Voltage Switching

What sort of "device"? How often does the output change, and how much current do you need to draw?

Nobody asks the relevant questions.

But if you are talking signal with not much current and on-off switch a simple NPN transistor switch will invert the signal for you.

Emitter to ground, base connected to your signal with a current limiting resistor in series, collector load resistor pulls the voltage to 24 volts when the transistor is off (24 volts not present on base resistor) and 0 volts on collector (when 24 VDC is present).

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Thanks, I will give this a go.

Also, consider inverting the signal at the input of your device. I can't tell you which way would work better though, because you gave us so little information.

Single-ended or differental? Are you able to access the device circuit and power supplies? Or must you connect to it, without modifying the device? When it provides 24V, what impedance and current compliance does it have? When it outputs 0V, is this at a high impedance (effectively open, if single-ended?) What supplies do you have for your own circuit? What are you then driving with your output?

Jon

Since inquiring minds want to know, I will try to get more detailed. The device I am trying to interface with is a PLC. On this PLC, I am using two DO's, that at the off state, output 24VDC, max 2A. When a DO is switched on, the output drops to 0V by connecting to an earth ground in the PLC. I am inputting to an actuator controller that requires the off state to be 0V and the on state to be 24VDC with max .

25A. So the signals are backwards. When the PLC is at 24V, the controller needs 0V (at rest); then I flip a switch to create a move, and the PLC is at 0V but the controller required 24V(move signal). I hope this did not confuse everyone.

I think you need something like this solid state relay. and you will have to mount it on a heat sink surface for it to carry 25 amps.

Connect the control input between the +24 volt supply and the PLC DO. Connect the output between the +24 volt supply and the load.

Sorry, that was .25A or 1/4A. Word wrap ;)

Well, that's a horse of a different color.

Try:

plugged into this: These are the mini I/O modules and screw terminal plug board on this catalog page:

I could guess, but how fast are these signals required to be? What kind of capacitance are you driving? (Do you need active high and active low drive? Or can you accept passive drive on one side of this?) Have you tried 'default's suggestion to you?

You still haven't mentioned what your supplies are, but may I assume you have access to the 24V and ground rails? Any other rails?

If you want inversion and active high and active low drive at fairly good rates of change in both directions, you may need 3 BJTs. Something like this: (read with fixed-spaced font such as Courier, Courier New, etc.)

I assumed about 5mA being enough drive for your .25A output. Easy to adjust by changing R1 and R2. (R1 sees a little more than 5V and R2 sees most of the 24V. So figure from that.) The above is a pretty standard construction of an active BJT inverter, so nothing special here. You need to make sure that Q1 and Q2 can handle the 24V and current requirements (not too hard to do.)

I've omitted various speed-ups (across R1, R2, and from IN to the base of Q1), but in the small numbers of kHz it should look pretty good on a scope. There is an overlapping period when both Q1 and Q2 are on and that overlap period can be significantly shortened with the speed ups added. But it may be just fine, as above.

I'm a hobbyist and don't have much experience with 24V industrial PLCs or actuator controllers and the supplies you are likely to have. So keep that in mind.

Jon