Max ratings of electret mic

"pimpom"

See the schematic - it shows a resistor in series with the FET which MUST be there for it to work.

The supply voltage can be anything from 1.5 volts up to 12 volts, depending on the particular capsule while the resistor can be from 2.2kohms up to

The voltage appearing across the FET will be half or less than the supply voltage.

..... Phil

Thanks for the reply. I understand the principles and I already looked up some catalogs, but none specified the max P.S. voltage. What I wanted to know was whether it would be safe (for the FET) to operate the microphone at something like 9-12V. I guessed it would be, but wanted confirmation.

I expected that, like you said, the max ratings would differ for different models. But just as it would be unusual for a general-purpose low-power BJT to have a max Vce rating of less than 20V, I hoped that someone would be able to cite some voltage that could be expected to not exceed the max Vds rating of the vast majority of electret mikes.

Thanks for the reply. I understand the principles and I already looked up some catalogs, but none specified the max P.S. voltage. What I wanted to know was whether it would be safe (for the FET) to operate the microphone at something like 9-12V. I guessed it would be, but wanted confirmation.

I expected that, like you said, the max ratings would differ for different models. But just as it would be unusual for a general-purpose low-power BJT to have a max Vce rating of less than 20V, I hoped that someone would be able to cite some voltage that could be expected to not exceed the max Vds rating of the vast majority of electret mikes.

"pimpom"

P.S. voltage is one thing, max Vds of the FET is another.

The whole point is that there IS a current limiting resistor - and if the PS voltage goes up, the SO must the value of that resistor.

Plus - what the FUCK are you on about ????

Your dopey Q simply has no context.

Just like you.

..... Phil

Why? Since the electret itself is tied to gate and source, the limiting voltage is the max Vds of the FET. Sure, the load resistor drops some of the supply voltage, but by how much is not precisely predictable. The FET charcteristics are unknown; and even if typical values are given, there are tolerances - often as much as +/-50% for Idss. Then there's the swing from steady-state when there's an input. That swing may be of the order of millivolts under normal signal conditions, but there could be circumstances, intended or unintended, where the swing is much more, theoretically up to the P.S. voltage.

In typical applications, yes. But what if I or someone else want to use the unit in an Atypical application? For example, I may want to keep circuit component count to a minimum by supplying the mic directly from a convenient, well filtered supply of +20V, but, for some reason, also want to keep the load resistor low. Or even use an inductive load. The max Vds (and possibly dissipation) rating will then be the ultimate limiting factor.

See above.

That was uncalled for. But I'll take it in the spirit of Usenet and just shrug.