Circuit calculators

Calculators for everyday electronic circuit design. Work out power consumption and running cost, resistor dividers, LED current limiting resistors, power supply efficiency, op-amp gain and RC filter component values.

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  Frequency ⇔ wavelength

  Convert between frequency and wavelength, including the permittivity of the board. For antenna length and PCB transmission line design.

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  RC filter — cutoff frequency

  Work out the cutoff frequency of an RC filter from the resistance and capacitance, and pick component values for a low-pass filter.

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  Resistor voltage divider

  Calculate the mid-point voltage of a resistor divider, including the maximum and minimum once component tolerances are taken into account.

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  LED circuit design

  Calculate the current limiting resistor for an LED. Get the current and its spread from the supply, the Vf and the resistor value.

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  Power consumption from current and voltage

  Work out power consumption from current, voltage and duty cycle. For sizing a supply and for PWM or pulsed circuits.

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  Power supply efficiency

  Calculate the conversion efficiency of a DC-DC converter or power supply from its input and output voltage and current.

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  Inverting amplifier

  Calculate the gain of an op-amp inverting amplifier from the ratio of the feedback resistor to the input resistor.

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  Capacitance for a pulse current

  Calculate the capacitance needed to supply a pulse of current, from the output current, voltage and duration.

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  Electricity cost from rated power

  Estimate the running cost of a device from its rated power and hours of use. Get the cost per day, per month and per year.

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  Convert battery capacity in mAh to Wh

  Convert a battery capacity in mAh to energy in Wh. For IoT and portable device design.

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  Voltage drop across a resistance

  Calculate the voltage drop across a resistance from Ohm’s law, V = I × R, given the resistance and the current.

• Synchronous buck converter: efficiency, ripple and waveforms

  Calculate duty cycle, efficiency and output ripple for a synchronous buck converter, and see the inductor current and output ripple waveforms.

• FPGA/MCU I/O Buffer Standards & Drive Strength

  A reference on FPGA/MCU I/O buffer standards (LVCMOS, LVTTL and more), how Xilinx, TI, Renesas and STM32 configure them differently, plus a calculator that estimates rise time from drive current and load capacitance.