Power supply unit and image forming apparatus

Abstract

To provide a power supply device to be protected by appropriately controlling discharge time of a gate of a first transistor when the first transistor is turned off.SOLUTION: A power supply device includes: a first converter unit that generates a first voltage according to an input voltage regardless of a first mode and a second mode; a first transistor that is turned on during the first mode to output the first voltage as a second voltage and is turned off during the second mode to stop the output from the second voltage; a second converter that generates a third voltage during the first mode and stops generating the third voltage during the second mode; and a gate control unit that turns off the first transistor by conducting a discharge path connected to the gate of the first transistor in response to a decrease in the third voltage during the second voltage is outputted and suppresses conduction of the discharge path in response to a decrease in the third voltage while the output of the second voltage is stopped.SELECTED DRAWING: Figure 1

Description

Technical Field

[0005] ,

[0001] The present invention relates to a power supply device and an image forming apparatus.

Background Art

[0002] A power supply device having a semiconductor switch connected between a power supply and a load and turning on or off the power supply supplied to the load is known. In this type of power supply device, the semiconductor switch is protected by controlling the semiconductor switch according to the output current to the load and the elapsed time after the semiconductor switch is turned on (see, for example, Patent Document 1).

Summary of the Invention

[0006] The power supply can be protected by appropriately controlling the discharge time of the gate of the first transistor when the first transistor is turned off. [Brief explanation of the drawing]

[0007] [Figure 1] This is a circuit block diagram showing an example of a power supply device according to one embodiment of the present invention. [Figure 2] Figure 1 is a circuit block diagram showing an example of the converter section. [Figure 3] This is a circuit block diagram showing an example of another power supply unit. [Figure 4] The timing diagrams in Figures 1 and 3 show an example of the operation of the power supply unit. [Figure 5] This timing diagram shows another example of the operation of the power supply unit in Figure 1. [Figure 6] This is a circuit block diagram showing an example of a power supply device according to another embodiment of the present invention. [Figure 7] Figure 6 is a timing diagram showing an example of the operation of the power supply unit. [Figure 8] Figures 1 and 6 show an overall configuration diagram illustrating an example of an image forming apparatus equipped with a power supply unit. [Modes for carrying out the invention]

[0008] Embodiments will be described below with reference to the drawings. In the following, voltage lines through which voltage is transmitted will be denoted by the same reference numeral as the voltage name, and signal lines through which signals are transmitted will be denoted by the same reference numeral as the signal name. In each drawing, identical components will be denoted by the same reference numeral, and redundant explanations may be omitted.

[0009] Figure 1 is a circuit block diagram showing an example of a power supply device according to one embodiment of the present invention. The power supply device 100 shown in Figure 1 has the function of generating multiple types of DC voltages DC5X, DC5, and DC24 using an AC voltage Vin supplied from an AC power source such as a commercial power source and outputting them to a load. DC voltage DC5X is an example of a first voltage, for example, 5V. DC voltage DC5 is an example of a second voltage, for example, 5V. DC voltage DC24 is an example of a third voltage, for example, 24V. The power supply unit 100 includes a smoothing unit 20, a converter unit 30, a power supply unit 40, a converter unit 50, a discharge unit 60, transistors Q1 and Q2, resistors R1, R2, R3, diodes D1 and D2, and a capacitor C2. While not particularly limited, for example, transistors Q1 and Q2 are n-channel insulated-gate field-effect transistors. Converter unit 30 is an example of a first converter unit, and converter unit 50 is an example of a second converter unit.

[0010] The smoothing unit 20 includes a diode bridge DB that full-wave rectifies the AC voltage Vin and a capacitor C1 that smooths the full-wave rectified voltage, and outputs a DC voltage generated by smoothing. The converter unit 30 generates a DC voltage DC5X from the DC voltage output from the smoothing unit 20.

[0011] When the energy-saving signal ECO indicates the normal mode, the power supply unit 40 supplies a constant voltage received from the converter unit 30 to the converter unit 50. When the energy-saving signal ECO indicates the energy-saving mode, the power supply unit 40 stops supplying the constant voltage received from the converter unit 30 to the converter unit 50. The normal mode is an example of the first mode, and the energy-saving mode is an example of the second mode. For example, the energy-saving signal ECO is set to a low level during the normal mode and to a high level during the energy-saving mode. Hereinafter, the energy-saving mode will also be referred to as the energy-saving mode.

[0012] The converter unit 50 operates while receiving a constant voltage from the power supply unit 40 and generates a DC voltage DC24 from the DC voltage output from the smoothing unit 20. If the converter unit 50 does not receive a constant voltage from the power supply unit 40, it stops generating the DC voltage DC24. In other words, the converter unit 50 generates the DC voltage DC24 in normal mode and stops generating the DC voltage DC24 in energy-saving mode.

