Ni-MH Battery Charger For 230v (Transformer less / SMPS)

Hello ….

        It is my first blog. Basically I am an electronic enthusiast. But I love all fields of engineering works, where the engineering creativity exists. I start my first blog with an electronic circuit.

       Here I am making a Ni-MH battery charger which works from AC 230v. It is a SMPS base circuit. SMPS is a better alternative for the transformer based power supply. It has very good characteristics over the traditional transformer power supply. It has very good output voltage stability. It is less weight and it consumes only little space. So SMPS is preferred over the transformer power supply.


    The complete circuit making steps given in my instructable page. Please visit it. Link is given below.

https://www.instructables.com/member/YADUKRISHNAN+K+M/

SMPS

SMPS block diagram

         It is Switched Mode Power Supply. Here also use a transformer but it is work at high frequency. At high frequencies the impedance of the transformer winding increases so; we need a lower number of turns instead of the 50 Hz line frequency. So we reduce the size and weight problem. For high frequency there need a high frequency oscillator. It produce a square wave, its duty cycle is varied to make different average voltages to stabilize the output voltage irrespective of the input voltage variation. This method is known as PWM. By this we overcome the instability in output voltage in traditional transformer power supply. So, now a day we use SMPS instead of transformer power supply. But remember that transformer has its on properties, so for some specific purposes we use the transformer power supply.

Circuit Diagram

Charger circuit diagram

Components

IC - TL431 (1)

Transistor - Mje 13001 (1)

Zener - 5v2 / 0.5w(1)

Diode - 1N4007 (2) , 1N4148 (3)

Capacitor - 2.2uF/50v (1) , 3.3nF (1) , 100pF/1Kv (1) , 220uF/18v (1)

Resistor - 1K (1) , 56E (1) , 79E (1) , 470K (1) , 2.7K (1) , 10E (1)

preset resistor - 100K (1)

LED - green (1) , red (1)

SMPS transformer (1) - from old mobile charger

All components are obtain from old PCBs, It is good, Because it is a recycling process. So you try all components from old PCBs. OK.

Circuit Description

           Here the input AC is converted to DC by using a single diode half wave rectifier. No filter is used here because it consume less power, so no need of filter (we design as much as simple). Then its positive connected to the transformer primary winding, other terminal of primary is connected to ground via a driver transistor and a resistor. The transistor controls the PWM. The transistor is also work as oscillator. The resistor is low vale one, it is act as a fuse to protect the circuit when the transistor fails and also reduce the transient effects. The transistor base terminal is connected to ground and Vcc through resistor to bias the transistor. The oscillator circuit is work by using a transformer feed back circuit. Here the transformer has an auxiliary  winding it provide the necessary feedback for the oscillator. The auxiliary voltage is also proportional to the output voltage, so it is used to maintain the output reference voltage for voltage stability. The feedback voltage for oscillator is given through a capacitor to produce a lag. It is 180 degree out off phase with the base voltage. So the circuit continuously on and off , That is it is work as an oscillator. Its working frequency in the range of KHz. The diode and capacitor in the auxiliary act as a rectifier and filter to produce a dc voltage. It is a negative voltage. It is given to the base of the transistor through a zener diode to stabilize the output voltage by controlling the ON time of the transistor(PWM). That is, the voltage OFF the transistor when that voltage override the zener voltage(zener conduct in reverse bias only when the voltage higher than zener voltage). So by this the stabilization off output done.
          In the secondary side the diode and capacitor act as the rectifier and filter to produce a steady DC voltage. An indicator led is connect through a resistor to indicate the power on state. The TL431 IC is a programmable zener diode. It is set through a preset resistor at the reference pin to produce a negative output when the battery fully charged(output is when at 4.2v). An indicator led connected at the output to indicate full charge state.

Working

          When power supply is on the transistor on by get a positive voltage at the base through the resistor. So the transistor ON and complete the primary coil and flow a current through it and  this cause an induced emf at the auxiliary coil and in the secondary coil. The auxiliary coil is connected to base via a capacitor so at the base there get a negative voltage, this turnoff the transistor. So the negative voltage at the base vanishes and the transistor again turn on by the resistor and continuous this process. The zener diode is turnoff the transistor earlier when a higher voltage (above the zener voltage) is get at auxiliary coil. Auxiliary voltage is proportional to the output (secondary) voltage so the output voltage is stabilize by using the PWM method. The output working is not complex its just a rectification and filtering. 

Completed circuit component side

Completed circuit soldering side

The complete PCB making steps given in my instructable page. Please visit it. Link is given below.

https://www.instructables.com/member/YADUKRISHNAN+K+M/

Thank You.   

Bye...  See you in the next project.

For more project videos visit my YouTube channel "CreativE EngineerinG"