Re: Combined voltage regulator + supervisor in TO-220/TO-92 package?
From: Jamie (jamie_5_not_valid_after_5_Please_at_charter.net)
Date: 01/26/05
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Date: Wed, 26 Jan 2005 10:16:39 -0800
Erik Walthinsen wrote:
> I've got a circuit based on a ATtiny15L and Honeywell's HMR3100 compass
> module that appears to have only one remaining problem before I'm done
> with it. If the circuit is hooked up to a bench power supply, which is
> powered on with its front switch, the compass fails to initialize
> properly, and the circuit doesn't do its job. This is obviously due to
> a slow ramp-up of supply voltage/current from the bench supply. If the
> power is stable and a switch applies power to the target circuit, it
> works every time...
>
> Now, the problem is that the ATtiny15L is fully utilized: no free pins
> and almost all code space used (think 1010 out of 1024 bytes).
> Compounding this, the HMR3100 does not have an external reset pin...
> Therefore, I need to find a way to make sure that the compass does not
> get power until the supply is stable.
>
> However, the entire design is currently through-hole, and needs to stay
> that way for assembly purposes (it's really small and assembled by hand
> in really small quantity). Therefore I'd like to find a part to replace
> the standard 7805 regulator that will solve the problem.
>
> Basically, I'm after a TO-220 or TO-92 (or equiv 3-terminal) voltage
> regulator that will not enable its output until it can guarantee
> sufficient supply current to bring the regulated rail up immediately.
> Complicating this is the requirement that the regulator be able to
> operate with a supply voltage up to 36V...
>
> I could probably build a retrofit module with a regulator, on-board cap
> (currently 33uF on either side of the regulator), and supervisor chip
> connected to a mosfet/etc, but I'd really rather not have to do that, as
> that almost guarantees surface-mount parts.
>
> Any component suggestions would be appreciated, as would any other ideas
> on how to solve this. Then again, the problem may be made moot sometime
> today by way of product requirements being clarified (will a bench
> supply ever be used in the field [think middle of nowhere] with that
> particularly unlikely turn-on sequence?), but I'd rather have a solution
> available if not.
>
> TIA,
> Omega
> aka Erik Walthinsen
> omega@pdxcolo.net
off the top of my head. use a bipolar transistor that has enough current
handling to take care of the board supply by simply feeding the C and
using E as your output.
mean while, use a 555 timer as a Delay on that will drive the Transistor.
the 555 timer can be connected to the main source after the switch.
you may also want to look into the use of using a HexFex as the switch
instead of the Bipolar transistor, this would give you less loss.
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