High-efficiency linear direct-current power supply with transformer secondary tap capable of realizing zero-crossing automatic switching

Abstract

The utility model discloses a high-efficiency linear direct-current power supply with a transformer secondary tap capable of zero-crossing automatic switching, which is characterized in that a 220V power supply is subjected to voltage reduction through a transformer T, terminals 4, 3, 2 and 1 of the transformer respectively output different alternating-current voltages, the terminals 4 and 1 are connected with the input end of a bridge rectifier B, the terminals 3 and 2 are respectively connected with a working ground through backward diodes D6 and D5, and the working ground is connected with the working ground through the reverse diodes D6 and D5. A transistor T1, resistors R1, R2, R3 and R4, a potentiometer P1 and a voltage stabilizing diode D7 form a grid trigger circuit of a one-way silicon controlled rectifier Th1, when small and medium loads are loaded, reverse breakdown of the D7 is just achieved by adjusting the voltage of the P1 and the sliding end, T1 is conducted, the silicon controlled rectifier Th1 is cut off, and a terminal 4-2 or a terminal 1-3 of a transformer T supplies power to the loads; when the load is heavy, the Uo drops, the result is that the sliding end voltage of the P1 cannot enable the D7 to be reversely broken down, the D7 is cut off, the T1 is cut off, the Th1 is conducted, and the transformer terminal 4-1 or 1-4 provides a power supply for the load.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of transformer secondary tap can zero-crossing automatic switching high-efficiency linear DC power supply technology, due to automatic switching transformer tap, and at zero-crossing point switching, can reduce current impact, reduce noise and interference, of course, power loss of power supply circuit is also very small. BACKGROUND

[0002] In power electronic devices and systems, power supply is a very important component, among which linear power supply and switching power supply are two common power supply types.

[0003] Although linear power supply looks more bulky, the power of linear power supply is generally determined by transformer and regulating tube, the power of linear power supply is relatively low, but it does not introduce additional interference, so the electromagnetic interference of linear power supply is relatively small, and the ripple factor is also very low, almost negligible.

[0004] The regulation rate of linear power supply is generally higher, and the internal design is relatively simple, and it is very convenient to repair if there is a problem, as long as the technical personnel who know a little about electronic technology generally know how to repair, so the repair cost of linear power supply is generally much lower than that of switching power supply.

[0005] The lightning strike performance of linear power supply is good, because the transformer inside linear power supply is generally composed of 2 coils and core, and the voltage added to the two ends of the coil generally does not change suddenly, so it generally has strong inhibition to instantaneous high voltage. If it is accidentally struck by lightning, linear power supply can generally survive, while switching power supply is generally burned out.

[0006] The number of turns of coil and power of power frequency transformer are two parameters frequently mentioned in circuit, the number of turns of coil refers to the number of turns wound in coil, usually represented by N. And power refers to the size of energy transmitted and consumed in circuit, usually represented by P. In circuit, the number of turns of coil and power are closely related.

[0007] The influence of the number of turns of coil on circuit power depends on multiple factors, such as voltage and current. In some cases, increasing the number of turns of coil can increase the efficiency of circuit and improve power output, because in this case, the inductance value of coil will increase, thereby reducing the flow of current and converting more power supply energy into magnetic field energy.

[0008] When designing circuit, the number of turns of coil needed is determined according to the required power. If the required power is high, more turns of coil are needed to achieve the desired effect. On the other hand, if the required power is low, less turns of coil can meet the demand.

[0009] General linear power supply design, the primary and secondary winding turns of power frequency transformer is usually fixed, including the secondary multi-tap transformer design, the turns of each tap is actually fixed, the output voltage of each tap is different, the output power is also different; After the power supply design is completed, the maximum current (or maximum power) of the power supply (or a tap) is also fixed accordingly, then the selection of the load is only to connect the corresponding tap to be the most efficient application, at this time the circuit connection is often fixed and cannot be changed.

[0010] However, if there is a heavy load that needs to use the power supply corresponding to the tap, the output voltage of the power supply will certainly be reduced a lot, the power loss of the power supply will increase sharply, and of course the output efficiency will also be reduced a lot, which is not a high-efficiency power supply.

