5V step up converter
DC-DC converter printed circuit board
Using the TPS61087 integrated circuit from Texas Instruments you can build a high efficiency power supply with just few electronic components. This step up converter circuit can provide an output regulated voltage up to 18.5 volts and 0.3A load current for input voltages between 2.5 and 6 volts. The components from the follow circuit diagram are calculated for a 5V output voltage, using a lithium polymer battery for supply.
DC-DC converter schematic
The maximum current which can be delivered at 5V by this circuit is about 1.6A. By connecting pin 9 of TPS61087 to Vcc or ground the switching frequency can be set to 1.2MHz or 650kHz. This offers the possibility to optimize the design either for the use of small sized components or for higher system efficiency .
The output voltage can be calculated using this formula:
Vout=1,238Vx(1+R2/R3)
For R3=18k and R2=56k we have Vout=5.089V, if R2=47k then Vout will be 4.47V.
For low output ripple a low ESR ceramic capacitors must be used. The C4 capacitor connected to the soft start pin minimizes inrush current at startup. The thermal shutdown is triggered at a junction temperature of 150°C, preventing damages due to excessive heat. A NiZn core toroid for L1 inductor construction can be found in electronic ballast of some CFL ( Compact fluorescent Lamp ).Download circuit schematic in pdf format from here.
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Last updated January 2011