Flyback power supply for over-temperature protection during short circuit

Abstract

The utility model discloses a flyback power supply for over-temperature protection during short circuit, and the flyback power supply is characterized in that the OUTPUT end of a power supply chip U1 is connected with the grid electrode of an MOS tube Q1, and the GND end of the power supply chip U1 is grounded; one end of a secondary coil of the transformer is connected with one end of the diode D1; a first node is arranged between the diode D2 and the capacitor C2, a branch is led out from the first node and passes through a thermistor R2 and a resistor R5, one end, far away from the first node, of the resistor R5 is connected with a negative electrode of a power supply, a drain electrode of the MOS tube Q2 is connected with one end, far away from the resistor R5, of the thermistor R2, and a grid electrode of the MOS tube Q2 is connected to a connecting line of the thermistor R2 and the resistor R5. The drain electrode of the MOS tube Q2 is further connected with the VCC end of the power supply chip U1, and the source electrode of the MOS tube Q2 is connected with the GND end of the power supply chip U1. According to the application, the phenomenon of damage caused by over-high temperature of the diode D1 during short circuit can be avoided.

Description

Technical Field

[0001] The present application relates to the technical field of power supply circuits, and in particular to a flyback power supply with over-temperature protection during short circuit. Background Art

[0002] Flyback power supply is a common switching power supply topology, which has the characteristics of simple design and low cost, and is widely used in various consumer electronic products in life. Flyback power supply usually converts the input power into various voltages required by various consumer electronic products to meet the needs of production and life.

[0003] However, in actual application, when a short circuit occurs in the flyback power supply, it may cause serious safety problems and equipment damage. Therefore, the prior art generally limits the output power of the flyback power supply cycle by cycle through a current loop, so that the output voltage of the flyback power supply can automatically drop below the minimum operating voltage of its power chip, and the power chip stops working until the start capacitor is charged to the minimum starting voltage of the power chip, thereby realizing hiccup protection for the flyback power supply. However, after a short circuit occurs in the flyback power supply, the temperature of the secondary rectifier diode will be high due to the large current in the short-circuited winding. By limiting the output power of the flyback power supply cycle by cycle through a current loop, when the power chip is charged to the minimum starting voltage of the power chip, it will work again, and does not care about the temperature problem of the secondary rectifier diode. If it continues to work, the temperature of the rectifier secondary diode will continue to rise, resulting in a shortened device life or even device burnout. Utility Model Content

[0004] Based on this, in order to solve the above technical problems, a flyback power supply with over-temperature protection during short circuit is provided, which can avoid the problem of high temperature of the secondary rectifier diode caused by short circuit in the prior art, thereby damaging the flyback power supply.

[0005] A flyback power supply with over-temperature protection during short circuit, comprising: a capacitor C1, a capacitor C3, a resistor R1, a diode D1, a diode D2, a transformer T1, a resistor R5, a MOS tube Q1, a power chip U1 and a current detection circuit; the transformer T1 comprises a first primary coil, a second primary coil and a secondary coil; one end of the first primary coil is connected to a power supply port, the other end of the first primary coil is connected to the MOS tube Q1 and the current detection circuit in sequence and then connected to the first port of the capacitor C1; one end of the second primary coil is connected to the diode D1 and then connected to the second port of the capacitor C1; the OUTPUT of the power chip U1 The port is connected to the gate of the MOS tube Q1, and the GND port of the power chip U1 is grounded; one end of the secondary coil is connected to one end of the diode D2, one end of the resistor R5 is connected to the other end of the diode D2, and the other end of the resistor R5 is connected to the other end of the secondary coil, and the two ends of the resistor R5 are the output ends of the flyback power supply; the other end of the diode D2 is also connected to one end of the capacitor C3, and the other end of the capacitor C3 is grounded; one end of the resistor R1 is connected to the connection line between the power supply port and the first primary coil, and the other end of the resistor R1 is connected to the connection line between the diode D1 and the capacitor C1;

