predetermined time Tol, the Logic unit 404 determines that an overload condition has occurred. Note that since the IS terminal voltage Vis is a pulsating waveform, it may be smoothed using a diode and a capacitor (not shown), or the Logic unit 404 may perform calculations such as averaging. In other words, it is not necessarily required that the state of Vis > Vth1 continues for the predetermined time Tol; an overload condition may be determined if the average value of Vis output at the predetermined time Tol is greater than Vth1.

[0026] In S7, if the switching control unit 400 determines that an overload condition has been detected by the logic unit 404 for a predetermined time Tol, it determines that an overload is occurring continuously and proceeds to S13. In S13, the switching control unit 400 latches the switching control using the logic unit 404 and terminates the process. Here, the first process, latching, means maintaining the FET 107 in a state where it cannot be switched, and this state is maintained until the voltage supplied to the latched circuit drops to the voltage that releases the latch (hereinafter referred to as the latch release voltage). Since the primary side circuit including the FET 107 is continuously supplied with voltage from the AC power supply 101, the user needs to take action such as unplugging the power supply unit 100 from the outlet in order to release the latch. By unplugging, the supply of voltage from the AC power supply 101 stops, and the voltage of the primary side circuit drops. This allows the circuit to recover from the latched state.

[0027] In Embodiment 1, the latch unit 408 located inside the Logic unit 404 stops the latch, and the latch state is maintained until the voltage Vcc falls below the latch release voltage (in this case, 2V). That is, the latch release voltage is 2V. Alternatively, the latch stop may be released when the voltage Vreg falls below the latch release voltage (for example, 2V). S7 becomes Yes when, for example, an AC voltage is applied while the outputs of the secondary capacitor 152 are short-circuited. If the switching control unit 400 detects an overload condition between the start of switching operation and the time the output voltage Vout1 reaches the target voltage, it performs a first process to stop the switching operation until the voltage Vcc becomes a second voltage lower than the first voltage. When the first process (latch stop) is executed, the supply of voltage from the AC power supply 101 is stopped, and when the voltage supplied to the switching control unit 400 becomes a second voltage lower than the first voltage, the switching operation becomes resumable.

[0028] In S7, if the switching control unit 400 determines that the Logic unit 404 has not detected an overload condition within a predetermined time Tol, it proceeds to S8. In S8, the switching control unit 400 determines whether the Logic unit 404 has output a predetermined voltage Vout_th1 (24V) (target voltage) as the output voltage Vout1. In S8, if the Logic unit 404 determines that the predetermined voltage Vout_th1 has not been output as the output voltage Vout1, it returns to S8. Switching control continues during this time. In S8, if the switching control unit 400 determines that the Logic unit 404 has output a predetermined voltage Vout_th1 as the output voltage Vout1, it proceeds to S9. Since the predetermined voltage Vout_th1 (24V) (target voltage) has been output as the output voltage Vout1, in S9 the switching control unit 400 completes the startup by the Logic unit 404. Here, "completion of startup" refers to the state in which the output voltage Vout1 outputs a predetermined voltage Vout_th1 (24V), which can be confirmed, for example, by the AD converter (not shown) provided in the CPU500.

[0029] Subsequently, once the power supply unit 100 has finished starting up and the DC-DC converter 165 outputs the output voltage Vout2, the control unit 501 operates and the printer 700 starts operating. Unless an overload condition such as an output short circuit occurs or the AC voltage drops, the power supply unit 100 continues to output a predetermined voltage Vout_th1 (24V) to the output voltage Vout1.

[0030] In S10, the switching control unit 400 determines whether or not an overload condition has been detected by the logic unit 404. Factors that can cause an overload condition include, for example, a temporarily large load being placed on load 158. In S10, if the switching control unit 400 does not detect an overload condition by the logic unit 404, it returns to processing S10. If an overload condition is detected, it determines that a temporary overload has occurred and proceeds to processing S11. In S11, the switching control unit 400 stops switching by the logic unit 404 and sets the EN terminal to a low level (approximately 0V) (EN=Low).