[0013] The gate of transistor Q1 is connected to DC voltage line DC24 via resistors R1 and R2 and diode D2. Diode D2 has its anode connected to DC voltage line DC24 and its cathode connected to resistor R2. The drain of transistor Q1 is connected to DC voltage line DC5X, and the source of transistor Q1 is connected to DC voltage line DC5. Transistor Q1 turns on when it receives a high level at its gate and connects DC voltage line DC5X to DC voltage line DC5 to generate DC voltage DC5. For example, transistor Q1 turns on based on the converter section 50 generating DC voltage DC24 and remains on while DC voltage DC24 is being generated.

[0014] Transistor Q1 turns off when it receives a low level at its gate, disconnecting the DC voltage line DC5X from the DC voltage line DC5 and stopping the generation of DC voltage DC5. For example, transistor Q1 turns off based on the converter section 50 stopping the generation of DC voltage DC24 and remains off while the generation of DC voltage DC24 is stopped. Transistor Q1 is an example of a first transistor.

[0015] The power supply unit 100 continuously outputs a DC voltage DC5X while receiving an AC voltage Vin. While receiving an AC voltage Vin, the power supply unit 100 outputs a DC voltage DC24 in normal mode and outputs a DC voltage DC5 by turning on transistor Q1. While receiving an AC voltage Vin, the power supply unit 100 stops outputting DC voltages DC24 and DC5 in energy-saving mode.

[0016] Thus, in normal mode, the power supply unit 100 branches the DC voltage generated by the converter unit 30 into two systems and outputs them as DC voltages DC5X and DC5. For example, a load that receives DC voltage DC5X as its operating power supply has a control circuit that operates at all times to control the operating mode. For example, a load that receives DC voltage DC5 as its operating power supply has a control circuit that operates only in normal mode. For example, a load that receives DC voltage DC24 as its operating power supply has a drive mechanism, etc., that operates only in normal mode.

[0017] Capacitor C2, resistor R3, and transistor Q2 are connected in parallel between node ND1, which is the connection node for resistors R1 and R2, and the ground wire VSS. Transistor Q2 is turned off in normal mode when it receives a low-level energy-saving signal ECO at its gate. Transistor Q2 is turned on in energy-saving mode when it receives a high-level energy-saving signal ECO at its gate, and connects node ND1 and the gate of transistor Q1 to the ground wire VSS.

[0018] For example, the energy-saving signal ECO is generated by a control circuit that operates to control the operation mode upon receiving the DC voltage DC5X, and is output to the power supply device 100. During the energy-saving mode, the power supply device 100 stops the operation of the converter unit 50 and stops supplying the DC voltage DC5 from the converter unit 30 to the load. Also, in the system in which the power supply device 100 is mounted, the operation of the load that receives the DC voltages DC5 and DC24 is stopped during the energy-saving mode.

[0019] Thereby, during the energy-saving mode, the power consumption of the power supply device 100 and the system is reduced. Thus, the power supply device 100 can switch between an energy-saving state with low power consumption that outputs only the DC voltage DC5X and an operating state with high power consumption that outputs all of the DC voltages DC5X, DC5, and DC24 according to the logic level of the energy-saving signal ECO.

[0020] The discharge unit 60 has a diode D1 and a transistor Tr1 (NPN-type bipolar transistor) connected in series between the node ND1 and the DC voltage line DC24. The anode of the diode D1 is connected to the node ND1, and the cathode is connected to the collector of the transistor Tr1. The diode D1 and the transistor Tr1 are an example of a discharge path formed between the node ND1 (that is, the gate of the transistor Q1) and the DC voltage line DC24.

[0021] The base of the transistor Tr1 is connected to the DC voltage line DC5. The transistor Tr1 turns on when the DC voltage DC5 is at a normal value (for example, 5V). Thereby, the discharge path from the gate of the transistor Q1 to the DC voltage line DC24 is made conductive.

[0022] [[ID=1,6]]For example, when the converter unit 50 is normally generating the DC voltage DC24, the gate of the transistor Q1 and the node ND1 are set to the DC voltage DC24 by setting the resistance value of the resistance element R3 to be sufficiently larger than the resistance value of the resistance element R2, so that discharge by the discharge unit 60 is not performed.

[0023] When the DC voltage DC5 is at a normal value, the converter unit 50 stops operating. If the DC voltage DC24 drops towards the ground voltage VSS, the gate voltage of transistor Q1 rapidly decreases due to discharge via the discharge unit 60 (the discharge function is activated). As a result, transistor Q1 turns off, and the generation of DC voltage DC5 stops.