[0006] It also includes: a resistor R2, a resistor R3, and a MOS tube Q2; a branch is led out from the node where the resistor R1 is connected to the connection line between the diode D1 and the capacitor C1, passing through the thermistor R2 and the resistor R3 in sequence, an end of the resistor R3 away from the resistor R2 is connected to the first port of the capacitor C1, a drain of the MOS tube Q2 is connected to an end of the thermistor R2 away from the resistor R3, a gate of the MOS tube Q2 is connected to the connection line between the thermistor R2 and the resistor R3, a drain of the MOS tube Q2 is also connected to the VCC end of the power chip U1, and a source of the MOS tube Q2 is connected to the GND end of the power chip U1;

[0007] When the thermistor R2 is arranged on the PCB board, the thermistor R2 and the diode D1 are arranged adjacent to each other.

[0008] The above solution may optionally further include: a capacitor C2; the gate of the MOS tube Q2 is also connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the first port of the capacitor C1.

[0009] In the above scheme, optionally, the current detection circuit includes: a resistor R6, a capacitor C4, and a resistor R4; the capacitor C4 is connected in parallel with the resistor R4, one end of the resistor R6 is connected to one end of the capacitor C4, and the other end of the resistor R6 is connected to the ISENSE port of the power chip U1; a connection point between the capacitor C4 and the resistor R4 is connected to the MOS tube Q1, and another connection point between the capacitor C4 and the resistor R4 is connected to the other end of the capacitor C1.

[0010] This application has at least the following beneficial effects:

[0011] In the present application, when the flyback power supply PVB board is arranged electronically, a thermistor R2 is arranged near the rectifier diode D1 on the secondary coil of the transformer, and the thermistor R2 and the resistor R5 are connected to a branch derived from the connection line between the diode D2 and the capacitor C2, and the drain of the MOS tube Q2 is connected to the end of the thermistor R2 away from the resistor R5, the gate of the MOS tube Q2 is connected to the connection line between the thermistor R2 and the resistor R5, the drain of the MOS tube Q2 is also connected to the VCC end of the power chip U1, and the source of the MOS tube Q2 is connected to the GND end of the power chip U1. As a result, when the rectifier diode D1 on the secondary coil of the transformer heats up, the thermistor R2 decreases with the increase in temperature, the driving voltage of the MOS tube Q2 increases, the MOS tube Q2 is turned on, the power chip pin VCC is pulled down to the bottom, the power chip does not work, and the flyback power supply does not work as a whole. As a result, the rectifier diode D1 on the secondary coil of the transformer reduces its temperature through heat dissipation, the thermistor resistance increases, the driving voltage does not reach the driving voltage of the MOSFET device Q2, the MOS tube Q2 is turned off, and the power chip power supply circuit is supplied through the power chip. The power chip VCC voltage increases, and the flyback power supply system passes through the current loop again for hiccup protection. This circuit avoids the phenomenon that the secondary rectifier diode D1 is damaged due to high temperature during a short circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A circuit diagram of a flyback power supply with over-temperature protection during short circuit is provided for one embodiment of the present application. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0014] In one embodiment, Figure 1As shown, a flyback power supply with over-temperature protection during short circuit includes: a capacitor C1, a capacitor C3, a resistor R1, a diode D1, a diode D2, a transformer T1, a resistor R5, a MOS tube Q1, a power chip U1 and a current detection circuit; the transformer T1 includes a first primary coil, a second primary coil and a secondary coil; one end of the first primary coil is connected to the power supply port, and the other end of the first primary coil is connected to the MOS tube Q1 and the current detection circuit in sequence and then connected to the first port of the capacitor C1; one end of the second primary coil is connected to the diode D1 and then connected to the second port of the capacitor C1; OUTP The UT port is connected to the gate of the MOS tube Q1, and the GND port of the power chip U1 is grounded; one end of the secondary coil is connected to one end of the diode D2, one end of the resistor R5 is connected to the other end of the diode D2, and the other end of the resistor R5 is connected to the other end of the secondary coil, and both ends of the resistor R5 are output ends of the flyback power supply; the other end of the diode D2 is also connected to one end of the capacitor C3, and the other end of the capacitor C3 is grounded; one end of the resistor R1 is connected to the connection line between the power supply port and the first primary coil, and the other end of the resistor R1 is connected to the connection line between the diode D1 and the capacitor C1;

