24 V to 5V

[7frank7]

Hi,

I need an easy way of converting 24vdc to 5vdc.

I have an omron plc which i'm going to connect a panel mounted encoder http://www1.elfa.se/data1/wwwroot/webroot/Z_DATA/03584638_2.pdf
i run everything on 24Vdc but these encoders seem to only be available in 5V versions.
so if anyone has an easy way of doing this please share..
Thanks,

Frank

 

[audioguru]

Its current is only 0.5mA so a resistor and a 5.1V zener diode or a 5V little 78L05 regulator with two capacitors will make 5V for it.

 

[7frank7]

thanks fro replying,

any pointers on how to determine the size of the resistor?

Frank

 

[Diver300]

There are two outputs, so you need 1 mA for each encoder.

(24 - 5) / 0.001 = 19000 ohm

Use an 18k resistor with the 5.1 V zener.

 

[audioguru]

Many zener diodes do not work properly when their current is almost nothing.
Many 5.1V "400mW" zener diodes are tested at 45mA.
Use 1.8k for about 10mA in the zener diode.

 

[Arkham00]

The device you are trying to interface is not an "active encoder" that needs to be powered. It's just a double rotary switch mostly used on microcontroller boards (at 5Vdc) but it can be safely used at 24Vdc.

Just connect it to two standard inputs of your Omron PLC as if they were two standard pushbuttons.

 

[audioguru]

Why were we trying to power a mechanical switch?
Its max allowed current is 5mA but its spec's are measured when its current is only 0.5mA.

 

[7frank7]

Arkham, if that is indeed so, that would be a relief, i suppose i could just test it.

it was brought to my attention that i needed an open collector encoder and not a line driver,to be able to use it with the regular inputs. but i couldn't find that information in the datasheets.
if it is indeed a double rotary switch, i suppose there wouldn't be any info whether it's a line driver output or open collector.
can anyone confirm if this is so?

thanks,

frank

 

[7frank7]

Ok, so it is just a mechanical switch?

somehow i got hung up on the idea that it was an encoder that needed to be powered.

in case you didn't read my reputation it says NEWBIE.
thanks for putting up with me.

frank

 

[bountyhunter]

Hi,

I need an easy way of converting 24vdc to 5vdc.

Just connect the 24V to the input of a 7805 regulator. They are dirt cheap and require no other parts.

 

[arunb]

Just connect the 24V to the input of a 7805 regulator. They are dirt cheap and require no other parts.

that may work but the 7805 will get hot...

 

[bountyhunter]

that may work but the 7805 will get hot...

Nope, read the above posts where it says:

There are two outputs, so you need 1 mA for each encoder.

If you only need 2mA of load current, the power dissipation in the 7805 or 78L05 will be negligible.