A temperature controller with zero voltage switching control without zero-crossing detection circuit

Abstract

The utility model discloses a kind of zero-voltage switch control's temperature controller of no need zero-crossing detection circuit, the 1 end of AC sequentially passes through R1, C1, P1, R3, Rth connects the 2 end of AC, the lower end of C1 sequentially passes through R5, the E-C pole of T1, R3 connects the 2 end of AC, the E pole of T1 is connected the 2 end of AC through R4, the connecting point of R2, Rth connects the base of T1, the lower end of C1 sequentially passes through the anode of TH1, cathode connects the 2 end of AC, the C pole of T1 connects the gate of thyristor TH1, the lower end of C1 is simultaneously connected the 2 end of AC through D1, the cathode of D1 is connected the gate of TH2 through R6, the 1 end of AC sequentially passes through RL, TH2 connects the 2 end of AC, thyristor TH3 is connected in parallel with thyristor TH2, the 1 end of power supply AC is connected the gate of thyristor TH3 through R7, D2, R8, the cathode of D2 is connected the cathode of thyristor TH3 through C2.

Description

Technical Field

[0001] This utility model relates to a temperature controller circuit with zero-voltage switch control that does not require a zero-crossing detection circuit. A temperature controller can be made using this simple zero-voltage switch control technology. The circuit structure is different from that of common temperature controllers. The circuit is relatively novel and has a high cost performance. Background Technology

[0002] Zero-voltage switching technology is a new type of electrical appliance switching control technology that can complete the switching action when the power supply voltage is zero. Specifically, when the appliance is turned off, the zero-voltage switch will cut off the power supply and disconnect the appliance; when the appliance is turned on, the zero-voltage switch will wait for the power cycle to end and then reconnect at the beginning of the next cycle.

[0003] Therefore, zero-voltage switching control technology is also known as "zero-crossing control" technology. This technology not only protects electrical appliances but also saves energy. The advantages of zero-crossing control mainly include reducing current surges, lowering the risk of equipment damage, improving equipment reliability, reducing noise and interference, and extending equipment lifespan.

[0004] Zero-crossing control is mainly used in motor speed regulation, optocoupler triggering circuits, and control circuit output power adjustment.

[0005] To achieve zero-crossing control, a zero-crossing detection circuit is required. The basic principle of the zero-crossing detection circuit is to use a comparator or flip-flop to compare the input AC signal with the zero level. When the level of the input signal exceeds the zero level, a high-level signal is output and the flip-flop is activated; otherwise, a low-level signal is output and the flip-flop is deactivated.

[0006] In this way, as long as the signal crosses zero, the trigger will change its state, thereby achieving the purpose of signal detection.

[0007] The functions of a zero-crossing detection circuit include: detecting the duration of the AC cycle; controlling the conduction angle of the thyristor from the zero-crossing point to control the motor speed; controlling the power output; controlling the closing and opening of the relay at the AC zero-crossing point to eliminate relay contact sparking problems; and calibrating the synchronization function.

[0008] Thyristors, also known as silicon controlled rectifiers, are divided into unidirectional and bidirectional thyristors. Bidirectional thyristors are usually triggered by optocouplers with zero-crossing detection circuits. Unidirectional thyristors can generally only conduct in one direction. The conduction of a unidirectional thyristor requires two conditions to be met simultaneously: first, a positive voltage must be applied between the anode (A) and cathode (K) of the thyristor; second, a positive voltage must also be applied between the gate (G) and cathode. Both conditions must be met at the same time, and the second condition, the "gate-cathode" positive voltage, should ideally arrive before the first condition, the "anode-cathode" positive voltage. This will increase the success rate of triggering the thyristor to conduct.

[0009] The R / C series network exhibits capacitive characteristics, meaning the current through the R / C circuit leads the voltage across it. This implies that the voltage at the capacitive load terminal cannot change abruptly, but the current can. When the 220V sinusoidal power frequency voltage reverses from the negative half-cycle to the positive half-cycle, during the extremely short time of zero crossing, the leading current first forms a stable voltage in the Zener diode, which serves as the gate trigger voltage for the unidirectional thyristor. Immediately afterward, the power frequency voltage arrives, and the unidirectional thyristor conducts. When the power frequency voltage changes from the positive half-cycle to the negative half-cycle, even if the gate voltage still exists, the unidirectional thyristor cannot conduct and is cut off.

