shows a typical circuit for using the TLP250 as a MOSFET driver. VIN is the input drive signal that dictates the output state. Remember that VIN is referenced to Signal Ground. And that the TLP250 ground and load ground are referenced to the power ground, ie Vsupply and VMOS share the same reference ground as can clearly be seen from the circuit diagram and this ground is separate from Signal Ground. This clearly illustrates the isolation in MOSFET drive as the driving signal is isolated from the load supply.
When VIN = 1, Q1 is driven from the supply voltage (Vsupply) – the gate is pulled up to Vsupply level. Q1 turns on and current flows through the load – the load is driven from VMOS via the MOSFET.
When VIN = 0, Q1 is driven low – the gate is pulled down to its source level. Q1 turns off and the load is off.
Vsupply could be between 10V and 15V – 12V being a very common level used. R1 should be calculated by you depending on the amplitude of the input signal. I’ll give an example to clearly show you how (if you don’t know that already).
I’ve said above that 10mA (= 0.01A) for the forward current for the LED is a good value to use. So I’ll take that. Let’s say that the TLP250 is being driven from a microcontroller and the amplitude for the signal is 5V. I’ve said above that the forward voltage for the LED would typically be between 1.6V and 1.8V – I’ll take it to be 1.8V for this example