[0011] Therefore, a linear DC power supply can be designed more efficiently, which can automatically select the tap voltage of the secondary of the power transformer according to the size of the load current, for example, a stable load originally supplied by an 8V secondary power supply and high efficiency, if a heavy load wants to use the power supply temporarily, the larger load current will cause the output voltage to drop, causing large heat loss (copper loss and iron loss are the main causes of motor and transformer heating).

[0012] At this time, a thyristor can be used to switch the 8V tap to the 10V tap at the zero-crossing moment. As known from the above, increasing the number of turns can increase the efficiency of the circuit and improve the power output, so the heavy load can work stably under the 10V tap, and the efficiency is increased; If the heavy load returns to the normal load, the thyristor is cut off to restore the original tap power supply at the zero-crossing moment.

[0013] The output voltage of about 9V of the power supply is most suitable as the input voltage of the commonly used 5V voltage stabilizing circuit. Obviously, due to the automatic switching of the transformer taps and the switching at the zero-crossing point, current impact, noise and interference can be reduced, and of course the power loss of the power supply circuit is also small. SUMMARY

[0014] The technical problem to be solved by the utility model is to provide a high-efficiency linear DC power supply design technology which is different from the conventional design of transformer secondary tap, and which can automatically switch at zero-crossing.

[0015] In order to achieve the above object, the utility model provides a transformer secondary tap can pass zero automatic switching's high efficiency linear DC power supply, it includes 220V AC power supply, power frequency transformer circuit, small and medium power full bridge rectifier circuit, larger power full bridge rectifier circuit, unidirectional silicon controlled grid trigger circuit, unidirectional silicon controlled circuit, filter circuit, load circuit, 220V AC power supply passes through power frequency transformer circuit T voltage reduction, and the terminal 4 of power frequency transformer T secondary, terminal 3, terminal 2, terminal 1 respectively output different AC voltage, and rectifier bridge B constitutes the larger power full bridge rectifier circuit, and rectifier diode D1, rectifier diode D2, rectifier diode D5, rectifier diode D6 constitute the small and medium power full bridge rectifier circuit, and the terminal 4 of transformer T secondary connects the 1 end of rectifier bridge B, and the terminal 3 of transformer T secondary connects the working ground through reverse rectifier diode D6, and the terminal 2 of transformer T secondary connects the working ground through reverse rectifier diode D5, and the terminal 1 of transformer T secondary connects the 3 end of rectifier bridge B, and transistor T1, resistance R1, R2, R3, R4, potentiometer P1, stabilizing diode D7 constitute the unidirectional silicon controlled grid trigger circuit, and unidirectional silicon controlled Th1 constitutes the unidirectional silicon controlled circuit, and the 2 end of rectifier bridge B is connected with the 4 end of rectifier bridge B in proper order through resistance R3, the resistance body of potentiometer P1, resistance R4, the A-K pole of unidirectional silicon controlled Th1, and the 2 end of rectifier bridge B is connected with the 4 end of rectifier bridge B in proper order through resistance R2, the C-E pole of transistor T1, and the C pole of transistor T1 connects the G pole of unidirectional silicon controlled Th1, and the A pole of unidirectional silicon controlled Th1 connects the working ground, and the sliding end of potentiometer P1 connects the 4 end of rectifier bridge B through reverse stabilizing diode D7, resistance R1, and the anode of stabilizing diode D7 connects the base of transistor T1, and the 2 end of rectifier bridge B connects the working ground through the filter circuit, namely the positive end of forward electrolytic capacitor C1, and the positive end of electrolytic capacitor C1 outputs DC voltage Uo, and DC voltage Uo connects the working ground through the load circuit RL.

[0016] The power frequency transformer circuit, the primary of transformer T is connected with the power frequency AC power supply AC through switch S1 and safety tube F.

[0017] The secondary of the power frequency transformer circuit, namely transformer T is tapped according to 0V-2V-8V-10V, which corresponds to terminal 1, terminal 2, terminal 3 and terminal 4 respectively. BRIEF DESCRIPTION OF DRAWINGS

[0018] ATTACHED Figure 1 For further understanding of the utility model, constituting a part of the present application, attached Figure 1 It is the DC power supply principle diagram that transformer secondary tap can pass zero automatic switching. DETAILED DESCRIPTION

[0019] The embodiments of the present application are further illustrated below with reference to the drawings.

