5v to 24v at 100khz?

A

abicash

Member
Hello all

My requirement is to convert a 5v encoder signal to a 24v to be fed to a PLC i/p.
This runs at 100Khz and a marginal current is needed since the i/p of the PLC has a high enough input impedance.Can i just put a MOSFET in between?
Or any other known and proven technique?

Please provide an idea

Thanks and regards
 
Do you care if the signal gets inverted? Do you need two channels (quadrature)?
 
Thanks Mike for getting back

The encoder has 3 o/ps A and Abar , B and Bbar ,Z and Zbar

So would it be a good idea to use an optical isolator?
 
I'm puzzled? Are the signal pairs (e.g. A and A~) designed to drive a pair of wires differentially, like RS485? Depending on wire length, how noisy is the environment, I would be inclined to put a RS485 differential receiver near the PLC, followed by a level shifter from 5V to 24V going into a PLC pin, one PLC pin for each for the A, B and Z channels.
 
Last edited:
Hi Mike your are right.

I have a very preliminary idea about this and will get the Datasheets for the Encoder and the PLC input card later today.The 3 differential signals comment was made by the engineer who is handling this.So i AM thinking about adding an SN75176 at the input and then convert the TTL to 24V which is where i require all help.
The first thing hit me was using a MOSFET (P channel) then i realised that if i put an optical isolator i will achieve my goal and at the same time get isolation.
Can you comment?
 
I would look at how much current the encoder can source/sink at each differential pair. If you are planning to drive the photo-emitter in the opto-coupler directly from say the A A~ pins, then the A pin would be sourcing while the A~ pin would be sinking. You would like a minimum of ~ 10mA.

An open-collector photo-transistor on that side of the opto-coupler could be hooked emitter grounded, pullup returned to +24V with the collector also connected to the PLC input.

There are TTL input, high-voltage open-collector output level-shifters (a.k.a. Hex inverters/buffers) out there, too.
 
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Yes i think i can handle that...i need to know if it can handle the speed of 100khz?
A particular opto which you can suggest?
 
100KHz should be doable if you have 10mA of diode drive, and the right pullup resistor. Look here for starters.
 
Hi again

I got a more comprehensive detail now.
It is a 4 quadrature encoder with A and B as 2 digital signals with their complements.

I have attached the scheme which i tested on hardware.Is this ok?
Or can i just add another transistor at U1 (as an inverter) to eliminate U2?

Please advise

Thanks and regards
 

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