Project main features
High power 24V DC DC converter
The DC/DC converter has the following main features:
DC DC converter schematic description
Description of the DC/DC converter project .
The schematics for the DC/DC converter is built around the UC3843 generic, low cost PWM controller. This very common PWM controller generate a duty-cycle modulated square wave ranging from 0 to 100%, at a user fixed frequency of 100KHz. The operating frequency is fixed via the C13 capacitor. In practice the UC3843 sense the output voltage via the resistive partitor P1/R5 that (thanks to the P1 trimmer) allow the user to change the DC/DC output voltage.
The ESR value of the capacitors must be minimized at 100KHz frequency, the ESR resistance at 50-60Hz, commonly listed in the capacitors datasheets, is not useful for DC/DC converter selection.
: the inductor toroid must be selected with high care. The right toroid must have a quite low "Al" parameter (below 100nH/n^2) and have sufficient room to fit all thewire turns. In the reference example we used an iron powder toroid with the Al=80nH/n^2, with 15 turns of 1.25mm diameter wire. The inductor value should be in the range 15..20uH, and we obtained L1=80*15*15=18uH. The room in the PCB for the inductor is about 23-24mm, for this select an appropriate size for the toroid and wire.
DC/DC (below 100W) critical components partlist
In the "Below 100W" DC/DC converter version, the components are non critical, for this can be replaced with some equivalents with similar characteristics.
DC/DC (over 100W) critical components partlist
In the "Over 100W" DC/DC converter version, the components are critical, for this can be replaced with some equivalents with selected characteristics.
DC/DC converter non-critical components partlist
The non critical components are the following.
DC DC converter PCB assembly
Start the DC/DC assembly with the resistors and the capacitors. All the assembly should start with the lower height components. Mount a socket for the IC, then go to soldering the TO220 packages (mosfets and diode). These components are connected directly to a copper plane, for this the soldering iron temperature should be quite high (400-450 celsius degrees) in order to have a good junction. Mount at the end the inductor (remove the isolator with high care) and the input/output capacitors (470uF, 63V). To test the circuit, power supply the circuit with 12V and with a light load measure the output voltage: set via P1 the right voltage and check that there are no components with high temperature. Start to use the DC/DC converter, with attention to use "normal" components for power under 100W and "selected" components for power over 100W (see schematic description).
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