[0031] In S10, if the voltage at which the switching control unit 400 determines an overload state is Vth2, then the Logic unit 404 determines an overload state when Vis > Vth2. Here, the Logic unit 404 may immediately determine an overload state, or it may average the IS terminal voltage Vis with a capacitor (not shown). In S7, the overload threshold is set to Vth1, and in S10, the overload threshold is set to Vth2, which are different values ​​(Vth1 ≠ Vth2), but they may be the same (Vth1 = Vth2).

[0032] In S12, the switching control unit 400 determines whether a predetermined time of Trst has elapsed, based on the logic unit 404. If the switching control unit 400 determines in S12 that the predetermined time of Trst has not elapsed, it returns to S12; if it determines that the predetermined time of Trst has elapsed, it returns to S3. If the voltage Vreg in S3 outputs a predetermined voltage (approximately 4V), the control described above is performed again. That is, the switching operation is restarted in S5. The process in which the switching control unit 400 stops the switching operation (S11) and restarts the switching operation (S5) after the first time has elapsed (S12 Yes) is called the second process. If the switching control unit 400 detects an overload condition after the output voltage Vout1 reaches the target voltage, it executes the second process.

[0033] From now on, the operation of returning from S11 (switching stop) to S3 and outputting the output voltage Vout1 again will be described as restarting. If it is a temporary overload condition and the overload condition is released in S7, in other words, if the overload condition does not continue for a predetermined time in Tol, the output voltage Vout1 will be output again in S8. Another example in which the processing in S10 (whether it is an overload condition) is Yes is when the AC voltage drops. In this case, when the AC voltage drops while the printer 700 (its load 158) is operating at a predetermined load, the on-duty cycle of FET107 increases, so the on-time becomes longer compared to when the AC voltage is high, and as a result the IS terminal voltage Vis also increases. Then, even if the secondary side is not in an overload condition, the current flowing through FET107 increases, so switching is stopped in S11 to protect the element's rating and thermally.

[0034] If an overload condition is detected, there is no function to stop the latch (functions S7 and S13 in Figure 4), and the system is configured to restart. If the overload condition persists, the system will continue to restart, causing the output voltage to become unstable. In the case of the printer 700, this could lead to an unstable voltage supply to, for example, the display panel, potentially causing intermittent display issues and user confusion. This issue can be resolved by addressing that problem.

[0035] Thus, in this embodiment, if the Logic unit 404 detects an overload during the period until the power supply unit 100 has finished starting up (excluding the soft-start period), the switching control unit 400 estimates that an overload condition is continuously occurring and performs a latch stop. If an overload occurs shortly after the switching control unit 400 has started operating, it is highly likely that an overload will continue to occur not only during this period but also over other periods. Therefore, in this embodiment, a latch stop is selected.

[0036] On the other hand, if the Logic unit 404 detects an overload after the power supply unit 100 has finished starting up, the switching control unit 400 estimates that a temporary overload condition has occurred and performs a restart. As mentioned above, if a continuous overload occurs, there is a high probability that the switching control unit 400 is also under overload shortly after it starts operating. Conversely, if an overload occurs after the power supply unit 100 has finished starting up, there is a high probability that a temporary overload has occurred.

[0037] Furthermore, in preparation for the possibility of a continuous overload occurring after the power supply unit 100 has finished starting up, this embodiment also allows for determining whether an overload has occurred at a predetermined time Tol before performing a restart, and transitioning to latch stop at that timing. In other words, after the power supply unit 100 starts up, it is determined whether a continuous overload has occurred based on the length of time the overload has been present.

[0038] In Example 1, the latch was stopped using a latch unit 408 located inside the switching control unit 400. However, the latch may also be stopped by supplying an external signal to the Lat terminal of the switching control unit 400. Alternatively, the switching control unit 400 may use a CPU. When controlled by a CPU, the control timing can be determined, so the "predetermined time Tst elapsed" described in S6 of Figure 4 may be changed to "FB control started".

[0039] As explained above, according to Embodiment 1, the power supply unit 100 restarts if it becomes overloaded due to some factor after startup, or in the event of a temporary drop in AC voltage or a temporary overcurrent condition in the load. In addition, if the system has been continuously overloaded, it becomes possible to latch the switching when the power supply unit 100 restarts.

