how to simulate isolation circuit e.g Optocoupler

[kimi_]

As the title shows, how to choose the ground?

Can i use DGND for diode side and VSS set to zero as the ground for the npn side?

how about power？Is the different power name mean they are isolated?

how about oscilloscope? does the two channels be isolated？

Thanks !

[johnsold · Accepted solution]

SPICE simulations require that all parts of the circuit have a DC connection to node 0, commonly called ground.

You could build the isolated part of the circuit and designate a node isozero as the reference for that part of the circuit. Then connect a resistor with a very large value (1 Gohm) between node 0 and node isozero. As long as that is the only connection, no current will flow in the resistor and the circuit will behave as though it were isolated.

Lynn

[Chen_T]

Hi there,

For your first question, in Multisim we have a Optocoupler Family under the Misc Group. I can show you one typical connection for the Optocoupler in the following figure.

Usually, on the diode side, we make Pin 2 as the Interrupt source instead of connecting it to ground. By the way, in BJT you should call it VEE instead of VSS which is for FET component.

For your second question, I do not quite understand. What do you mean by "different power name"? 3.3V, 5V, 12V?

For you third question, in a traditional oscilloscope, the two channels are not isolated, but some latest scopes have IsolatedChannel Technology embedded. In some cases, floating measurement are found in power control circuits (uninterruptible power supplies, switching DC power supplies and motor controllers) and industrial equipment. In such application areas, voltages and currents may be sufficiently large to present a hazard to users and test equipment. Therefore, these isolated channel oscilloscope are designed.

Regards,

[kimi_]

hello Chen_T 

i'm so sorry that my english is poor,maybe you misunderstanding my questions. I just want the answer like johnsold reply.

my second question means "Does the power name VCC set to 3.3V and name VCC1 set to 5V came from one " or Are they isolated?

the third question is not for the real one, but for the visual scope in multisim, Does the two channels of the oscilloscope be isolated?

[Chen_T · Accepted solution]

Hi there,

If it is in simulation, VCC and VCC1 are isolated. For the visual scope in Multisim, the two channels  of the oscilloscope are isolated too.

Regards,