LED bulb driver circuit

 LED bulb driver circuit is an non isolated , transformerless power supply circuit which is used in LED bulbs to provide controlled dc voltage and current. In LED bulbs SMD LEDs are connected in series to produce light. The main problem which comes in LED bulbs is to provide constant voltage and current to all LEDs irrespective to input voltage, ambient temperature and current variations. In this article a general overview will be provided to understand LED bulb circuit working.

Main task in LED bulbs is to provide protection against over voltage, over current,  short circuit, over temperature for which a 8 pin IC is used. BP2831,  HW9315,  PT4554 are some LED driver 8 pin ICs. These ICs have inbult 500 V Power MOSFET in it, which is used to provide precise and controlled supply to series connected  LEDs. MOSFET is a gate controlled switching device which gives stable voltage and current to LEDs so that LED bulb works for long time efficiently. Further to control current and voltage a inductor is connected in series and capacitor is connected in parallel respectively. These IC senses all parameters and gives supply to gate accordingly to provide stabilze supply to LEDs.

LED driver circuit diagram:- 

When 230 V AC supply is given to the circuit, it get rectified to 311 volt dc voltage where it get further smoothed by a electrolytic capacitor C1. As Capacitor does not allow sudden change in voltage, it provide slow voltage rise at pin number 4 which acts as gate of POWER MOSFET when voltage rises upto threshold value then MOSFET get turn on and supply goes through series connected LEDs and inductor to Drain (Pin 5 & 6) then to source (Pin 7 & 8) and path gets complete.  

Here inductor provide smooth current to LEDs by opposing sudden change in current.
Fig. 1 LED driver Circuit using BP2831A IC

This LED driver IC changes switching of MOSFET in such a way that voltage across series connected LEDs remain always same irrespective to input voltage variations and corresponding excess voltage is dropped by series inductor L1. Frequency of MOSFET is decided by T/ON  and T/OFF time of MOSFET. value of inductor can be calculated by XL = 2πfL.

Author:- Amarjeet Singh Jamwal authored articles on Basic Electronics EngineeringElectric Traction, and Electronics Practical for INFO4EEE Website

link for more detail for data sheet is given below 

Link for BP2831A IC  

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