Low Loss Step Down Converter

Posted on Feb 5, 2014

This circuit arose from the need of the author to provide a 5 V output from the 24 V battery of a solar powered generator. Although solar power is essentially free it is important not to be wasteful especially for small installations; if the battery runs flat at midnight you`ve got a long wait before the sun comes up again. The basic requirement w

Low Loss Step Down Converter
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as to make an efficient step-down converter to power low voltage equipment; the final design shown here accepts a wide input voltage from 9 to 60 V with an output current of 500 mA. The efficiency is very good even with a load of 1 mA the design is still better than a standard linear regulator. The low quiescent current (200 µA) also plays a part in reducing losses. Some of the components specified (particularly the power MOSFET) are not the most economical on the market but they have been deliberately selected with efficiency in mind. When power is applied to the circuit a reference voltage is produced on one side of R2. D1 connects this to the supply (pin 7) of IC1 to provide power at start-up. Once the circuit begins switching and the output voltage rises to 5 V, D2 becomes forward biased and powers the IC from the output. Diode D1 becomes reverse biased reducing current hrough R1. When the circuit is first powered up the voltage on pin 2 of IC1 is below the reference voltage on pin 3, this produces a high level on output pin 6. The low power MOSFET T1 is switched on which in turn switches the power MOSFET T3 via R5 and the speed-up capacitor C4, the output voltage starts to rise. When the output approaches 5 V the voltage fed back to the inverting input of IC1 becomes positive with respect to the non inverting input (reference) and switches the output of IC1 low. T1 and T3 now switch off and C3 transfers this negative...

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