# How to limit current of an AC signal

For my project, I'm trying to work with the principle of electrovibration. This principle is about simulating textures using low current electricity on an insulated conductive surface (see Wikipedia).

In order to do this, I will be experimenting with generated AC signals of 80 to 160 Vpp at 60Hz to 400Hz. I will do this by using an DC - AC converter, usually used for EL lamp applications.

My only concern is how to limit the current coming from the converter. Are the techniques for limiting AC current the same as DC, by using a simple resistor? Or is it, as I expect, more complex?

I need to limit the current to 0.5mA, for safety reasons.

• If the signal is how you describe then using a resistor will limit the current as per a dc circuit. Nov 8 '13 at 13:36
• You might find the answer to this previous question useful.
– user31299
Nov 8 '13 at 13:46

First, you say the conductive surface will have insulation over it. That will limit the current by itself.

If you want to additionally limit current in case this insulation is removed or circumvented somehow, put a resistor in series with the voltage source. No, it's basically the same as with DC.

You say the highest voltage is 160 Vpp, which is 80 V peak, which is 57 V RMS if the waveshape is a sine. By Ohms law, 57 V / 500 µA = 114 kΩ. The common value of 120 kΩ should be fine.

To use AC in a lab power supply (the goal is to limit/measure current in lab, not to do it for a high power device) I thought to rectify voltage to get DC, sense/limit and alternate to a AC again with inverter. Maybe this is not the efficient way to do it, but I think it is simple.

• And how would you limit the current which is what the operator was asking (in 2013)? Jan 30 '20 at 13:58
• seriously you feel the need of reply only to criticize? I replied because I'm looking for an issue related with current limiting right now, I seen this question and I thought to reply because there is no verified answer here. And I think StackExchange is not only a place to answer instant questions but also a place where people can found a question and check the answers and learn. As I said in my comment, the easy way to do this is: "rectify voltage to get DC, sense/limit in DC and alternate to a AC again with inverter" Jan 30 '20 at 14:40
• The problem with this answer is that limiting the dc into an inverter does not ensure that the current out of the inverter will be also limited, or to the same level. So, what you have suggested is potentially lethal. We tend to respond strongly when someone suggests a dangerous method to a naive asker. Jan 30 '20 at 14:55
• Thanks for your reply Elliot. Why current after inverter is not limited if the DC powering it it is? Maybe is not in the same proportion because losses and AC sinewave (I suposse you need to take into account frequency and amplitude), but I don't see the lethal part you said. Jan 30 '20 at 15:01
• @danirebollo: Be cool! I didn't criticise although you may have taken it as such. I asked for clarification which is what the comments are for. Your answer is short on details. Welcome to EE.SE. Jan 30 '20 at 15:10