[0010] If two unidirectional thyristors are connected in parallel in opposite directions, the first unidirectional thyristor will conduct when the power frequency voltage crosses zero from the negative half-cycle to the positive half-cycle, and the second unidirectional thyristor will cut off when it crosses zero; the first unidirectional thyristor will cut off when the power frequency voltage crosses zero from the positive half-cycle to the negative half-cycle, and the second unidirectional thyristor will conduct when it crosses zero.

[0011] Therefore, the zero-voltage switching control technology, which utilizes the characteristic of capacitive loads where "current leads voltage", has a simpler circuit structure, lower cost, and higher efficiency compared to the traditional dedicated "zero-crossing detection circuit".

[0012] This simple zero-voltage switching control technology can be used to make a thermostat with a circuit structure that differs from common thermostats. The circuit is novel and cost-effective. Summary of the Invention

[0013] The technical problem to be solved by this utility model is to provide a design technology for a temperature controller circuit that is simpler in structure, lower in cost, more reliable in use, and more sensitive than conventional designs, using a zero-voltage switch control.

[0014] To achieve the above objectives, this utility model provides a zero-voltage switch-controlled temperature controller that does not require a zero-crossing detection circuit. It includes a series RC network circuit, a temperature adjustment circuit, a thermistor circuit, a positive half-cycle unidirectional thyristor TH2 trigger circuit, a negative half-cycle unidirectional thyristor TH3 trigger circuit, a positive half-cycle unidirectional thyristor, a negative half-cycle unidirectional thyristor, and a heater circuit. A resistor R1 connected in series with a capacitor C1 constitutes the series RC network circuit. A potentiometer P1 constitutes the temperature adjustment circuit, and an NTC thermistor Rth constitutes the thermistor circuit. One terminal of the power frequency AC is connected to the other terminal of the power frequency AC via resistor R1, capacitor C1, potentiometer P1, resistor R3, and thermistor Rth. Transistor T1, unidirectional thyristor TH1, and Zener diode D1 constitute the positive half-cycle unidirectional thyristor TH2 trigger circuit. The lower end of capacitor C1 is connected to the other terminal of the power frequency AC via resistor R5, the EC terminal of transistor T1, and resistor R3. The E terminal of transistor T1 is connected to the other terminal of the power frequency AC via resistor R4. Resistor R2 and NTC thermistor Rth... The connection point is connected to the base of transistor T1. The lower end of capacitor C1 is connected to the two terminals of the power supply AC via the anode and cathode of unidirectional thyristor TH1. The collector of transistor T1 is connected to the gate of unidirectional thyristor TH1. The lower end of capacitor C1 is also connected to the two terminals of the power supply AC via reverse Zener diode D1. Unidirectional thyristor TH2 constitutes the positive half-cycle unidirectional thyristor, and unidirectional thyristor TH3 constitutes the negative half-cycle unidirectional thyristor. The cathode of Zener diode D1 is connected to the gate of unidirectional thyristor TH2 via resistor R6. One end of the power supply AC is connected to the two ends of the power frequency power supply AC in sequence through the heater circuit RL and the forward unidirectional thyristor TH2. The reverse unidirectional thyristor TH3 is connected in parallel with the forward unidirectional thyristor TH2. The resistor R7, diode D2, and electrolytic capacitor C2 constitute the trigger circuit of the negative half-cycle unidirectional thyristor TH3. One end of the power frequency power supply AC is connected to the gate of the unidirectional thyristor TH3 in sequence through the resistor R7, the forward diode D2, and the resistor R8. The cathode of the diode D2 is connected to the cathode of the unidirectional thyristor TH3 through the forward electrolytic capacitor C2. Attached Figure Description

[0015] Appendix Figure 1 Appendix Figure 2 This document, attached to provide a further understanding of the present invention, forms part of this application. Figure 1 It is the capacitive load current leading the voltage; Appendix Figure 2 This is the electrical schematic diagram of a thermostat that uses zero-voltage switching control technology. Detailed Implementation

[0016] The embodiments of this utility model are further described below with reference to the accompanying drawings.

