Thanks! I have used MLCCs for bulk decoupling on some motor drives. They have three big advantages over aluminum electrolytics: 1) much longer life at high temperatures 2) very low ESR/ESL which can be distributed around the board to provide an overall very low impedance between any point on the power plane to any point on the ground plane, which comes in very handy to prevent ground bounce effects when switching FETs on and off hard at high currents 3) much better specs on internal heating from ripple current (by better specs, I don't necessarily mean that the MLCCs can handle more ripple current but rather that the electrolytic caps' ability to handle high frequency ripple depends on the details of internal heat transfer which are not characterized or controlled well by most manufacturers) The big disadvantages are higher cost, infancy reliability problems due to flex cracking, and capacitance change with voltage. I would often get requests to evaluate additional possible suppliers for these caps and I often had to check the dC/dV myself because many manufacturers do not provide that data, although the situation is getting better and most do provide it now. I was bitten by this the first time I used them - I was shocked to find that the voltage ripple on the motor drive bus was twice what I had calculated it should be, which I then traced back to the caps having roughly half their nominal capacitance at 50% bias (DC bias equal to half the rated max working voltage). At that time, Taiyo Yuden (where I was getting the caps) did not provide this info in their datasheets. I think they now do provide it. I got lucky because I had overspec'd the quantity of capacitance by about a factor of 2 because of uncertainties so it just worked out (with no additional margin). The device I built to perform this test works by simply connecting a very accurate low-value current source, with a compliance to at least 100V, to the capacitor under test. A microcontroller (NXP ARM, not PIC) watches the voltage rise, computes the slope at various points along the rise and computes the capacitance from the slope and the known current. The micro also has the task of stopping the current flow when the desired max voltage is reached. It reports the data over a USB-based virtual COM port in a text-based format. It can handle a range of 100pF to 100uF accurately (typically I get about 0.3% and I am still tweaking the firmware to use various techniques to try to be able to guarantee 0.5% at all times) Sean On Wed, Feb 14, 2018 at 3:01 PM, Van Horn, David < david.vanhorn@backcountryaccess.com> wrote: > Very good! Something more people should be paying attention to, I think. > > > -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf > Of Mario > Sent: Wednesday, February 14, 2018 11:14 AM > To: Microcontroller discussion list - Public. ; > Microcontroller discussion list - Public. > Subject: Re: [EE] 7-16V to 350-400V SMPS boost IC? > > At 02:44 2018-02-14, Sean Breheny wrote: > >I recently was able to make a simple boost converter (no transformer) > >to provide 120V DC at 2mA from a USB 5V supply. About 70% efficiency. > >This is part of a capacitance meter which can measure the variation in > >capacitance vs voltage for characterizing X7R and similar ceramic chip > caps, up to 100V. > > Coolness. > > Few know of this characteristic/limit of MLCC's, but much fewer actually > do even design tools to measure it. > > I would never use a MLCC where this info is not specified in the datashee= t. > I found that TDK does a very good job on it, but then again having a tool > to actually measure this is very cool. Congratulations. > > > > > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .