SPI Mode

Mode CPOL CPHA 0 0 0 Clock idle low, data is clocked in on rising edge, output data (change) on falling edge 1 0 1 Clock idle low, data is clocked in on falling edge, output data (change) on rising edge 2 1 0 Clock idle high, data is clocked in on falling edge, output […]

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MOV (Metal Oxide Varistor)

A MOV is normally open circuit. If the voltage across it exceeds its nominal rated voltage it will very quickly clamp it by becoming very low impedance, shunting an overload through it for instance. When shunting a MOV is dissipating all of the energy across itself and therefore it’s often used in combination with a […]

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PTC / Thermistors

PTC stands for Positive Temperature Coefficient and is simply another name for a thermistor. A PTC device will have a nominal resistance, for instance 1kohm, that it is normally at. If it gets hot then its resistance increases. PTC’s are often used to protect inputs for instance in multimeters but not they are no fast-acting. […]

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Resistors voltage tolerance

Increasing voltage capability Place resistors in series. For example, 5x 200kohm 100V resistors is equivalent to 1 x 1Mohm 500V resistor. Using multiple lower voltage resistors is often cheaper than a single high voltage resistor. Also multiple resistors provides increased creepage distance against a single resistor of the same footprint (can be handy to avoid […]

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Multimeter Input Stage

Input Impedance Voltage Measurement Most multimeters will have an input impedance of 10Mohm. This means it will effectively apply a resistance across what you measure of 10Mohm, potentially affecting the measurement if the source has a high impedance Current Measurement Will depend on the meter, but it might be say 1ohm for the mA range […]

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Collector-Emitter Sustaining Voltage

Transistors are often specified with two collector-emitter max voltages: (Vces) collector-emitter voltage (Vbe=0V) (Vceo) collector-emitter voltage (Ib=0A) Vceo(sus) is the Collector-Emitter Sustaining Voltage and its confusing. It’s basically the the collector-emitter breakdown voltage with the base open circuit, which is the most vulnerable state for a transistor. This diagram from Electrical Ratings and Characteristics of […]

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Mosfet Design Checklist

The basic key checks for using a Mosfet in a circuit design: Drain-source voltage Absolute max rating is well above the max voltage being switched.Allow for maximum voltage peeks and pulses that may be present. Gate-source voltage The voltage you will apply to the gate is within this absolute max rating. Drain current (continuous and […]

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AC vs DC

AC RMS AC is typically quoted as the AC RMS Voltage. E.g. UK mains voltage of 230V AC is 230V RMS. Peek AC Voltage Calculating the peek voltage of an AC RMS voltage: VAC * sqrt (2) Example: 230 V AC RMS * sqrt (2) = 325 V peek Example: 1500 V AC RMS * […]

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Screened Cables

Braided Screen Good strength and flex life (needed in applications with repeated cable flexing) Does work well at all frequency types but performs well and is recommended at low frequency to medium frequencies. Disadvantages Braided shield does not guarantee 100% coverage, typical 70% to 95% coverage (depends on how tight the branded formation is woven) […]

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Flex PCB’s

General design tips Designing a flex PCB is no different to designing a regular PCB in terms of how you go about designing it. Corners Avoid using right angle corners, use curves, to reduce strain on the copper that could lead to it cracking Planes Avoid using solid copper regions, use cross hatch instead. Components […]

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