A switching power supply circuit with long power-off holding time

Abstract

The present invention relates to a switching power supply circuit with a long power-off holding time, the circuit comprises a power supply input terminal, a filter capacitor C3, a transformer T1 and a power supply output terminal Vout connected in sequence; the switching power supply circuit also comprises a charging current control module, a charging voltage control module, a power drive module and a delay module, the charging current control module is respectively connected to the power supply input terminal, the charging voltage control module and the power drive module, the power drive module is respectively connected to the charging voltage control module and the delay module, and the delay module is connected in parallel with the filter capacitor C3. Compared with the prior art, the present invention has the advantages of reduced volume and reduced cost.

Description

Technical Field

[0001] The invention relates to a switching power supply circuit, in particular to a switching power supply circuit with a long power-off holding time. Background Art

[0002] In order to cope with short-term input voltage drops, the existing switching power supply requires a power-off hold time. Many high-reliability situations require a longer power-off hold time. Usually the power-off hold time is achieved by an electrolytic capacitor, and the capacitor energy storage is calculated as: 1 / 2CV 2 , so there are two common methods to achieve this:

[0003] The energy storage voltage of the capacitor is raised, and an active PFC circuit is used to raise the voltage of the bus capacitor; in addition, the input capacitor capacity is increased. The active PFC circuit is relatively complex and the implementation cost is high. Increasing the input capacitor will cause a large surge current when starting up, and the air switch is easy to trip.

[0004] Generally, the input voltage range is very wide. In order to cope with a certain holding time, the worst requirement is to input the minimum input voltage of the specification. The capacity determines the holding time, so the capacitor voltage must ensure the holding time under the conditions of the highest input voltage and the capacity must ensure the minimum working voltage. That is, choose the capacitor with the highest voltage and the largest capacity. As a result, the capacitor will have very high cost and large volume. Therefore, how to design a switching power supply circuit that limits the charging current and voltage and ensures that the working voltage of the capacitor is the minimum working voltage has become a technical problem that needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a switching power supply circuit with a long power-off holding time.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] According to one aspect of the present invention, a switching power supply circuit with a long power-off holding time is provided, the circuit comprising a power input terminal, a filter capacitor C3, a transformer T1 and a power output terminal Vout connected in sequence; the switching power supply circuit also comprises a charging current control module, a charging voltage control module, a power drive module and a delay module, the charging current control module is respectively connected to the power input terminal, the charging voltage control module and the power drive module, the power drive module is respectively connected to the charging voltage control module and the delay module, and the delay module is connected in parallel with the filter capacitor C3.

[0008] As a preferred technical solution, the power drive module includes a resistor R1, a resistor R2, a resistor R3, a voltage regulator diode ZD1 and a MOS tube Q2, and the resistor R1, the resistor R2 and the resistor R3 are connected in series in sequence;

[0009] The gate of the MOS tube Q2 is respectively connected to one end of the resistor R2, one end of the resistor R3 and the cathode of the voltage-stabilizing diode ZD1, the source is respectively connected to the other end of the resistor R3 and the anode of the voltage-stabilizing diode ZD1, and the drain is connected to the delay module.

[0010] As a preferred technical solution, the charging current control module includes a transistor Q3, a resistor R4 and a resistor R5;

[0011] The base of the transistor Q3 is connected to one end of the resistor R5 and the charging voltage module, the emitter is connected to one end of the resistor R4 and the positive electrode of the voltage zener diode ZD1, and the collector is connected to the negative electrode of the voltage zener diode ZD1.

[0012] The other end of the resistor R4 and the other end of the resistor R5 are connected to the power input terminal respectively.

[0013] As a preferred technical solution, the charging voltage control module includes a resistor R6 and a Zener diode ZD2, one end of the resistor R6 is connected to the base of the transistor Q3, the other end of the resistor R6 is connected to the positive electrode of the Zener diode ZD2, and the negative electrode of the Zener diode ZD2 is connected to the resistor R1.

[0014] As a preferred technical solution, the delay module includes a diode D2 and a capacitor C1, the anode of the diode D2 is connected to the power input terminal, and the cathode of the diode D2 is connected to the cathode of the voltage stabilizing diode ZD2 and the resistor R1 through the capacitor C1.

[0015] As a preferred technical solution, during charging, the current passes through the MOS tube Q2 and the resistor R4 to charge the capacitor C1; the resistor R1, the resistor R2, the resistor R3, and the voltage regulator diode ZD1 provide a driving voltage for the MOS tube Q2. When current flows through the resistor R4, a voltage drop is generated, and when the current exceeds the set threshold voltage, the transistor Q3 is turned on, and the driving voltage of the MOS tube Q2 is lowered, thereby achieving the purpose of controlling the charging current.

