A protection circuit for suppressing impulse current of a power frequency transformer
By combining the power frequency transformer's energy extraction isolation, rectification, and voltage regulation circuits, and utilizing components such as current transformers and bidirectional thyristors, the problem of excessive transformer starting current causing fuse burnout was solved, thus achieving power supply stability and cost control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- JIANGSU HUAZHOU ELECTRIC CO LTD
- Filing Date
- 2025-05-13
- Publication Date
- 2026-07-14
AI Technical Summary
R-type power frequency transformers have a large inrush current when energized, which can easily burn out fuses. Increasing the fuse size also leads to increased transformer power and higher costs.
By employing a combination of energy extraction isolation circuit, rectifier circuit, voltage regulator circuit, and suppression circuit, and using components such as current transformer, rectifier bridge, Zener diode, and bidirectional thyristor, the starting current is converted and limited to avoid the impact of instantaneous large current on the fuse.
It effectively prevents fuses from burning out, reduces the failure rate of intrinsically safe power supplies, avoids the high costs associated with increased transformer power, and achieves reliable electrical isolation and stable voltage output.
Smart Images
Figure CN224502923U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a protection circuit for suppressing inrush current in power frequency transformers within the field of transformer protection technology. Background Technology
[0002] Although R-type power frequency transformers have the advantages of small size and high efficiency, in actual use, due to the closed magnetic circuit of this type of transformer, the inrush current of the power-on excitation is large, often 2 to 5 times the rated current value. At the moment of power-on startup, the fuse is easily damaged by the large instantaneous current. If a fuse with a larger rated current value is selected, the power of the transformer needs to be increased, which in turn increases the overall cost of the intrinsically safe power supply. Utility Model Content
[0003] The purpose of this invention is to provide a protection circuit for suppressing inrush current in power frequency transformers, preventing instantaneous large currents from burning out the transformer fuses, thereby reducing the failure rate of intrinsically safe power supplies and avoiding the high costs associated with increasing transformer power.
[0004] To achieve the above objectives, this utility model provides a protection circuit for suppressing inrush current of a power frequency transformer, including an energy extraction isolation circuit connected to a rectifier circuit, a rectifier circuit connected to a voltage regulator circuit, a voltage regulator circuit connected to a suppression circuit, an energy extraction isolation circuit also connected to the L terminal of an AC power supply and the suppression circuit, a suppression circuit connected to one end of a fuse F1, and the other end of the fuse F1 connected to one end of the primary side of a transformer T1.
[0005] Compared with the prior art, the beneficial effects of this utility model are that the energy extraction isolation circuit obtains the voltage required by the subsequent circuit from the AC power supply and forms reliable electrical isolation. The AC voltage is converted into DC voltage by the rectifier circuit, and a stable voltage output is provided by the voltage regulator circuit. Finally, the suppression circuit avoids the impact of the instantaneous inrush current on the fuse F1, preventing the instantaneous large current from burning out the transformer fuse, thereby reducing the failure rate of the intrinsically safe power supply and avoiding the high cost caused by increasing the power of the transformer.
[0006] As a further improvement of this utility model, the energy extraction isolation circuit includes a current transformer L1. Pins 1 and 2 of the current transformer L1 are connected to the L terminal of the AC power supply and the suppression circuit, respectively. Pins 3 and 4 of the current transformer L1 are connected to the rectifier circuit.
[0007] In this way, through the action of the current transformer L1, after the transformer is energized, the starting current is converted into a proportional voltage. Moreover, the primary and secondary sides of the current transformer L1 transfer energy through the change of the magnetic field, thus forming an effective and reliable electrical isolation.
[0008] As a further improvement of this utility model, the rectifier circuit includes a rectifier bridge BD1. The two input terminals of the rectifier bridge BD1 are connected to pins 3 and 4 of the current transformer L1, respectively. The output terminal of the rectifier bridge BD1 is connected in parallel with capacitor C4, and capacitor C4 is connected to the voltage regulator circuit.
