Post by thread:Recommended Brounout Protection Circuit doesnt wor

I have tried the recommended brownount protection circuit p. 2-415 in the PIC microcontroller databook. I used a 2N3906 for the pnp transistor and a 3.9v zener diode for a cutoff at 4.6v. I tried it without the PIC and monitored the output voltage. There was no switch in logic state on the output when I dropped the supply voltage, only a linear drop. I even tried other pnp transistors and even npn transistors and switching connections of the emmitter and collector. No luck. Does anyone know of a SIMPLE circuit that will do the same thing or indicate what I may be doing wrong? Neil Gandler

NEIL GANDLER wrote: > > I have tried the recommended brownount protection circuit p. 2-415 in > the PIC microcontroller databook. > I used a 2N3906 for the pnp transistor and a 3.9v zener diode for > a cutoff at 4.6v. I tried it without the PIC and monitored the output > voltage. There was no switch in logic state on the output when I dropped the > supply voltage, only a linear drop. I even tried other pnp transistors > and even npn transistors and switching connections of the emmitter and > collector. No luck. Does anyone know of a SIMPLE circuit that will > do the same thing or indicate what I may be doing wrong? > > Neil Gandler The combination of a high gain transistor with the typical 3.9V Zener doesn't yield a crisp transfer function with this simple circuit with no hysteresis. Zeners have worse and worse 'knees' as you get down in the lower Voltages. Reduce the resistance of the collector load resistor (40K in their diagram) and your circuit will behave a little better. At 40K, only 100uA collector current will raise it to 4V! Beta of a 2N3906 could be 200 or more, so a small Zener leakage is all it takes. Of course, you're wasting current in the collector load resistor, so what else can be done? Some possibilities: 1. Use several forward biased switching diodes in series instead of the zener. 2. Use a couple of red LEDs in series instead of the Zener. LEDs have very sharp knees, and you get a power indicator in the bargain. 3. Use a reset IC with Schmitt input such as MAX809 or MC33164 instead. -- Paul Mathews, consulting engineer AEngineering Co. spam_OUToptoengTakeThisOuTwhidbey.com non-contact sensing and optoelectronics specialists

In article <.....01I7KUQI131I8XKP1BKILLspam@spam@ubvms.cc.buffalo.edu>, NEIL GANDLER <V064MB9KKILLspamUBVMS.CC.BUFFALO.EDU> writes > >I used a 2N3906 for the pnp transistor and a 3.9v zener diode for >a cutoff at 4.6v. I tried it without the PIC and monitored the output >voltage. There was no switch in logic state on the output when I dropped the >supply voltage, only a linear drop. I even tried other pnp transistors >and even npn transistors and switching connections of the emmitter and >collector. No luck. Does anyone know of a SIMPLE circuit that will >do the same thing or indicate what I may be doing wrong? Not very good, is it ? If you can afford a bit more than the cost of a transistor and a zener try a dedicated IC such as Maxim MAX700. Well worth it if dodgy PSUs are likely. Power-on reset and brownout protection is something Microchip ought to sort out properly on the chip. Karel -- ++++++++.....khladkyKILLspam.....khdesign.demon.co.uk++Manchester M14 6BF England++++++++

At 07:39 PM 7/27/96 -0500, Neil Gandler wrote: > I have tried the recommended brownount protection circuit p. 2-415 in >the PIC microcontroller databook. --- snip --- I have used and highly recommend the 3 pin voltage detectors from Seiko S-805 and S-807 series. You can get open drain, or CMOS output. TO-92, SOT23 or SOT89 packages Available in voltage ranges from 1.0 to 7.7 volts. I generally pay about $.30 to .35 in thousands. Can't get much simpler than this. They also have some really low quiescent current regulators. And they now have both regualtor and detector in 1 package. Hope this helps. Gary Skinner, Electronic Solutions Inc Design of custom control circuits Denver CO 303-469-9322

On Sun, 28 Jul 1996, gary skinner wrote: > At 07:39 PM 7/27/96 -0500, Neil Gandler wrote: > > I have tried the recommended brownount protection circuit p. 2-415 in > >the PIC microcontroller databook. > --- snip --- > > I have used and highly recommend the 3 pin voltage detectors from Seiko > S-805 and S-807 series. You can get open drain, or CMOS output. > TO-92, SOT23 or SOT89 packages > Available in voltage ranges from 1.0 to 7.7 volts. > I generally pay about $.30 to .35 in thousands. > Do you have a tel# for Seiko. Are they available in small quantities? Sounds what I'm looking for. The To-92 package is perfect. Neil

>On Sun, 28 Jul 1996, gary skinner wrote: > >> At 07:39 PM 7/27/96 -0500, Neil Gandler wrote: >> > I have tried the recommended brownount protection circuit p. 2-415 in >> >the PIC microcontroller databook. >> --- snip --- >> >> I have used and highly recommend the 3 pin voltage detectors from Seiko >> S-805 and S-807 series. You can get open drain, or CMOS output. >> TO-92, SOT23 or SOT89 packages >> Available in voltage ranges from 1.0 to 7.7 volts. >> I generally pay about $.30 to .35 in thousands. >> > >Do you have a tel# for Seiko. Are they available in small quantities? >Sounds what I'm looking for. The To-92 package is perfect. > You might also consider the mitsubishi 51943A series, The one we use for 5v PIC applications is 51943A this is available in TO-92 package approx $0.40. Trips at approx 4.25v with 50 mv hysteresis. The 51943B is an open collector version of the same thing.

Also check out the Panasonic MN1381 series power supervisors. You can get them from Digi-key, about $0.74 in 100 qty. At 12:50 AM 7/29/96 -0400, you wrote: {Quote hidden}>On Sun, 28 Jul 1996, gary skinner wrote: > >> At 07:39 PM 7/27/96 -0500, Neil Gandler wrote: >> > I have tried the recommended brownount protection circuit p. 2-415 in >> >the PIC microcontroller databook. >> --- snip --- >> >> I have used and highly recommend the 3 pin voltage detectors from Seiko >> S-805 and S-807 series. You can get open drain, or CMOS output. >> TO-92, SOT23 or SOT89 packages >> Available in voltage ranges from 1.0 to 7.7 volts. >> I generally pay about $.30 to .35 in thousands. >> > >Do you have a tel# for Seiko. Are they available in small quantities? >Sounds what I'm looking for. The To-92 package is perfect. > > Neil > >

At 12:50 AM 7/29/96 -0400, you wrote: >Do you have a tel# for Seiko. Are they available in small quantities? >Sounds what I'm looking for. The To-92 package is perfect. US 310-517-7771 Japan 043-211-1213 Germany 001-49-6102-297-0 sorry to be so slow getting back to you. Gary Skinner, Electronic Solutions Inc Design of custom control circuits Denver CO 303-469-9322