----- Original Message ----- From: "Bob Japundza" To: Sent: Friday, September 06, 2002 10:56 AM Subject: [EE]: delayed startup power supply > I have been looking into some of the offerings TI has for supervisory > circuits, with the idea if creating a power supply for my project that > will delay startup. Delay the application of the regulated DC for a second or two after a request for "Power On" is received? Sounds good. I designed a power-on circuit for that Heathkit SS-8000 (which became the SS-9000 with the subsequent addition of a WARC band!) that drove the "main DC power relay" - the circuit quickly 'tested', then applied DC to the radio in order to insure it was within an acceptable range (and polarity!) before it allowed the relay to "close" and apply "DC prime power" through to the rest of the radio. > However, I am not clear on how you could tie these devices into > a regulator. Therein lies the rub - so let's set forth the design rules and the rationale behind them first. > Basically, I would like to design a power supply that will > shut down power to the whole board if any transients are detected > and reset everything (lcd, eeproms, etc.) on power up. Sounds like you need (preliminarily): 1) Pre-Brownout detect (maybe an 'early' detect that is meant for an NMI (a non-maskable interrupt to that signals an impending "power down" event) 2) Brownout reset, occurs some defined time *after* 1) above and depends on system dynamics such as power supply cap reserve and it's ability to source unregulated DC for the regulator. Normally this signal in past days would stop system clocks and inhibit RAM write enable lines (if RAM was battery backed-up that is!), etc. 3) The third event - remove the actual regulated DC from the device. Some regulators have "power down" control inputs, or, someting can be designed into existing designs. The easiest way is via relay or s series FET and simply remove "DC Prime (V batt) power input". RF Jim > The design is going to be used in a homebuilt aircraft and > I want my project to shut itself off when a transient is > detected (starting the engine) and come back up automatically > in a second or two after things stabilize. Can anyone point > me in the right direction? > > -- -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.