So if the output is set to 60V and the input ranges from say 20V to 40V, the maximum load (with a suitably designed practical inductor) isĮxample2: The required application conditions are Vin ranging from 4.5V to 5.5V. These define the input/output voltage conditions for any suitable application. We see that the input voltage must be below 40V and the output voltage must be below 65V (since Vswmax > Vo and VICmax > Vinmax). We read off the equations corresponding to Figure 10 in this table and we get the following checklistĥ. The relevant selection criteria for suitability are in Table 4. For more detailed design equations for this topology one can refer to the design table under 'Boost' in AN-1246 at. Now we consult Figure 10 (Part 1 of this article). The corresponding figure is Figure 10 (in Part 1 of this article).ģ. Referring to the summary chart for Type 1 in Figure 18 (Part 1 of this article), we see that it can be used as say a positive to positive Boost. We identify that the LM2585 is a Type 1 IC by our nomenclature.Ģ. The following steps are required in this analysis.ġ. Can it be used in a Boost topology? And for what applications? Its input operating voltage range is 4V to 40V. The MIN value of its internal current limit (see its Table of Electrical characteristics) is 3A. The datasheet is available at for more details. We now present some typical examples to clarify the procedure further.Įxample1: The LM2585 is a '3A Flyback regulator'. If not, an additional external rail will need to be created to run the op-amp stage. Note that if the required minimum Vaux+ value, is still low enough, it may be possible to connect it to an available DC rail. This limit equation is therefore also provided in Table 4. Since the voltages on these pins are fixed by virtue of the resistors, if the resistors are considered fixed, the only way is to ensure that the common-mode condition is met is to set the op-amp supply rail Vaux+ sufficiently higher. We require that the voltage on both the input pins of the op-amp stay within this allowed range, or the op-amp cannot be considered fully functional. For the LM324 series this number is specified to be 1.5V below the upper supply rail and this parameter is hereby called v' in this article. For example, note that an op-amp has a specified input voltage common mode range. Some of the relevant aspects of op-amps must be kept in mind. This means that irrespective of how the schematic actually labels them, i.e., which is Vo (or –Vo) and which is ground, these nodes must connect to the upper and lower output rails respectively. Note that the inputs to the op-amp are labeled Vo_hi and Vo_lo. They are respectively alternatives to Figure 11 (negative to positive Buck-Boost using Type 1 IC), and Figure 12 (negative to negative Buck using Type 1 IC). They are shown in Figure 23 and Figure 24. There are two ways of setting up such a differential amplifier. As mentioned, a more accurate sensing scheme for better output regulation can be implemented by using an op-amp (like the LM324). Returning to some of the issues in Part 1 of this article, in Figure 11 and Figure 12, a crude voltage dependent current source was used for output regulation.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |