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 Forum index » DIY Hardware and Software » Circuit Bending
Voltage divider VS Voltage Regulator
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MatthewMachinist



Joined: May 19, 2020
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PostPosted: Tue May 19, 2020 1:00 am    Post subject: Voltage divider VS Voltage Regulator Reply with quote  Mark this post and the followings unread

Hi,

I am working on my first electronics project where I am "designing" a few elements myself. My project is a one shot circuit to active analog drum sounds. I would like to power it with Eurorack supply voltage @12 volts. Output will be 5 volts.

Now I though this would be easy as I should just use a voltage divider, however I found this information on the sparkfun website...

"As tempting as it may be to use a voltage divider to step down, say, a 12V power supply to 5V, voltage dividers should not be used to supply power to a load.
Any current that the load requires is also going to have to run through R1. The current and voltage across R1 produce power, which is dissipated in the form of heat. If that power exceeds the rating of the resistor (usually between ⅛W and 1W), the heat begins to become a major problem, potentially melting the poor resistor.
That doesn't even mention how inefficient a voltage-divider-power-supply would be. Basically, don't use a voltage divider as a voltage supply for anything that requires even a modest amount of power. If you need to drop down a voltage to use it as a power supply, look into voltage regulators or switching supplies."

Now unfortunately for my application I don't know the amps being drawn by the circuit so I can't crunch the numbers. But I am wondering about the statement that "voltage dividers should not be used to supply power to a load." My question is... don't all voltage dividers supply power to a load?

Am I better off looking for a voltage regulator for my application?

Thanks,
Matt.
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Grumble



Joined: Nov 23, 2015
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PostPosted: Tue May 19, 2020 1:15 am    Post subject: Reply with quote  Mark this post and the followings unread

If you are using a voltage divider (without any buffering) to supply power to a circuit, you'd be better of with a voltage regulator, because of what your quote states.
But if you are using a voltage divider to just get a reference voltage (which doesn't draw more current than some uA's and is NOT used for frequency settings) you could use a voltage divider.
Usually a buffer is placed after the voltage divider to make it less prone to drawing power from the divider but then it indeed looks more like a voltage reference- or voltage regulator.
But why do you want to supply the circuit from 5 volt?
The cmos 4000 series can be powered from 12 volt and the output can then be fed into a voltage divider and buffered.

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Blue Hell
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PostPosted: Tue May 19, 2020 1:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Edit: Grumble was faster .. lol .. anyway .. maybe this adds some extra useful info

Yeah you really should use a regulator of sorts for this.

The main reason for it ... you already mentioned it yourself, you don't know the Amps .. but worse .. the Amps will vary depending on what your circuit is currently doing, so in a way .. you can't know the Amps.

So depending on what the circuit does it will draw more or less current making the voltage from the divider to go down or up, and this may "work its way back" into your circuit, causing instabillities, unwanted or unexpected behaviour.

Or to say it in more theoretical words ... your power supply, or in the usual sense technically a voltage source, should have an output impdance as close to zero as possible.

A "regulator of sorts" I started with, it does not need to be the standard 3 pin regulator .. you could actually use the (resistive) voltage divider when you would buffer it's output, maybe with a transistor or, depending on the expected load, maybe even an opamp.

Usually though the three pin regulator thingie is just the easiest way to do it.

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also .. could someone please turn down the thermostat a bit.
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MatthewMachinist



Joined: May 19, 2020
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PostPosted: Tue May 19, 2020 2:27 am    Post subject: Thanks Reply with quote  Mark this post and the followings unread

Thanks for the replies guys, that really helped fill a couple of gaps in my knowledge base, I will definitely head in the voltage regulator direction. I have found a design based on the LM7805 which looks ideal.
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