[0024] If the DC voltage line DC5 becomes 0V due to a short circuit, transistor Tr1 turns off, and the discharge path between the gate of transistor Q1 and the DC voltage line DC24 by the discharge unit 60 is interrupted (discharge function is disabled).

[0025] Thus, the discharge unit 60 has the function of enabling or disabling the discharge path of the gate of transistor Q1 depending on the generation state of the DC voltage DC5. The discharge unit 60 is an example of a gate control unit that discharges the gate of transistor Q1 in response to a decrease in the DC voltage DC24 while the DC voltage DC5 is output, thereby turning off transistor Q1. Furthermore, the discharge unit 60 is an example of a gate control unit that suppresses the discharge of the gate of transistor Q1 in response to a decrease in the DC voltage DC24 while the output of the DC voltage DC5 is stopped.

[0026] Figure 2 is a circuit block diagram showing an example of the converter sections 30 and 50 in Figure 1. The converter section 30 includes a transformer T1, a transistor Q3, a control section 31 including a pulse width determination section 32 and a current detection section 33, a constant voltage generation section 34, an output feedback section 35, and a smoothing section 36, and operates as a flyback converter.

[0027] The control unit 31 operates by receiving power from the auxiliary winding of the transformer T1. The current detection unit 33 of the control unit 31 detects the current on the primary side of the transformer T1. The output feedback unit 35 feeds back the output voltage on the secondary side of the transformer T1 to the control unit 31.

[0028] The control unit 31 determines the pulse width of the voltage applied to transistor Q3 using the pulse width determination unit 32, based on the current detection result on the primary side and the feedback result of the output voltage on the secondary side. Furthermore, if the current detection unit 33 detects a current that exceeds a threshold, the control unit 31 stops the switching operation of transistor Q3 by setting the pulse width to 0. In addition, if the current detection unit 33 has detected a current that exceeds the threshold for a certain period of time, the control unit 31 stops the latch.

[0029] The converter unit 50 includes a control unit 51 and a main circuit 52. In normal mode, the control unit 51 operates by receiving power from the transformer auxiliary winding of the converter unit 30 via the power supply unit 40 and controls the operation of the main circuit 52. The main circuit 52, under the control of the control unit 51, generates a DC voltage DC24 using the DC voltage output from the smoothing unit 20.

[0030] The control unit 51, for example, provides feedback control to the main circuit 52 so that the voltage obtained by dividing the DC voltage DC24 generated by the main circuit 52 approaches the reference voltage. In energy-saving mode, the control unit 51, which is not supplied with power from the power supply unit 40, stops operating. Therefore, in energy-saving mode, the feedback control of the main circuit 52 by the control unit 51 is stopped, and the generation of the DC voltage DC24 by the main circuit 52 is stopped.

[0031] Figure 3 is a circuit block diagram showing an example of another power supply unit. Detailed explanations of elements identical or similar to those in Figure 1 are omitted. The power supply unit 200 shown in Figure 3 includes a smoothing unit 20, a converter unit 30, a power supply unit 40, a converter unit 50, transistors Q1 and Q2, resistors R1, R2, and R3, a diode D2, a capacitor C2, a current detection unit 70, and a stop unit 80. In the power supply unit 200, the configuration and connection relationships are the same as those of the power supply unit 100 in Figure 1, except that it does not have the discharge unit 60 shown in Figure 1.

[0032] The current detection unit 70 is connected to the DC voltage line DC5 and detects the output current of transistor Q1. The stop unit 80 has the function of suspending control of the gate voltage of transistor Q1 until a predetermined time has elapsed since transistor Q1 was turned on. However, the power supply unit 200 does not control the discharge time of the gate of transistor Q1 when the DC voltage DC24 is stopped. For this reason, for example, if the gate voltage of transistor Q1 cannot be quickly reduced when an AC voltage Vin is momentarily interrupted, the converter unit 30 may latch and stop.

[0033] Figure 4 is a timing diagram showing an example of the operation of power supply unit 100 in Figure 1 and power supply unit 200 in Figure 3. Figure 4 shows the operation when a momentary interruption of the AC voltage Vin occurs.

[0034] In the power supply unit 100, when an interruption in the AC voltage Vin occurs, the DC voltage (input voltage) output from the smoothing unit 20 decreases. Consequently, the output of the DC voltage DC24 from the converter unit 50 is stopped, and the DC voltage DC24 decreases toward the ground voltage VSS (Figure 4(a)).

[0035] When a momentary interruption occurs, transistor Q1 outputs a DC voltage DC5, and transistor Tr1 in the discharge section 60 is ON (Figure 4(b)). Therefore, current can flow through diode D1 in response to the decrease in DC voltage DC24, rapidly lowering the gate voltage of transistor Q1 and immediately turning off transistor Q1 (Figure 4(c)). With transistor Q1 turned off, the DC voltage DC5 drops to the ground voltage VSS (Figure 4(d)).

