A simple Zener diode voltage regulator might do the trick. I punched the maximum values you mentioned into this online calculator
and it appears a 14 Ohm resistor (so you'd use a 15R) along with the 3.6V Zener diode will cover it off nicely. A very cheap solution too.
OK, I tried that. It works pretty well, although I got 3.4V from a diode labelled 3.6V.
The only worrying thing was that the load can drop down to zero and when that happens the diode gets quite warm. If I go that route I might have to add a PNP transistor to be able to power the whole thing off when it's not being used.
First are you sure that the project needs exactly 3.6V? Maybe 3.3V is OK - but you've neglected to provide
any hard information about this project like a link to tech-specs or a datasheet - please do so.
Yep. It has an SD card reader on it. The SD card spec allows cards up to 3.6V, 3.3V doesn't work for many cards.
The device is this: http://www.ebay.com/sch/i.html?_nkw=WTV020-SD-16P
You can read about all the problems it causes in the "audio" forum: http://arduino.cc/forum/index.php/topic,117009.0.html
I was playing with one yesterday and I found out that all
the problems vanish if you raise the voltage a bit. I'm not designing a PCB or anything fancy like that, I just want to stick one in a toy I'm making for a nephew. It's probably going to be driven by an ATtiny84 with a regulated 5V wall-wart.
I've tried putting 2 diodes together which should drop 1.4V in theory but in practice it was all over the place, anywhere between 4.5V and 3.0V depending on what the device was doing.
Wow, this device sure has variable current needs.
Yep. It can drop down to almost zero when it's idle and when it's driving a speaker it can vary quite a bit.
Before anyone can give you truly meaningful advice, we'd need to know a little more. Can you tell us:
1) What the device is (link to spec sheet would be nice)?
2) Voltage tolerance of the device?
3) Current requirements of eh device?
4) Any other hard facts that might be pertinent to your use of the device?
1) See above
2) The chip is a WTV020 - datasheet here
Operating voltage: 2.5-2.6V
Maximum rating VCC-GND: -0.5~4.5V
3) Current can vary between 2uA in standby up to 150mA max (depending on the speaker). I put a big capacitor on the supply line and measured a fairly steady 60mA consumption with my speaker.
My module does nothing at all with the SD cards I have here when it's connected to the 3.3V output of an Arduino. It works perfectly with a 3xAAA battery pack (about 3.8V measured) or using the Zener diode trick above (around 3.4V measured).