Programmable voltage level generator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Programmable voltage level generator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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In modern air conditioners, it is possible to programmatically change the temperature they maintain. A variant of the simplest heat stabilizer with a similar mode is presented in "Radio", 1999, No. 1, p. 36, 37. This article describes a stepwise voltage generator that can be built into almost any heat stabilizer and at the same time provide four levels of temperature maintenance. We do not exclude that radio amateurs will find another use for such a generator.

The scheme of the proposed device is shown in the figure. The frequency of the pulse generator on the elements DD1.1-DD1.3 is determined by the RC circuits switched by the multiplexer DD2.1, which, in turn, is controlled by the counter DD3, powered by the pulse generator. Multiplexer DD2.2 works synchronously with DD2.1, alternately supplies voltage to the output from the divider R6-R11.

Programmable voltage level generator

When power is applied, the C6R5 differentiating circuit generates a positive polarity pulse that sets the counter on the DD3 chip to zero. Low levels from the outputs of the counter are fed to inputs 1 and 2 of the DD2 chip and to the enable input of the pulse generator. In the DD2 multiplexer, the inputs and outputs X and X0, Y and Y0 are interconnected. The output of the device receives voltage from the engine of the resistor R7.

The generator starts to work on the elements DD1.1-DD1.3. The period of the pulses at its output is determined by the resistance of the resistor R1 and the total capacitance of the capacitors C1 and C2. After a time corresponding to 32 pulse periods, a high level appears at the output 2 of the counter DD3.2. The second phase of the device begins. The voltage is supplied to the output from the engine of the resistor R8, and the pulse period of the generator is determined by the resistance of the resistor R2 and the sum of the capacitances of the capacitors C1 and C3.

So four phases of the device operation will be formed, each of which has its own duration and its own voltage level at the output Y of the DD2.2 multiplexer. After the end of the fourth phase, a high level will appear at the output 8 of the counter DD3.2, which will disable the operation of the generator, and can also be used to signal the end of the process. If the input 1 of the DD1.1 element is disconnected from the meter output and connected to a common wire, the four-phase cycles will continue until the power is turned off.

The capacitance of capacitors C1-C5 can be selected in the range from 20 pF to 2 μF, and the resistance of resistors R1-R4 - from 10 kOhm to 10 MΩ. Therefore, by an appropriate choice of these elements, it is possible to obtain ratios of phase durations reaching up to 10 9, which is more than enough in any practical cases. For most applications, the number of timing capacitors can be reduced, but it is important that one of them is always connected in place C1. Resistors R1-R4 can be variable or trimmer, which will allow you to quickly change the program.

If the output of such a generator in the thermostat is connected to one of the inputs of the comparator (to the second input of which a thermistive divider is connected), the temperature can be maintained according to a program that has four steps. This can be especially useful in an electric oven - some dishes, the taste of which not everyone has forgotten, require a change in temperature during cooking according to a certain program. In this case, a thermocouple should serve as a temperature sensor.

Author: S. Biryukov, Moscow

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