how to convert .5 volts to 5 volts

[originator]

I have screwed up two different servo motor controllers somehow. The output called PFIN or position finished is usually 24 volts or nothing, 24 being ON, and nothing being motor in motion. These controllers are a lot of bucks and since now the damaged outputs(open collector pnp) are putting out 0v for ON and .5v for OFF, maybe I can salvage these two controllers by converting the small voltages to 5 volt logic. I tried using a simple switching transistor(2222) to turn on 5 volts but it wouldnt do it. Any ideas on how to do this?

 

[itsmoked]

Ugh.... In my opinion you are on a fools errand. If they are screwed up then they aren't really running to any spec... So a circuit based on ...(what) is likely to always give more problems....

If you know you have a blown open collector transistor just fix it... You don't even need the same kind if you can't read the part. Just something close.

If you must use the crummy output then you need to use an op-amp as a comparator to compare the drives output to 0.25V. If over that: one state, under that the other..
Google comparitors ..lots of pages.

 

[logbook]

So an open collector transistor needs a pull-up resistor to make it give an output. If the output should go to 24V then presumably there is a pullup resistor to 24V, or at least there should be. This resitor is probably supposed to be 1K to 10K, something like that.

If this open-collector transistor output was accidentally connected to the 24V rail directly, that would explain the fried output. Likewise if the load was 10R or similar.

Notice that now the output is inverted. Are you sure you have a pull-up on it? You should apply nothing to teh base to get no collector current to give 24V. If you apply base current you get 0.7V on the base. If there is no pullup resistor then the base-collector junction may allow current to flow giving the signal you are seeing.

 

[felixc]

Are you able to open them and try to find out what part is dead? Chances are that there are one or two discrete parts that you could replace.

 

[originator]

I have gone all through the controller and looked at most everything I can test to see if it might be the voltage firing the transistor to the outside world. Everything is surface, many have no markings that are usuble for identification. What appears to be the outputs are 6 pin parts, 3 on a side, 24 lives on pin 1 on all of them. The volatages inside this thing are not what I have seen, they change from 0, 2.6, to 5 on most parts when you change positions on the motor. That is above my head. I did manage to successfully get one unit to turn on and off an NPN transistor going straight into the base, 5V on the collector and 5/0 logic on the emitter, so that unit is reliable up to this point, the other only fires the .5V on certain position moves, not all, which leads me to believe that the position finish output is really a cumulative output of a number of other outputs in the box. I will be ordering one controller only for now it seems, better than 2!

The manual does not mention using a pullup, and they actually use only a 2k resistor and led for their demonstration units. I was using a 4.7k into a photocoupler to create some 5v logic, still unsure how I smoked it, unless without seeing it I dragged 24 across a trace.

Thanks for the suggestions.

 

[OperaHouse]

Six pin part sounds like an opto isolator with the transistor section being the output device. Got a part number on it? An open collector device would need a pull up/down resistor to make it work.

 

[RudyL54]

Too bad!You can't salvage something that is already damaged. It might be putting out 0.5 volt now but later it won't function anymore. I suggest you scrap that idea of raising up the voltage to 5 volts.

Sorry but that's the way it is. The 0.5 volt could only be temporary and soon the damage could get worst.