polfort

Hi there. Looking at the schematic (http://cds.linear.com/docs/Datasheet/3471fb.pdf) on page 16, I am asking myself what kind of diodes are recommended for a boost topology. It is certain that it should be a fast switching diode, its capacity should be as low as possible. What I am in doubt of is the minimum reverse voltage it must handle. I am only referring to the boost up circuit build up around switch 1. As far as I understand, the maximum reverse voltage in that circuit is equal to the max. output voltage. I

Of course I know about setting the feedback ratio using the voltage divider, this is a fundametal of the LT3471. Anyway thank You for that advise. In the meantime I have found another solution for limiting the switching current. Actually I should have thought about it earlier.. By using a RC combination at the Pins Vshdn I am able to limit the current to a value about 1.2A. This is a kind of soft start. For more details I refer to the datasheet. regards ps: the reason I didnt want to add external switching transistors is, that I already have one LT3471 in my design. Thus I didnt want to use two different IC

Hi there. Looking at page 16 of this datasheet: http://cds.linear.com/docs/Datasheet/3471fb.pdf I am wondering if I could lower the Voltage at pins 10 & 6 using some diodes in series. Why I want to do so: (Just looking at one part, namely the positive voltage) The internal switching transistors of the LT3471 are capable of switching a maximum Voltage of 42V, however I want to produce a output voltage of +45V. This would result in exceeding that max. voltage about 5V + the forward voltage of D1. What do You think about it? The second issue is the following: The max. current through the switching transistors is: 1.3A. I already simulated that circuit with LTspice and realised, that the max. current flowing into pin 10 is about 2A. Not continously of course and only during the first 400us. The peaks are 126ns wide and occur with a frequency of 125kHz (8us spacing between them) The switch current limit is specified as 2.6A at min. duty cycle and 2A at max. duty cycle. I am quite not sure if that is the current through the switching transistors.. Hmm, it should.. Hope You could follow..

Just in case that someone else is looking for such a solution.. Meanwhile I have found a Full/Low Speed USB Digital Isolator: ADuM4160

Hello out there. I am wondering if I could build some device based on optocouplers (or other solution), to seperate a USB device from the PC to make it potential free. Of course the device to be seperated could not be powered via USB. In other case I would be forced to use at least a transformer to power the device through USB. Does anyone know how to do that or has even seen such thing before? Any ideas for a solution? Best regards, polfort

The high current occurs as high peaks (in simulation). I think that even if there are onyl small peaks the core could get saturated if I dont choose a proper one. Have already seen inductors with I_sat about 10A Maybe I should look for a transformer to have three coils on one core... I am not sure If I explained the resonance frequency issue well.. By looking after some inductors to fit my requirements I saw resonance frequency as one limiting value among others like I_sat. I dont really understand how the resonance would affect my cirucuitry.. But I think my system works with frequencies much lower than the resonance frequency of the inductor i would choose, so it must be all right..

Hello. I am looking for a Inductor which I want to use in a SEPIC DC/DC Converter. What I need are thre coils (each 25uH) at one core. Saturation current and resonance frequency are not exactly specified yet. After simulating the whole thing with LTspice I_sat turned out the be about 9A. Not sure if I can lower that current. I dont how the resonance frequency should be chosen. My converter works at 600kHz so 2MHz resonance frequency should be ok? What coils should I look for? Best regards, polfort

Thank You. Especially for that Application Note. Which is very useful and helps to calculate the proper values. Besides it makes clear the functionality of a SEPIC converter in detail :) Best regards, polfort

Hello. If You look at Page 32 of this Datasheet: http://cds.linear.com/docs/Datasheet/3757fa.pdf, there is the LT3757 as a SEPIC Converter, delivering +-0.4A at +-12V. Could You tell me if it