Printer slow start power supply protection circuit

Abstract

The invention relates to the technical field of printer protection circuits, and discloses a printer slow start power supply protection circuit, which comprises a slow start module for controlling a direct current voltage input to a main control unit to slowly rise and a protection module for cutting off power supply when a power supply is reversely connected or the input voltage is abnormal, the slow start module comprises a PMOS transistor and a PNP transistor, the source electrode of the PMOS transistor is connected with the power input end, and the drain electrode of the PMOS transistor is connected to the main control unit. Through cooperative control of the PMOS tube and the capacitor charging loop, accurate slow start of direct-current voltage is realized, and current impact is effectively suppressed; according to the printer power supply system, power supply reverse connection or under-voltage abnormity is rapidly responded through combination of an NMOS tube and a voltage stabilizing diode, a power supply protection main control unit is cut off in real time, meanwhile, a low-cost and high-integration-level protection mechanism is constructed through discrete components, the printer power supply system has the advantages of being high in reliability, adjustable in parameter and low in power consumption, and the safety and economical efficiency of the printer power supply system are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of printer protection circuits, and in particular to a printer slow-start power supply protection circuit. Background Art

[0002] In electronic devices like printers, the main control unit (CPU) is a core component, and its power supply stability is directly related to the reliability and service life of the device. Because transient surges in the DC power supply (such as inrush current and voltage spikes) during printer startup or power switching can overload and damage the CPU's semiconductor devices, the design of the power supply protection circuit is crucial.

[0003] Traditional power protection solutions usually use the following technical means:

[0004] Reverse polarity protection: A series diode or fuse is used to prevent incorrect power polarity. However, the diode voltage drop causes additional power consumption, while the fuse has a slow response speed and cannot be reused.

[0005] Voltage stabilization circuit: A linear regulator or switching power supply is used to maintain a stable output voltage. However, this type of circuit has limited ability to suppress transient changes in the input voltage and is relatively expensive.

[0006] Soft start control: Some solutions use RC delay circuits or NTC thermistors to limit the starting current. However, RC circuits cannot accurately control the voltage rise slope, while NTC thermistors have the defects of temperature dependence and long recovery time.

[0007] Furthermore, existing designs for undervoltage protection often rely on voltage detection chips or comparator circuits. While these can achieve threshold determination, they increase circuit complexity and cost. Therefore, we propose a printer soft-start power protection circuit to address these issues. Summary of the Invention

[0008] The printer slow-start power supply protection circuit proposed by the present invention solves the problems in the background art.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] The printer slow-start power supply protection circuit includes a slow-start module for controlling the DC voltage input to the main control unit to slowly rise, and a protection module for cutting off the power supply when the power supply is reversed or the input voltage is abnormal;

[0011] The slow start module includes:

[0012] A PMOS tube, whose source is connected to the power input terminal and whose drain is connected to the main control unit;

[0013] A PNP transistor, whose emitter is connected to the power input terminal, the base is grounded via a first resistor network, and the collector is connected to the gate of the PMOS transistor;

[0014] A capacitor C4 is connected between the gate of the PMOS transistor and ground, and forms a charging loop with the first resistor network. The gate-source voltage of the PMOS transistor is adjusted in stages through the charging process of the capacitor C4, which is used for slow starting of the input voltage.

[0015] The protection module includes:

[0016] The gate of the NMOS tube is connected to the positive terminal of the power input through the voltage regulator diode D2, the source is grounded, and the drain is connected to the ground network;

[0017] When the power supply is reversed or the input voltage is lower than a preset threshold, the NMOS tube is turned off to disconnect the ground network, thereby preventing current from being output to the main control unit.

[0018] Optionally, the first resistor network includes resistors R4, R6 and R8 connected in series, which are used to adjust the charging rate of the capacitor and control the on-time of the PMOS tube.

[0019] Optionally, the breakdown voltage of the voltage stabilizing diode D2 is 10V, which is used to clamp the gate voltage of the NMOS tube to a safety threshold.

[0020] Optionally, the charging circuit of the soft start module further includes a resistor R7, which is used to accelerate the gate charging of the PMOS tube in the initial conduction stage.

[0021] Optionally, the preset threshold of the protection module is determined by the gate-source threshold voltage of the NMOS tube and the breakdown voltage of the Zener diode.

[0022] Optionally, the capacitance value of the capacitor C4 is configured according to the voltage rise rate requirement of the main control unit to adjust the slow start time.

[0023] The beneficial effects of the present invention are:

[0024] Through the coordinated action of a PMOS transistor, PNP transistor, capacitor, and resistor network, the gate-source voltage is adjusted in stages, achieving a smooth rise in the DC input voltage. Compared to traditional RC circuits or NTC thermistors, this solution can precisely control the voltage rise slope, preventing damage to the main control unit caused by transient current surges, while also eliminating the drawbacks of temperature dependence and long recovery time.

