Electronic load switch. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic load switch. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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Sometimes it becomes necessary to alternately switch several loads with electronic keys instead of a mechanical switch. A search in the literature led to an interesting circuit solution published in Radio No. 12, 1989.

The electronic load switch operates as follows. When power is applied, the capacitor C1 begins to charge through the resistor R4. The low voltage on the capacitor C1 at the first time sets the output of the element DD1.4 log. "0". At the outputs of the elements DD2.1, DD2.2, DD3.1, a log is set. "1", the outputs DD1.1, DD1.2, DD1.3 are also set to log. "1", at the output of the element DD3.2 -log. "0". The HL4 LED lights up, indicating the readiness of the device, but no load is turned on. To turn on, for example, the load Rn1, you must press the button SB 1. At the same time, a log is set at the output of the element DD1.1. "0", at the output of the element DD3.2 - log. "1", and the HL4 LED goes out; a log is set at the output of the DD1.4 element. "1" because C1 is already charged; a log is set at the output of the DD2.1 element. "0", at the output of the element DD4.1 - log. "0".

The HL1 LED lights up and signals the load is on. The VU1 optocoupler opens the triac VS1, which, in turn, switches the load Rн1. Elements of the D4 chip are used as repeaters with a high load capacity. When you press, for example, the SB3 button, the load Rн1 will be turned off first of all, since a log is set at the output of the DD1.3 element. "0", at the output of the element DD2.1 - log. "1", and the load Rn1 is turned off. At the output of the DD3.1 element, a log is set. "0", at the output of the element DD4.3 - also a log. "0", the HL3 LED lights up, and the load Rn3 is turned on.

The circuit design of the circuit excludes even a short-term inclusion of two loads. You can turn off any of the loads by pressing the SB4 button. If desired, you can turn on the fourth load by adding a circuit of an opto-switch and a triac to the HL4 LED circuit, similar to the circuits discussed above. The power of the switched load is determined only by the maximum current of the applied triac. Thus, by pressing the low-current button SB, you can switch the load from hundreds of watts to several kilowatts.

The modified scheme is shown in the figure.

(click to enlarge)

Details

To power the circuit, a transformer with a bridge diode rectifier and a filter is used, with an output voltage of 9 V. The supply voltage of the microcircuits is stabilized by a DA1 microcircuit of type 7805. The microcircuits indicated in the diagram can be replaced by domestic analogues: KR74EN08A. Buttons SB555-SB1 type SWT74-10 can be replaced by any domestic ones.

According to the materials of the journal Radioamator.

Publication: cxem.net

See other articles Section Clocks, timers, relays, load switches.

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