[0017] A silicon controlled rectifier (SCR) is a high-power electrical component, also known as a thyristor. It boasts advantages such as small size, high efficiency, and long lifespan. In automatic control systems, it serves as a high-power driving device, enabling the control of high-power equipment with low-power controls. It is widely used in AC / DC motor speed control systems, power regulation systems, and servo systems.

[0018] Thyristors are divided into unidirectional and bidirectional types. A bidirectional thyristor, also called a three-terminal bidirectional thyristor or TRIAC for short, is structurally equivalent to two unidirectional thyristors connected in reverse. This type of thyristor has bidirectional conduction capability, and its on / off state is determined by the control electrode G. Applying a positive (or negative) pulse to the control electrode G will turn it on in the forward (or reverse) direction. The advantage of this device is its simple control circuit and the absence of reverse withstand voltage issues, making it particularly suitable for use as an AC contactless switch. Bidirectional thyristors are generally triggered using an optocoupler with a zero-crossing detection circuit.

[0019] A unidirectional thyristor can generally only conduct in one direction. Its operating characteristics are as follows: when a positive voltage is applied between the anode A and the cathode K, and the required positive trigger voltage is applied between the control electrode G and the cathode K, the thyristor is triggered to conduct. At this time, A and K are in a low-resistance conducting state. After the unidirectional thyristor conducts, even if the controller G loses the trigger voltage, as long as the positive voltage is still maintained between the anode A and the cathode K, the unidirectional thyristor will continue to be in a low-resistance conducting state.

[0020] The unidirectional thyristor only changes from a low-resistance conducting state to a high-resistance cutoff state when the voltage at anode A is removed or the polarity of the voltage between anode A and cathode K is changed (AC zero crossing). Once the unidirectional thyristor is cut off, even if a positive voltage is reapplied between anode A and cathode K, a positive trigger voltage must be reapplied between the control electrode G and cathode K for the unidirectional thyristor to conduct again. The conducting and cutoff states of the unidirectional thyristor are equivalent to the closed and open states of a switch, and it can be used to make a contactless switch.

[0021] Capacitive load current leads voltage by 90 degrees

[0022] A capacitive load is a load with capacitance parameters, characterized by current leading voltage by 90 degrees, such as... Figure 1 As shown, the voltage of a capacitive load cannot change abruptly during charging and discharging, so its corresponding power factor is negative, while the power factor of an inductive load is positive.

[0023] The formula for calculating reactance Z is:

[0024]

[0025] Where j represents the imaginary unit, X L Indicates resistance, X C Indicates capacitive reactance, when XL -X C When X > 0, the circuit behaves inductively; when X < 0, the circuit behaves inductively. L -X C When X < 0, the circuit behaves capacitively; when X < 0, the circuit behaves capacitively. L -X C When the resistance is 0, the circuit behaves as a pure resistor. Therefore... Figure 1 The circuit exhibits capacitive behavior, belonging to the capacitive circuit category, with the current leading the voltage by 90 degrees. The capacitive reactance X of capacitor C1... C You can calculate it like this.

[0026]

[0027] The reason why current leads voltage can also be explained by the basic principles of circuits. In AC circuits, the phase difference between voltage and current depends on the circuit impedance. For capacitive loads, the capacitance causes the current to lead the voltage by 90 degrees. This is because the way a capacitor stores charge in an AC circuit causes the current to change first, followed by the voltage, thus creating a phase difference.

[0028] Capacitive and inductive loads have opposite effects in a circuit. Inductive loads (such as motors and transformers) cause the current to lag the voltage by 90 degrees, while capacitive loads cause the current to lead the voltage by 90 degrees.

[0029] Temperature controller using zero-voltage switching control technology

[0030] Electric heaters are typically equipped with a thermostat, allowing users to set a target temperature. When the ambient temperature reaches the set value, the thermostat automatically cuts off the power and stops heating. Once the temperature drops, the thermostat reconnects the power and resumes heating, thus maintaining a stable ambient temperature.

[0031] Zero-crossing triggering is a common control method in thermostats. It achieves precise control of the appliance by detecting the zero-crossing point of a sine wave. The zero-crossing point refers to the value of the sine wave function at 0. When the value of the sine wave function changes from positive to negative, or from negative to positive, it is called a zero-crossing point. In AC circuits, the zero-crossing point is a very important reference point; understanding the zero-crossing point allows one to determine the period and phase of the entire sine wave.

