--_003_4EB9556E6040903sbbrs_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable On 08-Nov-11 15:07, alan smith wrote: > For some reason I am really struggling with this, should be simple. So l= ets look at the two circuits > > The PNP transistor approach...seems simple but I am trying to understand = how its supposed to work. > > The base is grounded...so the C-E wont be turned on. The collector has a= -5V thru a 4.7K resistor, the emitter has a 1K in series with the input si= gnal. The output is from the collector. So when 0V is on the emitter, the= output is pulled to the -5V reference. When the emitter has 5V on it, it = turns on? Seems to me the base needs to have the input signal, so when 5V = is driving it, it turns on and grounds the output, and when off...it floats= to the -5V? > > 2. Using a buffer. I havent found a buffer that swings -5V to ground.,..= all I have seen are 0 to 5V, other than a LM5112 can swing negative but its= a driver but might work. > > 3. Adding a diode....cathode to the output, with a resistor to ground on = the anode....is this so it become negative biased? such that with a positi= ve input, the diode wont conduct, and the resistor pulls to ground...and wh= en it swings negative the output will then turn on? If I need to clamp to = -5V, would a zener work in this case? You should really consider using LTSPICE or similar simulation software=20 for this kind of problems. Spehro's simple circuit works well. I draw another one if you need=20 stiffer output. This is for digital 0V/5V input giving -5V/0V output. Djula > > > > ----- Original Message ----- > From: Kerry Wentworth > To: Microcontroller discussion list - Public. > Cc: > Sent: Wednesday, November 2, 2011 9:09 AM > Subject: Re: [EE] -5V to 0V swing from a +5 input (again) > > Then just swap pins 2 and 3. > But why not run the signal through one of the transmitters, and put a > diode in series with the output? Cathode to transmitter output, anode > to resistor to ground, take signal out from anode. > > Kerry > > > alan smith wrote: >> what I need is when the input is +5 and need it to be -5 out, and when i= ts low...the output to be low...so basically inverting it. >> >> >> >> ----- Original Message ----- >> From: Kerry Wentworth >> To: Microcontroller discussion list - Public. >> Cc: >> Sent: Monday, October 31, 2011 9:19 AM >> Subject: Re: [EE] -5V to 0V swing from a +5 input (again) >> >> I don't remember the details of what you are looking for, but for >> argument's sake, let's assume you want +5V in to give 0V out, and 0V in >> to give -5V out. >> >> You could use an LM311 voltage comparator. Use your +8V and -8V (or +- >> 5V) to power it. Tie the output pin (7) to ground and tie the "ground" >> pin to a pulldown resistor to -5V. Tie the + input (2) to a voltage >> between 0V and 5V (say 2.5V). Apply the signal to the - input (3). >> >> Kerry >> >> >> alan smith wrote: >> >>> hello...this goes back to a question I asked a few weeks ago. Basicall= y it was asking about generating a -5V signal from a +5V input. >>> >>> So I settled on a ADM222, old style RS232 driver and sure enough I can = get the -8V drive. But what I need is -5V so thinking....on the charge pum= p -V pin, putting a zener to clamp the voltage to -5V....or....feeding that= -V pin with a regulated -5V, wondering if that might work. >>> >>> However the other problem is, when the input is positive, the output go= es positive, and I need that to be at the reference 0V level. I tried to u= se a pull down to ground on the +V charge pump, but that just pulled it fro= m +8V to +5V. I'm not an analog oriented person so...wondering if there is= some sort of opamp based design that can only allow the negative swing to = go thru, and if its ever positive, keep it at the ground reference. What h= appens if you ground the positive rail on an opamp and just provide negativ= e power? >>> >>> >>> >>> >> >> > --_003_4EB9556E6040903sbbrs_ Content-Type: image/png; name="Digital_0V_5V_to_-5V_0V.PNG" Content-Description: Digital_0V_5V_to_-5V_0V.PNG Content-Disposition: attachment; filename="Digital_0V_5V_to_-5V_0V.PNG"; size=1746; creation-date="Tue, 08 Nov 2011 08:17:54 GMT"; modification-date="Tue, 08 Nov 2011 08:17:54 GMT" Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSUhEUgAAAWYAAAEFAQAAAAD4PXBPAAAACXBIWXMAAAsTAAALEwEAmpwYAAAA IGNIUk0AAHolAACAgwAA+f8AAIDpAAB1MAAA6mAAADqYAAAXb5JfxUYAAAYYSURBVHja7FpNbBRl GH6+2S1dQOmiJmCCsAYTiRf1ooUEOwcOmGACN+OB0BsXIyYmEoLdkQMHYoLeiEntGq4euLUR4o5i oolGSIxRoriDGGnkZ6c/dKftzLweWHdnvu/9ZueDNoB2Tu3u03ef732f9+d7u4Jg8FhYQf8/0IER 2jJC9zkmaFFJ/Rplo8lL/VoQmfpeWGXCJJaZLWHutGwT23N/V5Yt8qEReq23fD6he9F3D50s2CY6 IbF8mSbMTumu1KoV9P1Fk2uS87FlYntuKWpV9IrM+CkHCH3lIEREFF2i9BPfJKLbQ9KrluYzsQgE LZdnQgdl9MsOMK3xt3C4bPfkV4tZ7jh7XHPKy/IpbxDNfUOb0q+C9M/tofh6lfUJ9yy6CtE7f1SP JbsNqtIMxbd4f8dMWygCddaDNdmFF2EDwGZeVTHbcsRrjsy7SRQ3F+tddi0iejdqUIuomVMndz6s rPhkskpRq9XoWpgdonhxsUktJQIWUNguigjwfmcsEqPCQogvy0oEigD6CSHKQ92xqECIUdria3Pe l1tMAE9bISyU5G7GqrOtwfocUSOpwcZitUUzZ7d/P6R6UDElHAvAQmP0usPwduUq5JEDlAXgJrqm zjYcC0Bc/gMAalxl89IjF6bXBee+G3wVNFWWmBySZ+kdLvqcgA4DoJJcIWRXNUcBYU+Xtm4E4qKU 8yQr1kcAlDdv/gtAuEqOjoyuIAC2tVkJ2YOBEjav86bfSax/0WsU9LbOaP+pcNORpzeJKBnj1vZx ImonVJ2pPqFafy5IaEs/KqJ9TJ/tJDeYKays6zvxhIpepetSccTkCqaEEG93K1PXdmQz6AEiGiAG HXgmnbvJoMUZHfpHx8T2JzpIWUU75CM6qhslmko2uKBBnfn9MlqwspWqu5VVf5WuaiXKt36wOZBG B3z7Bq9BHwCEzXvEltEeABR28TyOiX3pTKtCsM27TkQH4k4Ktk9rY0R7xHXn5apZyVLHiMy7nHXp cWV0CQAWfh+9xn5ItHO25iSiVASAyL9QdzkNirEjYn2qSwEowYEmgY5RujcAoNKURrHDxRfSaHIQ F6/CZc95+sQP6WwQNkKc0w1wfuSmJ7wy5osf/XqKUxUNj3+2IVljKWrpIv8WN7MVjW4Cwghd0NWT qa7ure4POmWd5Oog9hrdYIpG6DX5K1s+pyTRttHNq/YQ3hingl57GefzLrr/UMYtcy8AsqMEE78X i+bBBDqrWk0JIcoYy3nKASLyERv5JOyi5zN6qzgDQHx1qSvTgV6WCycf1F3BladtA/QGyos+94V3 UAdRu+tIWJ8tkpPPNjlhHRblPKUQcB5Rb413HnXCE4fjWaHVlNxdMRO54mhuf4/278FgT3RbVbuA UxlandijxnKframD8RG1sG5pVHqNhPlUFZugO97KZzswQk/nR/vo229g+0+TTIsGTdCty7YBevXW 93bOXp7MiS58K8aO1N/Je8pNwLGvKzkbcBk0PF5dnT/yp0/QE/ljGfqxlxtNw8ejD/LORyicx7On lqXG+np0xXdy2t4G0EVS+mrGNjH8OC/veSEsPKf01aluHUza7g9AN6Ua6AP+mHt3fSdp+xdAvLj2 9YybrnzKq3knvAenuy4rmhmtPD36GRW9O13Gk+jVKvqxtOkkuqD2nT6H2ybq1kTzVy5wW6JoB9BS mdx6dJI7pRgFflPRE+l9Z4d3Sd36AeTNXOR4hztZ2nRznOMtRljauliGmFXRkxAb2Wx4UopEO7rr 13O2reeVSDDRTd531KFAiW7CA9d0Kz9u48cT1yq2N3GLX0903jbTIM878mw2mMEgx4SqNVaDzRqH Lka8Bn3ieMc/11nacz9xvMl3eQ2GHJP4cYfVIPo4JsEbW+ZVJjPUekmzGY6rCjrUb4ZzaDAZeWbo df571f5BRsvziZltpP6vKD/t24W8BdXe+/1lO6V+E7+ik4cdnfivYaz+ZVDS90un5ydnV7asb9bt VnlW9OgJppNo0fJbABade/HJXX+LLP5QvRJnVPtJ9ZS1JdIJsStBHbqg+nvpvlnnLXFPEyvfGV5B 3190bKbBfwYAWMzERspWrC0AAAAASUVORK5CYII= --_003_4EB9556E6040903sbbrs_ Content-Type: text/plain; name="ATT00001.txt" Content-Description: ATT00001.txt Content-Disposition: attachment; filename="ATT00001.txt"; size=208; creation-date="Tue, 08 Nov 2011 08:17:54 GMT"; modification-date="Tue, 08 Nov 2011 08:17:54 GMT" Content-Transfer-Encoding: base64 LS0gDQpodHRwOi8vd3d3LnBpY2xpc3QuY29tIFBJQy9TWCBGQVEgJiBsaXN0IGFyY2hpdmUNClZp ZXcvY2hhbmdlIHlvdXIgbWVtYmVyc2hpcCBvcHRpb25zIGF0DQpodHRwOi8vbWFpbG1hbi5taXQu ZWR1L21haWxtYW4vbGlzdGluZm8vcGljbGlzdA0K --_003_4EB9556E6040903sbbrs_-- .