Current limiting /diodes or discreets? 4

[Generalx5]

what is the common way of supplying low currents to an IC or microchip without having to tap into a secondary low supply source. I want to run an IC right from the high amp source, I've looked at Current limiting diodes and wondered if those little diodes could handle high input currents. Whats the key to supplying low currents? for microchips, h-bridges, mos-Drivers, logic inveters. etc. Often those things are rated for only a few miliamps.....any higher would do significant damage. Please let me in on the secrets to obtaining low currents.

 

[benta]

Skogs, the input signal to an RC servo is indeed a pulse train of pulses with a length of 1...2 ms, 1.5 ms being the "neutral" posistion.
Repetition rate is usually 20 ms, amplitude is 0/4.8 V.
This signal is never used directly to control a motor, but converted to a full 0...100% output of some kind (can be analog, can be PWM normally at a completely different frequency than the control signal).

Hope this helps,

Benta.

 

[richs]

Skogsgurra writes:

"I have been using a very nice little micro lately. It is small, low cost and has a prototype board that costs around USD 25 in single quantity. "

The "propeller" is indeed a nice little micro. However the eight blade processor architecture might be a little much for some of the readers of this post.

I have looked at the data sheet for it and did some pencil sketches with it. Seems like it was designed for a video controller series of applications. At least that's my impression.

As of this point, I might suggest an alternative processor for those who are getting started in control applications. With a more "conventional" processor, there will be folks out on the internet able to help one develop code and have "walked the path before", as it were.

For those folks that have used micros before and feel comfortable delving into a new architecture then this chip provides IMHO an interesting set of capabililtes.

The folks that brought us the PIC Stamps have really come up with a unique concept. It was interesting to see this product come from this company.

Just my thoughts.

Cheers,

Rich S.

 

[Generalx5]

Yes, Although the PWM signal is not directly used to control a motor, it is however used on the LMD18201 as a duty cycle PWM signal. I believe the chip reads the PWM signal and generates its own outputs that pulse at a variable frequency, but is dependant on the PWM signal.

 

[Skogsgurra]

Re: Propeller.

It was IR that pointed me to that device. And I am ever so grateful.

Imagine having eight 80 MHz processors on on chip. Each processor having 2 32 bit counters with 32 different op-modes. Including PLL, PWM, VCO, counting with 16 programmable input conditions (edge detection and such).

The fact that there are also eight NTSC/PAL engines doesn't bother me a bit. If I do not need them, I don't use them. And, guess what? The people at Parallax have run some temperature tests. minus 73 degrees C and plus 190 degrees C seems to be a reality. Those guys are very special. And nice, too.

There are lots of application SW coming with the board. You do not need to write many lines of code if you don't want to.

Price for a complete protoboard with everything you need plus lots of breadboarding area is hard to beat at 25 dollars a piece. And nice double-sided, glass epoxy, plated-through it is.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Generalx5]

When the data sheet says that a Logic High Input Current is 10 micro amps(max), as the limit, does this refer to the maximum amount of current allowed on that pin, or does it represent the maximum amount of current that pin can draw is 10micro amps?

 

[Skogsgurra]

You can apply the right voltage without worring too much about that current issue. It is there to tell you how much current the pin will consume, worst case.

Generally, current data tell you what the consumption will be (usually worst case) when you apply nominal (or maximum) voltage to a circuit. There are a few exceptions to this - the LED being one - where the operating point is given in mA and those devices need a series resistor or a current source device (like the constant current diodes). But normally, you do not use any series resistors or other means to limit current.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Generalx5]

Thanks again Skogsgurra =D