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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Power supply-timer, 220/9 volts 1 ampere. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies The power supply offered to the attention of readers is designed to work in conjunction with radios, radios and other middle-class household equipment that does not have a built-in timer. In addition, it can be used as a timer with a fixed response time to control any devices powered by the lighting network. The power supply unit differs from similar devices in its increased performance: convenient push-button control, complete disconnection from the network from any mode (by a button, by a timer signal, in case of a short circuit at the output), a timer that can be turned on and adjusted with one button. Main Specifications
The device (Fig. 1) consists of the power supply itself on the T1 transformer, the VD1 diode bridge, the DA1 microcircuit voltage regulator: a manual and automatic disconnection unit from the network, including a triac VS1, a relay K1, a transistor VT1, and a timer with time-setting R8-R12C7 and bit VT2R4 circuits, as well as the control unit on the DD1 chip.
A distinctive feature of the power supply is the presence of a disconnecting unit, made on the triac VS1, included in the primary winding circuit of the TT mains transformer. Due to this, the entire device is disconnected from the network from the side of the supply voltage, and the applied circuit solution is much simpler and more reliable than, for example, described in the article [1]. The state of the triac VS1 is controlled by the SB1 "On" button and the blocking contacts of relay K1.1. Capacitors C1 - C4 eliminate the multiplicative background and network interference. Relay K1 with related elements operates in the automatic shutdown unit of the unit. To turn on the relay, a pulse principle is used, which allows to significantly reduce the current consumption. Turning off the relay, which results in the disconnection of the entire device from the network, is possible in three cases: manually - with the SB2 "Off" button; according to the timer signal - transistor VT1 connected in parallel to the button; in case of overload or short circuit at the output or at the input of the stabilizer DA1. As a threshold element, a field-effect transistor VT1 with a high slope of the transfer characteristic and a low resistance of the open channel is used, which contributes to a clear operation of the timer. A timing capacitor C2 is connected to the gate of the transistor through a resistive divider R3R7. The presence of the divider is due to the desire to obtain the maximum exposure time with small values of the elements of the charging circuit. Its effectiveness is illustrated by the charging characteristic of the capacitor C7.1.0 modeled in Micro-Cap 7 (Fig. 2), which was obtained for the first stage of the timer at R12 = 300 kOhm, C7 = 470 μF.
The graph shows that without a divider, transistor VT1 opens at a gate voltage of 1,8 V (point 1 on the graph), and the exposure time is 31 s. With the divider R2R3, this time increases by almost 10 times (point 2), since the capacitor C7 is now charged to almost four times the voltage. For other stages, the time constant is determined by the resistors R8-R12 of the control node matrix turned on at this moment. Transistor VT2 is designed to quickly discharge the timing capacitor C7 before each new cycle of the timer. The main difference between the timer is the original control device, made on a decimal counter DD1. The counter is controlled by the CN input, to which the SB3 button is connected. In turn, the outputs of the microcircuit are connected to a resistive-diode matrix R8-R12VD2-VD6. Diodes VD2-VD6 are necessary to decouple the active output of the microcircuit (which has a high level) from others connected at that moment to a common wire. The purpose of the C11R7 circuit is to set the counter to zero when turned on. Capacitor C10 suppresses the "bounce" of the contacts of the SB3 button and prevents external interference from entering the CN input, which can cause a counter false alarm. The device works as follows. To turn on the power supply, press the SB1 button, as a result of which the triac VS1 opens and the supply voltage is supplied to the device. The charging current pulse of the capacitor C6 turns on the relay K1, the contacts of which K1.1 block the button SB1, leaving the entire device on. Resistor R1 sets the holding current of relay K1 at about 10 mA. In this mode, the unit provides power to the radio or radio receiver with a stabilized voltage of 9 V. At the same time, it is fully protected from overload and short circuit: in the event of a sharp increase in load current, the voltage at the output of the DA1 microcircuit drops, the holding current of relay K1 becomes insufficient and the relay, turning off, de-energizes the whole device, closing the triac VS1. For "manual" (without time delay) turning off the unit and the equipment fed by it, briefly press the button SB2. This turns off the relay K1, the contacts of which K1.1 open the control circuit of the triac VS1, and the latter, closing, disconnects the device from the network. The operation of the timer needs a separate explanation. When the power is turned on, the timer is set to the zero state by applying a short reset pulse to the input R of the counter DD1 through the capacitor C11. After that, a single signal appears at output 0 (pin 3), and zero at all other outputs. The high-level voltage from output 0 through the resistor R4 is supplied to the base of the transistor VT2, opening it. Transistor VT2 by the collector-emitter section shunts the capacitor C7 and discharges