[0015] It also includes: a resistor R2, a resistor R3, and a MOS tube Q2; a branch is led out from the node where the resistor R1 is connected to the connection line between the diode D1 and the capacitor C1, passing through the thermistor R2 and the resistor R3 in sequence, an end of the resistor R3 away from the resistor R2 is connected to the first port of the capacitor C1, a drain of the MOS tube Q2 is connected to an end of the thermistor R2 away from the resistor R3, a gate of the MOS tube Q2 is connected to the connection line between the thermistor R2 and the resistor R3, a drain of the MOS tube Q2 is also connected to the VCC end of the power chip U1, and a source of the MOS tube Q2 is connected to the GND end of the power chip U1;

[0016] When the thermistor R2 is arranged on the PCB board, the thermistor R2 and the diode D1 are arranged adjacent to each other.

[0017] Specifically, in the above scheme, the prior art generally detects that the output voltage is too large through the acquisition circuit, and reduces the PWM control signal of the switch tube Q1 through the power chip U1, thereby causing the output voltage to drop. At this time, the second primary coil cannot supply power to the capacitor C2, causing the power supply U1 to be below the minimum working voltage, thereby realizing the hiccup protection of the flyback power supply. However, due to the large current of the secondary coil, the temperature of the rectifier diode D1 on the secondary coil is high, resulting in a shortened device life or even device burnout.

[0018] Therefore, an NTC thermistor R2 is added near the secondary rectifier diode D1 with a higher temperature. When the secondary rectifier diode D1 reaches a certain temperature, the resistance of the NTC thermistor R2 decreases, driving the MOSFET device Q2. The chip power supply pin is pulled down to the ground, and the flyback system stops working, protecting the safety of the rectifier diode D1 device.

[0019] In the above-mentioned flyback power supply with over-temperature protection during short circuit, a thermistor R2 is arranged near the rectifier diode D1 on the secondary coil of the transformer when the flyback power supply PVB panel is arranged electronically, the thermistor R2 and the resistor R5 are connected to a branch derived from the connection line between the diode D2 and the capacitor C2, the drain of the MOS tube Q2 is connected to the end of the thermistor R2 away from the resistor R5, the gate of the MOS tube Q2 is connected to the connection line between the thermistor R2 and the resistor R5, the drain of the MOS tube Q2 is also connected to the VCC end of the power chip U1, and the source of the MOS tube Q2 is connected to the GND end of the power chip U1. As a result, when the rectifier diode D1 on the secondary coil of the transformer heats up, the thermistor R2 decreases with the increase in temperature, the driving voltage of the MOS tube Q2 increases, the MOS tube Q2 is turned on, the power chip pin VCC is pulled down to the bottom, the power chip does not work, and the flyback power supply does not work as a whole. As a result, the rectifier diode D1 on the secondary coil of the transformer reduces its temperature through heat dissipation, the thermistor resistance increases, the driving voltage does not reach the driving voltage of the MOSFET device Q2, the MOS tube Q2 is turned off, and the power chip power supply circuit is supplied through the power chip. The power chip VCC voltage increases, and the flyback power supply system passes through the current loop again for hiccup protection. This circuit avoids the phenomenon that the secondary rectifier diode D1 is damaged due to high temperature during a short circuit.

[0020] In one embodiment, it further includes: capacitor C2; the gate of the MOS transistor Q2 is also connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the first port of the capacitor C1. In this embodiment, the capacitor C3 plays a filtering role in the circuit to prevent the MOSFET device Q2 from being mis-conducted.

