Low frequency pulse generator

Thread Starter

Alexvatt

Joined Aug 24, 2013
31
I need a pulse generator to drive a plating cell which has a resistance of roughly 1-2 ohm. I want to drive it with a squire pulses with the frequencies in the range of 1-60Hz and fixed current of 5-10A.
I want to use Arduino that will drive a MOSFET via octocoupler and a linear regulated 30V, 20A DC power supply. The circuit diagram is attached. Will low resistance of the load be a problem for IPP096N03L MOSFET?

Thank you for help.
 

Attachments

wayneh

Joined Sep 9, 2010
16,128
I'd like to hear an expert opinion on the drain-source breakdown voltage specification of 30V. Since that's the same as the supply voltage, it's a question mark.

Otherwise it looks OK to me. At 10A load and an on resistance of 8mΩ, power dissipation will be under 1W and well within specifications.
 

praondevou

Joined Jul 9, 2011
2,942
The load current is no problem if you mount it to a heatsink. Do not exceed VDS. I would not even work continuously near it.

If you work with 30V take at one with a VDS of at least. The wires in your circuit are inductances, turning current off can cause unexpected voltage peaks, possibly exceeding 30V.

The 5V input is negative?
 

wayneh

Joined Sep 9, 2010
16,128
...a plating cell which has a resistance of roughly 1-2 ohm.
If those values are true, you'll have 30-15A of current when the MOSFET is on, not the 5-10A you mentioned. The PWM can reduce the time-average-current, and perhaps that is what you meant?

If you're plan is to switch by PWM a 30A load, I'd look for a MOSFET rated to 60A continuous or more. The 35A rating of this one is too scary.
 

Thread Starter

Alexvatt

Joined Aug 24, 2013
31
The load current is no problem if you mount it to a heatsink. Do not exceed VDS. I would not even work continuously near it.

If you work with 30V take at one with a VDS of at least. The wires in your circuit are inductances, turning current off can cause unexpected voltage peaks, possibly exceeding 30V.

The 5V input is negative?
I think 5V is positive
 

Thread Starter

Alexvatt

Joined Aug 24, 2013
31
If those values are true, you'll have 30-15A of current when the MOSFET is on, not the 5-10A you mentioned. The PWM can reduce the time-average-current, and perhaps that is what you meant?

If you're plan is to switch by PWM a 30A load, I'd look for a MOSFET rated to 60A continuous or more. The 35A rating of this one is too scary.
I'm not planning to exceed 10A current in this set up otherwise my load will melt.
 

Thread Starter

Alexvatt

Joined Aug 24, 2013
31
I don't need 30V to get 10A, but 30V is max voltage. The power source that I can get and that is reasonably cheap has a variable voltage and current output so I can set it to 10A.
 

THE_RB

Joined Feb 11, 2008
5,438
A plating cell will have a changing resistance based on temperature and the object being plated.

You would benefit a lot from using a constant current pulse (not a constant voltage pulse), so plating would be more reliable and repeatable.
 

wayneh

Joined Sep 9, 2010
16,128
Although you may not intend to ever max out the dial on the power supply, I think it would be prudent to design (choose a MOSFET) for that worst case. Murphy's law ensures it WILL happen otherwise. A fuse to protect the MOSFET and the plater is a good idea.
 

Thread Starter

Alexvatt

Joined Aug 24, 2013
31
A plating cell will have a changing resistance based on temperature and the object being plated.

You would benefit a lot from using a constant current pulse (not a constant voltage pulse), so plating would be more reliable and repeatable.
I'm using a current source.
 

Thread Starter

Alexvatt

Joined Aug 24, 2013
31
Although you may not intend to ever max out the dial on the power supply, I think it would be prudent to design (choose a MOSFET) for that worst case. Murphy's law ensures it WILL happen otherwise. A fuse to protect the MOSFET and the plater is a good idea.
It makes sense I will likely eventually need a larger current and more powerful source.
 

THE_RB

Joined Feb 11, 2008
5,438
I'm using a current source.
Your circuit won't work with a current source, because you need a voltage source of a fixed voltage or >X voltage to operate the opto and the FET gate.

If you did intend that the plating power comes from a current source, then you need to specify that the control circuit of opto and FET gate is powered from a separate voltage source. :)
 

ronv

Joined Nov 12, 2008
3,770
looks really good but I'm not sure if I can drive it with 5V.
I think we thought you were using a 30 volt supply so it would have about 15 volts of gate drive. But if you are gong to use a constant current source all bets are off if the current is set to low. But, that begs the question of why do you need PWM if you can adjust the current and voltage already?
 
Top