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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Triac power regulator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers A compact electronic controller that allows you to smoothly and over a fairly wide range change the brightness of the glow of the filaments of incandescent lamps, the power of a household electric heater or the speed of rotation of the shaft of an AC motor, even an inexperienced radio amateur can make. After all, the proposed device is based on a technical solution familiar to many from the publications of previous analogues and well-proven: on a triac with economical control by the phase-pulse method. In addition, the circuit diagram is supplemented by a thoroughly developed printed circuit board topology with a specification of the location of the mounting elements. Yes, and radio components in the design are used quite common. Among the advantages, one should also note the use of CMOS microcircuits, which make it possible to reduce the current consumed by the control system in all modes to a minimum of 1,5 mA and therefore not completely disconnect it from the network. And the replacement of a typical toggle switch with a small-sized button, located together with an LED indicator near the load, increases the convenience of turning it on and off. Of course, this is still not ideal. Not all logical elements of microcircuits are involved in the work. Unused inputs have to be connected to the "common" wire. Almost the entire circuit is powered by a DC source collected on VD1-VD3, C2, C4 and C5. Moreover, the capacitor C2 acts as a quenching reactance. Diodes VD1, VD2 form a full-wave rectifier, the voltage of which is maintained at 10 V by the zener diode VD3 and smoothed by the total capacitance C4 and C5. Capacitor C4 shunts mainly high-frequency interference coming from the household power supply, but not suppressed by a large-capacity "electrolyte" due to its significant parasitic inductance. The next feature of this power supply is directly related to triacs. Indeed, most of such characteristic semiconductor devices can be opened (with a "positive" voltage at the anode) by pulses of any polarity applied to the control electrode relative to the cathode, and with "negative" Ua - only negative. Therefore, the positive terminal of the power source in question is connected only to the triac cathode, and negative pulses will be formed on the control electrode at a voltage of any polarity on the anode. To clarify the essence, it is useful, I think, to recall that the phase-pulse method allows you to control the power in the load by changing that part of the mains voltage half-cycle during which the triac passes current. This means that for the correct operation of the device, it is necessary first of all to highlight the beginning of each half-cycle (which corresponds to the instantaneous voltage in the network equal to or close to zero), and then for 10 ms (the duration of the half-cycle of the mains voltage with a frequency of 50 Hz) to form an impulse. And the sooner we open the triac, the more power will be allocated to the load. The pulse shaper with a frequency of 100 Hz is assembled on the elements VT1, VT2, R3, R4, R7. With the advent of a positive half-cycle on the upper (according to the circuit) network wire, the voltage of the "opening" polarity is applied to the emitter junction of the transistor \/T1. The semiconductor triode really becomes open, and its Uk becomes close to Ue. The voltage drop across the resistor R3 approaches 1 V of the open emitter junction of the transistor VT1, so the "reverse-biased" emitter junction of the transistor \/T2 does not break through. With a negative half-cycle, the semiconductor triodes change roles. Resistor R4 limits the current through the bases of the transistors. And R7, being a collector load \ / T1 and VT2, sets the zero potential at input 1 of the logic element DD1.1 (with closed semiconductor triodes).
At times when Unetwork is close to zero, the current does not flow through the above transistors, since the voltage drop across the resistor R3 is not enough to unlock them. This means that Uk turns out to be equal to the voltage at the negative terminal of the power source. As a result, short negative pulses are obtained corresponding to the beginning of each half-cycle of the network. In the on state at the input 2 DD1.1 high voltage level. Therefore, the negative pulses arriving at the first input are inverted by the logic element and through the emitter follower (transistor \/T5) charge the capacitor C8 almost to the power supply voltage. Discharge - through the chain R8R9 and \/ T4. When the voltage drops to the threshold elements DD1.2, DD1.3 switch. The "decline", coming from the DD1.3 element, is differentiated by the C9R12 circuit and, already in the form of a pulse with a duration of about 12 μs, it turns on (through the DD1.4 inverter and the \/T6 transistor operating as a current amplifier) the triac VS1. The variable resistor R9 regulates the duration of the discharge of the capacitor C8, which means that they change the moment the triac is turned on and the effective voltage at the load. The capacitance of the capacitor C9 determines the very duration of the triac opening pulse, the resistor R12 sets the potential at the input of the logic element DD1.4. As for the VD6 zener diode, it provides a reliable start of the device. On the inverter DD2.1 and the trigger DD3.1 assembled node on - off the controller. From the same node, control signals go to other parts of the circuit. Transistor VT4 is used to smoothly turn on the load, and elements DD2.2, DD2.3 together with VT7 and VD5 provide button illumination. When the device is initially turned on or after a power failure, the C3R2 circuit generates a positive pulse at the R input of the DD3.1 logic element, setting it to the zero state, at which the load is turned off. Performing the functions of a T-trigger, DD3.1 is sensitive to positive voltage drops at input C. With each