[0040] As described above, according to Example 1, the power supply can be appropriately protected according to the overload condition that occurs. [Examples]

[0041] The case where the power supply unit 100 of Example 2 is applied to the printer 700 will be described. Components identical to those in Example 1 are given the same reference numerals and their descriptions are omitted. In Example 1, the configuration was such that a latch stop occurred when a Tol overload condition was detected for a predetermined time, starting from the timing when the soft start period had elapsed (Figure 4 S7). In Example 2, the configuration is described in which a latch stop occurs when a Tol overload condition is detected for a predetermined time, starting from the timing when the output voltage Vout1 outputs a predetermined voltage.

[0042] [Control in Example 2] The configuration of printer 700 is the same as in Figure 1, the circuit diagram is the same as in Figure 2, and the internal block diagram of the switching control unit 400 is the same as in Figure 3. Therefore, the same reference numerals used in Figures 1 to 3 are used. Figure 5 shows the flowchart of Example 2. Here, the same steps as in the flowchart of Figure 4 of Example 1 are given the same step numbers. The difference from the flowchart of Example 1 (Figure 4) is that S6 in Example 1 has become S16.

[0043] In S16, the switching control unit 400 determines whether a voltage equal to or greater than a predetermined voltage Vout_th2 (third voltage) has been output as the output voltage Vout1 using the monitor circuit 600 (see Figure 6(a)), which will be described later. Based on this, the switching control unit 400 determines whether or not an overload condition can be detected. In other words, in Embodiment 1, the completion of the soft start operation was determined by measuring the elapsed time, but in Embodiment 2, the completion of the soft start operation is determined based on the output voltage Vout1. As a result, it becomes possible to determine whether or not an overload condition is present, excluding transient overload conditions caused at the start of switching. If the switching control unit 400 determines in S16 that the predetermined voltage Vout_th2 has not been output as the output voltage Vout1, it returns to processing S16. If it determines that the predetermined voltage Vout_th2 has been output, it proceeds to processing S7.

[0044] [Monitor Circuit] Figure 6(a) shows a monitor circuit 600 that monitors the output voltage Vout1 of Embodiment 2. The monitor circuit 600 includes a CPU 500 and resistors 166 and 167. The CPU 500 operates based on the output voltage Vout2. The voltage obtained by dividing the output voltage Vout1 by resistors 166 and 167 is input to the Vmon2 terminal of the CPU 500. The Vmon2 terminal is an AD conversion unit (analog-to-digital conversion unit), and with this configuration, the CPU 500 can monitor the output voltage Vout1. This allows it to determine in S16 of Figure 5 whether the output voltage Vout1 is greater than or equal to the output voltage Vout_th2 (in this case, 5V).

[0045] [Transmission circuit] Figure 6(b) shows a transmission circuit 650 that transmits to the switching control unit 400 that the output voltage Vout1 of Embodiment 2 has output a predetermined voltage. When the predetermined voltage Vout_th2 is output as the output voltage Vout1, the CPU 500 of the monitor circuit 600 outputs a high-level (approximately 3.3V) signal from the SSout terminal. The voltage output from the SSout terminal is divided by resistors 168 and 169 and supplied to the base terminal of transistor 170. This turns on transistor 170. When transistor 170 is turned on, the output voltage Vout2 is supplied via resistor 172, and the photodiode 171d of photocoupler 171 conducts. As a result, the phototransistor 171t of photocoupler 171 conducts, and the voltage Vcc is supplied to the SS terminal of the switching control unit 400 via resistor 173. Inside the switching control unit 400, when the SS terminal reaches a high level (10V in this case), it determines that a predetermined voltage Vout_th2 has been output as the output voltage Vout1, or in other words, that an overload condition can be detected, and proceeds to S7 in Figure 5. Regarding Figure 5, the subsequent operations are the same as in Embodiment 1, so the explanation is omitted.

[0046] As explained above, in Example 2, it is possible to stop the latch if an overload condition occurs, starting from the timing when the secondary output voltage reaches a predetermined voltage. As described above, according to Example 2, the power supply can be appropriately protected according to the state of the overload that occurs. [Examples]

[0047] Example 3 describes a configuration in which an overload condition is determined based on the primary voltage and primary current. Components identical to those in Examples 1 and 2 are given the same reference numerals and their explanations are omitted.