[0036] When transistor Q1 is turned off, the connection between the output of converter unit 30 and the DC voltage line DC5 is interrupted, and the load connected to the output of converter unit 30 becomes smaller. Therefore, converter unit 30 can continue to operate without latching even when a momentary interruption of the AC voltage Vin occurs. In other words, converter unit 30 can continue to output a normal DC voltage DC5X even when a momentary interruption occurs (Figure 4(e)). The output current of converter unit 30 decreases because the load connected to the output of converter unit 30 becomes smaller (Figure 4(f)).

[0037] As the momentary interruption is resolved, the amplitude of the AC voltage Vin returns to normal, and the converter unit 50 resumes generating the DC voltage DC24 (Figure 4(g)). As the DC voltage DC24 rises, the gate voltage of transistor Q1 rises, and transistor Q1 turns on (Figure 4(h)). As a result, the output of the DC voltage DC5 is resumed (Figure 4(i)). Because the load connected to the output of the converter unit 30 increases when transistor Q1 turns on, the output current of the converter unit 30 increases (Figure 4(j)). Then, the converter unit 30 returns to a normal state.

[0038] In this way, by providing the power supply unit 100 with a discharge unit 60 that includes a transistor Tr1 which turns on or off according to the voltage value of the DC voltage DC5, the transistor Q1 can be quickly turned off when a momentary power interruption occurs. As a result, the output load of the converter unit 30 is reduced, so excessive protection due to latch stop can be suppressed, and the generation of DC voltages DC24 and DC5 can be resumed after the momentary power interruption is resolved.

[0039] In the power supply unit 200, similar to the power supply unit 100, if an interruption in the AC voltage Vin occurs, the DC voltage (input voltage) output from the smoothing unit 20 decreases. Consequently, the converter unit 50 stops outputting the DC voltage DC24, and the DC voltage DC24 drops to the ground voltage VSS (Figure 4(k)).

[0040] Since the power supply unit 200 does not have the discharge section 60 shown in Figure 1, there is no discharge path that would cause a sharp drop in the gate voltage of transistor Q1. Therefore, even if the DC voltage DC24 drops to the ground voltage VSS, the gate voltage of transistor Q1 decreases gradually, and transistor Q1 does not turn off during a momentary power interruption (Figure 4(l)).

[0041] Because transistor Q1 remains in the ON state, the converter section 30 continues to operate even when the load connected to the output is large and the input voltage is low. As a result, the primary current of the converter section 30 also increases, causing the converter section 30 to latch and stop.

[0042] When the latch stops, the converter unit 30 stops generating the DC voltage DC5X (Figure 4(m)). The cessation of DC voltage DC5 generation also stops the output of DC voltage DC5 (Figure 4(n)). Then, the output current of the converter unit 30 becomes zero (Figure 4(o)). Since the latch stop state persists even after the momentary interruption is resolved, the entire power supply unit 200 remains shut down.

[0043] In the power supply unit 200, if the load connected to the output of the converter unit 30 is light, the latch may not stop, and the outputs of DC voltages DC5X, DC24, and DC5 may recover after the momentary interruption is resolved. However, because transistor Q1 remains on instead of turning off when the momentary interruption occurs, the startup sequence after the momentary interruption differs from the normal sequence.

[0044] For example, in a normal startup sequence, the output starts in the order of DC voltages DC5X, DC24, and DC5. However, after a momentary power interruption is resolved, the output starts in the order of DC voltages DC5X, DC5, and DC24. If the startup sequence is different, unexpected errors may occur in the system in which the power supply unit 200 is installed.

[0045] Figure 5 is a timing diagram showing another example of the operation of the power supply unit 100 in Figure 1. Figure 5 shows the operation when the discharge function of the discharge unit 60 is disabled during a short circuit of the DC voltage line DC5. The operation timings shown in brackets in Figure 5 show the operation when the discharge function of the discharge unit 60 is enabled during a short circuit of the DC voltage line DC5. For example, the brackets in Figure 5 show the operation when the discharge unit 60 in Figure 1 does not have transistor Tr1.

[0046] The converter unit 30 detects a short circuit in the DC voltage line DC5 by detecting, based on the DC voltage DC5X, that the DC voltage DC5 has dropped to or near the ground voltage VSS. When the converter unit 30 detects a short circuit, it stops the switching operation of transistor Q3 (Figure 2) (Figure 5(a)). As a result, the power supply from the converter unit 30 to the converter unit 50 stops, the operation of the converter unit 50 stops, and the DC voltage DC24 drops to the ground voltage VSS (Figure 5(b)).