[0032] It is known that detecting zero crossings requires a dedicated zero-crossing detection circuit, but this thermostat design achieves zero-crossing control of the heater's on / off state without using a dedicated zero-crossing detection circuit. This is achieved using a zero-voltage switch-controlled thermostat, such as... Figure 2 As shown.

[0033] As can be seen, the temperature controller includes a series resistor-capacitor network circuit, a temperature regulation circuit, a thermistor circuit, a positive half-cycle unidirectional thyristor trigger circuit, a negative half-cycle unidirectional thyristor trigger circuit, a positive half-cycle unidirectional thyristor, a negative half-cycle unidirectional thyristor, and a heater circuit.

[0034] This circuit uses an NTC thermistor Rth as a two-point regulator for the temperature sensor. Since the load current for temperature control is only conducted at the zero-crossing point of the power supply, there is no need to add any circuit to suppress interference.

[0035] A thermistor is a type of sensor resistor whose resistance changes with temperature. Based on their temperature coefficient, they are classified into positive temperature coefficient (PTC) thermistors and negative temperature coefficient (NTC) thermistors. The resistance of a PTC thermistor increases with increasing temperature, while the resistance of a NTC thermistor decreases with increasing temperature.

[0036] The function of the RC series network R1 / C1 is to ensure that the circuit provides a suitable voltage for triggering transistor T1 when the power frequency AC power supply voltage drops to a low level.

[0037] Transistor T1, unidirectional thyristor Th1, and Zener diode D1 constitute the positive half-cycle unidirectional thyristor Th2 trigger circuit, while resistor R7, diode D2, and electrolytic capacitor C2 constitute the negative half-cycle unidirectional thyristor Th3 trigger circuit.

[0038] First, it's important to understand that during the positive half-cycle of the AC power supply, only the unidirectional thyristor Th2 can conduct, while Th3 cannot. Similarly, during the negative half-cycle, only Th3 can conduct, while Th2 cannot. Furthermore, electrolytic capacitor C2 only has a charging path when Th2 conducts during the positive half-cycle, thus providing the trigger current for Th3 to conduct during the negative half-cycle. If Th2 does not conduct during the positive half-cycle, then Th3 cannot conduct during the negative half-cycle either.

[0039] The following analysis examines the on / off states of thyristors Th2 and Th3 under two scenarios: positive and negative half-cycles, using the AC power frequency voltage source.

[0040] When the AC voltage source is in the positive half-cycle, Th2 is conditionally turned on at zero crossing and Th3 is turned off in reverse.

[0041] When the power frequency AC voltage AC is in the positive half-cycle ( Figure 2 (This is marked as the positive half-cycle). The RC network R1 / C1, resistors R5 and R4 provide a bias voltage to the collector of transistor T1.

[0042] If the ambient temperature is higher than the expected set value (set by potentiometer P1), the resistance of the NTC thermistor Rth will be very low, and the base voltage of transistor T1 will decrease. Based on the capacitive characteristics of the RC network R1 / C1, the power frequency current through R1 / C1 will pass before the power frequency voltage, causing transistor T1 to turn on. The gate trigger current of unidirectional thyristor Th1 will be provided in advance, and then the power frequency voltage through R1 / C1 will also arrive, Th1 will turn on, the Zener diode D1 will be short-circuited, and the gate of unidirectional thyristor Th2 will not have a trigger current and will be in the off state. Since unidirectional thyristor Th3 can only conduct in one direction, Th3 cannot conduct during the positive half-cycle of the power frequency power supply. At this time, the heater RL will lose power and stop working.

[0043] As the ambient temperature gradually decreases, when it falls below the expected temperature set by P1, the resistance of the NTC thermistor Rth rises rapidly, transistor T1 is turned off, and the gate of the thyristor Th1 is also turned off due to the lack of trigger current.

