Which Power Supply?

[grrr_arrghh]

Hi.

I hate batteries. I don't see the point of charging them if I can just power the project direct from the mains.

Lacking the confidence to build my own power supplies, I want to buy them.

However, how do I know if I need linear or stepped, Regulated or UnRegulated, and what power do I need?

Thanks for any help.

Tim

 

[andrew2022]

get a regulated 12v supply and use that as the main low voltage transformer. if you need lower voltages from that, you can use voltage regulators

 

[gerty]

For bench testing/fabrication I use a variable ,regulated power supply. When the project is done I usually go with one of the 'wall wart' plug in supplies of the correct voltage/current..Most bench supplies have a amp meter built in , which would also let you know total current requirements.
As for linear or switching that's usually irrelavent , switching is usually smaller in size when you get up into the larger currents and is usually has better filtering.

 

[stevez]

"It depends" is the best answer. We need to know more about the applications, especially voltage and current.

Some thoughts that might be helpful.

You need to know if you need AC or DC. Obviously you are replacing batteries but if the batteries are powering filaments then either AC or DC might work.

You need to know the voltage. For many applications the exact voltage isn't that critical - plus or minus 10%. What I'd avoid doing - using a 12 volt supply where you need 9 volts or 6 volts - or 15 volts. It might or might not work but worse, it might damage what you are powering.

You need to have some idea of the current requirements. There is no great precision required here except that the power supply must be capable of supplying more current than the load requires.

Regulated or unregulated does mean something. A regulated supply is likely to cost more money but will work even where unregulated power is required. It might be overkill but the lack of unregulation is not likely to be a problem. The reverse is not true. If your load requires regulation and you provide unregulated power it might or might not work.

Linear, switching or other modes refer to the method by which the voltage is regulated or controlled. Linear power supplies are often thought to be simpler and quieter (RF) than switching but there are some switching supplies out there that are quite simple and quiet. Linear might not be as efficient, especially at higher powers, so more heat might result.

If your needs are DC and you know the highest voltage/current you'll require you can purchase a well regulated supply to meet those needs then as suggested, add step-down regulators. You will need a large enough difference between the power supply voltage and the voltages below to allow regulators to work. In this arrangement you'll be tied to the base power supply - often quite acceptable on the bench but cumbersome otherwise. Note that interaction between loads is possible if they are noisy or sensitive.

Note that you need to address overcurrent protection in the form of electronic limiting as well as fuse or circuit breaker. You need to protect the power supply but also make sure that you don't damage what you are powering or the wiring to it - worse yet cause a fire or injury. The mains side requires a good deal of caution as well.

Some things may be affected by the elimination of batteries and connection to external supplies. The power leads can act as antennas or destabilize a sensitive circuit. There are remedies for this but it's something you should know.

 

[grrr_arrghh]

"It depends" is the best answer.

Damn, I though you'd say that.

Ok, more details.

I only need one voltage this could be 9,12 or possibly 15v (DC).

The application is a small op-amp based mixer/preamp.

I don't have a bench supply, however, I could connect a multimeter (set to ammeter) in series with the battery when I use it. Would this give me an idea of the current needed? (presumably I could then use this measurment to work out what fuse I need?)

What is electronic limiting?

You reckon that linear or stepped doesn't make that much difference, and regulated will cover all eventualities?

Thanks for the help.

Tim

 

[stevez]

It would seem that a current measurement as you describe will give you the information required as far as the load.

I need to clarify one thing - my comment on voltage not being critical would apply to things like a CD player, radio or other non-critical device. If you were powering things like logic devices directly then the voltage does matter. As I recall old TTL chips needed 4.75 to 5.25 volts to work right- outside of that they may not function.

Electronic limiting are my words to describe things like the current limiting features in an LM723. If current exceeds a set amount the power supply voltage is reduced so that the current is at or less than the setpoint. When the overload is removed the voltage returns to normal.

In my opinion regulation won't hurt anything. I am sure there are exceptions but most of the time supplying a steady voltage does more good than harm.

Usually a linear supply is made up of a transformer, rectifier, filtering capacitors and a regulator section. The regulator section works to maintain a steady voltage (within limits) and also serves to further filter any AC hum or transients. A switching power supply is quite different but the output goals are very similar. I don't know enough to comment on which is better or worse. It does seem that a switching supply has the potential to be much more efficient.

The only concern I'd have (I don't have enough knowledge to know for sure) relates to multiple devices on the same power supply. The load that your op amp imposes on the power supply may mirror the output energy. If the power supply is substantial as compared to each op amp then the effect on the power bus is likely to be trivial however this might then appear on the power input to all other op-amps. You could add capacitors or other devices to reduce or eliminate this if it's even a problem. The very simplest example of this is when my wife turns on the clothes iron in one room and I see it cycle on/off as the light in my office dims.

Hope this helps.