12 Volt Zener Regulated Charger

12V Voltage Regulated Charger

Most of the battery chargers do not have current and voltage regulation provisions. The step down voltage is simply used for charging. These chargers develop internal resistance so the output voltage drops when the battery is connected to the charger. Moreover, fluctuations in the AC line also affect the charging process. This current and voltage regulated charger eliminates these drawbacks and can provide well regulated 12 volt DC for charging.

0-15 1 Ampere step down transformer drops 230 volt AC into 15 volt AC which is rectified through the bridge rectifier comprising D1 through D4. The rectified DC is then made ripple free by C1 and send to the collector of the medium power NPN transistor T1 to give regulated output. Resistor R1 and Zener diode ZD are used for both voltage and current regulation. Output current from the emitter of T1 depends on the value of R1 which can be changed according to the requirement using the ohms law.

12 volt Zener diode gives constant 12 volts to the base of T1 so that output voltage remains 12 volt irrespective of the input fluctuations. Diode D5 is polarity protector that prevents short circuiting if the polarity of the battery is reversed. LED indicates the charging process.

Voltage Regulated Charger Circuit Schematic

12 Volt Zener Regulated Charger

12 Volt Zener Voltage Regulated Charger Circuit Schematic


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  • Colin Mitchell

    A battery reaches about 13.6v when charging and this voltage is reached very quickly due to the bubbles of gas on the plates creating a voltage called “floating charge.”
    This means a charger with an output of 13.8v will only have a HEAD VOLTAGE of 0.2v and will only deliver a few hundred milliamp.
    So your suggestion is quite worthless.
    Before giving any suggestion, build the circuit and test it yourself before giving worthless advice to unsuspecting beginners.

  • V.Sambath kumar

    Hi Mohan,

    The circuit can be modified to get better results by changing the value of the zener diode to 15v and there by getting 13.8v for charging,
    can also provide a 3watts resistor in series to the +ive ter of bat for
    limiting the charging current,depending on the bat ah for example 22 ohms for 7.5Ah bat.
    Thank you
    Regards V.Sambathkumar.

  • lim

    Sir, what need to be change when we required an output of 5V and 2A maximum current???

  • malvare

    The best solution is a LM317 regulated power supply circuit with an extra transistor if you needs more than 1A and very good heat sinks

  • bikram

    not mention about the npn transistor no like c945 or s 9014 why u not regulate negative supply in output section why nt used electolytic smoother……………… not well regulated circuit try ur own risk please take improvement..

  • Danny Ronquillo

    we already used regulated 6A, 14Volts DC power supply to charge 42AH UPS battery and it draws 5.5A charging current @ 13Volts DC.

  • Colin Mitchell

    It is similar to some of the older mobile phone charger circuits. Mobile phone-charger circuits have a lower ouput voltage.

  • Phani

    Is this circuit same as that the circuit in a mobile phone charger have ?

  • Phani

    Is this circuit same as that the circuit in a mobile phone have ?

  • wasim

    can any one help me to build a 5V 500mA transformerless power supply for leds

    • Colin Mitchell

      You have already tried to get replies to this request on other forums. The answer is NO. You don’t now how dangerous a transformerless power supply is.

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