occurrence of such a drop, this logic element changes its state to the opposite. The R1C1 chain suppresses contact bounce, and the resistor R1 included in it sets the desired potential at the input of the inverter DD2.1. Pressing any of the SB buttons causes a positive voltage drop at the output of this element, switching the trigger DD3 to a single state. The resulting high level signal goes to DD1.1, allowing it to work. This creates favorable conditions for charging the capacitor C6 to 10 V through the resistor R6. The channel resistance of the transistor VT4 gradually decreases and after 5-7 s reaches its minimum. But the channel of the transistor VT4 is connected in series with the resistor R9 in the discharge circuit of the capacitor C8, and with an increase in the voltage at the gate of VT4, the power in the load will gradually increase to the level set by the resistor R9. Resistor R10 creates a minimum negative gate bias to fully turn off the regulator when resistor R9 has zero resistance. The need for such a bias voltage is due to the fact that after turning on the device there should not be time for an emergency situation to occur when the load is still de-energized, and the capacitor C7 acts as an alternating voltage shunt for the resistor R10, excluding it from the discharge circuit of the above C8. A low level from the inverse trigger output closes VT3 and disables switching of inverters DD2.2, DD2.3. A high level is maintained on the transistor VT7, and the VD5 LED is off. The next press on any of the SB buttons again switches the trigger to the zero state. Logic "0" from the output 13 of the trigger will prohibit switching element DD1.1, its output will be set to a high level. Consequently, the transistor VT6 will be constantly open, the capacitor C8 is charged, and the load itself (for example, a light bulb) is de-energized. The logical unit, coming from the output 12 of the trigger through the current-limiting resistor R6, will open the transistor VT3, through which the capacitor C6 will quickly discharge, and this will ensure that the device is ready for a new turn on. A high level at inputs 13 and 9 of logic elements DD2.2, DD2.3 will allow them to pass negative pulses from transistors VT1, VT2. These pulses open the transistor VT7 for a short time, and the LED lights up. Resistor R13 limits the average current through VD5 (so as not to overload the power supply, otherwise the voltage it produces will start to drop). Almost the entire home-made regulator (with the exception of connectors, a fuse, a triac and an LED) is mounted on a printed circuit board made of one-sided foil fiberglass. Transistors VT1, VT2, VT7 can be low-power silicon, but always rp-r structures, with a current transfer coefficient of more than 100. Almost the same requirements for the choice of VT3, VT6, except for the structure itself. She's here p-pn. As VT5, a semiconductor triode of the KT201 series (with any letter index at the end) is acceptable. You can also use silicon low-power transistors of the np-p structure, securing such a replacement by turning on VD4 (in the figure this is highlighted by a dashed outline). The diode will protect the emitter junction from reverse voltage breakdown, which appears after the VT5 transistor closes. In place of VT4, all field-effect transistors of the KP305 series work equally well. Not very strict criteria for the selection of other radio components. The VT3 zener diode is no exception here - anyone with a stabilization voltage of 10 V will do. Diodes from the KD509, KD510, KD522 series. Capacitors: C5 type K50 - 24, K50 - 29; C6, C7 - K53; C3 - any oxide; C4, C9 - silicon; C1, C2, C8 - metal-film types K70 - K78 (moreover, C2 has a rated operating voltage of at least 250 V). A variable resistor - of any type, its body is connected to the "positive" wire of the power circuit for shielding purposes. Fixed resistors - type C2 - 33N, MLT. As for the fuse FU1, then, of course, it must correspond to the current of a particular load. Debugging the device is reduced to the selection of the resistor R10 according to the following method (it is presented concisely). Pin 2 of the DD1.1 element is temporarily disconnected from the circuit and connected to pin 1. By installing a 10 kΩ variable resistor instead of R100, reduce its resistance to zero. They turn on the triac regulator in the network and wait a minute or two until the electrolytic capacitor C2 is charged through the "low-capacity" C10 to a nominal voltage of 5V. By controlling the shape of the pulses in the load using the oscilloscope, the resistance of the variable resistor is increased - replacing R10 until the triac stops opening. Then the load is turned on and off several times, using the existing adjustment elements, so that the transistor / T4, working properly, securely locks VS1. After that, the variable resistor is replaced by a constant one and the connection of output 2 DD1.1 is restored according to the diagram. Practice shows: by installing and selecting the resistor R11, it is possible to achieve that the maximum resistance of the resistor R9, operating as a rheostat, will correspond to zero voltage at the load. And in order to minimize the voltage drop across the triac when the load is fully turned on, it must be opened after the start of the half-cycle as quickly as possible. This means that the zero-crossing mains voltage pulse shaper must generate sufficiently short pulses. To minimize them, you should increase the resistance of the resistor R3 and select R7. It is undesirable to follow the path of lowering the R4 rating - this is energy waste. And further. When establishing and practically using a triac controller, one must not forget that when the device is connected to the network, everything, including the variable resistor, is under its high voltage. And they don’t joke with alternating current 220 V, even if the body of an electronic homemade product is made of good-quality insulating material. Author: A.Rudenko
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