High-voltage startup circuit for switching power supply and capable of effectively reducing standby power consumption

Abstract

A high-voltage startup circuit with a simple structure, used for a switching power supply and capable of effectively reducing standby power consumption. It includes a working voltage input terminal connected to the primary winding of the transformer of the switching power supply, a pulse voltage output terminal connected to the power supply terminal of the main control chip of the switching power supply, and a grounding terminal connected to the ground pin of the main control chip. A timing chip and a self-locking circuit are also provided between the working voltage input terminal and the pulse voltage output terminal. The timing chip, at the moment of starting the switching power supply, makes the pulse voltage output terminal output a high level, and after a set delay time, makes the pulse voltage output terminal and the voltage output terminal of the timing chip in an open circuit state; the self-locking circuit, after a set delay time, locks the high-voltage startup circuit in the standby state and makes the leakage current between the working voltage input terminal and the grounding terminal less than 0.1 mA. Its standby power consumption can be reduced from 73 mW (220 VAC input, no-load loss) in the prior art to 28 mW.

Description

Technical Field

[0001] The present invention relates to a chip startup circuit, and particularly to a control circuit for a high-voltage startup circuit of a switching power supply. Background Art

[0002] Generally, for the main control chip in a switching power supply, a high-voltage startup circuit is required to provide a startup voltage for it at the moment of power-on. After the main control chip enters the normal working state, the task of the high-voltage startup circuit is completed.

[0003] In the existing high-voltage startup circuits, those skilled in the art often use two triodes and multiple resistors to form a self-locking circuit. After the high-voltage startup circuit completes the startup of the main control chip, the high-voltage startup circuit enters the standby state. As Figure 1 shown, the high-voltage startup circuit is composed of a PNP transistor Q1, an NPN transistor Q2, a diode D1, a bias resistor R1, a resistor R3, and a capacitor C1.

[0004] The "Pin H" terminal in the above high-voltage startup circuit is connected to the primary of the switching power supply transformer through resistors R32 and R33 in the switching power supply (see the circuit schematic diagram in Figure 2 shown); one path of the "Pin E" terminal in the high-voltage startup circuit is connected to the auxiliary winding of the transformer through the second MOS transistor, diode D2, and resistor R12 in the switching power supply, and the other path is connected to the power supply terminal VDD of the main control chip; the "Pin G" terminal in the high-voltage startup circuit is connected to the ground terminal GND of the main control chip.

[0005] The working principle of starting the main control chip is as follows:

[0006] At the moment of power-on, the "Pin H" terminal in the high-voltage startup circuit obtains a voltage, and through resistor R1 and the "Pin E" terminal, provides the first high-level pulse voltage to start the main control chip U1 of the switching power supply. At the same time, transistor Q1 conducts through the bias resistor R1, and then charges capacitor C1. When the charge of capacitor C1 reaches the threshold value of transistor Q2, transistor Q2 conducts and pulls down the collector potential of transistor Q2, and diode D1 turns off. The "Pin E" terminal will no longer supply power to the main control chip U1 (at this time, the auxiliary winding of the transformer provides the normal working voltage for the main control chip U1). Thus, the high-voltage startup circuit completes the task of starting the main control chip. At the same time, the base of transistor Q1 is also at a low potential and continues to conduct, and transistor Q2 will also continue to conduct. At this time, the high-voltage startup circuit is locked and in the standby state.

[0007] The capacitor C1 in the high-voltage startup circuit is used for the delayed conduction of transistor Q2.

[0008] The deficiencies of the above high-voltage startup circuit are as follows:

[0009] The transistor Q1 needs to be configured with a bias resistor R1 to work properly. When the high-voltage startup circuit is in the standby state, since the collector potential of the transistor Q2 is relatively low while the "Pin H" terminal is still at a high potential, there is still a relatively large current flowing through the bias resistor R1. As a result, the standby power consumption of the high-voltage startup circuit in the standby state is still relatively large. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a high-voltage startup circuit with a simple structure, for a switching power supply and capable of effectively reducing standby power consumption.