[0025] Leveraging the fast response characteristics of the NMOS transistor and Zener diode, the ground network is immediately disconnected when the power polarity is reversed, protecting the main control unit without the additional power consumption caused by the diode voltage drop. When the input voltage falls below the preset threshold, the NMOS transistor quickly shuts down, blocking the power supply and preventing the main control unit from malfunctioning due to insufficient voltage.

[0026] The use of discrete components to build functional modules eliminates the need for complex voltage detection chips or comparator circuits, significantly reducing hardware costs and circuit complexity.

[0027] By configuring the capacitor and resistor network parameters, the soft-start time can be flexibly adjusted to meet the voltage rise rate requirements of different main control units. The low on-resistance design of the MOS transistor reduces energy loss and improves overall energy efficiency. Integrating soft-start, reverse polarity protection, and undervoltage protection into a single circuit simplifies system layout, while improving protection response speed and reliability, and extending the life of the printer's main control unit.

[0028] The present invention realizes precise slow start-up of DC voltage and effectively suppresses current shock through the coordinated control of PMOS tube and capacitor charging circuit; combines NMOS tube and voltage regulator diode to quickly respond to power reverse connection or undervoltage abnormality, and cuts off the power supply to protect the main control unit in real time. At the same time, it uses discrete components to build a low-cost, highly integrated protection mechanism, which has the advantages of strong reliability, adjustable parameters and low power consumption, and significantly improves the safety and economy of the printer power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a circuit diagram of the printer soft-start power supply protection circuit of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0031] Reference Figure 1 , a printer slow-start power protection circuit, the circuit includes a slow-start module and a protection module, the slow-start module and the protection module are introduced in detail below.

[0032] 1. Slow start module

[0033] PMOS transistor Q1: Source S is directly connected to the power input terminal VCC_BAT, receiving the DC input voltage. Drain D is connected to the power input port VCC_MAIN of the main control unit. Gate G is connected to the collector C of PNP transistor Q2 through resistor R7.

[0034] PNP transistor Q2: Emitter E is connected to power input terminal VCC_BAT. Base B is grounded via a first resistor network consisting of resistors R4, R6, and R8 in series. Collector C is connected to gate G of PMOS transistor Q1 via resistor R7.

[0035] Capacitor C4: One end is connected to the gate G of the PMOS transistor Q1, and the other end is grounded. Together with resistors R4, R6, and R8, it forms a charging circuit.

[0036] 2. Protection module

[0037] NMOS transistor Q3: Gate G is connected to the positive power input terminal VCC_BAT through Zener diode D2. Source S is grounded, and drain D is connected to the ground network GND_MAIN. If the power supply is reversed or the input voltage is abnormal, NMOS transistor Q3 turns off, disconnecting the ground network.

[0038] Zener diode D2: The breakdown voltage is 10V, and it is used to clamp the gate voltage of the NMOS tube Q3 to a safe threshold.

[0039] The working principle and implementation steps are as follows:

[0040] 1. Implementation of slow start function

[0041] The first stage is the initial stage of conduction.

[0042] At the moment the power is turned on, VCC_BAT turns on Q2 through the emitter-base loop of the PNP transistor Q2. At this time, the potential of the collector C of Q2 is rapidly pulled down, and the gate G of the PMOS tube Q1 is quickly charged to VCC_BAT through R7, causing the gate-source voltage Vgs of Q1 to quickly drop below the threshold, and Q1 is temporarily turned off.

[0043] The second stage is the slow start process.

[0044] As the base of Q2 gradually lowers its potential through the network of R4, R6, and R8, Q2 turns off. Simultaneously, VCC_BAT charges C4 through the charging circuit formed by R4, R6, R8, and capacitor C4. During the charging process, C4 is equivalent to a gradually increasing dynamic resistor, which acts in series with R8 to divide the voltage, causing the gate potential of the PMOS tube Q1 to slowly decrease. When Vgs reaches the turn-on threshold of Q1, Q1 gradually turns on, and the VCC_MAIN voltage slowly rises, completing the slow start. Through the synergistic effect of the PMOS tube Q1, PNP transistor Q2, capacitor C4, and resistor network, the gate-source voltage is adjusted in stages to achieve a smooth rise in the DC input voltage. Compared to traditional RC circuits or NTC thermistors, this solution can accurately control the voltage rise slope, avoiding damage to the main control unit caused by instantaneous current shocks, while eliminating the defects of temperature dependence and long recovery time.

