RisingEdge
Member
Hi group!
Repeatedly found answers to some questions in the PLC's programming world, now I decided to ask the question directly) Now I am designing I/O terminal, discrete signals, analog, PROFIBUS, MB, and so on... The plans are cool) But the conversation will not be about this, but about discrete outputs, if not strange... I have already been tormented with protecting the output transistor from a short circuit, the main question is what the device should do when one of the outputs is short-circuited. In my subjective experience, we have 2 options: limiting the current or disconnecting the transistor from the switched bus, 24 or 0 volts. Self-restoring fuses or just using fuses is somehow not nice ... Although using an internal fuse is still in the plans)
I’ve been working on options with current limiting for a week now and it doesn’t lead to anything good, Ohm’s law still can’t be deceived ... To limit the current, you need a couple of parts: an amplifier to measure the shunt current and a comporator that will control the gate of the output transistor. But in the event of a short circuit, all voltages will drop across the transistor, and if we limit the current to 500 mA, then 12 watts will be released on the transistor. The digital is brutal) I immediately refused this option. There is an option with switching to the current source, in case the load current exceeds the setpoint. But the best option that I found is integrated voltage / current stabilizers. In this case, the power released will not be a high, up to 2 watts, but the internal stabilizer circuit will take 2-3 volts. And from beautiful 24 volts it will be 20-22...
I like the option of disconnecting the transistor from the switched bus more. We measure the current with an isolated amplifier and push it into the uC. In case of excess current, disconnect the transistor from the bus. It seems to be beautiful ... But there are some minuses, and the main problem is the processing of this signal in uC. Although, I have enough experience to competently and accurately respond to overcurrent events.
However, the very concept of disabling the output is in question, because i have never seen such functionality.
The reverse of some controllers also did not please, somewhere there is no protection at all, and where I did not figure it out)
Disconnecting the transistor from the bus is good, but it’s not possible to do such a function for every channel) In addition, I want to get away from the usual source/sink output and use a push pull. My Wishlist) And why not ...
In general, I have the following questions for you: what should be the reaction of the device in the event of a short circuit (limitation or shutdown)? Is the concept of such an exit good (push pull)? Is using resettable fuses doomed to failure?
I will be glad to give reasoned answers and wish you good luck in mastering the world of PLC's programming!
Repeatedly found answers to some questions in the PLC's programming world, now I decided to ask the question directly) Now I am designing I/O terminal, discrete signals, analog, PROFIBUS, MB, and so on... The plans are cool) But the conversation will not be about this, but about discrete outputs, if not strange... I have already been tormented with protecting the output transistor from a short circuit, the main question is what the device should do when one of the outputs is short-circuited. In my subjective experience, we have 2 options: limiting the current or disconnecting the transistor from the switched bus, 24 or 0 volts. Self-restoring fuses or just using fuses is somehow not nice ... Although using an internal fuse is still in the plans)
I’ve been working on options with current limiting for a week now and it doesn’t lead to anything good, Ohm’s law still can’t be deceived ... To limit the current, you need a couple of parts: an amplifier to measure the shunt current and a comporator that will control the gate of the output transistor. But in the event of a short circuit, all voltages will drop across the transistor, and if we limit the current to 500 mA, then 12 watts will be released on the transistor. The digital is brutal) I immediately refused this option. There is an option with switching to the current source, in case the load current exceeds the setpoint. But the best option that I found is integrated voltage / current stabilizers. In this case, the power released will not be a high, up to 2 watts, but the internal stabilizer circuit will take 2-3 volts. And from beautiful 24 volts it will be 20-22...
I like the option of disconnecting the transistor from the switched bus more. We measure the current with an isolated amplifier and push it into the uC. In case of excess current, disconnect the transistor from the bus. It seems to be beautiful ... But there are some minuses, and the main problem is the processing of this signal in uC. Although, I have enough experience to competently and accurately respond to overcurrent events.
However, the very concept of disabling the output is in question, because i have never seen such functionality.
The reverse of some controllers also did not please, somewhere there is no protection at all, and where I did not figure it out)
Disconnecting the transistor from the bus is good, but it’s not possible to do such a function for every channel) In addition, I want to get away from the usual source/sink output and use a push pull. My Wishlist) And why not ...
In general, I have the following questions for you: what should be the reaction of the device in the event of a short circuit (limitation or shutdown)? Is the concept of such an exit good (push pull)? Is using resettable fuses doomed to failure?
I will be glad to give reasoned answers and wish you good luck in mastering the world of PLC's programming!