[0011] To solve the above technical problem, the technical solution adopted by the present invention is as follows:

[0012] The high-voltage startup circuit of the present invention for a switching power supply and capable of effectively reducing standby power consumption includes a working voltage input terminal connected to the primary winding of the transformer of the switching power supply, a pulse voltage output terminal connected to the power supply terminal of the main control chip of the switching power supply, and a ground terminal connected to the ground pin of the main control chip. It is characterized in that: a timing chip and a self-locking circuit are further provided between the working voltage input terminal and the pulse voltage output terminal, wherein,

[0013] The timing chip, at the moment of starting the switching power supply, makes the pulse voltage output terminal output a high level, and after a set delay time, makes the pulse voltage output terminal and the voltage output terminal of the timing chip in an open state;

[0014] The self-locking circuit, after the set delay time, locks the high-voltage startup circuit in the standby state and makes the leakage current between the working voltage input terminal and the ground terminal less than 0.1 mA.

[0015] The working voltage input terminal is connected to the primary winding of the transformer of the switching power supply through the resistor R32 and resistor R33 in the switching power supply; one path of the pulse voltage output terminal is connected to the auxiliary winding of the transformer through the second MOS transistor, diode D2 and resistor R12 in the switching power supply, and the other path is connected to the power supply terminal VDD of the main control chip.

[0016] The timing chip is a chip of the NE555DG4 model of the TI brand, and the connection of each pin of the timing chip is as follows:

[0017] Its power supply terminal is connected to the working voltage input terminal;

[0018] Its voltage output terminal is connected to the pulse voltage output terminal through the positive and negative poles of the diode D1;

[0019] One of its reset terminals is connected to the self-locking circuit, and the other is connected to the working voltage input terminal through a resistor R4;

[0020] After its threshold voltage terminal is connected to its trigger terminal, one path is grounded through a capacitor C3, and the other path is connected to the working voltage input terminal through a resistor R3 and a resistor R1;

[0021] Its discharge terminal is connected in parallel to the connection point of resistor R1 and resistor R3;

[0022] A resistor R2 is provided between the positive electrode of the diode D1 and the ground.

[0023] The self-locking circuit is composed of an N-type MOS transistor Q1 and a P-type MOS transistor Q2. Among them,

[0024] For MOS transistor Q1, its source is grounded; one path of its gate is connected to the voltage output terminal of the timing chip through a resistor R7 via the positive and negative electrodes of the voltage stabilizing diode ZD1, and the other path is connected to the source of MOS transistor Q2. A capacitor C3 is connected in parallel between its gate and source; its drain, the gate of MOS transistor Q2, and the reset terminal of the timing chip are connected in parallel and connected to the working voltage input terminal through a high-resistance resistor R4;

[0025] The drain of MOS transistor Q2 is connected to the working voltage input terminal;

[0026] The resistance value of the high-resistance resistor R4 is not less than 5 megohms.

[0027] The voltage stabilizing diode ZD1 is a BZX84-C10 model diode of the VISHAY brand.

[0028] The model of the diode D1 is 1N4148WS.

[0029] When the high-voltage startup circuit of the present invention is adopted on the switching power supply, the standby power consumption after the switching power supply completes the startup and works normally can be effectively reduced. The standby power consumption can be reduced from 73 mW (220VAC input, no-load loss) in the prior art to 28 mW. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of a high-voltage startup circuit for a switching power supply in the prior art.

[0031] Figure 2 It is a schematic diagram of the circuit of the switching power supply.

[0032] Figure 3 It is a schematic diagram of the high-voltage startup circuit of the present invention.

[0033] Figure 4 For Figure 3 It is the internal logic block diagram of the timing chip adopted by the circuit.

[0034] The reference numerals are as follows: Detailed implementation mode

[0035] The high-voltage startup circuit for a switching power supply and capable of effectively reducing standby power consumption according to the present invention is composed of a timing chip, a self-locking circuit, and several components such as resistors and capacitors.

[0036] Its function is: when the switching power supply (see the circuit schematic diagram of the switching power supply in Figure 2 shown) is powered on instantaneously, it is used to start the main control chip U1 in the switching power supply to enter the normal working state.

