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Mains-powered LED night-light

I'm probably re-inventing the wheel, but here are a few variations of a mains-powered night-light f

  1. alec_t
    I'm probably re-inventing the wheel, but here are a few variations of a mains-powered night-light for 230-250V, adaptable for 110-120V.
    The component values given are for 240V 50Hz operation with an LED current of ~ 7mA. I've found that quite sufficient for a night-light for a child's bedroom.
    If you do need a brighter light the current can be increased in proportion to the value of the capacitor C (e.g. double the capacitance gives 14mA), or additional LEDs (or LED inverse-parallel pairs in the case of the second circuit) can be connected in series with the LED(s) shown. If C is increased then a 1/2W resistor should be used for R.

    Circuit operation
    The fuse protects the circuit and its value must not be increased.
    The reactance of C behaves like a 'resistor' to drop the voltage. For 240V 50Hz mains the RMS current through it will be ~ 7mA (70mA per microfarad). When first switching on the light the current may be much higher but is limited by R to protect the LED(s) and capacitor.
    In the first circuit, a bridge rectifier feeds the LED so that it conducts on both halves of the mains cycle. This doubles the light output compared to half-wave rectification and also reduces flicker.
    In the second circuit, one LED conducts on one half-cycle and the other LED conducts on the other half cycle. Each LED protects the other from reverse voltage greater than ~3V.
    The only 'wasted' power for the circuits shown is ~ 49mW in R.

    Adaptation for 110/120V operation
    Double the capacitance of C and use a 1/2W resistor for R. Assuming a 60Hz supply the current will be ~8mA

    All components are potentially at mains voltage and could give a fatal shock unless care is taken to shield them from touch. They must be housed in a fire-resistant insulated enclosure. For added safety a 1 megohm bleed resistor should be connected across the capacitor to discharge it when the mains is switched off.