[0016] As a preferred technical solution, the charging voltage of the circuit is controlled by the voltage stabilizing diode ZD2 and the resistor R6. When the input voltage exceeds the value of the voltage stabilizing diode ZD2, the transistor Q3 is turned on to lower the driving voltage of the MOS tube Q2.

[0017] As a preferred technical solution, when discharging, when the voltage of the filter capacitor C3 drops below the voltage of the capacitor C1, the capacitor C1 is connected in parallel with the filter capacitor C3 through the diode D2 to extend the holding time of the switching power supply.

[0018] As a preferred technical solution, the power input terminal is a DC input terminal.

[0019] As a preferred technical solution, the power input end includes an AC input end and a rectifier bridge connected in sequence.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1) The capacity of the capacitor of the present invention is constant, and the working voltage of the capacitor is ensured to be the minimum working voltage, thereby reducing the volume and the cost;

[0022] 2) The present invention also limits the charging current of the capacitor, reduces the inrush current during startup, and does not cause the power supply system to trip. The air switch for power supply can select a current close to the normal working current, making the power supply safer and more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a specific circuit diagram of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0025] Example 1

[0026] like Figure 1 As shown, a switching power supply circuit with a long power-off holding time includes a power input terminal, a filter capacitor C3, a transformer T1 and a power output terminal Vout connected in sequence; the switching power supply circuit also includes a charging current control module 2, a charging voltage control module 3, a power drive module 1 and a delay module 4, the charging current control module 2 is respectively connected to the power input terminal, the charging voltage control module 3, and the power drive module 1, the power drive module 1 is respectively connected to the charging voltage control module 3 and the delay module 4, and the delay module 4 is connected in parallel with the filter capacitor C3.

[0027] The power drive module 1 includes a resistor R1, a resistor R2, a resistor R3, a voltage zener diode ZD1 and a MOS tube Q2, wherein the resistor R1, the resistor R2 and the resistor R3 are connected in series in sequence; the gate of the MOS tube Q2 is respectively connected to one end of the resistor R2, one end of the resistor R3 and the negative electrode of the voltage zener diode ZD1, the source is respectively connected to the other end of the resistor R3 and the positive electrode of the voltage zener diode ZD1, and the drain is connected to the delay module 4.

[0028] The charging current control module 2 includes a transistor Q3, a resistor R4 and a resistor R5; the base of the transistor Q3 is respectively connected to one end of the resistor R5 and the charging voltage module, the emitter is respectively connected to one end of the resistor R4 and the positive electrode of the Zener diode ZD1, and the collector is connected to the negative electrode of the Zener diode ZD1; the other end of the resistor R4 and the other end of the resistor R5 are respectively connected to the power input end.

[0029] The charging voltage control module 3 includes a resistor R6 and a voltage regulator diode ZD2. One end of the resistor R6 is connected to the base of the transistor Q3, the other end of the resistor R6 is connected to the positive electrode of the voltage regulator diode ZD2, and the negative electrode of the voltage regulator diode ZD2 is connected to the resistor R1.

[0030] The delay module 4 includes a diode D2 and a capacitor C1. The anode of the diode D2 is connected to the power input terminal, and the cathode of the diode D2 is connected to the cathode of the voltage stabilizing diode ZD2 and the resistor R1 through the capacitor C1.

[0031] The power input terminal includes an AC input terminal and a rectifier bridge connected in sequence.

[0032] The working principle of the present invention is as follows:

[0033] The AC input is rectified by a rectifier bridge, filtered by filter capacitor C3, and transmits energy to the power output terminal Vout through transformer T1.

[0034] During charging, the current passes through the MOS tube Q2 and the resistor R4 to charge the capacitor C1; the resistor R1, the resistor R2, the resistor R3, and the voltage zener diode ZD1 provide a driving voltage for the MOS tube Q2. When current flows through the resistor R4, a voltage drop is generated, and when the current exceeds the set threshold voltage, the transistor Q3 is turned on, and the driving voltage of the MOS tube Q2 is lowered, thereby achieving the purpose of controlling the charging current.

[0035] The charging voltage of the circuit is controlled by the voltage stabilizing diode ZD2 and the resistor R6. When the input voltage exceeds the value of the voltage stabilizing diode ZD2, the transistor Q3 is turned on to lower the driving voltage of the MOS tube Q2.