[0037] Similar to the high-voltage startup circuit in the prior art, the connection modes of several important nodes of the high-voltage startup circuit of the present invention to the switching power supply are as follows:

[0038] Its working voltage input terminal (i.e., the "Pin H" terminal in Figure 3 ) is connected to the primary winding of the transformer of the switching power supply and obtains voltage at the moment when the switching power supply is powered on. In the switching power supply, between this working voltage input terminal and the primary winding of the transformer, resistors R32 and R33 for voltage division are also connected in series.

[0039] Its pulse voltage output terminal (i.e., the "Pin E" terminal in Figure 3 ) is connected to the power supply terminal of the main control chip of the switching power supply (i.e., the 5th pin "VDD" terminal of the main control chip U1 in Figure 2 ) and is ready to provide a high-potential pulse voltage for starting the operation of this main control chip.

[0040] Its grounding terminal (i.e., the "Pin G" terminal in Figure 3 ) is connected to the ground pin of the main control chip.

[0041] After the main control chip U1 is started and operates normally, this pulse voltage output terminal stops providing electric energy to the main control chip, and the main control chip U1 obtains the rated working voltage from the auxiliary winding of the transformer through the second MOS tube (LDO low-dropout linear regulator), diode D2, and resistor R12 in the switching power supply. Thus, the high-voltage startup circuit completes the startup task and enters the standby sleep state.

[0042] 1. Timing chip

[0043] At the moment of starting the switching power supply, this timing chip makes the pulse voltage output terminal output a high level, and after a set delay time, makes the pulse voltage output terminal and the voltage input terminal of this timing chip in an open-circuit state.

[0044] The timing chip adopts a chip of the NE555DG4 model of the TI brand, and the functions of its respective pins are as follows (see Figure 4 shown):

[0045] Pin 1 (Ground): The ground wire (or common ground), usually connected to the common ground of the circuit.

[0046] Pin 2 (Trigger): This pin triggers the NE555 to start its time cycle. The upper edge voltage of the trigger signal must be greater than 2 / 3 VCC, and the lower edge must be lower than 1 / 3 VCC.

[0047] Pin 3 (Output): When the time cycle starts, the output pin of the 555 moves to a high potential that is 1.7 volts less than the power supply voltage. At the end of the cycle, the output returns to a low potential around 0 volts. The maximum output current at high potential is approximately 200 mA.

[0048] Pin 4 (Reset): When a low logic potential is sent to this pin, it resets the timer and makes the output return to a low potential. It is usually connected to the positive power supply or left unused.

[0049] Pin 5 (Control): This pin allows the trigger and threshold voltages to be changed by an external voltage. When the timer operates in the stable or oscillating mode, this input can be used to change or adjust the output frequency.

[0050] Pin 6 (Threshold Voltage Terminal): It is Threshold. When the voltage of C1 discharges to less than 2 / 3 VCC, this threshold is triggered.

[0051] Pin 7 (Discharge): This pin has the same current output capacity as the main output pin. When Pin3 is at a low level, Pin7 is in a low-resistance state (conductive to the ground), and when Pin3 is at a high level, Pin7 is in a high-resistance state.

[0052] Pin 8 (V+): This is the positive power supply voltage terminal of the 555 timer IC. The supply voltage range is +4.5 volts (minimum) to +16 volts (maximum).

[0053] 2. Self-locking Circuit

[0054] After the set delay time, that is, after the pulse voltage output terminal and the voltage input terminal of the timing chip are in an open state, the high-voltage startup circuit is locked in the standby state, and the leakage current between the working voltage input terminal Pin H and the ground terminal Pin G is less than 0.1 mA.

[0055] 3. The specific structure of the high-voltage startup circuit of the present invention is as follows (see Figure 2 、 3 shown):

[0056] 1) Connection of the timing chip

[0057] The power supply terminal Pin 8 of the timing chip is connected to the working voltage input terminal Pin H;

[0058] Its voltage output terminal Pin 3 is connected to the pulse voltage output terminal Pin E through the positive and negative electrodes of diode D1;

[0059] Its reset terminal Pin 4 is connected to the self-locking circuit on one hand, and on the other hand, it is connected to the working voltage input terminal Pin H through resistor R4;

[0060] After its threshold voltage terminal Pin 6 is connected to its trigger terminal Pin 2, one way is grounded through capacitor C3, and the other way is connected to the working voltage input terminal Pin H through resistor R3 and resistor R1;

[0061] Its discharge terminal Pin 7 is connected in parallel to the connection point of resistor R1 and resistor R3;

[0062] A resistor R2 is provided between the positive electrode of diode D1 and the ground.