[0020] Silicon Controlled Rectifier, SCR for short, is a kind of high-power electrical component, also known as thyristor. It has the advantages of small size, high efficiency and long service life. In the automatic control system, it can be used as a high-power driving device to control high-power equipment with small-power control. It has been widely used in AC motor speed regulation system, power regulation system and follow-up system.

[0021] Silicon Controlled Rectifier is divided into single-direction silicon controlled rectifier and double-direction silicon controlled rectifier, double-direction silicon controlled rectifier is also called three-terminal double-direction silicon controlled rectifier, TRIAC for short. The structure of double-direction silicon controlled rectifier is equivalent to two single-direction silicon controlled rectifiers connected in reverse. This kind of silicon controlled rectifier has the function of double-direction conduction, and its on-off state is determined by the control electrode G. When a positive pulse (or negative pulse) is added to the control electrode G, the double-direction silicon controlled rectifier is turned on in the positive direction (or negative direction). The advantage of this device is that the control circuit is simple and there is no problem of reverse voltage resistance, so it is particularly suitable for use as an AC non-contact switch. Double-direction silicon controlled rectifier is generally triggered by a photoelectric coupler with zero-crossing detection circuit.

[0022] Single-direction silicon controlled rectifier can only conduct in one direction. Its working characteristics are as follows: when a forward voltage is added between the anode A and the cathode K, and the required forward trigger voltage is added between the control electrode G and the cathode K, the silicon controlled rectifier is triggered to conduct. At this time, the A and K are in a low-resistance conduction state. After the single-direction silicon controlled rectifier is turned on, even if the trigger voltage of the controller G is lost, as long as the voltage between the anode A and the cathode K remains positive, the single-direction silicon controlled rectifier will continue to be in a low-resistance conduction state.

[0023] Only when the voltage of the anode A is removed or the voltage polarity between the anode A and the cathode K is changed (AC zero-crossing), the single-direction silicon controlled rectifier will change from a low-resistance conduction state to a high-resistance cut-off state. Once the single-direction silicon controlled rectifier is cut off, even if the positive voltage between the anode A and the cathode K is added again, the single-direction silicon controlled rectifier can only be turned on again by adding a forward trigger voltage between the control electrode G and the cathode K. The on-off state of the single-direction silicon controlled rectifier is equivalent to the closing and opening state of a switch, and it can be used to make a non-contact switch.

[0024] Zero-crossing control

[0025] Zero-crossing control circuit is a kind of circuit for controlling the output of AC voltage. The output of control voltage can protect the motor, electrical equipment and other devices from being damaged due to overcurrent. In an AC circuit, the waveforms of current and voltage are sinusoidal, and the period is one complete waveform. The zero-crossing control circuit switches the circuit at the zero point of the upward or downward sinusoidal wave of AC voltage, so as to control the output voltage of the circuit.

[0026] Zero-crossing control can protect electrical equipment, in an alternating current circuit, the size of the current will change with the size of the voltage, so that electrical equipment will be damaged because of high voltage or excessive current, zero-crossing control circuit can control the output of the alternating voltage, avoid the instantaneous change of current and voltage, so as to protect electrical equipment.

[0027] The power loss of the power grid can be reduced, there is a certain resistance, inductance and capacitance in the alternating current circuit, the voltage and current will cause a certain phase difference, resulting in power loss. The zero-crossing control circuit reduces the phase difference between voltage and current by controlling the output of the circuit, thereby reducing the power loss of the power grid and improving the utilization rate of electric energy.

[0028] The output power of the electrical equipment can be controlled, the zero-crossing control circuit can control the output power of the electrical equipment by controlling the output time of the circuit to adjust the size of the voltage.

[0029] In summary, zero-crossing control circuit is a common circuit, it can protect electrical equipment, reduce the power loss of the power grid, control the output power of electrical equipment, etc. With the continuous progress of science and technology, the application range of zero-crossing control circuit is becoming more and more extensive.

[0030] If you want to realize zero-crossing control, you need a zero-crossing detection circuit, the basic principle of zero-crossing detection circuit is to use comparator or flip-flop circuit to compare the input alternating current signal with zero level, when the level of input signal exceeds zero level, a high level signal is output, the flip-flop will be activated; otherwise, a low level signal is output, the flip-flop will lose the activation state.

