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# 24 volts DC to 5 volts

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#### danfman

##### Newbie level 2
It's been a few years since I had an electronics course, so I need help
with a relatively easy question.

I need to reduce 24 volts DC to 5 volts DC. I think it's just a matter
of a couple resistors but am unsure. The amperage is relatively low
(not sure exactly).

Can anyone help? Details would be much appreciated.

Thanks,
-Dan

24 V to 5 V DC

It depends on what you are driving with the 5V.

If it is driving a high-impedance input, then you can probably get away with a voltage divider (2 resistors).

If you are driving a low-impedance input, then you'll probably need to do some kind of active circuit to provide the drive. An op-amp or a transistor circuit of some kind might be the way to go.

If this is to provide power for something, then you're best off with a voltage regulator circuit.

If you provide some more info on what you're doing, then you can probably get more detail on a solution.

Hi, you can use a three terminal positive voltage regulator ic (7805) (7805.jpg), here is a datasheet and guide how to use it
Code:
http://pdf.alldatasheet.com/datasheet-pdf/view/69437/KEC/7805.html

or you can simple use a zener diode, but you must know a current, like on the second picture (zener.JPG):

You may use the LM2575-5 from, It is a switching regulator.

Re: 24 V to 5 V DC

I am trying to varify the functionality of an encoder. If you don't know an encoder is basically a device that creates pulses. I want to varify the encoder is actually sending the right amount of pulses to the receiving board using my hand held pulse counter. But the encoder generates 24 volts signals and my pulse counter can't handle anything but 5 volts.

I looked up the voltage divider circuit and it's associated formula, but how exactly would I specify the right resistors?

Thanks again.

You could take a variable resistor and adjust it to get the right ratio. A 4k7 might do.

The combination of the series resistance and the input and cable capaitance will round off the edges of you pulses. If you are dealing with fast pulses, perhaps 100KHz or higher you might have a problem.

>how exactly would I specify the right resistors?

You either have to do some mathematics or you get a pile of resistors and start putting them across a 24V supply and measuring what voltage you get.

You probably don't want to draw more than 10mA from the 24V source so you need resistors of about 3k3 or larger.

Here is a handy calculator you can play with
https://www.electronics2000.co.uk/calc/calcdiv.htm

Starting with a 3k3 series resistor and trying a few standard values for the shunt resistor finds
that 3k3 and 910ohms drops 24V to 4.7V

It is worth considering the tolerance of the 24V signals, if the encoder is run from a 24V battery supply it might be as high as 29V when the batterys are being charged.

Hello....
You can use the voltage regulator LM317, Input and output can be range from 3 to 40 VDC, here have attachment please read it carefully and the connection.

danfman said:
It's been a few years since I had an electronics course, so I need help
with a relatively easy question.

I need to reduce 24 volts DC to 5 volts DC. I think it's just a matter
of a couple resistors but am unsure. The amperage is relatively low
(not sure exactly).

Can anyone help? Details would be much appreciated.

Thanks,
-Dan

You may like to put 2 resistors in series (see below)
You will require: Resistor (R1)190 Ohms - 2W or greater and (R2)50 Ohms (0.6W or greater). If you do not have the exact values stated then you will not get exactly 5 volts.

Make sure that your load (what you want to use the 5v for) is a lot higher then 50 Ohms.

(The two resistors should be connected in series)
That is:
Connect the + side of the 24V battery to R1.
Connect R2 to the other of R1.
Connect the other side of R2 to the negative side of the battery .

I looked up the voltage divider circuit and it's associated formula, but how exactly would I specify the right resistors?

Voltage divider formulla Vout= Vin*(Rout/(Rout+Rs))
5=24*(Rout/(Rout+Rs))
Rs is resistor which located between output and input.
and Rout are equivalent resistor between output and ground.

I use the IC MC34063. dil 8 pins

The circuit is for the down 5V to 24V
or the up 24v to 5v.
the schematics is in the file:

LM317 or LM2576,both need peripheral equipment which you may find on the reference documents.

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