|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Scheme of a switching stabilizer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Surge Protectors The switching regulator circuit is not much more complicated than the usual one (Fig. 1.9), but it is more complicated to set up. Therefore, insufficiently experienced radio amateurs who do not know the rules for working with high voltage (in particular, never work alone and never tune the device with two hands - only one!), I do not recommend repeating this scheme. On fig. 1.9 shows the electrical circuit of a switching voltage regulator for charging cell phones.
The circuit is a blocking oscillator implemented on a transistor VT1 and a transformer T1. The diode bridge VD1 rectifies the alternating mains voltage, the resistor R1 limits the current pulse when turned on, and also acts as a fuse. Capacitor C1 is optional, but thanks to it, the blocking oscillator works more stably, and the heating of transistor VT1 is slightly less (than without C1). When the power is turned on, the transistor VT1 opens slightly through the resistor R2, and a small current begins to flow through the I winding of the transformer T1. Due to inductive coupling, current also begins to flow through the remaining windings. At the upper (according to the scheme) output of winding II, a positive voltage of a small value, through a discharged capacitor C2, opens the transistor even more, the current in the transformer windings increases, as a result, the transistor opens completely, to a state of saturation. After a while, the current in the windings stops increasing and starts to decrease (transistor VT1 is fully open all this time). The voltage on the winding II decreases, and through the capacitor C2, the voltage at the base of the transistor VT1 decreases. It begins to close, the voltage amplitude in the windings decreases even more and changes the polarity to negative. Then the transistor is completely closed. The voltage on its collector increases and becomes several times greater than the supply voltage (inductive surge), however, thanks to the R5, C5, VD4 chain, it is limited to a safe level of 400 ... 450 V. Thanks to the elements R5, C5, the generation is not completely neutralized, and after a while the polarity of the voltage in the windings changes again (according to the principle of operation of a typical oscillatory circuit). The transistor starts to turn on again. This continues indefinitely in a cyclic mode. On the remaining elements of the high-voltage part of the circuit, a voltage regulator and a node for protecting the transistor VT1 from overcurrent are assembled. Resistor R4 in the circuit under consideration acts as a current sensor. As soon as the voltage drop across it exceeds 1 ... 1,5 V, the transistor VT2 opens and closes the base of the transistor VT1 to the common wire (forces it to close). Capacitor C3 speeds up the reaction of VT2. Diode VD3 is necessary for the normal operation of the voltage regulator. The voltage regulator is assembled on a single chip - an adjustable zener diode DA1. For galvanic isolation of the output voltage from the mains, optocoupler VO1 is used. The operating voltage for the transistor part of the optocoupler is taken from the winding II of the transformer T1 and smoothed by the capacitor C4. As soon as the voltage at the output of the device becomes greater than the nominal, a current will begin to flow through the zener diode DA1, the optocoupler LED will light up, the collector-emitter resistance of the phototransistor VO1.2 will decrease, the transistor VT2 will open slightly and reduce the voltage amplitude at the base of VT1. It will open more weakly, and the voltage on the transformer windings will decrease. If the output voltage, on the contrary, becomes less than the nominal one, then the phototransistor will be completely closed and the transistor VT1 will "swing" in full force. To protect the zener diode and the LED from overcurrent, it is advisable to include a resistor with a resistance of 100 ... 330 Ohm in series with them. Establishment The first stage: it is recommended to turn on the device for the first time through a lamp 25 W, 220 V, and without capacitor C1. The engine of the resistor R6 is set to the lower (according to the diagram) position. The device is turned on and immediately turned off, after which the voltages on the capacitors C4 and C6 are measured as quickly as possible. If there is a small voltage on them (according to the polarity!), It means that the generator has started, if not, the generator does not work, you need to search for an error on the board and installation. In addition, it is advisable to check the transistor VT1 and resistors R1, R4. If everything is correct and there are no errors, but the generator does not start, swap the