3 ~ 7V negative voltage converter tracking power input
Circuit function
In a logic system working with a + 5V power supply, if the analog circuit uses a + 5V unipolar power supply, the accuracy near zero volts will deteriorate. In this case, using a negative power supply will receive good results. If the power consumption is very small, it is more convenient to use a voltage converter. The typical product is ICL7666, but the regulation performance of this product is not very good.
Circuit working principle
This circuit uses a special converter IC MAX634 to convert the + 3 ~ + 7V power supply to -3 ~ -7V, and the tracking action is understandable from the point where the resistances of R3 and R4 connected to the VPO terminal are equal.
Considering that it may be applied in battery-driven instruments, the MAX634 is equipped with a low battery detection circuit and uses R1 and R2 to set the voltage. The internal reference voltage is 1.25V. If a + 5V power supply is used, if it is output from LBO, according to 5 / 1.25 = 4, the voltage division ratio of 1/4 should be used (R1 = 3R2)
The ripple in the output is the same as the oscillation frequency (about 47KHZ), about 100MVP-P.
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