07-15-2014 08:27 AM - edited 07-15-2014 08:28 AM
So if you need more power at 120kHz or higher frequencies, give a PWM with one or n digital output(s) a try.
Your LC tank do the filtering and the energy is the pulse width of your class C output.
I found this, maybe it helps
i have modified the 'Create DO array.vi' and the clock frequency coerce property and the factor 1000 , but just to get an idea....
PWMresolution x Clockfrequency must meet a valid counter freq. !!
and the duty cycle shouldn't be more than 0.5 😉
NOT tested ... I don't have the hardware
Still stuff to modify 😉
07-15-2014 12:47 PM
Thanks Henrik! I have started to see if I understand the program but initially I am getting an error about sampling which is not supported by thehardware! Do you perhaps know if it is about the program or my USB 6218 doesnot support this!
And about the Class C output, could you clarify if your intention is to use the DO as the input to the class C amp. and then doing the AM modulation or your intention is to do demodulation for PWM. I cannot go for PWM demoulation since the demodulator is an envelop detector and it has been already built.
07-16-2014 04:35 AM - edited 07-16-2014 04:37 AM
What I understand so far, (some more detail would really help) is that you what to drive a sending coil with a 120kHz (or higher) carrier and do a amplitude modulation.
With the AO you don't have enougth power and limited by the 250kHz sample frequence.
It's no proplem to drive the output with a squarewave. (That what I mean with class C, ignore it , or read about amplifier topologies 😉 )
By using the the digital output you can generate higher frequencies, and by changing the duty cycle you can AM modulate your LC (tank) circuit.
Since the DO can drive more current, and you have 8 DOs you can use, you have more power (up to 50mA, see spec)
Another point: If you can add resistors and capacitors to your coil, why not a single transistor?
here is a quick schematic
give it a try 🙂 you can run it with a AO or the DO ....
D1 R1 and C1 limit (protect) the 5V out of the 6218 (you use about 22mA ...)
you can use nearly any small NPN transistor you can find ....
and match the capacitor C2 to resonance!