[0047] When the DC voltage line DC5 is short-circuited, transistor Tr1 in the discharge section 60 receives a DC voltage DC5 with a voltage value corresponding to the low level and turns off, disabling the discharge function of the discharge section 60. Therefore, when the DC voltage line DC5 is short-circuited, the gate of transistor Q1 does not discharge even if the DC voltage DC24 decreases. The gate voltage of transistor Q1 gradually decreases, for example, through the path from resistors R1 and R3 to the ground wire VSS (Figure 5(c)).

[0048] The converter unit 30 latches shut based on the fact that a low voltage (e.g., ground voltage VSS) of the DC voltage DC5X (i.e., DC voltage DC5) persists for a certain period of time before transistor Q1 turns off. In other words, a power supply unit 100 having a discharge unit 60 that can be set to an inactive state allows the power supply unit 100 to perform its protection function against short circuits. Thus, by not only providing a discharge unit 60 in the power supply unit 100, but also by switching between an enabled and inactive state of the discharge function according to the output state of the DC voltage DC5, circuits such as the converter unit 30 within the power supply unit 100 can be appropriately protected.

[0049] In contrast, as shown in the brackets, when the DC voltage line DC5 is short-circuited and the discharge function of the discharge unit 60 is active, the gate voltage of transistor Q1 immediately drops toward the ground voltage VSS when the DC voltage line DC5 is short-circuited (Figure 5(d)). As a result, transistor Q1 turns off before the converter unit 30 latches shut.

[0050] When transistor Q1 is turned off, the converter section 30 is disconnected from the short circuit point by transistor Q1. As a result, the converter section 30 no longer detects a short circuit in the DC voltage line DC5, and the switching operation of transistor Q3 is resumed (Figure 5(e)).

[0051] The restart of the switching operation of transistor Q3 resumes the generation of DC voltage DC5X (Figure 5(f)). Power supply from converter section 30 to converter section 50 is also resumed. As a result, converter section 50 resumes the generation of DC voltage DC24 (Figure 5(g)). With the restart of DC voltage DC24 generation, the gate voltage of transistor Q1 rises in accordance with the rise in DC voltage DC24, and when it exceeds the threshold voltage VT of transistor Q1, transistor Q1 turns on (Figure 5(h)).

[0052] When transistor Q1 is turned on, the converter unit 30 and the short-circuit location are connected via transistor Q1. As a result, the converter unit 30 detects the short circuit in the DC voltage line DC5 again and stops the switching operation of transistor Q3 (Figure 5(i)). Because the above operation is repeated, the converter unit 30 is repeatedly started up without latching down, and the protection function of the power supply unit 100 against short circuits cannot be activated.

[0053] In this embodiment, the power supply unit 100 is provided with a discharge unit 60 including a transistor Tr1 that turns on or off according to the voltage value of the DC voltage DC5. This allows switching between an enabled state and an disabled state of the discharge function, thereby appropriately protecting the circuits within the power supply unit 100. Specifically, the power supply unit 100 can be protected by appropriately controlling the discharge time of the gate of transistor Q1 when transistor Q1 is turned off.

[0054] For example, by providing the discharge unit 60 in the power supply unit 100, transistor Q1 can be quickly switched off when a momentary power interruption occurs. This reduces the output load of the converter unit 30, thereby suppressing excessive protection due to latch stoppage, and after the momentary power interruption is resolved, the generation of DC voltages DC24 and DC5 can be resumed.

[0055] When the DC voltage line DC5 is short-circuited, the discharge function of the discharge unit 60 is disabled, which allows the converter unit 30 to be latched and the power supply unit 100's protection function against short circuits to be activated.

[0056] Furthermore, even if the power supply unit 100 has a function to suspend control of the gate voltage of transistor Q1 until a predetermined time has elapsed since transistor Q1 was turned on, providing the discharge unit 60 allows transistor Q1 to be quickly turned off when a momentary power interruption occurs.

[0057] Figure 6 is a circuit block diagram showing an example of a power supply device according to another embodiment of the present invention. Elements identical or similar to those in the embodiments described above are denoted by the same reference numerals, and detailed descriptions are omitted. The power supply device 110 shown in Figure 6 adds a voltage detection unit 90 and a transistor Tr2 (NPN bipolar transistor) to the power supply device 100 in Figure 1. Transistor Tr2 is an example of a second transistor.

[0058] When the voltage detection unit 90 detects that the DC voltage DC5 is below a predetermined voltage higher than 0V (i.e., when it detects a low voltage that is not a short circuit), it outputs a base current to the base of transistor Tr2 to turn on transistor Tr2.