[0048] [Power supply] Figure 7 shows the circuit diagram of Embodiment 3. The difference from Embodiment 1 is that the power supply unit 100 has a primary voltage detection unit 200, which is a third detection means. The voltage induced in the auxiliary winding Nb by the switching of FET 107 is separated from the path of diode 109 by diode 201 and stored in capacitor 202. The voltage charged in capacitor 202 is divided by resistors 203 and 204 and input to the Vmon1 terminal of the switching control unit 400.

[0049] Since the primary winding Np and the auxiliary winding Nb are wound in the same direction, the voltage induced in the auxiliary winding Nb is proportional to the voltage induced in the primary winding Np. Furthermore, since the primary winding Np is wound in a so-called forward winding, the voltage induced in the primary winding Np is proportional to the AC voltage Vdc. In other words, the AC voltage Vdc and the voltage induced in the auxiliary winding Nb are also proportional. Moreover, since the AC voltage Vdc is the voltage obtained by full-wave rectifying the AC voltage of the AC power supply 101 and smoothing it with the primary electrolytic capacitor 104, if we let the effective voltage value of the AC voltage of the AC power supply 101 be Vac and ignore the forward voltage of the diode bridge 103, then equation (1) approximately holds true.

number

[0050] If we denote the resistance values ​​of resistors 203 and 204 as R203 and R204, respectively, and the voltage at the Vmon1 terminal (hereinafter referred to as the Vmon1 terminal voltage) as Vmon1, the number of turns of the primary winding Np as Np, and the number of turns of the auxiliary winding Nb as Nb, then equation (2) approximately holds true.

number

[0051] [Switching Control Unit] Figure 8 shows an internal block diagram of the switching control unit 400 of Embodiment 3. The difference from Embodiment 1 is that the switching control unit 400 is equipped with a multiplier 410. The IS terminal voltage and the Vmon1 terminal voltage are input to the multiplier 410, and the output of the multiplier 410 is input to the Logic unit 404. The multiplier 410 multiplies the Vmon1 terminal voltage and the IS terminal voltage, and outputs the multiplication result to the Logic unit 404. Based on the multiplication result input from the multiplier 410, the Logic unit 404 can estimate the power information P (which is also the power value) consumed downstream of the primary electrolytic capacitor 104. If the IS terminal voltage is Vis, then approximately equation (3) holds true.

number

[0052] In this way, the switching control unit 400 detects an overload condition based on the current detection result from the resistor 112 and the detection result from the primary voltage detection unit 200. That is, the switching control unit 400 detects an overload condition based on the IS terminal voltage and the Vmon1 terminal voltage. For this reason, the switching control unit 400 also functions as a first detection means for detecting an overload condition.

[0053] The flowchart for Example 3 is shown in Figure 4. Although the control in Example 3 is the same as in Example 1, the method for detecting the overload state in S7 and S10 is different. In S7, the third threshold for determining that an overload state exists is Pth1. The Logic unit 404 determines that an overload state exists if the power information P obtained from equation (3) is greater than the threshold Pth1 (P>Pth1). In S10, the fourth threshold for determining that an overload state exists is Pth2. The Logic unit 404 determines that an overload state exists if the power information P obtained from equation (3) is greater than the threshold Pth2 (P>Pth2). The Logic unit 404 may determine that an overload state exists immediately, or it may proceed to S6 after detecting an overload state for a predetermined time. In this example, Pth1 and Pth2 are different values ​​(Pth1≠Pth2), but they may be the same value (Pth1=Pth2). Furthermore, the determination of an overload state based on power information P may be applied to the control shown in Figure 5 of Example 2.

[0054] [Decision-making based on power and decision-making based on electric current] This section explains the difference between a configuration that detects an overload condition using the product of the current flowing on the primary side and the voltage on the primary side, i.e., power, and a configuration that detects an overload condition based on the IS terminal voltage (Vis) indicating the current flowing on the primary side, as in Example 1. Vth1 and Vth2 in Example 1 and Pth1 and Pth2 in Example 3 will be explained assuming the same values ​​(Vth1=Vth2, Pth1=Pth2). First, in the control method of Example 1, if the resistance value of resistor 112 is R112 and the current value flowing is Iis, then equation (4) holds true.

