LM3914 - 10 Step Sequential Traic Trigger Driver

  This circuit uses a LM3914 Dot/Bar Display Driver to sequentially activate ten optocoupled triac gate drivers. The circuit uses a Resistor / Capacitor (RC) circuit as the timing method.

  The timing is not particularly precise and is nonlinear due to the charging voltage curve of RC circuits but for sequence times of less than a minute it should be adequate. However, longer sequence times means larger delays between each steps.

  Using a constant current type regulator in place of the 133K ohm resistor would improve timing linearity.

  The circuit shown was developed for a particular use and so the component values are specific to that application.

  The trigger step voltages are at 0.5 volt intervals from 0.5 to 5.0 volts. The timing of the circuit is shown in graphical form below the schematic.

Resistance, Capacitance, Voltage, And Charging Time Calculator (@ www.csgnetwork.com)

  If power on is counted, the sequence can be eleven steps in length.

  The LM3914 Dot/Bar Display Driver datasheet should be thoroughly understood to make the best use of this device.

  The example circuit drives optocoupler triac gate drivers but any type of optocoupler could be used. A LED bar graph could be added in series with the coupler LEDs to give a visual indication of the sequence position.

  Adding a SPDT switch and resistor to the charging circuit would allow the outputs to be switched off in reverse order.


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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

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17 March, 2017