[0059] Transistor Tr2 has its collector connected to the gate of transistor Q1 via node ND1 and resistor R1, and its emitter is grounded. Therefore, when the DC voltage DC5 falls below a predetermined voltage value that is higher than 0V, the gate of transistor Q1 is grounded, and transistor Q1 turns off.

[0060] Figure 7 is a timing diagram showing an example of the operation of the power supply unit 110 in Figure 6. Figure 7 shows the operation when an output abnormality occurs in the converter unit 50 due to an abnormality in the feedback system circuit, such as the control unit 51 of the converter unit 50 in Figure 2. Before the output abnormality occurs, the DC voltages DC24 and DC5 (DC5X) are output normally (Figures 7(a) and (b)). Also, the voltage detection unit 90 does not output base current to the base of transistor Tr2 in order to detect the normal DC voltage DC5, and transistor Tr2 is turned off (Figure 7(c)).

[0061] Subsequently, an output abnormality occurs in the converter section 50, and for example, the DC voltage DC24 drops to an intermediate value between the normal value and the ground voltage VSS (Figure 7(d)). Due to the drop in the DC voltage DC24, current flows from the gate of transistor Q1 to the DC voltage line DC24 via the discharge section 60. As a result, the gate voltage of transistor Q1 decreases toward the voltage value of DC24 (Figure 7(e)).

[0062] The decrease in the gate voltage of transistor Q1 causes transistor Q1 to operate in the non-saturation region (Figure 7(f)). This increases the voltage drop between the drain and source of transistor Q1, causing the DC voltage DC5 to decrease (Figure 7(g)). The voltage detection unit 90 detects the decrease in DC voltage DC5 (it is not a short circuit). The voltage detection unit 90 then outputs a base current to the base of transistor Tr2, turning on transistor Tr2 (Figure 7(h)).

[0063] When transistor Tr2 is turned on, the gate voltage of transistor Q1 drops toward the ground voltage VSS, and transistor Q1 turns off (Figure 7(i)). When transistor Q1 is turned off, the output of the DC voltage DC5 is stopped (Figure 7(j)). This prevents transistor Q1 from continuing to operate in a non-saturated state, thus protecting transistor Q1 from failure or damage.

[0064] In contrast, if the power supply unit 110 does not have a voltage detection unit 90 and transistor Tr2, and the DC voltage DC24 remains low due to an abnormality in the feedback system of the converter unit 50, the gate voltage of transistor Q1 may remain low. In this case, transistor Q1 may continue to operate in the non-saturation region. Furthermore, while transistor Q1 is operating in the non-saturation region, the DC voltage DC5 also decreases due to the voltage drop between the drain and source of transistor Q1. In this case, the losses of transistor Q1 increase, and transistor Q1 may fail or be damaged.

[0065] As described above, the same effects as those of the embodiments described can be obtained in this embodiment as well. For example, by providing a discharge unit 60 in the power supply unit 110 that includes a transistor Tr1 which turns on or off according to the voltage value of the DC voltage DC5, the enabled and disabled states of the discharge function can be switched, and the circuits in the power supply unit 110 can be properly protected.

[0066] Furthermore, in this embodiment, the voltage detection unit 90 and the transistor Tr2 are provided in the power supply unit 110. This prevents the transistor Q1 from continuing to operate in a non-saturated state in the event of an output abnormality in the converter unit 50, thereby protecting the transistor Q1 from failure or damage.

[0067] Figure 8 is an overall configuration diagram showing an example of an image forming apparatus equipped with the power supply unit 100 in Figure 1 and the power supply unit 110 in Figure 6. The image forming apparatus 1 shown in Figure 8 is a digital multifunction printer (MFP: Multi-Function Printer) that has functions such as copying, printing, scanning, and facsimile. The image forming apparatus 1 can switch between operating modes that realize the copying, printing, scanning, and facsimile functions, respectively, using application switching keys on the operation panel of the image forming apparatus 1. When the copying function is selected, the image forming apparatus 1 enters copy mode; when the printing function is selected, it enters print mode; when the scanning function is selected, it enters scanner mode; and when the facsimile function is selected, it enters facsimile mode.

[0068] Furthermore, the image forming apparatus 1 switches its internal state to a normal mode or an energy-saving mode (power-saving mode) depending on the state of its internal circuitry. For example, the normal mode has an operating mode (operating state) and a standby mode (standby state).

[0069] For example, the operating mode includes copy mode or print mode for printing images or text data onto paper media. Print mode includes the operation of printing received data onto paper media in facsimile mode. The operating mode also includes scanner mode for scanning documents or transmission / reception operations in facsimile mode. The state of the internal circuitry is switched by user operation of the control panel or control within the image forming apparatus 1.