number

[0055] For example, let's assume that the AC voltage specifications of AC power supply 101 are 100Vac to 127Vac, the secondary voltage (output voltage Vout1) is 24V, and the load current is 15A, and the overload threshold (Pth1) is 360W (=24V × 15A). Considering 100Vac, which is the lower value within the AC voltage specifications of AC power supply 101, from equation (1) 100Vac becomes 141Vdc, and the threshold for the overload current value Iis can be calculated as approximately Pth1(360W) / 141Vdc = 2.55A. At this time, the current value Iis at 127Vac, which is the higher value within the AC voltage specifications of AC power supply 101, is also 2.55A, so Pth1 becomes 127Vac × √2 × 2.55 = 458W, and when converted to load current, it becomes 458W / 24V = 19A. In other words, the secondary load current value at which an overload condition is detected differs depending on the value of the AC voltage. Specifically, it is 15A at an AC voltage of 100Vac and 19A at an AC voltage of 127Vac. On the other hand, in the method of Example 3, an overload condition is detected when power equivalent to 360W is detected. Since it is possible to detect an overload condition at approximately the same power even if the AC voltage fluctuates, the secondary load current will also be almost the same.

[0056] As explained above, according to Example 3, by detecting the overload condition using power, it becomes possible to detect the overload condition with an equivalent secondary current value, regardless of the value of the AC voltage. Thus, according to Example 3, the power supply can be appropriately protected according to the overload condition that occurs. [Explanation of Symbols]

[0057] 100 Power supply 107 FET 108 Transformers 400 Switching Control Unit

Claims

1. A transformer having a primary winding, a secondary winding, and an auxiliary winding, A switching element connected to the primary winding and performing switching operation, A first control means that operates when a first voltage is supplied and controls the switching operation of the switching element, A power supply device comprising, which supplies an output voltage corresponding to the voltage induced in the secondary winding, It is equipped with a first detection means for detecting an overload condition, The first control means is, If the first detection means detects an overload condition between the start of the switching operation and the time the output voltage reaches the target voltage, the first process is executed to maintain the state in which the switching operation is stopped. If the output voltage reaches the target voltage and the first detection means detects that an overload condition has occurred, the second process is executed to stop the switching operation and restart the switching operation after a first time has elapsed. A power supply device characterized in that the first detection means detects the overload state after the switching operation has started and a period of time during which the soft start operation has elapsed.

2. A transformer having a primary winding, a secondary winding and an auxiliary winding, A switching element connected to the primary winding and performing switching operation, A first control means that operates when a first voltage is supplied and controls the switching operation of the switching element, A power supply device comprising, which supplies an output voltage corresponding to the voltage induced in the secondary winding, It is equipped with a first detection means for detecting an overload condition, The first control means is, If the first detection means detects an overload condition between the start of the switching operation and the time the output voltage reaches the target voltage, the first process is executed to maintain the state in which the switching operation is stopped. If the output voltage reaches the target voltage and the first detection means detects that an overload condition has occurred, the second process is executed to stop the switching operation and restart the switching operation after a first time has elapsed. A power supply device characterized in that the first detection means detects the overload condition after the switching operation is started and the output voltage becomes a starting voltage lower than the target voltage.

3. The power supply device according to claim 1 or 2, characterized in that when the first process is executed, the supply of voltage from the AC power supply is stopped, and the voltage supplied to the first control means becomes a second voltage lower than the first voltage, thereby enabling the switching operation to be restarted.

4. The system includes a second detection means for detecting the current flowing through the primary winding, The power supply device according to claim 3, characterized in that the first detection means detects the overload condition when the current value detected by the second detection means in the first and second processes is greater than the first threshold value.

5. The system includes a second detection means for detecting the current flowing through the primary winding, The first detection means is, In the first process, if the current value detected by the second detection means is greater than the first threshold, the overload condition is detected. The power supply device according to claim 3, characterized in that, in the second process, the overload condition is detected when the current value detected by the second detection means is greater than a second threshold that is different from the first threshold.

6. A second detection means for detecting the current flowing through the primary winding, A third detection means for detecting the voltage induced in the auxiliary winding, Equipped with, The power supply device according to claim 3, characterized in that the first detection means detects the overload condition when the power value obtained based on the detection results of the second detection means and the third detection means in the first and second processes is greater than the third threshold.