[0021] During the hiccup protection of the flyback power supply, the temperature of the rectifier diode D1 on the secondary coil is relatively high. The NTC thermistor R2 is arranged around the rectifier diode D1 through PCB layout to realize the function of NTC thermistor R2. As the temperature increases, the resistance value of the NTC thermistor R2 decreases, and the driving voltage of the MOS tube Q2 increases until the voltage reaches the driving voltage of the MOS tube Q2, driving the MOS tube Q2, and the chip power supply pin is pulled down to the ground, pulling the power chip VCC voltage below the working voltage, and the system stops working. C3 plays a filtering role in the circuit to prevent the MOS tube Q2 from being mis-conducted. When the diode temperature decreases through heat dissipation, the resistance value of the NTC resistor increases, and the voltage does not reach the driving voltage of the MOS tube Q2. The MOS tube is turned off and charged through the power chip power supply circuit. The power chip VCC voltage increases, and the flyback power supply system passes through the current loop again for hiccup protection. This circuit avoids the phenomenon that the secondary rectifier diode D1 is damaged due to high temperature during a short circuit.

[0022] In one embodiment, the current detection circuit includes: a resistor R6, a capacitor C4, and a resistor R4; the capacitor C4 is connected in parallel with the resistor R4, one end of the resistor R6 is connected to one end of the capacitor C4, and the other end of the resistor R6 is connected to the ISENSE port of the power chip U1; a connection point between the capacitor C4 and the resistor R4 is connected to the MOS tube Q1, and another connection point between the capacitor C4 and the resistor R4 is connected to the other end of the capacitor C1.

[0023] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0024] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the utility model patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A flyback power supply with over-temperature protection during short circuit, comprising: Capacitor C1, capacitor C3, resistor R1, diode D1, diode D2, transformer T1, resistor R5, MOS tube Q1, power chip U1 and current detection circuit; The transformer T1 includes a first primary coil, a second primary coil and a secondary coil; one end of the first primary coil is connected to the power supply port, and the other end of the first primary coil is connected to the MOS tube Q1 and the current detection circuit in sequence and then connected to the first port of the capacitor C1; one end of the second primary coil is connected to the diode D1 and then connected to the second port of the capacitor C1; the OUTPUT port of the power chip U1 is connected to the gate of the MOS tube Q1, and the GND port of the power chip U1 is grounded; one end of the secondary coil is connected to one end of the diode D2, one end of the resistor R5 is connected to the other end of the diode D2, and the other end of the resistor R5 is connected to the other end of the secondary coil, and the two ends of the resistor R5 are the output ends of the flyback power supply; the other end of the diode D2 is also connected to one end of the capacitor C3, and the other end of the capacitor C3 is grounded; one end of the resistor R1 is connected to the connection line between the power supply port and the first primary coil, and the other end of the resistor R1 is connected to the connection line between the diode D1 and the capacitor C1; The invention is characterized in that it also includes: a resistor R2, a resistor R3, and a MOS tube Q2; a branch is led out from the node where the resistor R1 is connected to the connection line between the diode D1 and the capacitor C1, and passes through the thermistor R2 and the resistor R3 in sequence, an end of the resistor R3 away from the resistor R2 is connected to the first port of the capacitor C1, a drain of the MOS tube Q2 is connected to an end of the thermistor R2 away from the resistor R3, a gate of the MOS tube Q2 is connected to the connection line between the thermistor R2 and the resistor R3, a drain of the MOS tube Q2 is also connected to the VCC end of the power chip U1, and a source of the MOS tube Q2 is connected to the GND end of the power chip U1; When the thermistor R2 is arranged on the PCB board, the thermistor R2 and the diode D1 are arranged adjacent to each other.

2. The flyback power supply with over-temperature protection during short circuit according to claim 1, characterized in that: Also includes: Capacitor C2; the gate of the MOS tube Q2 is also connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the first port of the capacitor C1.

3. The flyback power supply with over-temperature protection during short circuit according to claim 1, characterized in that: The current detection circuit includes: a resistor R6, a capacitor C4, and a resistor R4; the capacitor C4 is connected in parallel with the resistor R4, one end of the resistor R6 is connected to one end of the capacitor C4, and the other end of the resistor R6 is connected to the ISENSE port of the power chip U1; a connection point between the capacitor C4 and the resistor R4 is connected to the MOS tube Q1, and another connection point between the capacitor C4 and the resistor R4 is connected to the other end of the capacitor C1.

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