Showing posts with label v. Show all posts
Showing posts with label v. Show all posts
Friday, October 17, 2014
LED at 230 V
Small circuit to run a LED on line voltage (English)
This little circuit allows to connect a LED to line voltage. A LED can not handle with 230V AC and needs a current which is limted to ca. 15mA. The first issue is simply solved with a diode which eliminates the voltage in reverse-biasing. The current is limited by the combination of the resistor and capacitor. Used at AC capacitors work as frequency dependent resistors. You can simply calculate the capacitive resistance of the capacitor by the following formula:
Based on a frequency of 50Hz and a capacity of 220nF you get a reactance of ca. 16kΩ. This is just perfect for a LED. The resistor prevents that the capacitor does not charge that abruptly.
Hinweis
Attention. This circuit works with life threatening line voltage. All parts of this circuit are connected to the grid! You have to make sure that it is not possible to touch any parts of the circuit at any time. You have to unplug the circuit everytime you want to check it.Part list
- C1: foil capacitor 220nF, 250V~ (stick to the values!)
- R1: 2,2kΩ
- R2: 220Ω
- D1: 1N4007 (or comparable; must be suitable for 220V/230V)
- LED1: standard LED
Circuit diagram
Source by : Benedikt Wirmer
Tuesday, January 21, 2014
15 V output regulated power supply circuit with uA723 and 2N3055
The supply receive from 220 /120/110 Volt AC , then lowered by the transformer . Then receives +20 Volts DC from rectifier / filter section. This applied to pin 11 and 12 of the IC uA723/LM723 , as well as to the collector of the 2N3055 series pass transistor. The output through R1 and R2, providing about 7 V with respect to ground at pin 4. The reference terminal at pin 6 is tied directly to pin 5 , the non inverting input of the error amplifier . For fine trimming the output voltage , a potentiometer can be installed between R1 and R2. A 100-pF capacitor from pin 13 to pin 4 furnishes gain compensation for the amplifier.
Base drive to the 2N3055 pass transistor is furnishes by pin of the uA723. Since desired output of the supply is 1 Ampere, maximum current limit is set to 1,5 Ampere by resistor Rsc whose value is 0,422 Ohm. A 100uF electrolytic capacitor is used for ripple voltage reduction at the output. A 1 kOhm output resistor provides stability for the power supply under no - load conditions. The 2N3055 pass transistor must be mounted on an adequate heatsink.
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