7. A second detection means for detecting the current flowing through the primary winding, A third detection means for detecting the voltage induced in the auxiliary winding, Equipped with, The first detection means is, In the first process, if the power value obtained based on the detection results of the second detection means and the third detection means is greater than the third threshold, the overload condition is detected. The power supply device according to claim 3, characterized in that, in the second process, the overload condition is detected when the power value obtained based on the detection results of the second detection means and the third detection means is greater than a fourth threshold that is different from the third threshold.

8. A power supply device comprising a transformer having a primary winding, a secondary winding, and an auxiliary winding; a switching element connected to the primary winding and performing a switching operation; a first control means that operates when a first voltage is supplied and controls the switching operation of the switching element, and which supplies an output voltage corresponding to the voltage induced in the secondary winding, Image forming means for forming an image on a recording material, A second control means for controlling the power supply device and the image forming means, An image forming apparatus comprising, The power supply device has a first detection means for detecting an overload condition, The first control means is, If the first detection means detects an overload condition between the start of the switching operation and the time the output voltage reaches the target voltage, the first process is executed to maintain the state in which the switching operation is stopped. If the output voltage reaches the target voltage and the first detection means detects that an overload condition has occurred, the second process is executed to stop the switching operation and restart the switching operation after a first time has elapsed. An image forming apparatus characterized in that the first detection means detects the overload state after the switching operation has started and a period of time during which the soft start operation has elapsed.

9. A power supply device comprising: a transformer having a primary winding, a secondary winding and an auxiliary winding; a switching element connected to the primary winding and performing a switching operation; a first control means that operates when a first voltage is supplied and controls the switching operation of the switching element, wherein the power supply device supplies an output voltage corresponding to the voltage induced in the secondary winding, Image forming means for forming an image on a recording material, A second control means for controlling the power supply device and the image forming means, An image forming apparatus comprising, The power supply device has a first detection means for detecting an overload condition, The first control means is, If the first detection means detects an overload condition between the start of the switching operation and the time the output voltage reaches the target voltage, the first process is executed to maintain the state in which the switching operation is stopped. If the output voltage reaches the target voltage and the first detection means detects that an overload condition has occurred, the second process is executed to stop the switching operation and restart the switching operation after a first time has elapsed. An image forming apparatus characterized in that the first detection means detects the overload state after the switching operation is started and the output voltage becomes a starting voltage lower than the target voltage.

10. The image forming apparatus according to claim 8 or 9, characterized in that when the first process is performed, the supply of voltage from the AC power source is stopped, and the voltage supplied to the first control means becomes a second voltage lower than the first voltage, thereby enabling the switching operation to be restarted.

11. The power supply device has a second detection means for detecting the current flowing through the primary winding, The image forming apparatus according to claim 10, characterized in that the first detection means detects the overload state when the current value detected by the second detection means in the first and second processes is greater than the first threshold value.

12. The power supply device has a second detection means for detecting the current flowing through the primary winding, The first detection means is, In the first process, if the current value detected by the second detection means is greater than the first threshold, the overload condition is detected. The image forming apparatus according to claim 10, characterized in that, in the second process, the overload condition is detected when the current value detected by the second detection means is greater than a second threshold that is different from the first threshold.

13. The power supply device includes a second detection means for detecting the current flowing through the primary winding and a third detection means for detecting the voltage induced in the auxiliary winding. The image forming apparatus according to claim 10, characterized in that the first detection means detects the overload state when the power value obtained based on the detection results of the second detection means and the third detection means in the first and second processes is greater than the third threshold.

14. The power supply device includes a second detection means for detecting the current flowing through the primary winding and a third detection means for detecting the voltage induced in the auxiliary winding. The first detection means is, In the first process, if the power value obtained based on the detection results of the second detection means and the third detection means is greater than the third threshold, the overload condition is detected. The image forming apparatus according to claim 10, characterized in that, in the second process, the overload state is detected when the power value obtained based on the detection results of the second detection means and the third detection means is greater than a fourth threshold that is different from the third threshold.

15. The image forming apparatus according to claim 9, characterized in that the second control means detects the voltage value of the output voltage and transmits the detected voltage value to the first control means.

Images