Load connection indicator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Load connection indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Miscellaneous electrical devices

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Looking for a light switch or an outlet in the dark is an unpleasant task. It is much more pleasant when you see a glowing indicator in the dark and focus on it. It is especially useful to equip with such an indicator those sockets that power devices that do not have on indicators and fuses. I offer an improved version of the device, equipped with a fuse blown indicator.

When there is no contact between the plug of the connected load and the socket, the indicator does not light up, indicating that there is no “power take-off” by the load. If the load is taking power, the blue indicator is lit, and when the load is drawing excessive power, the fuse blows and the red flashing LED turns on.

The load connection indicator (PSI) consists of (Fig. 1):

fuse FU1 with blown indicator on elements VD1, VD2, R1, HL1, C1;
power bypass circuit on the VD6 diode;
load current sensor on diodes VD4, VD5 and detector VD7, R2, C2;
key field effect transistor VT1;
display unit on the elements VD8, HL2, R4, R3, VD3.

Load connection indicator

When the FU1 fuse blows, if the load is connected to the XS1 socket, the current flows through the elements of the blown indicator that were previously shunted by the zero resistance of the fuse. Rectifier diode VD1 passes only negative

half-waves of the mains voltage that come through the current-limiting resistor R1 to the storage capacitor C1 and the load connected in parallel to it - a blinking HL1 LED. VD1 protects HL1 from reverse voltage, and the Zener diode VD2 protects HL1 from direct current overload.

When the load is not connected to the socket XS1, no current flows through the diodes VD4.VD6, the storage capacitor C2 is discharged and the field effect transistor VT1 is closed.

The channel resistance (source-drain) is very high, and the HL2 indicator is off.

When the load is connected to the socket XS1, the load current flows through the back-to-back diode VD6 and the chain of diodes VD4, VD5. The negative half-waves of the mains voltage from the lower one according to the network wire scheme pass through VD6, and the positive ones through VD4 and VD5.

The direct voltage drop across the diodes VD4 and VD5 through the resistor R2 and the diode VD7 enters C2 and charges it to a value exceeding the cut-off voltage (+0,6 V) of the field-effect transistor VT1. Transistor VT1 opens and through its channel, VD8, HL2, R4 connected in parallel, and then current flows through R3 and VD3. LED HL2 glows brightly, signaling the connection of the load. Resistor R3 is current-limiting, diode VD3 prohibits the flow of current during reverse half-cycles of the mains voltage. Resistor R4 eliminates the backlight HL2 when VT1 is closed and, if necessary, is selected in the range from 3 to 8,2 kOhm.

The direct voltage drop across the current sensor (VD4, VD5) depends on the power of the connected load. In order for the indicator to "react" even to low-power (less than 1 W) devices, a relatively scarce field-effect transistor is used in the circuit. KP504A. It has a maximum source-drain voltage of 240 V and allows you to switch the current in the drain circuit up to 0,25 A. The control voltage at the gate relative to the source is from 0 to 10 V. Cut-off voltage. KP504A is +0,6 V. The maximum load power connected to the XS1 socket is determined by the limiting forward current of the VD4.VD6 diodes (1,7 A) and should not exceed 500.700 W.

The circuit uses resistors of the OMLT type. Capacitor C1 - type K50-35 or foreign production with an operating voltage of at least 16 V, C2 - KM. Diodes VD1, VD3, VD8 - KD105B, KD102A or other miniature ones with a permissible reverse voltage of at least 200 V, VD4.VD6 - KD226V, KD226G, KD226D, VD7 - germanium. D2 or. D9 with any letter. Zener diode VD2 - low-power, with a stabilization voltage of 3,9 ... 5,6 V, for example, KS139, KS147A, KS447A, KS156A. The HL1 LED can be replaced with a 5mm red MSD ARL-5013URC-B or a high brightness non-flashing MSD such as yellow ARL-5213UYC. In the latter case, the capacitor C1 can be excluded. The HL2 LED can be replaced with any low-voltage green (ARL-5213PGC), white (ARL-3214UWC) or blue (ARL-3214UBC) color, preferably high brightness.

Almost all elements of the device are placed on a printed circuit board, the drawing of which is shown in Fig.2. The board is built into a power outlet or into an adapter-splitter ("tee"), which is plugged directly into the outlet. It is possible to place it in the body of the socket block at the end of the extension cord - "carrying". Fuse FU1 for current. 3A - ceramic, miniature. It is installed in the head type fuse holder. DPB and is placed on the front panel of the socket so that it does not interfere with the inclusion of plugs. When the indicator is installed in the socket, the network wires that fit the socket contacts are carefully disconnected and connected to the board through the terminal clamp blocks.

So that when the FU1 fuse is blown, the HL1 LED turns on even if there is an open in the load circuit connected to the XS1 socket. between the anodes HL1 and VD4, a 2-watt resistor Rd with a resistance of 22 ... 36 kOhm should be connected (a place is provided for it on the printed circuit board).

Author: A.Oznobizin, Irkutsk

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