[0031] In this way, as long as the signal crosses zero, the flip-flop will change state, so as to achieve the purpose of detecting signal.

[0032] Transformer secondary winding zero-crossing automatic switching DC power supply

[0033] The core of the power supply circuit is to use a single silicon controlled rectifier SCR as a switching switch, and switch at the zero crossing point (0V voltage) of the sine alternating current power supply. Although this design realizes zero-crossing control, it does not use a dedicated zero-crossing detection circuit, and the structure is simpler and more cost-effective.

[0034] Zero-crossing control is controlled by transistor T1, T1 is off, and trigger current appears in the gate of silicon controlled rectifier, which is turned on; T1 is on, silicon controlled rectifier loses trigger current, and silicon controlled rectifier A-K is automatically cut off when the power supply is zero, as shown in the detailed schematic diagram. Figure 1

[0035] ​As can be seen, the circuit includes a 220V AC power supply, a power frequency transformer circuit, a small-to-medium power full-bridge rectifier circuit, a larger power full-bridge rectifier circuit, a thyristor gate trigger circuit, a unidirectional thyristor circuit, a filter circuit, and a load circuit.

[0036] The primary winding of transformer T is connected to the power frequency AC power supply via switch S1 and fuse F, forming the primary AC current path of transformer T. The secondary winding of the power frequency transformer T has four taps: 10V tap (number 4), 8V tap (number 3), 2V tap (number 2), and 0V tap (number 1). The complete secondary winding coil (numbers 4 to 1) can output 10V AC voltage, numbers 4 to 2 can output 8V AC, and numbers 3 to 1 can output 8V AC. This paper aims to output 9V DC voltage. Therefore, the 10V AC power output from the coils with taps 1 to 4 can be used as the input voltage for a higher power full-bridge rectifier circuit, and the 8V AC power output from the coils with taps 4 to 2 and 3 to 1 can be used as the input voltage for a medium-to-low power full-bridge rectifier circuit. Of course, both methods aim to output a stable 9V DC voltage.

[0037] Unidirectional thyristor Th1 is cut off under small to medium loads

[0038] Diodes D1, D2, D5, and D6 form a small-to-medium power full-bridge rectifier circuit. The cathode of diode D5 is connected to tap 2 of the secondary winding of transformer T, and the cathode of diode D6 is connected to tap 3 of the secondary winding of transformer T. Diodes D1, D2, D3, and D4 form a larger power full-bridge rectifier circuit.

[0039] Small to medium loads (RL) represent typical applications for the power supply in this design (i.e., normal operation, not heavy loads). Figure 1 As shown), when this power supply needs to provide small to medium load current, the thyristor Th1 is in the off state (normal state). The secondary rectifier ring of the power frequency transformer only passes through diodes D1, D2, D5, and D6. During the positive half-cycle of the mains power, the load current path is: transformer T secondary tap 4, diode D1, load, diode D5 (diode D6 is cut off by reverse voltage, which is easy to understand, because the positive terminals of D5 and D6 are short-circuited, the potential of the transformer secondary terminal number 3 is higher than the potential of the positive short-circuit point of D5 and D6), transformer secondary tap 2; during the negative half-cycle of the mains power, the load current path is: transformer T secondary tap 1, diode D2, load, diode D6 (diode D5 is cut off by reverse voltage, similarly, because the positive terminals of D5 and D6 are short-circuited, the potential of the transformer secondary terminal number 2 is higher than the potential of the positive short-circuit point of D5 and D6), transformer secondary tap 3.

[0040] In both cases, the AC voltage of the transformer secondary tap is 8V, the 2V tap is not used, and the 8V AC voltage is filtered by capacitor C1 to output a 9V DC voltage.

[0041] Transistor T1, resistors R1, R2, R3, R4, potentiometer P1, and voltage regulator diode D7 constitute a zero-crossing detection circuit.

[0042] When the load is small or medium, the power supply normally outputs a 9V DC stabilized power supply. By adjusting the potentiometer P1, the voltage at the sliding terminal is just enough to cause the voltage regulator diode D7 to be reverse-biased and conductive. The gate of the unidirectional thyristor Th1 does not have a triggering current to cut off, and the load current is as described above for small or medium load current paths.