[0044] When the power frequency voltage is in the negative half-cycle, capacitor C1 is charged with positive polarity at the bottom and negative polarity at the top. During the extremely short transition from the negative to the positive half-cycle of the power frequency power supply, based on the capacitive characteristics of the RC network R1 / C1, the terminal voltage of capacitor C1 cannot change abruptly. The current through capacitor C1 arrives before the voltage. The potential at the lower end of capacitor C1 is the superposition of the original stored voltage and the current power frequency voltage. The superimposed voltage provides a reverse voltage to the Zener diode D1 in advance. The 10V stable voltage of D1 provides a trigger current to the gate of the unidirectional thyristor Th2 in the positive half-cycle through the current-limiting resistor R6. Th2 conducts, and the sinusoidal AC voltage AC in the positive half-cycle provides the operating current to the heater RL through the conducting Th2. The thermostat starts heating, and the ambient temperature gradually rises.

[0045] If the ambient temperature exceeds the set temperature again, continue the above working process.

[0046] During the conduction of the thyristor Th2, the positive half-cycle AC signal sequentially charges the electrolytic capacitor C2 through resistor R7, unidirectional diode D2, and the conducting thyristor Th2. The charging voltage of capacitor C2 will provide the trigger voltage for the gate of the unidirectional thyristor Th3 during the negative half-cycle.

[0047] In summary, because the ambient temperature is lower than the set temperature, during the positive half-cycle of the power frequency power supply, the voltage across the Zener diode D1 leads the mains power supply voltage (based on the fact that the voltage across capacitor C1 cannot change abruptly). Therefore, when the power supply voltage transitions from the negative half-cycle to the positive half-cycle at the zero-crossing point, the unidirectional thyristor Th2 is triggered to conduct, while the unidirectional thyristor Th3 is reverse-biased and cut off. This state remains unchanged throughout the entire positive half-cycle. When the ambient temperature is higher than the set temperature, both unidirectional thyristors Th2 and Th3 are cut off.

[0048] When the AC voltage source is in the negative half-cycle, Th3 is conditionally turned on at zero crossing and Th2 is reverse-biased and cut off.

[0049] When the AC power supply is in the negative half-cycle, although the gate of the unidirectional thyristor Th2 can be provided with trigger current through the forward Zener diode D1 and resistor R6, the unidirectional thyristor Th2 can only be cut off because it only has a reverse AC voltage. Regardless of the state of the thermistor Rth, that is, whether the ambient temperature is higher or lower than the set temperature, the unidirectional thyristor Th2 will be reverse cut off and will not conduct.

[0050] When the ambient temperature is lower than the set temperature, as mentioned above, during the positive half-cycle of the power frequency AC power supply, the conduction of the thyristor Th2 provides a charging channel for the electrolytic capacitor C2, so there is charge stored in the capacitor C2.

[0051] When the power frequency voltage is in the negative half-cycle, the unidirectional diode D2 is reverse cut off. If the ambient temperature is still lower than the set temperature, the charging voltage of capacitor C2 provides trigger current to the gate of the unidirectional thyristor Th3 in the negative half-cycle through the trigger resistor R8. At the beginning of the transition of the power frequency sinusoidal voltage from the positive half-cycle to the negative half-cycle, that is, at the zero crossing moment, the unidirectional thyristor Th3 in the negative half-cycle is triggered to conduct, and the heater RL is heated by the thyristor Th3.

[0052] When the ambient temperature is higher than the set temperature, regardless of whether the power frequency voltage is in the positive or negative half-cycle, the thyristor Th2 is cut off. Therefore, the electrolytic capacitor C2 has no chance to charge. Thus, when the ambient temperature is higher than the set temperature, the unidirectional thyristor Th3 also has no chance to conduct regardless of whether the power frequency power supply is in the positive or negative half-cycle. The heater stops working, and the ambient temperature gradually decreases.

[0053] When the ambient temperature is lower than the set temperature, continue the above working process.

[0054] To summarize, when the AC power frequency voltage source is in the negative half-cycle... Figure 2 The thermostat operates in a relatively simple way: only when the ambient temperature is lower than the set temperature, Th3 can conduct during the negative half-cycle, provided that Th2 is conducting during the positive half-cycle; if the ambient temperature is higher than the set temperature, Th2 will be cut off regardless of whether it is positive or negative half-cycle, which will cause Th3 to be cut off during both positive and negative half-cycles.

[0055] Precautions

[0056] Since all parts of this circuit design carry 220V AC power, special attention must be paid to safety during debugging, and the voltage rating of the components should have a margin when selecting them.

