What would be a good solid state switch in this situation?

Question

I am building an automotive switch box and have a 12 volt system however the switchbox will contain Integrated Circuits (5v max) so I am reducing the voltage in the switchbox for the ICs.
The main reason for ICs and not just plain switches is for programmability and some other functions. For the question at hand, I will have 5 volts or 0 volts respectively coming out of the IC but the items to be switched work on 12 volts and the modules to be controlled have a tricky setup because they require a positive 12 volts into the module to switch the module on.
(What happens is the module has a positive and negative wire run directly to the battery so the module itself is live all the time however it has an +12v input that internally switches on the purpose of the module. Basically it needs +12v on a 3rd input to turn on)
What I currently do pre-switchbox is have 12 volts off the battery run to a toggle switch which when turned on provides the needed 12 volts.
With the ICs and without relays (need the 3rd input to become live as fast as possible and my understanding is relays do not have as fast a capability as solid state)
Because of the type of IC, I can have it put out 5v on the respective output unless I want 0v or put out 0v until I want the circuit live and then put out 5v. (2nd method preferred as a fail-safe that the IC is not putting out due to malfunction, the circuit is not live.)
So the IC only puts out 5v whereas the input of the module needs 12v. I don't like the idea of a transformer either. I would like to use transitors but cannot find a suitable solution that takes a 5v input and forwards the 12v.

Conclusion-With 5v/0v coming out of the IC, a 12v line coming off the battery, and a line to the 3rd input line on the module, I need the 12v to forward to the 3rd line input based on what is coming out of the IC.

Answer 1

Trying to summarize this (too long) discourse, you need to convert 0 to 5 volt logic levels to 0 to 12 volt switching levels. Is that correct?



If phase inversion is OK, you can use a 7406 TTL. Or use a 7407 if you need the signals in phase, ie, not inverted. Both parts have 6 buffers in the package. Use 1k pullup resistors to +12 volts on the outputs of the package.



If you have to go in the opposite direction, convert a 0 to 12 volt logic level to a 0 to 5 volt signal, you will need different parts. I'll have to research that, email me.



You do realize that having sensitive ICs near high current motors or solenoids or even relays, will be a problem. The high currents switching will induce transients in the ICs and cause them to malfunction. Worse case, you will need to enclose the ICs in metal boxes with feedthrough caps to bring in needed signals.



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Answer 2

Use an open collector device as in the link. This has an external pull-up resistor (say 10K ohms) to the +12V.



You can use an ordinary NPN transistor like a 2N2222 for an external driver in the same way. The IC logic output (0/5V signal) passes through a 22K ohm resistor to the base of the transistor. The collector of the transistor goes to the control input of your device, and also has a 10K pull-up resistor to +12V. The emitter of the transistor is connected to common (the -12V = negative rail of the logic circuitry). This transistor inverts the logic, so +5V causes the output to be 0V, and 0V causes the output to be +12V. I wouldn't be worried about fail safe too much.



If the power for the logic circuit is off, the transistor is off, so its output will be +12V unless the +12V is from the same supply as the logic circuit.



One point you didn't mention is the loading of the 12V control input. I assume it is just a logic device of some sort, not a relay.

Answer 3

Use a 7406 open collector buffer/inverter chip. One of its design functions is TTL (5V) to CMOS(12V) conversion. http://pdf1.alldatasheet.com/datasheet-pdf/view/27979/TI/SN74LS06D.html Use a buffer transistor after the inverter for higher current outputs.

Answer 4

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