[0043] When the load is large, the unidirectional thyristor Th1 conducts the load current path

[0044] If the power supply needs to carry a large load, the power supply needs to provide a large load current, and the output voltage Uo will drop (less than 9V). As a result, the voltage at the sliding terminal of the potentiometer P1 cannot cause the voltage regulator diode D7 to be reverse-biased and conductive, which is equivalent to D7 being reverse-biased and conductive. The transistor T1 is cut off, eliminating the condition where the gate of the thyristor Th1 is short-circuited. The output DC voltage Uo less than 9V provides a triggering current for the unidirectional thyristor Th1 through the resistor R2, and Th1 is immediately conductive.

[0045] As long as this happens, the 10V AC voltage between the secondary taps 4~1 of the transformer T will be rectified by the full-bridge D1~D4, and the diodes D5, D6 will be reverse-biased and cut off (the principle is the same as above, the potentials at the secondary taps 3 and 2 of the transformer are higher than the positive short-circuit point potentials of D5, D6). During the positive half-cycle of the mains, the load current path is: transformer T secondary tap 4, diode D1, load, diode D3, transformer T secondary tap 1; during the negative half-cycle of the mains, the load current path is: transformer T secondary tap 1, diode D2, load, diode D4, transformer T secondary tap 4.

[0046] Note that the ground point of the load RL has not changed, and is still connected as shown in Figure 1 , which is one of the ingenious aspects of this design.

[0047] Analysis of zero-crossing conduction and zero-crossing cutoff of unidirectional thyristor

[0048] The zero-crossing control technology has many advantages. This design also uses zero-crossing control technology to make the thyristor Th1 conduct at zero-crossing of the power supply and cut off at zero-crossing, but does not use a dedicated zero-crossing detection circuit.

[0049] See Figure 1Because the voltage across the voltage stabilizing diode D7 is always the lowest when the secondary of the power transformer is at the zero-crossing point, by adjusting the wiper potential of the potentiometer P1, the voltage stabilizing diode D7 can be reverse-biased off, and the thyristor Th1 is also always turned on at this zero-crossing moment, so that the large current pulse and other interference pulses when the thyristor is turned on can be prevented, and therefore the circuit does not need to be further equipped with an interference suppressor.

[0050] As for how the thyristor realizes zero-crossing cutoff, the principle is even simpler. If the load RL is changed to a typical small or medium load, the output voltage Uo of the DC power supply will certainly rise above 9V, and the rise of the wiper voltage of the potentiometer P1 leads to the reverse breakdown of the voltage stabilizing diode D7, the transistor T1 is turned on, and the gate trigger current of the unidirectional thyristor Th1 disappears. Then, when the power input voltage is at the lowest end (zero-crossing point), the voltage between the "anode" and the "cathode" of the thyristor Th1 disappears, and both conditions for the turn-on of the unidirectional thyristor disappear, and the Th1 naturally cuts off at zero-crossing.

[0051] Debugging and production

[0052] When the DC power supply is debugged, attention should be paid to the output voltage Uo value corresponding to the time when the wiper voltage of the potentiometer P1 leads to the voltage stabilizing diode D7 exiting the reverse breakdown and entering the reverse-biased off state. The basic idea is that when the load is heavy, the output voltage Uo value just makes the voltage stabilizing diode D7 exit the reverse breakdown state, and at this time the unidirectional thyristor TH1 is turned on. Then when the load is light, the Uo value increases, the D7 is reverse-biased, and the TH1 is cut off.

[0053] It should also be noted that the secondary tap switching of the power supply should not be too frequent, i.e. when the load is slightly heavier, the secondary tap is immediately switched to No. 4~1, leading to a sudden rise of the output voltage beyond 9V by a large margin, and then immediately switched back to the original tap, forming an oscillation. The reason is still the debugging of the position of the wiper of the potentiometer P1.

[0054] However, the probability of this problem occurring is not high. Because after the unidirectional thyristor TH1 is turned on due to the heavy load, the voltage at the wiper of the potentiometer P1 will be further reduced, thereby further ensuring that the unidirectional thyristor TH1 is in the on state, and only when the load suddenly changes from heavy to light, the output voltage Uo increases greatly, leading to the reverse breakdown of the voltage stabilizing diode D7, causing the unidirectional thyristor TH1 to be cut off, and the circuit returns to the initial state. Conversely, only when the load is heavy, the output voltage Uo decreases greatly, leading to the reverse-biased off of the voltage stabilizing diode D7, causing the unidirectional thyristor TH1 to be turned on, and a slightly heavy load will not cause the voltage stabilizing diode D7 to be reverse-biased off, but remain in the original state.