terminals of the winding II (or I, but not both at once!) And check the performance again. The second stage: turn on the device and control with your finger (only not by the metal pad for heat dissipation) the heating of the transistor VT1, it should not heat up, the 25 W light bulb should not glow (the voltage drop across it should not exceed a couple of volts). Connect some small low-voltage lamp to the output of the device, for example, designed for a voltage of 13,5 V. If it does not light up, swap the terminals of the winding III. And at the very end, if everything is working fine, they check the performance of the voltage regulator by rotating the engine of the construction resistor R6. After that, you can solder the capacitor C1 and turn on the device without a current-limiting lamp. The minimum output voltage is about 3 V (the minimum voltage drop at the DA1 pins exceeds 1,25 V, at the LED pins - 1,5 V). If you need a lower voltage, replace the Zener diode DA1 with a resistor with a resistance of 100 ... 680 Ohms. The next setting step requires setting the output voltage of the device to 3,9 ... 4,0 V (for a lithium battery). This device charges the battery with an exponentially decreasing current (from about 0,5 A at the beginning of the charge to zero at the end (for a lithium battery with a capacity of about 1 Ah, this is acceptable). In a couple of hours of charging mode, the battery gains up to 80% of its capacity. About details A special structural element is a transformer. The transformer in this circuit can only be used with a split ferrite core. The operating frequency of the converter is quite large, so only ferrite is needed for transformer iron. The converter itself is single-acting, with constant bias, so the core must be split, with a dielectric gap (one or two layers of thin transformer paper are laid between its halves). It is best to take a transformer from an unnecessary or faulty similar device. In extreme cases, you can wind it yourself: the core section is 3,5 mm2, winding I - 450 turns with a wire with a diameter of 0 mm, winding II - 1 turns with the same wire, winding III - 20 turns with a wire with a diameter of 15 ... 0,6 .0,8mm (for 4,5V output voltage). When winding, strict observance of the direction of winding is required, otherwise the device will work poorly, or will not work at all (you will have to make efforts when adjusting - see above). The beginning of each winding (in the diagram) is at the top. Transistor VT1 - any power of 1 W or more, collector current of at least 0,1 A, voltage of at least 400 V. The current gain must be greater than 30. Transistors MJE13003, KSE13003 and all other type 13003 of any company are ideal. As a last resort, domestic transistors KT940, KT969 are used. Unfortunately, these transistors are designed for a voltage limit of 300 V, and at the slightest increase in the mains voltage above 220 V, they will break through. In addition, they are afraid of overheating, i.e., they need to be installed on a heat sink. For transistors KSE130O3 and MJE13003, a heat sink is not needed (in most cases, the pinout is the same as for domestic KT817 transistors). Transistor VT2 can be any low-power silicon, the voltage on it should not exceed 3 V; the same applies to the diodes VD2, VD3. Capacitor C5 and diode VD4 must be rated for a voltage of 400.600 V, diode VD5 must be rated for the maximum load current. The diode bridge VD1 must be rated for a current of 1 A, although the current consumed by the circuit does not exceed hundreds of milliamps, because when turned on, a rather powerful current surge occurs, and the resistance of the resistor must be increased. It is impossible to limit the amplitude of this throw - it will get very hot. Instead of the VD1 bridge, you can put 4 diodes of the type 1N4004 ... 4007 or KD221 with any letter index. Stabilizer DA1 and resistor R6 can be replaced with a zener diode, the voltage at the output of the circuit will be 1,5 V more than the stabilization voltage of the zener diode. The "common" wire is shown in the diagram only to simplify the graphics, it must not be grounded and (or) connected to the device case. The high voltage part of the device must be well insulated. Author: Kashkarov A.P.
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Casio watch in the style of the series Stranger Things ▪ Alpha Bonfire Pocket Bonfire ▪ 5 copies of Earth discovered ▪ Microbial colonies on jewelry ▪ Car projector understands gestures and human speech
▪ section of the site Labor protection. Selection of articles ▪ article ENT diseases. Lecture notes ▪ Lungwort's article is obscure. Legends, cultivation, methods of application ▪ Article Distorber for electric guitar. Encyclopedia of radio electronics and electrical engineering
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page