An LED is a special type of diode used as an Optoelectronic device. Like a PN junction diode, it conducts when forward biased. However a special feature of this device is its ability to emit signal in the visible band of the electromagnetic spectrum. A major concern to drive an LED is to provide an almost constant current input. Often LED is driven using batteries or control devices like microcontrollers. However these have their own disadvantages, for example-low battery life etc. A feasible approach would be driving the LED using AC to DC power supply. Though AC to DC power supply using transformer is quite popular and widely used, for applications like driving loads like LED, it proves to be quite costly and moreover it is not possible to produce a low current signal using transformer.
Keeping in mind all the factors, here we design a simple circuit driving a series of LED from 230V AC. This is accomplished using a capacitor based power supply. This is a low cost and efficient circuit and can be used at homes.
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230v LED Driver Circuit Principle:
The basic principle behind this circuit is transformer less power supply. The main component is the X-rated AC capacitor which can reduce the AC voltage to a suitable amount. These capacitors are connected line to line and are designed for high voltage AC circuits. This reduced AC voltage is then rectified, filtered and regulated to produce a low voltage signal to drive two LEDs in series.
230v LED Driver Circuit Diagram:
230V LED Circuit Design:
Here the main intention is to drive a series combination of LEDs by passing a current of about 20mA through them. The first component to design the circuit is a voltage regulator. This can be provided using a Zener diode, but since Zener diode can get heated up easily, we prefer using a voltage regulator IC which could provide accurate results. Here we use LM78L12 voltage regulator IC delivering output voltage of about 12V at maximum 100mA current.
The minimum input voltage for the IC to maintain line regulation is around 18V. Keeping this in mind and the DC rectified voltage of around 20V, we get the minimum negative peak of ripple voltage to be around 2V. The ripple voltage is double the minimum peak and is around 4V. The value of filter capacitor can be calculated keeping in mind the ripple voltage, ripple frequency, quiescent current drawn by the regulator and the maximum load current. This can be established mathematically as:
C = (Iq+Io)/(F * Vr)
For Lm78L12, Iq is around 6mA, the required output current, Io is around 20mA, ripple frequency is double the line frequency of 50Hz and Vr is around 4V. Substituting the values, we get capacitor to be around 65uF. However keeping in account the facts of practical aspects, we chose a 47uF, 25V capacitor.
Since a bridge rectifier is better in full wave rectification with more efficiency, here we use a bridge rectifier with four diodes. The diodes are selected keeping in mind the PIV rating of 100V. Here we use 1N4007.
For a voltage of 230V and output current of 20mA, the required impedance is about 11.5k ohms. For a frequency of 50 Hz, the value of capacitance is seen to be around 0.13uF. However such a value is quite low and we instead chose a value of 0.47uF producing output current of about 33mA. (Based on calculations, a 1uF capacitor can produce current of about 72 mA.
How to Operate LED Driver Circuit?
The resistors R1 and R2 limit the inrush current from the AC mains supply. This AC voltage is further reduced by the AC capacitor C1 which drops the voltage by around 210V. This reduced AC voltage is then rectified by the bridge rectifier to obtain a rectified DC voltage of about 20V. This DC voltage is then filtered by the filter capacitor which allows the AC ripple signals to pass through it and the DC signal is thus fed to the regulator IC. This filtered and rectified DC signal is then regulated by the IC voltage regulator. The voltage regulator used here ensures a maximum output current of 100mA, which is further reduced to 20mA using the resistor. Thus a regulated output of about 12V, 20mA is used to drive two red LEDs.
The resistor R1 acts as a bleeder resistor allowing the capacitor C1 to discharge once the power is switched off. This provides a great deal of safety.
Applications of 230V LED Driver Circuit:
- This circuit can be used for home lightening systems.
- It can be used as an indicator circuit.
- One can fix this circuit with the door bell to give indication.
Limitations of LED Driver Circuit:
- Since 230V AC supply is being directly used here, this circuit can be dangerous.
- This circuit is best suited for domestic applications using single phase supply. This is because in case of three phase supply, if any of the phases accidently touches the input terminal, it can prove to be quite dangerous.
- The capacitor can produce spikes at mains fluctuations.