[0070] For example, the image forming apparatus 1 includes an automatic document feeder (ADF), an image reading device 3, a writing unit 4, a printer unit 5, an operation panel 11, a control device 12, and a power supply unit 13.

[0071] The power supply unit 13 is either the power supply unit 100 in Figure 1 or the power supply unit 110 in Figure 6. The power supply unit 13 supplies the generated DC voltage DC24 to various loads such as the printer unit 5. Examples of loads include various motors, a charger for charging the photoreceptor drum 6, and the developing rollers of the developing device 7.

[0072] The power supply unit 13 supplies the generated DC voltage DC5 to the control device 12 as the operating power source for the CPU, memory, etc. mounted on the control device 12. The power supply unit 13 also continuously supplies the generated DC voltage DC5X to the control board, to which the operation panel 11 is connected, as the operating power source for the CPU (Central Processing Unit), memory, etc. mounted on the control board.

[0073] The printer unit 5 includes a photosensitive drum 6, a developing unit 7, a transport belt 8, a fixing unit 9, and a storage space for the paper tray 10. The automatic document feeder 2, image scanning unit 3, writing unit 4, printer unit 5, and control panel 11 are examples of the main body that forms the image.

[0074] The printer unit 5 creates a toner image to be transferred to paper or other media based on the image information. The printer unit 5 is an example of an image forming unit that forms an image. Below, we will briefly explain an example of the image formation process in the image forming apparatus 1, specifically when the operating mode is set to copy mode.

[0075] In copy mode, multiple originals to be copied are placed in the automatic document feeder 2, or the originals to be copied are placed on the image scanner 3. When the start button displayed on the control panel 11 is pressed, the automatic document feeder 2 feeds the originals one by one to the image scanner 3. The image scanner 3 reads the image information of each of the originals sent sequentially from the automatic document feeder 2 or of the originals placed on the image scanner 3. The image information read by the image scanner 3 is processed, for example, by the image processing unit installed in the control unit 12.

[0076] The writing unit 4 converts the image information processed by the image processing unit into optical information. The photoreceptor drum 6 is uniformly charged by a charger positioned opposite the photoreceptor drum 6, and then exposed to laser light containing the optical information converted by the writing unit 4. Exposure forms an electrostatic latent image on the photoreceptor drum 6. The developing unit 7 develops the electrostatic latent image on the photoreceptor drum 6 and forms a toner image on the photoreceptor drum 6. The transport belt 8 transfers the toner image to paper or the like. The fixing unit 9 fixes the toner image to the paper or the like. The transfer paper with the copied image of the original is then discharged from the discharge unit.

[0077] For example, the standby mode (=normal mode) described above is the state in copy mode until the start button is pressed, and the operating mode (=normal mode) is the state from when the start button is pressed until the paper media is ejected. In the normal mode in which the power supply unit 13 generates DC voltages DC24, DC5, and DC5X, loads such as motors are operating or ready to operate in response to the DC voltage DC24.

[0078] After the operation mode ends, the image forming apparatus 1 returns to standby mode, and if standby mode continues for a predetermined time, it enters energy-saving mode (sleep state). The power supply unit 13 then receives a high-level energy-saving signal ECO and stops generating DC voltages DC24 and DC5. If the operation panel 11 is operated during energy-saving mode, the image forming apparatus 1 returns to standby mode. In this case, the power supply unit 13 receives a low-level energy-saving signal ECO and resumes generating DC voltages DC24 and DC5.

[0079] The control panel 11 accepts various inputs in response to user operations and displays various information on its display unit. For example, the information displayed on the control panel 11 may include information indicating the operation that was accepted, information indicating the operating status of the image forming apparatus 1, or information indicating the settings status of the image forming apparatus 1. The control board to which the control panel 11 is connected operates continuously by receiving a DC voltage of DC5X. Therefore, the control panel 11 can accept various inputs not only in normal mode but also in energy-saving mode. The control panel 11 is an example of an external interface unit that accepts operations from the outside.

[0080] The control device 12 controls the overall operation of the image forming apparatus 1, including the control of the printer unit 5, communication control, and input control to the operation panel 11, by having a control program executed by a built-in CPU or other controller. The control device 12 then performs image processing or data processing by executing an image processing program or data processing program to form an image to be transferred to paper media, etc. Since the control device 12 operates by receiving a DC voltage DC5, it stops operating during energy-saving mode.

[0081] Figure 8 shows an example in which the power supply unit 100 shown in Figure 1 or the power supply unit 110 shown in Figure 6 is mounted on the image forming apparatus 1 as power supply unit 13. However, the power supply unit 100 shown in Figure 1 or the power supply unit 110 shown in Figure 6 can be supplied with multiple types of DC voltages DC24, DC5, and DC5X, and can be mounted on electronic equipment in which DC voltages DC24 and DC5 are not used during energy-saving mode.

