How to make a flashing switch from a Transistor

Thread Starter

Selvedin

Joined Jan 25, 2021
15
Hello guys,
I need to make a circuit in which a transistor acts like a flashing switch. I watched some videos but the Problem is that I don't have the exact same components as in the Video shown and so my project fails.
Can you help me?

Kind regards to all good people
 

dl324

Joined Mar 30, 2015
12,677
The components used in those types of circuits aren't typically very critical. Post a schematic for the circuit you found and what you tried.
 

SamR

Joined Mar 19, 2019
3,180
I assume this is a 2 transistor and capacitors flip-flop circuit? Or using a transistor switch on the output of a 555 timer? Please post the schematic you have so we know what we are working with.
 

Reloadron

Joined Jan 15, 2015
5,876
Probably a reverse Vbe relaxation oscillator.

Bob
That's my guess and using a single transistor you would want a Unijunction Transistor and not just any transistor will work. Using two transistors you want to Google Bi-Stable Multi-Vibrator.

You really need to provide a link to the circuit you are trying to build.
 

SamR

Joined Mar 19, 2019
3,180
LOL I remember seeing that circuit and thinking OOOps someone forgot to bias the base. Should play with it some day...
 

Thread Starter

Selvedin

Joined Jan 25, 2021
15
Thanks for the replays. I don't have a scheme, because on every video they do it on a different way. I am just searching for the easiest way to make it.
It should handle 12V and about 1A. The switching period should be at least 2 times per second.

Kind regards
 

DickCappels

Joined Aug 21, 2008
7,155
The circuit posted by MrChips is an easy way to go, but for each kind transistor the optimum resistance and the power supply voltage can vary. Some people try to run it from 9V and give up.

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The circuit above is very reliable and repeatable, just try to get the capacitors and resistors to be about the same.
 

dl324

Joined Mar 30, 2015
12,677
The above circuit will likely have problems with the LED that's supposed to be off lighting dimly from the base current for the transistor that's on. You can get around that by taking the LEDs out of the base current paths or using MOSFETs instead of BJTs. Some put a resistor in parallel with the LEDs...
 

Tonyr1084

Joined Sep 24, 2015
5,804
How fast do you want it switching? Is one state (ON or OFF) meant to be longer than the other, say - ON for 1/2 second and OFF for 10 seconds? Are you opposed to using a relay?
 

ElectricSpidey

Joined Dec 2, 2017
1,529
I think the circuits in post #10 & #6 will need buffering to drive 1 amp LEDs.

The simplest is not always the easiest.

Perhaps a quad Schmitt inverter, with one configured as the osc. and the other three to provide the Q and not Q outputs...then two* MOSFETS to drive the LEDs.

*if two LEDs are needed.
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
5,804
Not sure what the TS wants to switch on and off in a flashing manor. If it's as simple as a 12 volt light bulb that runs at 35 watts, that should be easily done with an old fashioned blinker control module from an older model car. They can be found in auto parts stores. Electronic modules are also available in auto parts stores.
 

BobaMosfet

Joined Jul 1, 2009
1,502
Hello guys,
I need to make a circuit in which a transistor acts like a flashing switch. I watched some videos but the Problem is that I don't have the exact same components as in the Video shown and so my project fails.
Can you help me?

Kind regards to all good people
This is how you get to where *you* have the ability to determine how to make it work with what you have :)

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3
 

Thread Starter

Selvedin

Joined Jan 25, 2021
15
How fast do you want it switching? Is one state (ON or OFF) meant to be longer than the other, say - ON for 1/2 second and OFF for 10 seconds? Are you opposed to using a relay?
Hello, I need this to make an electric fence, with an ignition coil. In order to run the ignition coil it needs to switch on and off about 4x in a second.
 

Thread Starter

Selvedin

Joined Jan 25, 2021
15
I think the circuits in post #10 & #6 will need buffering to drive 1 amp LEDs.

The simplest is not always the easiest.

Perhaps a quad Schmitt inverter, with one configured as the osc. and the other three to provide the Q and not Q outputs...then two* MOSFETS to drive the LEDs.

*if two LEDs are needed.
I need it to run an ignition coil for an electric fence
 

Thread Starter

Selvedin

Joined Jan 25, 2021
15
Not sure what the TS wants to switch on and off in a flashing manor. If it's as simple as a 12 volt light bulb that runs at 35 watts, that should be easily done with an old fashioned blinker control module from an older model car. They can be found in auto parts stores. Electronic modules are also available in auto parts stores.
Yea, I know, relays can do great things here, but I was more into MOSFETs because I am begginer with electric componenst and want to learn more about them and how to use it in some projects
 
I need this to make an electric fence, with an ignition coil. In order to run the ignition coil it needs to switch on and off about 4x in a second.
Where was that 17 posts ago - ?

555 astable circuit + external power MOSFET.

Two-transistor multivibrator circuit + external power MOSFET.

CD4093 Schmitt Trigger oscillator circuit + external power MOSFET.

Unijunction transistor relaxation oscillator circuit + external power MOSFET.

Opamp Schmitt Trigger oscillator circuit + external power MOSFET.

ak
 
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