[0063] 2) Structure of the self-locking circuit

[0064] The self-locking circuit is composed of an N-type MOS transistor Q1 and a P-type MOS transistor Q2. Among them,

[0065] For MOS transistor Q1, its source is grounded; its gate is connected to the voltage output terminal Pin 3 of the timing chip through resistor R7 via the positive and negative electrodes of zener diode ZD1 on one hand, and on the other hand, the gate is connected to the source of MOS transistor Q2. A capacitor C3 is connected in parallel between its gate and source; its drain, the gate of MOS transistor Q2, and the reset terminal Pin 4 of the timing chip are connected in parallel and then connected to the working voltage input terminal Pin H through a high-impedance resistor R4;

[0066] The drain of MOS transistor Q2 is connected to the working voltage input terminal Pin H;

[0067] The resistance value of the high-impedance resistor R4 is not less than 5 megohms.

[0068] The zener diode ZD1 is a diode of BZX84-C10 model of VISHAY brand.

[0069] The model of the diode D1 is 1N4148WS.

[0070] 4. Working principle

[0071] The present invention uses a NE555 pulse trigger circuit and peripheral components to form a single-pulse generator of the high-voltage startup circuit of the present invention. The first pulse is supplied to the main control chip of the switching power supply to turn it on, and then the high-voltage startup circuit is quickly turned off.

[0072] At the moment of power-on, the working voltage input terminal Pin H obtains a high potential from the primary winding of the switching power supply. Besides providing the working voltage for the timing chip, this high potential charges the capacitor C1 through the resistor R1 and the resistor R3. Meanwhile, the voltage output terminal Pin 3 of the timing chip outputs a high-level pulse voltage, and this high-level pulse voltage is supplied to the power supply terminal VDD of the main control chip U1 of the switching power supply through the diode D1 and the pulse voltage output terminal Pin E to start the operation of the main control chip U1.

[0073] When the capacitor C1 is charged to a voltage higher than the upper threshold of the threshold voltage terminal Pin 6, the capacitor C1 forms a discharge loop through the resistor R3, the discharge terminal Pin 7 of the timing chip and the ground terminal. When the voltage of the capacitor C1 drops to the lower threshold of the threshold voltage terminal Pin 6, the internal comparator of the timing chip flips, and the voltage output terminal Pin 3 outputs a low level. The diode D1 is reverse cut-off, and the pulse voltage output terminal Pin E stops supplying power to the main control chip of the switching power supply (at this time, the VCC voltage output by the auxiliary winding of the transformer will not flow back to the timing chip either).

[0074] Meanwhile, when the voltage output terminal Pin 3 outputs a high level, the zener diode ZD1 is reversely broken down, so that the gate of the MOS transistor Q1 obtains a potential. Since the reset terminal Pin 4 of the timing chip is at a high potential, the MOS transistor Q1 is turned on.

[0075] When the MOS transistor Q1 is turned on, it pulls down the voltage of the gate of the MOS transistor Q2, causing the MOS transistor Q2 to be turned on. After a chain reaction, the circuit is locked, and the reset terminal Pin 4 of the timing chip remains at a low potential continuously until the power is turned off and restarted to release. Since the resistance value of the high-resistance resistor R4 is very high, the current flowing from the working voltage input terminal Pin H to the reset terminal Pin 4 through this high-resistance resistor R4 is extremely small (usually less than 0.1 mA). Therefore, this state can be regarded as an open circuit. That is to say, when the high-voltage startup circuit is in the standby sleep state, the current flowing through the resistors R32 and R33 in the switching power supply is also extremely small, thus effectively reducing the power consumption.

[0076] Since the reset terminal Pin 4 remains at a low level continuously, the voltage output terminal Pin 3 outputs a low level continuously, so that the high-voltage startup circuit enters the standby sleep state after starting the main control chip U1 of the switching power supply.