[0045] 2. Protection function implementation

[0046] Reverse Power Protection: If the power supply polarity is reversed, Zener diode D2 is reverse-blocked, and the gate of NMOS transistor Q3 loses forward voltage, shutting down Q3 and disconnecting the ground network GND_MAIN. This prevents the main control unit from forming a circuit and shutting off power. Leveraging the fast response characteristics of NMOS transistor Q3 and Zener diode D2, the ground network is immediately disconnected in the event of reverse power polarity, protecting the main control unit without the additional power consumption caused by the diode voltage drop.

[0047] Undervoltage protection: When the input voltage falls below a preset threshold (determined by the breakdown voltage of D2 and the Vgs threshold of Q3), D2 fails to breakdown, Q3's gate voltage is insufficient, and it shuts down, disconnecting the ground network and preventing current from flowing to the main control unit. When the input voltage falls below a preset threshold (determined by the breakdown voltage of the Zener diode and the NMOS threshold voltage), the NMOS transistor quickly shuts down, blocking power supply and preventing malfunctions of the main control unit due to insufficient voltage.

[0048] The key component parameters are configured as follows:

[0049] Capacitor C4: The capacity is selected according to the voltage rise rate requirement of the main control unit, and the typical value is 10μF-100μF.

[0050] Resistor network: The resistance values of R4, R6, and R8 jointly determine the charging time constant of C4. For example, R4 = 10kΩ, R6 = 20kΩ, and R8 = 30kΩ.

[0051] Zener diode D2: The breakdown voltage is fixed at 10V and is used to limit the gate voltage of Q3.

[0052] PMOS transistor Q1 and NMOS transistor Q3: Select models with low on-resistance Rds(on) to reduce power consumption.

[0053] It is worth noting that the use of discrete components (such as MOS transistors, voltage regulators, resistors, and capacitors) to construct the functional module eliminates the need for complex voltage detection chips or comparator circuits, significantly reducing hardware cost and circuit complexity, making it particularly suitable for low-cost printer designs. By configuring the parameters of the capacitor (C4) and the resistor network, the soft-start time can be flexibly adjusted to meet the voltage rise rate requirements of different main control units. The low on-resistance (Rds(on)) design of the MOS transistor reduces energy loss and improves overall energy efficiency. Integrating soft-start, reverse polarity protection, and undervoltage protection functions into a single circuit simplifies system layout, while improving protection response speed and reliability, and extending the service life of the printer's main control unit. This circuit achieves a smooth DC voltage rise by controlling the conduction process of the PMOS transistor in stages, effectively preventing damage to the main control unit due to transient current surges. Furthermore, the synergistic effect of the NMOS transistor and voltage regulator diode quickly cuts off power in the event of reverse polarity or undervoltage, significantly improving the reliability and safety of the printer.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. Printer slow start power protection circuit, characterized in that: It includes a slow start module for controlling the DC voltage input to the main control unit to rise slowly, and a protection module for cutting off the power supply when the power supply is reversed or the input voltage is abnormal; The slow start module includes: A PMOS tube, whose source is connected to the power input terminal and whose drain is connected to the main control unit; A PNP transistor, whose emitter is connected to the power input terminal, the base is grounded via a first resistor network, and the collector is connected to the gate of the PMOS transistor; A capacitor C4 is connected between the gate of the PMOS transistor and ground, and forms a charging loop with the first resistor network. The gate-source voltage of the PMOS transistor is adjusted in stages through the charging process of the capacitor C4, which is used for slow starting of the input voltage. The protection module includes: The gate of the NMOS tube is connected to the positive terminal of the power input through the voltage regulator diode D2, the source is grounded, and the drain is connected to the ground network; When the power supply is reversed or the input voltage is lower than a preset threshold, the NMOS tube is turned off to disconnect the ground network, thereby preventing current from being output to the main control unit.

2. The printer slow-start power protection circuit according to claim 1, characterized in that: The first resistor network includes resistors R4, R6 and R8 connected in series, and is used to adjust the charging rate of the capacitor and control the on-time of the PMOS transistor.

3. The printer slow-start power protection circuit according to claim 1, characterized in that: The breakdown voltage of the voltage stabilizing diode D2 is 10V, and is used to clamp the gate voltage of the NMOS transistor to a safety threshold.

4. The printer slow-start power protection circuit according to claim 1, characterized in that: The charging circuit of the soft start module further includes a resistor R7 for accelerating the charging of the gate of the PMOS tube in the initial conduction stage.

5. The printer slow-start power protection circuit according to claim 1, characterized in that: The preset threshold of the protection module is determined by the gate-source threshold voltage of the NMOS tube and the breakdown voltage of the voltage regulator diode.

6. The printer slow-start power protection circuit according to claim 1, characterized in that: The capacitance value of the capacitor C4 is configured according to the voltage rise rate requirement of the main control unit and is used to adjust the slow start time.

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