Switches controlled by the input signal amplitude are used as input signal level indicators, input signal level analyzers, power supply voltage indicators, and so on. Such switches are usually made as a line of comparators or bipolar or field-effect transistors in combination with an input resistive voltage divider.
The switch described below is made using MOSFET Q1–Q11 2N7000 and is characterized by a fairly simple scheme, the ability to increase the number of switching channels, as well as the presence of non-overlapping switching windows. This feature allows you to use a multi-position switch controlled by amplitude as a multi-load switching device with control from multiple equivalent control panels using just through two wires.
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These panels contain several switches and resistors that are connected in series with them, and the unused pins of the switches are connected together a nd connected via the control line to the device’s power bus, and the unused pins of the resistors are also connected together and connected via the control line to the Multi-position switch input.
The multi-position switch, Figure 1, works as follows. The input signal is fed to the resistive divider R1–R6. From resistive divider R1–R6 through resistors R7–R12 control signals are sent to the gates of field-effect transistors that control loads R13–R18. In parallel to the control circuits (source-gate) of transistors, transistors are connected that provide sequential shunting of these circuits as the input voltage increases.
Figure 1 Electrical diagram of a six-position switch controlled by applying different levels of voltage to its input.
In the initial state, if there is no control voltage, a high-level voltage is present at all six outputs of the device, almost equal to the power supply voltage of the multi-position switch (from 6 to 60 V).
For the first of the channels, the output voltage drops almost to zero, Figure 2, when a voltage from 2.4 to 4.1 V is applied to the input of the switch.
Figure 2 Dynamics of electrical processes (switching output stages) of a multi-position switch when a linearly increasing voltage is applied to its input.
For the second channel, the switch state switching window is in the range from 4.9 to 8.0 V. for the third channel – from 9.5 to 12.8 V; for the fourth – from 15.2 to 21.6 V; for the fifth – from 25.3 to 32.7 V and for the sixth-over 38 V.
The maximum input voltage of a multi-position switch no more than 40 V. Under this condition, the maximum possible voltage on the gates of transistors does not exceed their maximum permissible passport values (no more than 20 V).
If desired, the voltage switching ranges of channels can be adjusted by selecting the values of the input resistive divider R1–R6.