[0057] Will using an NTC thermistor to control the switching on and off of transistor T1 cause the heater to frequently switch on and off near the "temperature control point"? If so, it could easily damage the heating device. In fact, this concern does not exist, because the thermistor's resistance change has hysteresis characteristics.

[0058] Hysteresis control is primarily achieved through the temperature sensitivity of NTC thermistors. When the temperature rises, the resistance of the NTC thermistor drops rapidly, thus affecting the current or voltage in the circuit and achieving the control objective. This control method has a certain degree of hysteresis; that is, the resistance of the NTC thermistor will only drop significantly after the temperature reaches a certain level to achieve the hysteresis effect; similarly, the resistance of the NTC thermistor will only rise significantly after the temperature drops to a certain level. This characteristic makes NTC thermistors very useful in applications requiring temperature control or current limiting, such as in home appliance repair and temperature control equipment. By adjusting the position or number of NTC thermistors, precise temperature control and protection functions can be achieved.

[0059] Therefore, this type of temperature controller using zero-voltage switching control technology has the following advantages: 1) The circuit is simple and the components are reduced, especially eliminating the need for a power transformer and the trigger circuit of the thyristor; 2) The controllable power is large, up to 4KW; 3) Because it is a zero-crossing switch, the temperature controller has less interference to other equipment, and its own power devices are not easily damaged by overvoltage or overcurrent; 4) Zero-crossing control does not use a dedicated zero-crossing detection circuit.

[0060] The above embodiments are only used to illustrate and not limit the technical solutions of this utility model. Although the utility model has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the utility model without departing from the spirit and scope of the utility model. Any modifications or partial substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A zero voltage switching controlled thermostat without zero crossing detection circuit, characterized in that, The temperature controller includes a series RC network circuit, a temperature adjustment circuit, a thermistor circuit, a positive half-cycle unidirectional thyristor TH2 trigger circuit, a negative half-cycle unidirectional thyristor TH3 trigger circuit, a positive half-cycle unidirectional thyristor, a negative half-cycle unidirectional thyristor, and a heater circuit. A resistor R1 and capacitor C1 form the series RC network circuit. A potentiometer P1 forms the temperature adjustment circuit. An NTC thermistor Rth forms the thermistor circuit. Terminal 1 of the AC power supply is connected sequentially through resistor R1, capacitor C1, and potentiometer P1. Resistor R3 and thermistor Rth are connected to terminals 2 of the power supply AC. Transistor T1, unidirectional thyristor TH1, and Zener diode D1 constitute the positive half-cycle trigger circuit of unidirectional thyristor TH2. The lower end of capacitor C1 is connected to terminals 2 of the power supply AC via resistor R5, the EC terminal of transistor T1, and resistor R3. The E terminal of transistor T1 is connected to terminals 2 of the power supply AC via resistor R4. The junction of resistor R2 and NTC thermistor Rth is connected to the base of transistor T1. The lower end of capacitor C1 is connected to terminals 2 of the power supply AC via the anode and cathode of unidirectional thyristor TH1. The collector of transistor T1 is connected to the gate of unidirectional thyristor TH1. The lower end of capacitor C1 is also connected to terminals 2 of the power supply AC via reverse Zener diode D1. The positive half-cycle unidirectional thyristor TH2 constitutes the positive half-cycle unidirectional thyristor, and the negative half-cycle unidirectional thyristor TH3 constitutes the negative half-cycle unidirectional thyristor. The cathode of the Zener diode D1 is connected to the gate of the unidirectional thyristor TH2 through the resistor R6. Terminal 1 of the power frequency AC is connected to terminal 2 of the power frequency AC in sequence through the heater circuit RL and the positive unidirectional thyristor TH2. The reverse unidirectional thyristor TH3 is connected in parallel with the positive unidirectional thyristor TH2. The resistor R7, diode D2, and electrolytic capacitor C2 constitute the trigger circuit of the negative half-cycle unidirectional thyristor TH3. Terminal 1 of the power frequency AC is connected to the gate of the unidirectional thyristor TH3 in sequence through the resistor R7, the forward diode D2, and the resistor R8. The cathode of the diode D2 is connected to the cathode of the unidirectional thyristor TH3 through the forward electrolytic capacitor C2.

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