Warning Buzzer Circuit for Redundant Power Supply

[strape81]

Hi all,

I need a warning buzzer circuit for a redundant power supply. The system is consisted of two power supplies (output: 12V) and after each power supply I use a decoupling diode. The buzzer will work when one the power supplies fails.

Please could you give me some ideas or a direction? If a circuit is available then I will be thankful.

Thanks a lot in advance!!!

 

[jeffrey samuel]

very simple if you are using a dc source then just use a resistor and a not gate connected in parallel to the supply

the op of the not is coupled to a bell or warning led that will produce the required result

 

[sky_123]

I recently had a requirement to do a similar thing (I wanted a buzzer to alarm if the primary power to my router died),
and in the end, I just went for something simple and super-old-tech - a non-rechargeable battery-powered buzzer. The battery will last for years,
and will sound an alarm for hours before it dies (my backup supply is non-rechargeable since it will be a rare ocurrence for me). This meets my needs perfectly.

The buzzer can be held in the 'off' position in any method you choose - e.g. a relay.

 

[jeffrey samuel]

the simpler the method the more effective it will be kindly dont complicate this as they may turn mind numbing

 

[strape81]

Thanks Jeffrey...I believe in simple, effective and reliable solutions too...

I have made a search and I could not find an IC that could fit my application. I need two NOT-Gates and the buzzer works at 12V/6mA. The voltage and the current specs could be found but the inverter ICs have usually 6 NOT-Gates which make them unattractive considering the costs. So I decided to search for a TTL NOT-Gate circuit and I found a the attached circuit.
Has somebody implemented that?

 

[jeffrey samuel]

ttl logics are cool replacement but are not the effective cost of a single ttl NOT higher than that of 1 ic 7404

 

[sky_123]

If you want the discrete device route, then this will work.

Replace R1 with your buzzer. When the 12V power is disconnected (e.g. via a switch) then the buzzer will sound.
A 12V buzzer should be fine running off 9V.
You don't need to use 9V, just make sure it is a value close to 12V, or a slightly lower voltage, for this circuit to work.
Or a single relay is cheap, if this is a 1-off circuit not for production.

 

[chuckey]

Wire a diode bridge between the two positive output (AC terminals). Connect a 12V solid state buzzer between the + and - DC terminals.
Frank

 

[EngrRaymondC]

Hello Strape,

I think this simple circuit will do the trick. Simulated it using Multisim and seemed to work fine. Just change the LED to a buzzer of your need. Hope this helps.

 

[jeffrey samuel]

Hello Strape,

I think this simple circuit will do the trick. Simulated it using Multisim and seemed to work fine. Just change the LED to a buzzer of your need. Hope this helps.

View attachment 79481

an excellent design but if you want individual alarms then use an OR gate instead of the AND gate
that should suit you

 

[EngrRaymondC]

Yeah, I think if he wants an alarm for each power supply, then simply use an inverter for each supply so when either one goes low, one of the alarm will trip off. But if both power supply will be down, both alarms will sound.

 

[strape81]

Thanks a lot for your answers!!!

I have made two one-transistor-inverters and it works fine! Simple and reliable!!!

 

[jeffrey samuel]

cool if we managed to solve your issue