[0036] During discharge, when the voltage of the filter capacitor C3 drops below the voltage of the capacitor C1, the capacitor C1 is connected in parallel with the filter capacitor C3 through the diode D2, so as to extend the holding time of the switching power supply.

[0037] The capacitance of filter capacitor C3 is small, ensuring the required capacity for normal operation, so that the surge current of power-on is small, and a smaller air switch can be selected. When the input (AC or DC) is powered on, capacitor C1 is charged through MOS tube Q2, and the charging current is limited by transistor Q3 and resistor R4. When the input is powered off, capacitor C1 is connected in parallel with filter capacitor C3 through diode D2 to increase the holding time of the switching power supply.

[0038] Example 2

[0039] The power input terminal is a DC input terminal, which is directly filtered by the filter capacitor C3 and transmits energy to the power output terminal Vout through the transformer T1. The rest is the same as in the first embodiment.

[0040] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A switching power supply circuit with a long power-off holding time, the circuit comprising a power input terminal, a filter capacitor C3, a transformer T1 and a power output terminal Vout connected in sequence; characterized in that: The switching power supply circuit further includes a charging current control module, a charging voltage control module, a power drive module and a delay module, wherein the charging current control module is respectively connected to the power input terminal, the charging voltage control module and the power drive module, wherein the power drive module is respectively connected to the charging voltage control module and the delay module, and the delay module is connected in parallel with the filter capacitor C3; The power drive module includes a resistor R1, a resistor R2, a resistor R3, a voltage stabilizing diode ZD1 and a MOS tube Q2, wherein the resistor R1, the resistor R2 and the resistor R3 are connected in series in sequence; The gate of the MOS tube Q2 is respectively connected to one end of the resistor R2, one end of the resistor R3 and the cathode of the voltage-stabilizing diode ZD1, the source is respectively connected to the other end of the resistor R3 and the anode of the voltage-stabilizing diode ZD1, and the drain is connected to the delay module.

2. A switching power supply circuit with a long power-off holding time according to claim 1, characterized in that: The charging current control module includes a transistor Q3, a resistor R4 and a resistor R5; The base of the transistor Q3 is connected to one end of the resistor R5 and the charging voltage module, the emitter is connected to one end of the resistor R4 and the positive electrode of the voltage zener diode ZD1, and the collector is connected to the negative electrode of the voltage zener diode ZD1. The other end of the resistor R4 and the other end of the resistor R5 are connected to the power input terminal respectively.

3. A switching power supply circuit with a long power-off holding time according to claim 2, characterized in that: The charging voltage control module includes a resistor R6 and a voltage regulator diode ZD2. One end of the resistor R6 is connected to the base of the transistor Q3, the other end of the resistor R6 is connected to the positive electrode of the voltage regulator diode ZD2, and the negative electrode of the voltage regulator diode ZD2 is connected to the resistor R1.

4. The switching power supply circuit with a long power-off holding time according to claim 3, characterized in that: The delay module includes a diode D2 and a capacitor C1. The anode of the diode D2 is connected to the power input terminal, and the cathode of the diode D2 is connected to the cathode of the voltage stabilizing diode ZD2 and the resistor R1 through the capacitor C1.

5. The switching power supply circuit with long power-off holding time according to claim 4, characterized in that: During charging, the current passes through the MOS tube Q2 and the resistor R4 to charge the capacitor C1; the resistor R1, the resistor R2, the resistor R3, and the voltage zener diode ZD1 provide a driving voltage for the MOS tube Q2. When current flows through the resistor R4, a voltage drop is generated, and when the current exceeds the set threshold voltage, the transistor Q3 is turned on, and the driving voltage of the MOS tube Q2 is lowered, thereby achieving the purpose of controlling the charging current.

6. The switching power supply circuit with a long power-off holding time according to claim 4, characterized in that: The charging voltage of the circuit is controlled by the voltage stabilizing diode ZD2 and the resistor R6. When the input voltage exceeds the value of the voltage stabilizing diode ZD2, the transistor Q3 is turned on to lower the driving voltage of the MOS tube Q2.

7. The switching power supply circuit with a long power-off holding time according to claim 4, characterized in that: During discharge, when the voltage of the filter capacitor C3 drops below the voltage of the capacitor C1, the capacitor C1 is connected in parallel with the filter capacitor C3 via the diode D2, thereby extending the holding time of the switching power supply.

8. The switching power supply circuit with long power-off holding time according to claim 1, characterized in that: The power input terminal is a DC input terminal.

9. The switching power supply circuit with long power-off holding time according to claim 1, characterized in that: The power input end includes an AC input end and a rectifier bridge which are connected in sequence.

Images