Alright, I'll start with a new question. Based on the recent emails, I have no idea whether or not this belongs in this forum, but I will ask anyway. I am working on a linear regulator that is exhibiting very poor transient response. At first I assumed that the amount of output capacitance was to blame. After dropping the amount of output capacitance, I found little change. I have another board that uses the same circuit (same NPN-BJT, different decoupling, same load, better layout) which does not have the problem. I attempted to mimic the good board's output decoupling, but the result was the same. I then noticed that the good board was using a tantalum output capacitor, while I am using Ceramic. I am aware that tantalums do have a higher ESR than ceramics, so I attempted to use a tantalum. The result was that the base started to oscillate (became un-stable). I then tried adding a resistor in series with a ceramic cap to "simulate" a higher ESR value. This actually seemed to help a little, but not enough to declare any type of success. Since the base does not oscillate when using the ceramics, I assume that the regulator is stable. I began to suspect a problem with base drive current. The transistor I am using is an NPN that has a Hfe of 100 at Vce = 2V and Ic of 1A. My measured transient is less than 1A (~850mA). The base driver is capable of sourcing 20mA. I am using 3.3V to make 1.2V. With my calculations, I don't see a problem with base drive vs. gain. Some questions: What else might be contributing to my slow response times? Does anyone have a suggestion for obtaining an accurate bode plot of a linear regulator freq response? I would like to figure out a way to check phase margin. On the same topic... I have learned that a good method for estimating the variety of decoupling caps required in a PDS is to look at the problem in the freq domain. Based on my max transient, I have calculated that I would need about 30uF of capacitance on the output. But this contradicts what is recommended on the output of a linear regulator doesn't it? Most of the time, only values between 4.7uF and 10uF are used. Wouldn't 30uF on the output slow the response time? In my circuit, I have noticed the circuit does respond faster with less capacitance, but the overall ripple is greater.... What is the best way to balance these conflicting requirements BEFORE I get in the lab? Thanks. Chris ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu