I have some parts ordered to breadboard the original idea, of all things i did not have the correct zener lol, I need to keep this as small and cheap as possible, the items im making are only sold for about 20 bucks each and to keep that price i need the power items to be about 3 bucks max, im not making them in bulk so i cant get a good price on some of this stuff.

Basically it will power an ATtiny45, two 5 volt relay coils and a small 3mm led, in actually thinking about it it will only have to power the ATtiny and one of the other items at the same time, I could really get away with about 40-50 mA of power.

The other circuits i have looked at have capacitors going from just after the resister to ground with a 104 0.1uF cap, what would this be for?

Any time you don't have the right zener - there's always the TL431.

Sometimes listed as a "programmable zener" its actually a comparator with built in 2.5V Vref, in use, you roll the comparator off with a lot of nfb to put it in linear operation, the cathode terminal feeds a voltage divider with the tap to V-in.

There's a wealth of datasheets & appnotes online to tell you all the nitty-gritty details - and if you search hard enough, some crafty little tricks that aren't in the appnotes.

 

The other circuits i have looked at have capacitors going from just after the resister to ground with a 104 0.1uF cap, what would this be for?

There is a sticky note for this here:

http://forum.allaboutcircuits.com/threads/decoupling-or-bypass-capacitors-why.45583/

 

Any time you don't have the right zener - there's always the TL431.

Sometimes listed as a "programmable zener" its actually a comparator with built in 2.5V Vref, in use, you roll the comparator off with a lot of nfb to put it in linear operation, the cathode terminal feeds a voltage divider with the tap to V-in.
................................

It actually has an internal compensated op amp, not a comparator. But, of course, it can be used as a comparator, depending upon the external circuit design.

 

It actually has an internal compensated op amp, not a comparator. But, of course, it can be used as a comparator, depending upon the external circuit design.

I'm just going by what the manufacturer calls it.

 

I need to build a cheap regulator to drop a voltage of about 7.5 - 13.5 to a constant around 5 volts, I will be driving two small relay coils (30 mA each) and a attinny45, I also see where some people put capacitors in there regulators, what is that for and what would i need? Any insite on my design would be appreciated

The TL431 "programmable zener" can handle 100mA - but you have to watch power dissipation when you set it for higher voltages.

If you want more than 100mA, you can add a PNP emitter follower to the TL431 cathode in a similar manner to a Sziklai pair;

http://en.wikipedia.org/wiki/Sziklai_pair

 

I just spoke to one of the electrical engineers at work and he came up with this regulator, MCP1702, its a fixed 4 volt regulator but should work with the relays im using, they are 5v relays but have an on voltage of 3.75v

http://www.mouser.com/ProductDetail...4002E-CB/?qs=sGAEpiMZZMsnDbBzJh6VGJVwzmifrdNJ

I worked with an lm317 last night but could could not get a stable voltage above 3.02v, with a 4.7v input (4.7v - 10v range), The dropout kicked in to soon. I could make it work but would have to get different relays that cost 3 times the cost of the 5v relays.

 

Why would you ask about 7.5V to 10V input, then try to do the job with 4.7 Volts of input?
Why would you need to regulate 4.7 volts down to run a 5 volt relay?

 

I just spoke to one of the electrical engineers at work and he came up with this regulator, MCP1702, its a fixed 4 volt regulator but should work with the relays im using, they are 5v relays but have an on voltage of 3.75v

http://www.mouser.com/ProductDetail...4002E-CB/?qs=sGAEpiMZZMsnDbBzJh6VGJVwzmifrdNJ

I worked with an lm317 last night but could could not get a stable voltage above 3.02v, with a 4.7v input (4.7v - 10v range), The dropout kicked in to soon. I could make it work but would have to get diffrent realays that cost 3 times the cost of the 5v relays.

Why would you ask about 7.5V to 10V input, then try to do the job with 4.7 Volts of input?
Why would you need to regulate 4.7 volts down to run a 5 volt relay?

Sorry,

Its an evolving project that has changed behind the seen, I just never updated the original post, The base values are a little more defined now, The info i was given up front changed so i adapted but did not update this thread.

Input 4.7v to 10v
Output 4.0v (best case) any lower and the relay will change to a more expensive part

 

Are you concerned about the efficiency of the regulator?

 

No,

Its will only be used about 60 seconds at a time and about 20 times in a 6 hour span, they will run off a 2s or 3s lipo (receiver regulates down to 4.7), but some people run modified receivers or external power up to 10 volts.

I thought about two power connectors, one for a standard 4.7v - 5.5v input and a high power input for people running over 5.5 volts. but it just complicates it and a chance for somone to hook it up wrong.

 

I just spoke to one of the electrical engineers at work and he came up with this regulator, MCP1702, its a fixed 4 volt regulator but should work with the relays im using, they are 5v relays but have an on voltage of 3.75v
.

That's probably the holding voltage - the pull-in voltage won't be much lower than the rating it says on the label.

 

Ill have to test, This is the relay im looking at

http://www.digikey.com/product-detail/en/EE2-5NU/399-11056-5-ND/4291122