[0009] In this way, rectifier bridge BD1 converts the AC voltage output by current transformer L1 into DC voltage. Capacitor C4 is connected to the output terminal of rectifier bridge BD1, which can improve the load characteristics of the rectifier circuit and provide a stable voltage output for the subsequent voltage regulation circuit.
[0010] As a further improvement of this utility model, the voltage regulator circuit includes a transistor Q1, one end of a capacitor C4 is connected to the collector of transistor Q1 and one end of a resistor R1, the other end of capacitor C4 is connected to one end of capacitor C1, the base of transistor Q1 is connected to the other end of resistor R1 and the negative terminal of Zener diode ZD1, the positive terminal of Zener diode ZD1 is connected to one end of capacitor C1, the other end of capacitor C1 is connected to one end of resistor R1, the emitter of transistor Q1 is connected to the negative terminal of diode D2, the positive terminal of Zener diode ZD1 is connected to the positive terminal of diode D2, and a capacitor C3 is connected in parallel across diode D2.
[0011] The function of resistor R1 is to provide bias current to transistor Q1, so that transistor Q1 conducts, and at the same time provide operating current to Zener diode ZD1. Zener diode ZD1 is connected to the base of transistor Q1, so the base voltage of transistor Q1 is stabilized at a fixed value by Zener diode ZD1.
[0012] As a further improvement of this utility model, the suppression circuit includes a resistor R4. One end of the resistor R4 is connected to one end of the capacitor C3 and grounded. The other end of the resistor R4 is connected to the positive terminal of the diode D1. The positive and negative terminals of the diode D1 are connected to pins 2 and 1 of the optocoupler U1, respectively. Pins 3 and 4 of the optocoupler U1 are connected to the control electrode of the bidirectional thyristor Q2 and one end of the resistor R5, respectively. The first anode of the bidirectional thyristor Q2 is connected to one end of the resistor R3. The second anode of the bidirectional thyristor Q2 is connected to one end of the resistor R7, one end of the resistor R6, and the other end of the resistor R5, respectively. A resistor R3 is connected between the second anode of the bidirectional thyristor Q2 and the control electrode. The second anode of the bidirectional thyristor Q2 is connected to one end of the resistor R2. One end of the resistor R2 is connected to pin 2 of the current transformer L1 and one end of the capacitor C2, respectively. The other end of the resistor R2 is connected to the other end of the resistor R7. One end of the resistor R7 is connected to one end of the fuse F1. The other end of the capacitor C2 is connected to the other end of the resistor R6.
[0013] When the transformer is powered on, the current-limiting effect of resistors R2 and R7 first reduces the instantaneous current at startup to within the range that fuse F1 can withstand. After the transformer is energized, the bidirectional thyristor Q2 is turned on, short-circuiting the current-limiting resistors R2 and R7. This allows the voltage across the AC power supply to be fully applied to the primary coil of transformer T1, restoring the voltage at the transformer input and putting the transformer into normal working condition, providing reliable voltage output and avoiding the impact of the instantaneous inrush current at startup on fuse F1. Attached Figure Description
[0014] Figure 1 This is the circuit diagram of this utility model. Detailed Implementation
[0015] The present invention will be further described below with reference to the accompanying drawings:
[0016] like Figure 1 The circuit shown is a protection circuit for suppressing inrush current of a power frequency transformer. It includes an energy extraction isolation circuit, which is connected to a rectifier circuit. The rectifier circuit is connected to a voltage regulator circuit, which is connected to a suppression circuit. The energy extraction isolation circuit is also connected to the L terminal of the AC power supply and the suppression circuit. The suppression circuit is connected to one end of a fuse F1, and the other end of the fuse F1 is connected to one end of the primary side of the transformer T1.
[0017] The energy extraction isolation circuit includes a current transformer L1. Pins 1 and 2 of the current transformer L1 are connected to the L terminal of the AC power supply and the suppression circuit, respectively. Pins 3 and 4 of the current transformer L1 are connected to the rectifier circuit. The rectifier circuit includes a rectifier bridge BD1. The two input terminals of the rectifier bridge BD1 are connected to pins 3 and 4 of the current transformer L1, respectively. The output terminal of the rectifier bridge BD1 is connected to the voltage regulator circuit.
