Homemade simple - thermostat

The heater tube 1N4148, the temperature range of such a semiconductor temperature sensor can reach -55~+150:, the temperature coefficient is good in the forward current I. The external components only need one current limiting resistor (see), and the temperature measuring circuit is simple and reliable. However, care should be taken not to apply epoxy or other poor thermal conductors as a protective layer on the outer Qin, otherwise the temperature measurement accuracy will be affected.

The pole tube, the forward voltage drop Vj is 0*痹鸡; (Because the component itself has a practical dimming table lamp, many of the electronics enthusiasts want to see themselves in the electronic newspapers and magazines. Make one piece. After it is made, it can be paid for practical application, and it has a psychological satisfaction, which also enhances the self-confidence of learning electronic technology. If it can improve or modify the original circuit in practice, it will not only improve Interests, but also a sense of accomplishment, can encourage enthusiasts to continue to learn electronic technology theory to guide practice.

Here is an example of an electronic production for the enthusiasts: the introduction of the happiness card dimming table lamp on the 5th edition, which has an interest in its principle. For convenience, the circuit is redrawn as shown. It is a four-segment touch dimming table lamp, but it does not use an ASIC. Instead, it uses two general-purpose CMOS integrated circuits, which is very suitable for self-made, and the circuit is clever. There are three points: First, the principle of dimming, the conduction angle of the thyristor is provided by the 50Hz AC mains to trigger the reference, and is determined by the C2, R4 and R5 charge and discharge time constants; second, the brightness control of the table lamp is controlled by the JK The two-stage flip-flop is composed of different output states under the action of the touch pulse; the third is that each time the touch is made, the sound and the effect of the simultaneous change of the sound and light have a fresh feeling.

In the process of self-made, I often encounter the same components at hand and worry, experienced fans can choose to substitute according to the actual situation, I have no 16-pin dual JK trigger CD4027, I chose the 14-pin dual D The trigger CD4013 is substituted, because in principle they can form a two-stage flip-flop, so the circuit is redrawn, and the Zener tube also uses 6.3V instead of 5.8V. Some components are also modified according to the effect. Finally, The completed circuit is as shown.

In the production process, can not be expected to be a success, because there are many factors affecting the circuit work, such as the variable value of components, six non-gate circuit damage in CD4069, double D trigger CD4013 trigger flip is wrong, etc. In short, anything can happen, but the work done after overcoming various difficulties, although in the eyes of others, such as the chicken belly is insignificant, but the producer himself is not happy, happy, sometimes a little self-satisfied, this may be many electronic hobbies Personal experience.

In the circuit, there are two places that can be personally modified: electricity, complete the conduction angle change, and R4 and R5 are connected to the output of the two-stage flip-flop, when an output is low, Connected to the output terminal, the resistor acts as the discharge of C2. R4 has a larger resistance than R5, and the discharge is less, so that the conduction angle of the thyristor is small, and the desk lamp is dark. Therefore, only R4 discharges, the table lamp is the darkest; R5 Discharge, the desk lamp is brighter; R4, R5 are discharged in parallel and the desk lamp is the brightest. The four output terminals of the two-stage flip-flop are flipped under the action of the trigger pulse. The circuit uses a low-level trigger VS, so the trigger sensitivity is higher, and the trigger current lGr=16mA can trigger the 6~12A thyristor to conduct. Considering that the cold resistance of the electric heater is about 0.6 of the thermal resistance, the starting current is large, and the maximum load power of the 12A thyristor is less than or equal to 1600W. To control more powerful equipment, switch to a larger current thyristor. Because the thyristor is hot, the heated equipment is kept at a constant temperature.

Adjust the RP to set the constant temperature, first put the RP so that VS has just turned off. You don't have to adjust it later, unless you set the temperature separately. It can also be divided into several scales on the corresponding position of the RP knob on the panel, which is more convenient to use.

R12 is a positive feedback resistor. R12 is not connected when starting the test. When the input voltage of A3 is close to the threshold voltage, the output voltage of A3 is lowered, it cannot be turned over quickly, VS cannot be turned off, and the incandescent lamp connected in parallel with the electric heater becomes dark and flickers frequently. . After adding R12, the hysteresis characteristic is introduced, and the response speed of A3 is accelerated to eliminate the above phenomenon by ±1 ft, which can meet the technical requirements of the general thermostat. The R12 resistance of this circuit is the experimental value. If it is too large, it will not work. If it is too small, the accuracy will be deteriorated due to the increase of the hysteresis. See the board.

The ICTs required are often much smaller than the ICT (maximum) provided in the manual. If the conduction cannot be triggered, the R11 resistance should not be reduced to increase the Ict. Otherwise, the DC supply voltage will drop slightly when V is turned on, which will deteriorate the accuracy. The DC power supply can be changed to a circuit. Remove the VD1~VD4 on the original circuit board. C1 and C2 can be modified to install all components except the 3W small transformer on the original circuit board. Others do not need to be changed. Then reduce the resistance of R11, for example, change to 330 or 220fl to make ICT=35~50mA, enough to trigger high-power thyristor. The thyristor with higher power should be installed on the heat sink with a large enough area, and the thick power line should be directly connected to T1, T2 and the load. Then connect the board with a thinner wire (eg). The lightly loaded thyristors below 3A can be soldered directly to the board.

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