[0055] In actual production of the direct current power supply, the power frequency transformer T can adopt a 12V power supply transformer, and the transformer secondary is tapped as follows: 0V-2V-8V-10V, when the load current is 1.5A, a 2A transformer is enough; if the load current is 2A, a 3A transformer is needed.

[0056] In summary, the transformer secondary tap zero-crossing automatic switching high efficiency linear DC power supply has the characteristics of automatic control of input voltage (secondary voltage) with load current, and uses the zero-crossing point as a safety point to realize the conduction and cutoff of thyristor, but does not use a dedicated zero-crossing detection circuit, making the circuit safe, reliable, simple, and with few components, which is really economical and affordable, with high performance-price ratio.

[0057] Another feature is that the switching between light load rectifier circuit and heavy load rectifier circuit does not need to be realized through a physical switch, but is automatically realized by using the inherent reverse blocking characteristic of the rectifier diode, making the circuit more simple.

[0058] The above examples are only used to illustrate but not to limit the technical solutions of the present application, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that the present application can still be modified or replaced equivalently without departing from the spirit and scope of the present application, any modification or partial replacement should be covered in the scope of the claims of the present application.

Claims

1. A high efficiency linear DC power supply with transformer secondary tap zero crossing automatic switching, characterized in that, The linear DC power supply comprises a 220V AC power supply, a power frequency transformer circuit, a small and medium power full-bridge rectifier circuit, a large power full-bridge rectifier circuit, a unidirectional thyristor gate trigger circuit, a unidirectional thyristor circuit, a filter circuit, and a load circuit. The 220V AC power supply is stepped down by the power frequency transformer circuit T. Terminals 4, 3, 2 and 1 of the secondary of the power frequency transformer T output different AC voltages, respectively. The rectifier bridge stack B constitutes the large power full-bridge rectifier circuit. Rectifier diodes D1, D2, D5 and D6 constitute the small and medium power full-bridge rectifier circuit. Terminal 4 of the secondary of the transformer T is connected to the 1 end of the rectifier bridge stack B. Terminal 3 of the secondary of the transformer T is connected to the working ground through the reverse rectifier diode D6. Terminal 2 of the secondary of the transformer T is connected to the working ground through the reverse rectifier diode D5. Terminal 1 of the secondary of the transformer T is connected to the 3 end of the rectifier bridge stack B. The transistor T1, resistors R1, R2, R3, R4, the potentiometer P1 and the stabilizing diode D7 constitute the unidirectional thyristor gate trigger circuit. The unidirectional thyristor Th1 constitutes the unidirectional thyristor circuit. The 2 end of the rectifier bridge stack B is connected to the 4 end of the rectifier bridge stack B in sequence through the resistor R3, the resistor body of the potentiometer P1, the resistor R4 and the A-K pole of the unidirectional thyristor Th1. The 2 end of the rectifier bridge stack B is connected to the 4 end of the rectifier bridge stack B in sequence through the resistor R2 and the C-E pole of the transistor T1. The C pole of the transistor T1 is connected to the G pole of the unidirectional thyristor Th1. The A pole of the unidirectional thyristor Th1 is connected to the working ground. The sliding end of the potentiometer P1 is connected to the 4 end of the rectifier bridge stack B through the reverse stabilizing diode D7 and the resistor R1. The positive pole of the stabilizing diode D7 is connected to the base of the transistor T1. The 2 end of the rectifier bridge stack B is connected to the working ground through the filter circuit, i.e. the forward electrolytic capacitor C1. The positive end of the electrolytic capacitor C1 outputs a DC voltage Uo. The DC voltage Uo is connected to the working ground through the load circuit RL.

2. The high efficiency linear DC power supply with transformer secondary tap automatic switching over zero according to claim 1, characterized in that: The power frequency transformer circuit is characterized in that the primary of the transformer T is connected to the power frequency AC power supply AC through the switch S1 and the safety tube F.

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