Isolated 4KV input.

[yanivmichaeli69]

Hi,
My design includes a desecrate input port that is isolated from the main board by an optocoupler and an isolated DC2DC.
When the user short the input port logic level of "0" is send to the CPU, otherwise the indication is logic level of "1".
See attached schematics.
My boss came to me and ask me if there another cost effective and solution, for example, if the isolated DC2DCcan be built in the optocoupler.
Does any one has an idea?
Regards,
Yaniv.

[coppice]

I haven't seen any opto-couplers integrated with power supplies. If there were they would be a specialist item, which would probably make them more expensive than what you have now. There are some digital isolators with built in isolated power, but they will definitely be more expensive than what you have now (assuming your DC-DC converter is constructed in a cost effective manner).

[Psi]

Can you not just specify that the external signal must provide its own power to the led?

You could also look at making your own transformer based micro DC/DC psu out of cheap discrete components.

[bktemp]

You could use a transformer for isolation. If its output gets shorted, the circuit can detect this.
A 1 or 2 transistor oscillator build around the transformer winding similar to a cheap metal detector circuit should work.

[coppice]

You could use a transformer for isolation. If its output gets shorted, the circuit can detect this.
A 1 or 2 transistor oscillator build around the transformer winding similar to a cheap metal detector circuit should work.

If there are spare resources on the MCU you can use a transformer and a capacitor to make a resonant circuit, get the MCU to kick it regularly, and use the MCU to detect how quickly the ringing fades. This kind of Q switched resonance is the basis for some extremely low power sensing techniques used commercially.

[yanivmichaeli69]

Hi, can someone specify a part no. for a digital isolator with integrated power supply?

[Jeroen3]

You do not need a regulated output voltage for a logic input. A simple transformer and some diodes can fix this.
Like this: http://www.digikey.nl/product-detail/en/750313626/1297-1104-2-ND/4692578
Pulses can come from the mcu, or a dedicated push-pull driver.

Or, ADUM5200 or SI88xx.

[mikeselectricstuff]

There are some digital isolators with inbuilt DC-DC, e.g. ADM2582 from AD,which is an isolated RS485 transceiver with onboard supply for the isolated supply.

For inputs there are also the IL610 family from NVE whne have passive inputs so don't need a supply on the input side

[bitslice]

Isolated input port.doc

what the?
 

[Zero999]

Isolated input port.doc

what the?
 

Indeed, what's wrong with using the correct format for pictures?

I've converted it to something more standard, see attached.

[yanivmichaeli69]

Thank`s You all for your helpful advice, I really appreciate your effort to help me.
Regards,
Yaniv.

[Marco]

If there are spare resources on the MCU you can use a transformer and a capacitor to make a resonant circuit, get the MCU to kick it regularly, and use the MCU to detect how quickly the ringing fades. This kind of Q switched resonance is the basis for some extremely low power sensing techniques used commercially.

I think you could just put one coil of a common mode choke in series with a DC blocking capacitor and a resistor and put a square wave on it. The amplitude of voltage over the resistor will let you determine whether the other coil is shorted.

As long as only temporary 4kv insulation is needed it's easy to find a cheap common mode chokes rated for that.