Hi Everyone!
I want to use Arduino digital pins with PWM to get below outputs.
Voltage 0-50V
Pulse amplitude: 0-100mA
Pulse width: 0-200us
Frequency: 0-1kHz
I need your help and suggestions for transistor types (BJT, Mosfet or Op-Amp) to achieve above frequencies and pulse widths, and sample circuit schematics.
Most basically circuitry will be like attached pictures.
Thank you,
E.
etezisci:
Pulse amplitude: 0-100mA
I hope you mean Pulse current 
But if you don't need it to be isolated you can just use the second diagram. 100mA is not that much, a BJT or a MOSFET wil be fine. (based on the info you gave).
And what do you want to drive? Do you really need to change the frequency as well?
Yes, pulse current sorry for that.
In my case, 100mA should be max current because I am going use it on skin with electrodes, I don't know the speed and bandwidth difference between transistors.
Can you suggest any BJT or MOSFET for my case, so I can check their data sheets?
thanks,
In my case, 100mA should be max current because I am going use it on skin with electrodes, I don't know the speed and bandwidth difference between transistors.
With 50V and human skin you shouldn't be getting anywhere near 100mA (under "normal" conditions), but a series resistor can limit the current.
100mA is truly dangerous. 0.5mA is painful enough.
I agree with MarkT, 100mA is great enough to possibly cause death. And depending on how you make contact with the skin and how sweaty you are, 50V could push that much current. Skin and flesh change when a lot of current flows, too, causing the resistance to go down.
duty cycle ?
50V is unlikely to force 100mA through skin, thankfully! 100mA passing through your body should be avoided for health and safety reasons...
Make sure you have appropriate measures in place to prevent harmful current from passing through the unfortunate user of your device, whatever it is.
DrAzzy:
50V is unlikely to force 100mA through skin, thankfully!
Want to bet your life on that? Skin conductivity rises massively if wet or sweating, skin and
tissue conductivity rises once current starts to flow too, 100mA is life threatening:
Low currents (70–700 mA) usually trigger fibrillation in the heart, which is reversible via defibrillator but is nearly always fatal without help.
As I am not going to apply 100mA(those are max values) DC current continuously (pulse width is 0-200us), It will not harm your skin(unless you lick it)
I have already tested it and these values are in safe zone.
Additionally, TENS devices also use 0-90V and 0-100mA in outputs, you can check it.
Finally, I need suggestions for MOSFET and BJT models which will work best in my limits.(for example: BDX53C or 2n2222 with IRF540n)
No, if it can provide 100mA it is life-threatening - you hope it is only sending such short pulses, but if
it malfunctions its a potentially lethal device. You need to add a charge limiting component to
guarantee software error cannot kill someone, or else you are failing in your duty of care to others.
TENS machines do not deliver DC (for a number of reasons) - they would use high-quality series capacitors so that a 100 mA current could not possibly be maintained for any significant duration (such as longer than 200 µs).
This is because with gel electrodes and significant voltage, it would be possible to deliver 100 mA or more.
The other thing to be aware of is that DC shocks are much much worse than AC because they cause
involuntary and severe muscle contraction (the results of which can be fatal in themselves).
Ask yourself "do I really know what I am doing here?" and "have I just been lucky not to electrocute
someone so far?". You need to find out what the medical limits are and design a fail-safe
circuit (one that cannot exceed the safe limits even if its components fail)