[0082] Examples of the present invention are as follows: <1> Regardless of whether it is the first mode or the second mode, a first converter unit generates a first voltage according to the input voltage, A first transistor that turns on during the first mode to output the first voltage as a second voltage, and turns off during the second mode to stop outputting the second voltage, A second converter unit that generates a third voltage during the first mode and stops generating the third voltage during the second mode, A gate control unit that, while the output of the second voltage is active, turns on a discharge path connected to the gate of the first transistor in response to a decrease in the third voltage, thereby turning off the first transistor, and while the output of the second voltage is stopped, suppresses the turning on of the discharge path in response to a decrease in the third voltage, A power supply device characterized by having the following features. <2> The gate control unit suppresses the turning on of the discharge path in accordance with the decrease in the third voltage when the voltage line outputting the second voltage is short-circuited. The aforementioned <1> The power supply unit described above. <3> The first voltage decreases along with the second voltage through the first transistor, which remains on due to the suppression of the discharge path being turned on. The first converter unit latches shut down based on the fact that the first voltage drop continues for a certain period of time. The aforementioned <2> The power supply unit described above. <4> A voltage detection unit for detecting the voltage value of the second voltage, The second transistor is connected between the gate of the first transistor and the ground wire, and when the voltage detection unit detects that the second voltage has dropped to a predetermined voltage higher than the ground voltage, the second transistor grounds the gate of the first transistor. The above is characterized by having <1> or the aforementioned <3> A power supply device as described in any of the following. <5> The aforementioned <1> or the aforementioned <4> A power supply unit as described in any of the following, An image forming unit that forms an image using the second voltage and the third voltage during the first mode, An external interface unit that accepts external operation using the first voltage during the second mode, An image forming apparatus characterized by having the following features.

[0083] Although the present invention has been described above based on various embodiments, the present invention is not limited to the requirements shown in the above embodiments. These points can be modified as long as they do not impair the spirit of the present invention, and can be appropriately determined according to their application. [Explanation of Symbols]

[0084] 1. Image forming apparatus 2. Automatic document feeder 3. Image reading device 4 Writing Unit 5. Printer Unit 6. Photoconductor drum 7. Developing device 8. Conveyor belt 9. Fixing device 10 Paper feed tray 11. Control Panel 12 Control device 13 Power supply 20 Smooth section 30 Converter section 31 Control Unit 32. Pulse width determination unit 33 Current detection unit 34 Constant voltage generation unit 35 Output Feedback Section 36 Smooth section 40 Power supply section 50 Converter section 51 Control Unit 52 Main circuit 60 Discharge section 70 Current detection unit 80 Stop part 90 Voltage detection unit 100, 110, 200 power supplies AC alternating current power supply D1, D2 diodes DB Diode Bridge DC5, DC5X, DC24 DC voltage ECO energy saving signal Q1, Q2, Q3 Transistors T1 Transformer Tr1, Tr2 Transistors Vin AC voltage [Prior art documents] [Patent Documents]

[0085] [Patent Document 1] Japanese Patent Publication No. 2019-62657

Claims

1. A first converter unit that generates a first voltage according to the input voltage, regardless of whether it is the first mode or the second mode, A first transistor that turns on during the first mode to output the first voltage as a second voltage, and turns off during the second mode to stop the output of the second voltage, A second converter unit that generates a third voltage during the first mode and stops generating the third voltage during the second mode, A gate control unit that, while the second voltage is output, turns off the first transistor by opening the discharge path connected to the gate of the first transistor in response to a decrease in the third voltage, and suppresses the opening of the discharge path in response to a decrease in the third voltage while the second voltage is stopped, A power supply device characterized by having the following features.

2. The gate control unit suppresses the conduction of the discharge path in accordance with the decrease in the third voltage when the voltage line outputting the second voltage is short-circuited. The power supply device according to claim 1, characterized by the following:

3. The first voltage decreases along with the second voltage through the first transistor, which remains on due to the suppression of conduction in the discharge path. The first converter unit latches shut down based on the fact that the decrease in the first voltage continues for a certain period of time. The power supply device according to claim 2, characterized by the following:

4. A voltage detection unit for detecting the voltage value of the second voltage, The second transistor is connected to the gate of the first transistor, and when the voltage detection unit detects that the second voltage has dropped to a predetermined voltage higher than the ground voltage, the second transistor grounds the gate of the first transistor. The power supply device according to claim 1, characterized by having the following features.

5. A power supply device according to any one of claims 1 to 4, An image forming unit that forms an image using the second voltage and the third voltage during the first mode, An external interface unit that accepts external operation using the first voltage during the second mode, An image forming apparatus characterized by having the following features.

Images