[0018] The voltage regulator circuit includes capacitor C4. One end of capacitor C4 is connected to the positive output terminal of rectifier bridge BD1, and the other end of capacitor C4 is connected to the negative output terminal of rectifier bridge BD1. One end of capacitor C4 is connected to the collector of transistor Q1 and one end of resistor R1. The other end of capacitor C4 is connected to one end of capacitor C1. The base of transistor Q1 is connected to the other end of resistor R1 and the negative terminal of Zener diode ZD1. The positive terminal of Zener diode ZD1 is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to one end of resistor R1. The emitter of transistor Q1 is connected to the negative terminal of diode D2. The positive terminal of Zener diode ZD1 is connected to the positive terminal of diode D2. A capacitor C3 is connected in parallel across diode D2.
[0019] The suppression circuit includes resistor R4. One end of resistor R4 is connected to one end of capacitor C3 and grounded. The other end of resistor R4 is connected to the positive terminal of diode D1. The positive and negative terminals of diode D1 are connected to pins 2 and 1 of optocoupler U1, respectively. Pins 3 and 4 of optocoupler U1 are connected to the control electrode of triac Q2 and one end of resistor R5, respectively. The first anode of triac Q2 is connected to one end of resistor R3. The second anode of triac Q2 is connected to one end of resistor R7, one end of resistor R6, and the other end of resistor R5, respectively. Resistor R3 is connected between the second anode and the control electrode of triac Q2. The second anode of triac Q2 is connected to one end of resistor R2. One end of resistor R2 is connected to pin 2 of current transformer L1 and one end of capacitor C2, respectively. The other end of resistor R2 is connected to the other end of resistor R7. One end of resistor R7 is connected to one end of fuse F1. The other end of capacitor C2 is connected to the other end of resistor R6.
[0020] In this invention, the energy extraction isolation circuit uses a current transformer L1. Through the action of the current transformer L1, after the transformer is energized, the starting current is converted into a proportional voltage. Then, through the action of the rectifier bridge BD1, the AC voltage output by the current transformer L1 is converted into a DC voltage. Energy is transferred between the primary and secondary sides of the current transformer L1 through changes in the magnetic field, thus forming effective and reliable electrical isolation.
[0021] A capacitor C4 is connected in parallel at the output of rectifier bridge BD1 to improve the load characteristics of the rectifier circuit and provide a stable voltage output for the subsequent voltage regulator circuit. Resistor R1 provides bias current to transistor Q1, turning it on, and simultaneously provides operating current to Zener diode ZD1. Zener diode ZD1 is connected to the base of transistor Q1, so the base voltage of Q1 is stabilized at a fixed value by the Zener diode. Since there is a PN junction diode between the base and emitter of the transistor, and the typical voltage across the diode is a stable 0.7V when it is conducting, the output voltage of this circuit equals the stable voltage of Zener diode ZD1 minus the typical voltage of the PN junction diode (0.7V). The capacitor C1 works in conjunction with transistor Q1 to utilize the amplification effect of the transistor, resulting in a filtering effect that is amplified several times at the output.
[0022] Resistors R2 and R7 are connected in series and then in parallel with the bidirectional thyristor Q2. When the transformer is powered on, the current limiting effect of resistor R2 and R7 first reduces the instantaneous current at startup to within the range that fuse F1 can withstand. After the transformer is energized, the bidirectional thyristor Q2 is turned on, short-circuiting resistor R2 and R7. This allows the full voltage of the AC power supply to be applied to both ends of the primary coil of transformer T1, restoring the voltage at the input of the transformer and putting the transformer into normal working condition, providing reliable voltage output, and thus avoiding the impact of the instantaneous inrush current at startup on fuse F1.
[0023] At the moment the transformer is powered on, the voltage across the current-limiting resistor is high. By using two resistors in series, the voltage across either resistor can be reduced, thereby reducing the power dissipation of the resistor. This allows for applications under high power and high voltage conditions using low-power devices.