it if there was a residual charge on it. This is the timer preparation cycle. Further operation of the timer is ensured by the control of just one button, without any additional switching, typical for other devices, for example, [2]. The operating mode is set in steps, by the number of short presses on the SB3 button. Each press switches the counter one step and sets the appropriate time delay. After the first press of the SB3 button, the DD1 counter counts one pulse, as a result of which a single signal is set at output 1 (pin 2). Transistor VT2 closes, and the voltage from output 1, close to the supply voltage, is fed through diode VD6 and resistor R12 to capacitor C7, charging it. The remaining outputs of the DD1 chip at this moment are decoupled by closed diodes VD2-VD5, which prevent the capacitor from discharging to a common wire. As capacitor C7 charges, the gate voltage of transistor VT1 increases. The time constant of the R12C7 circuit of the first stage is chosen such that the time to reach the threshold level is about 5 minutes. After this time, the transistor VT1 opens and shunts the winding of the relay K1, which, turning off, turns off the entire device, as described above. When you double-click on the SB3 button, a single signal appears already at output 2 (pin 4). Accordingly, now the charging circuit is formed by two resistors R11 and R12 connected in series, which increases the exposure time to 10 minutes. By pressing the SB3 button several times (up to five), the timer is programmed for the desired operating time within 5/10/15/20/25 minutes. The last press stops the counter, preventing further counting, since the maximum dwell time is set. This is achieved by applying to the input CP counter DD1 a single signal from output 5 (pin 1). By somewhat complicating the control unit, you can get even more convenient cyclic control with indication. How to do this is shown in Fig. 3. The counter operation algorithm was changed by applying a single signal from output 6 (pin 5) of the DD1 chip to input R. In addition, now the counter outputs 1-5 are connected to the display unit assembled on transistors VT3-VT7 and LEDs HL1-HL5.
In this device, each press of the SB3 button, in addition to switching the exposure mode, turns on one of the LEDs indicating the corresponding mode. The fifth pressing is not fixed, and the next sixth one again switches the counter to the zero state. In this case, the capacitor C7 is discharged and not a single LED is lit - the timer is off. Further, by pressing the SB3 button and guided by the HL1-HL5 LEDs, you can re-program the timer for the desired time. Thus, an infinite control loop with indication is implemented here, which is very convenient in practice. In the power supply, designed for a load current of 1 A, a standard network transformer T10-3 (T1) is used, the secondary windings of which are connected in series. Of course, you can use any other transformer, the voltage on the secondary winding of which under load is at least 8,5 V. Instead of the triac KU208G, it is permissible to use TS106-10, designed for higher current and having smaller dimensions. The K561IE8 chip is interchangeable with analogues from the 564, K176 series. The device uses a RES55A relay of version RS4.569.600-01, but it can be replaced by another small-sized reed relay with an actuation voltage of 4 ... 6 V and a holding current of not more than 7 mA. All three control buttons are non-fixed based on MP7 microswitches. Transistors KT315B can be replaced by KT315G, moreover, in order for the brightness of the LEDs in the device fig. 3 was the same and sufficient, transistors VT3-VT7 should be selected according to the current transfer coefficient h21E = 100 ... 120. It is not recommended to use transistors with a transfer coefficient of more than 140, since in this case the LED current will exceed the maximum allowable value (6 mA). Instead of red LEDs KIPD05A-1K, it is permissible to use KIPD05B-1L (green), KIPD05V-1Zh (yellow), but it should be borne in mind that the brightness of the indicator will decrease by about half. The versatility of the proposed device lies in the fact that it can be used as a separate timer that controls household electrical appliances by mains voltage. In this case, a load with a power of up to 1 kW (for the triac KU208G) or up to 2 kW (for the triac TS 106-10) is connected in parallel with the primary winding of the transformer T1, as shown in Fig. 1. The power supply in this case is only needed to power the timer itself, respectively, the power of the network transformer T1 can be reduced to a few watts, the capacitance of the capacitor C5 is reduced by about ten times, and the capacitor C9 is completely excluded. Instead of the VD1 bridge, you can install low-power silicon diodes. All the functions described above are preserved in this case, but the switching of the load is carried out from the "high-voltage side", and the disconnection from the network and the load and the timer occurs simultaneously. The device does not require adjustment. The only thing that may be required is the adjustment of the timer operation time with resistors R8-R12 in fig. 1 (R12-R16 in Fig. 3), especially in the upper stages, where the charging current is commensurate with the leakage current of the capacitor C7 and the divider current R2R3. In conclusion, we note that the proposed timer allows a wide range of upgrades. So, the number of control steps can be increased to ten (according to the number of outputs of the DD1 microcircuit), and the exposure time of each step is changed in any direction by selecting resistors R8-R12. Literature
Author: A.Pakhomov, Zernograd, Rostov region
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