Drop 13.28v to 12v

I have a power supply that provides 13.28v and want to reduce that to a regulated 12v for use by various circuits and components.

I have looked at the LM7812ACT ( http://za.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=7044029 ) but it has a "Dropout Voltage" of 2v, so I assume that by using this component, I am going to lose 2v and only get 11.28v out.

Changing the power source is not really something I want to do.

Any other suggestions ?

but it has a "Dropout Voltage" of 2v, so I assume that by using this component, I am going to lose 2v and only get 11.28v

No it means that it needs 2V more than it is trying to regulate. You will not get a regulated voltage at all. Look for regulators that say "low dropout" it should be possible to do what you want.

Any other suggestions ?

many circuit and components designed to work at 12vdc will work OK at 13.28vdc, that is only a +9.7% increase.

Is the 13.28vdc regulated to begin with? It must be as an unregulated power module would never have a 13.28vdc rating. If it is all ready regulated, one way to reduce the voltage a small amount is to pass it through a couple of series wired diodes, each diode would reduce the voltage about .4 to .6 vdc, so two series diodes might get you down to around 12.28vdc or so. Otherwise if you must use a regulator you will have to search for 'low dropout voltage regulators' that have 12vdc outout and rated for the current (or higher) then your circuit requires.


KE7GKP: What exactly is the nature of this "power supply that provides 13.28v". Is this some sort of regulated mains-powered unit? Is it a battery? What exactly is the load that you say needs 12V?

The question you have asked requires more details to answer properly.


The supply is a unit that came with our home alarm system. Plugs into 230vAC and has a 7aH battery to keep the system running when we have power outages. It is already installed. Not knowing the circuitry in this unit, I was thinking that converting to 12vDC and regulating would be a safe step before using the 12v at various points in the house for automation.

The 'load' will be a number of different items - some planned and others not even thought of yet. The existing list is things like : emergency LED lighting, smoke detectors, the BBQ rotissery ( tired of changing batteries ), indoor and ourdoor security beams, PIRs and sensors, etc

I think the diode idea that Lefty has is good : I have some 1N4007 diodes and the data sheet shows a Forward Voltage of 1.1v, so just one of those will drop the voltage to 12.18v. Only concern I have would be that I don't think ( newbee brain working here ) it would provide any kind of regulation, so possible the 'low dropout' regulators would be a better option, unless I can examine the supply's circuit to determine what regulation ( if any ) it has.

Your alarm system mains power unit will provide very little power, probably 0.25 amp at most. Your specified loads are voltage tolerant and would be perfectly happy running at 13.28. Consider that a sealed lead acid battery (SLA) can run as high as 14 volts without crippling the devices connected to it.

You might be better getting hold of an old laptop power unit that gives out around 17 volts or so and feed that through a regulator chip to get your 12 volts.

Or alternatively keep your old alarm system as a power module, complete with battery, and power from it. That way you can tolerate short term mains failures. No good having a mains powered smoke alarm or LED lighting if the mains has failed and you have no back-up battery. A bit like having a solar powered torch that only works when the sun shines.