[0024] After the transformer is powered on, an alternating current flows through the primary side of the current transformer L, inducing an alternating voltage on the secondary side. This voltage is rectified into a direct current voltage by the rectifier bridge BD1, supplying power to the voltage regulator circuit. Once the output voltage of the voltage regulator circuit stabilizes, the LED of the optocoupler U1 is turned on, which in turn turns on pins 3 and 4 of the optocoupler, thereby triggering the triac Q2 to conduct. When the triac Q2 is turned on, resistors R2 and R7 are short-circuited, and the transformer returns to normal operation.
[0025] When the device is powered on, capacitors C2 and R6 can reduce the voltage across the bidirectional thyristor Q2 before it turns on, thus protecting the bidirectional thyristor Q2 from damage.
[0026] This invention prevents the transformer fuse from burning out due to instantaneous high current, thereby reducing the failure rate of intrinsically safe power supplies and avoiding the high costs associated with increasing transformer power.
[0027] This utility model is not limited to the above embodiments. Based on the technical solutions disclosed herein, those skilled in the art can make some substitutions and modifications to some of the technical features without creative labor, and these substitutions and modifications are all within the protection scope of this utility model.
Claims
1. A protection circuit for suppressing inrush current in a power frequency transformer, characterized in that: It includes an energy extraction isolation circuit, which is connected to a rectifier circuit. The rectifier circuit is connected to a voltage regulator circuit, which is connected to a suppression circuit. The energy extraction isolation circuit is also connected to the L terminal of the AC power supply and the suppression circuit. The suppression circuit is connected to one end of fuse F1, and the other end of fuse F1 is connected to one end of the primary side of transformer T1. The suppression circuit includes resistor R4. One end of resistor R4 is connected to one end of capacitor C3 and grounded. The other end of resistor R4 is connected to the positive terminal of diode D1. The positive and negative terminals of diode D1 are connected to pins 2 and 1 of optocoupler U1, respectively. Pins 3 and 4 of optocoupler U1 are connected to the control electrode of triac Q2 and one end of resistor R5, respectively. The first anode of triac Q2 is connected to one end of resistor R3. The second anode of triac Q2 is connected to one end of resistor R7, one end of resistor R6, and the other end of resistor R5, respectively. Resistor R3 is connected between the second anode and the control electrode of triac Q2. The second anode of triac Q2 is connected to one end of resistor R2. One end of resistor R2 is connected to pin 2 of current transformer L1 and one end of capacitor C2, respectively. The other end of resistor R2 is connected to the other end of resistor R7. One end of resistor R7 is connected to one end of fuse F1. The other end of capacitor C2 is connected to the other end of resistor R6.
2. The power frequency transformer inrush current suppression and protection circuit according to claim 1, characterized in that: The energy extraction isolation circuit includes a current transformer L1. Pins 1 and 2 of the current transformer L1 are connected to the L terminal of the AC power supply and the suppression circuit, respectively. Pins 3 and 4 of the current transformer L1 are connected to the rectifier circuit.
3. The power frequency transformer inrush current suppression and protection circuit according to claim 2, characterized in that: The rectifier circuit includes a rectifier bridge BD1. The two input terminals of the rectifier bridge BD1 are connected to pins 3 and 4 of the current transformer L1, respectively. The output terminal of the rectifier bridge BD1 is connected in parallel with capacitor C4, and capacitor C4 is connected to the voltage regulator circuit.
4. The power frequency transformer inrush current suppression and protection circuit according to claim 3, characterized in that: The voltage regulator circuit includes a transistor Q1, one end of a capacitor C4 connected to the collector of transistor Q1 and one end of a resistor R1, the other end of capacitor C4 connected to one end of capacitor C1, the base of transistor Q1 connected to the other end of resistor R1 and the cathode of Zener diode ZD1, the anode of Zener diode ZD1 connected to one end of capacitor C1, the other end of capacitor C1 connected to one end of resistor R1, the emitter of transistor Q1 connected to the cathode of diode D2, the anode of Zener diode ZD1 connected to the anode of diode D2, and a capacitor C3 connected in parallel across diode D2.