Variable LED Flasher & Basic LED Flasher

[Zodac]

Hello,

I am looking to build 2 seperate flashers for emergency services applications. I have been building my own LED Emergency Lights for sometime, however I am limited to commercially available flasher and their sizes and restrictions.

I would like to be able to build a simple LED flasher for basic applications that would only flash between Left and right (2 Channel). This flasher only needs to alternate the light patten.

I would also like to build a multiple channel programable flasher for larger projects.

I have found a couple of different schematics here on the fourms, however I am only entery level into the electronics, and they do not look at tho the will work. I would like to have a flasher the would work be switching the power to the LED Matrix. The tricky part is every applications matrix could be different. (some with 48 LEDs some with 5900).

I think is the flashing circuit could just hand raw 12volt power to the matirx (already built and runs on 12v) through a relay if the componets can handle that.

Any help is appreciated, I am a very technical person and can follow directions alone once I have a grasp on the overview process.


THANKS

Robert

 

[colin55]

WARNING BEACON

Here is a 12v Warning Beacon suitable for a car or truck break- down on the side of the road. The key to the operation of the circuit is the high gain of the Darlington transistors. The circuit must be kept "tight" (thick wires) to be sure it will oscillate.
A complete kits of parts and PC board costs $5.00 plus postage from: Talking Electronics. Email HERE for details.
**broken link removed** ​

 

[audioguru]

Your extremely simple circuit causes avalanche breakdown of the emitter-base junction of your transistors which damages them. Their absolute maximum reverse emitter-base voltage is only 5V but your circuit feeds them reverse voltage, high current pulses of 10.3V.

Either the supply voltage should be reduced to 6V or diodes should be in series with the emitters of the transistors.

 

[ronv]

Maybe you could expand on what you want from the matrix?

 

[colin55]

My 20,000 BD679 transistors must be different to yours. I tested mine. They allow a reverse voltage of over 14v between base and emitter.

 

[audioguru]

My 20,000 BD679 transistors must be different to yours. I tested mine. They allow a reverse voltage of over 14v between base and emitter.

The BD679 is a registered part number so all max ratings are the same. Silicon emitter-base junctions have avalanche breakdown at around 6V to 7V.
I found 5 manufacturers with exactly the same max reverse emitter-base voltage of 5.0V.

 

[colin55]

That might be on the specification sheet but when you test them, they allow a voltage of more than 14v to appear across the base-emitter junction as a reverse voltage and thus this characteristic of 5v max. does not come into operation in the circuit presented. We have sold thousands of the FLASHING BEACON and not had a problem, so you cannot always rely on specification sheets.

 

[audioguru]

Colin,
Everybody (except you) know that a manufacturer's absolute max ratings for a transistor should never be exceeded.
Almost every silicon transistor has a 5V max allowed emitter-base rating. If the transistors could actually withstand 14V then why is the rating only 5V?

The emitter-base junction is not designed to dissipate heat. Avalanche breakdown of this junction causes hot spots that slowly destroy the hFE of the transistor.

 

[colin55]

There are thousands of transistors in hundreds of circuits where the maximum ratings are exceeded.
If a transistor works in a thousand products for 15 year's, there is no point in running around in circles.

 

[audioguru]

There are thousands of transistors in hundreds of circuits where the maximum ratings are exceeded.

Hee, hee, ho, ho, haw, haw!
And you don't use fuses nor circuit breakers in your home, never change the oil in your car engine, never check the tire inflation etc.