Thursday, January 5, 2012

How to Make an Electronic Toggle Switch Circuit

A toggle switch refers to a device which is used for switching an electrical circuit ON and OFF alternately whenever required. Normally mechanical switches are used for such operations and are extensively employed wherever electrical switching is required. However mechanical switches have one big drawback, they are prone to wear and tear and have the tendency of producing sparking and RF noise.

A simple circuit explained here provides an electronic alternative to the above operations. Using a single op amp and a few other cheap passive parts, a very interesting electronic toggle switch can be built and used for the said purpose.

Though the circuit also employs a mechanical input device but this mechanical switch is a tiny micro switch which just requires alternate pushing for implementing the proposed toggling actions. 

A micro switch is a versatile device and very much resistant to mechanical stress and therefore does not affect the efficiency of the circuit.

The figure shows a straightforward electronic toggle switch circuit design, incorporating a 741 opamp as the main part.

The IC is configured as a high gain amplifier and therefore its output has the tendency of easily getting triggered to either logic 1 or logic 0, alternately.

A tiny portion of the output potential is applied back to the non inverting input of op amp
When the push button is operated, C1 connects with the inverting input of the opamp. 

Assuming the output was at logic 0, the opamp immediately changes state.

C1 now begins charging through R1.

However keeping the switch pressed for a longer period of time will only charge C1 fractionally and only when it’s released does C1 begins charging up and continues to charge up to the supply voltage level.

Because the switch is open, now C1 gets disconnected and this helps it to “retain” the output information.

Now if the switch is pressed once again, the high output across the fully charged C1 becomes available at the inverting input of the opamp, the opamp yet again changes state and creates a logic 0 at the output so that C1 starts discharging bringing the position of the circuit to the original condition.

The circuit is restored and is ready for the next repetition of the above cycle.

The output is a standard triac trigger set up used for responding to the outputs of the opamp for the relevant switching actions of the connected load.


Parts List

R1, R8 = 1M,
R2, R3, R5, R6 = 10K,
R4 = 220K,
R7 = 1K
C1 = 0.1uF,
C2,C3 = 474/400V,
S1 = micro-switch Push Button,
IC1 = 741
Triac  BT136

6 comments:

  1. what is the value of zener Z1 used in the circuit.

    ReplyDelete
    Replies
    1. 12V............ the circuit is directly linked with AC mains, so be extremely careful....

      Delete
    2. Hi,
      how to connect led indicator to this circuit .so when switch is ON led is ON & when off led is off. what will be the limiting resistor for led?

      Delete
    3. positive---------^^^------->I-------pin6-----------^^^--------->I-----------ground

      limiting resistor 10k

      Delete
  2. Hi Swagatam

    Can this circuit be used with some modification for switching on say 12V devices? Or a latch circuit will be a better option. If yes, what mods?

    ReplyDelete
    Replies
    1. Hi Abu-Hafss,

      Yes this circuit can be effectivey used as a flip flop for operating any load may it be AC or DC at its output.

      For DC loads simply connect a mosfet in place of the triac and do the connections appropriately as necessary for a mosfet.

      Delete

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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.