Rectifier... on the logic element. Scheme, description

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Rectifier... on the logic element. 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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It is known that the input circuits of digital microcircuits of the CMOS structure are equipped with protective diodes. This circumstance in some cases allows "saving" parts (in particular, rectifier diodes) and space on the board, using free logic elements or flip-flops. How to do this will be discussed in the proposed article.

Each signal input of a logic element or other functional unit of a modern CMOS microcircuit, as you know, is shunted by protective diodes (for example, VD1-VD6 in the diagram of Fig. 1 in S. Biryukov's book "Digital Devices on MOS Integrated Circuits". - M .: Radio and communication, 1990). It can be seen that the protective diodes of the two inputs of the element form a bridge rectifier. If an alternating voltage is applied to these two inputs from the secondary winding of the mains transformer, as shown in Fig. 1, then it will be rectified by a diode bridge and fed to pins 14 and 7 of the microcircuit. The rectified voltage smoothes the capacitor C1.

Rectifier... on logic element

The remaining logical elements of the microcircuit can be used for their intended purpose, i.e., to perform logical operations on pulse signals, assembling RS flip-flops, building generators, etc. If the device consists of two or three cases, it is enough to connect their positive power leads and separately minus. The current drawn from the described rectifier must not exceed 20 mA.

If two logical elements are used in the power supply (Fig. 2), then the rectifier can withstand a load current of up to 40 mA, since the diodes in it will be connected in pairs in parallel. When four elements are used in the rectifier, the current consumed by the load should no longer be doubled due to the possible non-identity of the characteristics of the diodes - it is necessary to limit the current to 50 ... 60 mA. The voltage of the secondary winding of the transformer T1 should not exceed 10 ... 11 V (effective value).

Rectifier... on logic element

Not only logic elements can serve as a rectifier, but also other functional units, for example, the K561TM2 trigger. If you enable this trigger as shown in fig. 3, you will get a rectifier for a load current of up to 40 mA (the result will not change if input D is connected to input R, and input D is connected to S - C), and two anti-phase sequences of rectangular pulses with a frequency of 50 Hz can be removed from the trigger outputs. The same two sequences, by the way, are present at the outputs of the rectifier logic elements according to the circuit in Fig. 2. In cases where it is necessary to stabilize the output voltage of the rectifier, a low-power zener diode is connected in parallel with capacitor C1, and a ballast resistor is inserted into the circuit of one of the secondary winding terminals (Fig. 1).

Rectifier... on logic element

Of course, only those microcircuits can work as a rectifier, in which the inputs of the elements (functional units) are protected by diodes. It is very easy to make sure that these diodes are present - using any avometer connected with an ohmmeter.

Leaving in the rectifier according to the scheme of fig. 2 one input of any element is free and by applying pulses with a frequency f from an external generator to it, you will be able to simultaneously with rectification (load current - 20 mA) generate bursts of pulses at the output of this element. If the frequency f is greater than the mains frequency, these will be bursts of frequency f, repeating with the mains frequency, and if less, bursts of the mains frequency following with frequency f.

Author: A.Samoilenko, Klin, Moscow Region

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