Power supply question

HollyMinkowski

I'm up late working on my first test board for a dil prop.

I don't have any 3.3v regulators..I have some 317s but would rather not use one of the the 3 I have left for this.
I have a pile of old wall warts in various voltages both dc and ac..the dc ones have both polarities so there would
always be the danger of plugging in one that was reversed for the board. I thought of just adding a diode to protect
against reverse polarity but then I though why not use a tiny 4pin dil bridge rectifier..I have a bunch of those and
that way no matter what I plugged in I would get the proper polarity and it would even work with the ac wall warts
if I added a 1000uf/50v cap.

I want 3.3 and 5v on the board and as I have a lot of 1n4007 diodes couldn't I just use one 7805 to get the 5v
and add a few diodes to drop the v into the range for the propeller chip, thus ending up with both voltages.

Is my thinking sound on all this?

The little dil bridges are rated at 1 amp 50v...no way this board will use a whole amp anyway.

Tubular

I've suggested this before as a cheap and nasty solution, but most people are scared to try. I think it should be all right, but make sure you use a largish cap on the pseudo 3v rail to ensure you don't start with an overshoot (due to the initial tiny current through the diodes). Before connecting a prop suggest you check it using a 1500 ohm resistor to simulate the 2.2mA or thereabouts that the Prop takes when initially booting from EEPROM.

I'm only suggesting this because you have a big pile of props handy, right?

tubular

HollyMinkowski

@Tubular

"make sure you use a largish cap on the pseudo 3v rail"

How large is a "largish cap"

I have 10 dil props to play with, so I'll take a chance

HollyMinkowski

I wonder if anyone has tested the prop with short duration spikes of 5v to see if they
die instantly or survive the spikes and keep on working?

I saw that torture test video where they had the prop chip running in an oven and it kept on going.

A similar test using 1ms 5v pulses injected while the prop is running code would be interesting.

Post Edited (HollyMinkowski) : 6/15/2009 6:34:46 AM GMT

Tubular

Holly, assuming you're not driving any large loads, I was thinking something like 10uF tantalum, with the standard 100nF monolithic in parallel for high frequency switching. You're just trying to get it booted without overshoots; after that the caps are just there to sure ip the supply against high frequency transients..

Re the 5V, most here love their props too much - the idea or torturing them is unfathomable! But since you've got 10, once your project is up and running perhaps you could test them to extremes and post the results. I think Sapieha might win on the overclocking extreme tho

tubular

Sapieha

Hi Tubular.

I newer overclok CPU's with extreme voltage conditions.
My goal is always to overclok with standard voltages and only if ned with biger cooler.
And only to have beter power stablity to met CPU's power consumption

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
Don't guess - ask instead.
If you don't ask you won't know.
If your gonna construct something, make it·as simple as·possible yet as versatile as posible.


Sapieha

HollyMinkowski

@Sapieha

Hi, how fast have you been able to get the propeller to run reliably?
With what xtal frequency?

I have some 10mhz xtals that I am going to try and use, but at 8x not 16x
I just wonder how reliable that will be since the specs say 8mhz max. Only
reason I want to do it is because I have many 10mhz xtals.

I wonder if it would be OK to try overclocking with a v+ of 3.6 since the specs say the
propeller can use a v+ this high....the increased V might allow for higher speed..
when overclocking a PC boosting the v sometimes helps.

Sapieha

Hi HollyMinkowski

I run 2 Propellers in test more that 2 month with 15MHz x 8
No problems at all but read my thread on design PCB's.

10MHz x 8 is very reliable.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
Don't guess - ask instead.
If you don't ask you won't know.
If your gonna construct something, make it·as simple as·possible yet as versatile as posible.


Sapieha