[0077] Since the reset terminal Pin 4 remains low, the discharge terminal Pin 7 is open between the ground terminal, and the capacitor C1 will be recharged, but a discharge loop cannot be formed (the condition for discharging is that the transistor Q1 inside the timing chip needs to be turned on, but the transistor Q1 is controlled by the reset terminal Pin 4. Therefore, after the reset terminal Pin 4 is locked, it will remain low, and the transistor Q1 will no longer be turned on unless the device is powered off and restarted), that is, the working voltage input terminal Pin H, the resistor R1, the resistor R3, and the capacitor C1 are open between the ground terminal, and the conduction current is zero.

Claims

1. A high-voltage startup circuit for a switching power supply that can effectively reduce standby power consumption, comprising a working voltage input terminal connected to the primary winding of the transformer of the switching power supply, a pulse voltage output terminal connected to the power supply terminal of the main control chip of the switching power supply, and a ground terminal connected to the ground pin of the main control chip, characterized in that: A timing chip and a self-locking circuit are also provided between the working voltage input terminal and the pulse voltage output terminal. Among them, The timing chip makes the pulse voltage output terminal output a high level at the moment of starting the switching power supply, and makes the voltage output terminal of the pulse voltage output terminal and the timing chip in an open circuit state after a set delay time; The self-locking circuit locks the high-voltage starting circuit in the standby state after the set delay time, and makes the leakage current between the working voltage input terminal and the ground terminal less than 0.1 mA; The pins of the timing chip are connected as follows: Its power supply terminal is connected to the working voltage input terminal; Its voltage output terminal is connected to the pulse voltage output terminal through the positive and negative electrodes of diode D1; Its reset terminal is connected to the self-locking circuit on one hand and to the working voltage input terminal through resistor R4 on the other hand; After its threshold voltage terminal is connected to its trigger terminal, one path is grounded through capacitor C3, and the other path is connected to the working voltage input terminal through resistor R3 and resistor R1; The self-locking circuit is composed of an N-type MOS transistor Q1 and a P-type MOS transistor Q2. Among them, For MOS transistor Q1, its source is grounded; its gate is connected to the voltage output terminal of the timing chip through resistor R7 via the positive and negative electrodes of zener diode ZD1 on one hand and to the source of MOS transistor Q2 on the other hand. A capacitor C3 is connected across its gate and source; its drain, the gate of MOS transistor Q2 and the reset terminal of the timing chip are connected in parallel and connected to the working voltage input terminal through a high-impedance resistor R4; The drain of MOS transistor Q2 is connected to the working voltage input terminal; After the main control chip is started and works normally, the pulse voltage output terminal stops supplying power to the main control chip, and the main control chip obtains the rated working voltage from the auxiliary winding of the transformer through the second MOS transistor, diode D2 and resistor R12 in the switching power supply.

2. The high-voltage startup circuit for a switching power supply capable of effectively reducing standby power consumption according to claim 1, characterized in that: The working voltage input terminal is connected to the primary winding of the switching power supply transformer through resistor R32 and resistor R33 in the switching power supply; one path of the pulse voltage output terminal is connected to the auxiliary winding of the transformer through the second MOS transistor, diode D2 and resistor R12 in the switching power supply, and the other path is connected to the power supply terminal VDD of the main control chip.

3. The high-voltage startup circuit for a switching power supply and capable of effectively reducing standby power consumption according to claim 2, wherein: The timing chip is a chip of model NE555DG4 of TI brand, and its discharge terminal is connected in parallel to the connection point of resistor R1 and resistor R3; a resistor R2 is provided between the positive electrode of diode D1 and the ground.

4. The high-voltage startup circuit for a switching power supply and capable of effectively reducing standby power consumption according to claim 3, characterized in that: The resistance value of the high-impedance resistor R4 is not less than 5 megohms.

5. The high-voltage startup circuit for a switching power supply and capable of effectively reducing standby power consumption according to claim 4, wherein: The zener diode ZD1 is a diode of model BZX84-C10 of VISHAY brand.

6. The high-voltage startup circuit for a switching power supply capable of effectively reducing standby power consumption according to claim 4, characterized in that: The model of the diode D1 is 1N4148WS.

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