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Timer Based Cell Phone Charger Circuit

Timer Based Cell Phone Charger Circuit

A simple cell phone charger with timer circuit is presented in the following article, which could be used for charging a given Mobile phone for a specified predetermined length of time. The idea was requested by Mr. Saad.



Circuit Objectives and Requirements

  1. Could you design me this charger circuit ? Input 230V 60 Hz, and the output 3 USB port for charging Smartphones.
  2. What I need in this circuit is a Timer (Three sets of time), 30 mins, 60 mins and 120 mins.
  3. So I connect my phone to any of the three usb port and press (on/off) switch then the time start for example 60 mins then the power cut off.
  4. Hope you understand my request.

Circuit Diagram

Timer Based Cell Phone Charger Circuit

Circuit Operation

The proposed cellphone charger circuit with timer can be seen in the above figure, the design primarily comprises of an IC 4060 timer stage and a DC to DC multi cell phone charger stage.

The cell phone charger section is a standard LM338 based charger circuit, wherein the output is bifurcated into 5 individual charging outputs facilitating charging 5nos individual cellphones. From these outputs 3 channels could be utilized for the intended 3 cell phone charging, at a rate of 1500mAH each. The series resistors may be accordingly calculated using Ohms law, as given below

R = V/I = 5/1.5 =  3.33 ohms, 10 watts each

R2 in the LM338 circuit must be appropriately adjusted to achieve around 5V across the output terminals or across C2 terminals.

The timer stage is made up of the IC 4060 whose pinouts are also configured in its standard timer/counter mode.

P1 may be adjusted to get a delay time of around 120 minutes on pin#3, which would allow pin#2 to produce a delay of 60 minutes, and pin#1 a delay of 30 minutes.

Initially when power is applied across the indicated  mains input terminals, the cellphone charger circuit with timer does not respond and stays deactivated.

However, the moment the given push button is pressed, causes the N/O side of the relay to get connected with the other unconnected mains wire.

This momentarily connects the AC  mains with the transformer leads, which in turn powers the rectifier stage enabling a momentary DC supply input for the IC 4060 timer stage. 

This momentary supply to the IC 4060 stage activates the counting of the timer, and simultaneously produces an initial zero potential at the base of the relay driver BC557 transistor, switching ON the relay from N/C to N./O points.

As soon as this happens, the relay contacts now take-over the push-to-ON switch connections and allows the AC to flow through these contacts into the transformer primary.

This ensures that, now even if the push button is released, the circuit is able to get latched into the powered position enabling the LM338 to begin charging the attached cell phones and the timer IC 4060 to count the stipulated amount of time via the pot P1.

As soon as the counting of the IC 4060 gets elapsed, pin#3 (pin#1/2 whichever is selected) turns high, switching of the BC557 and the reverting relay contacts from N/O to N/C.

This action instantly switches OFF and disconnects the mains AC from the transformer, deactivating the whole process and bringing the whole system into its original standby position.

This cellphone charger timer circuit could be yet again initiated simply by pressing the push button for the next charging cycle.

Time Delay for the IC 4060 can be calculated using the formula:

f(osc) = 1 / 2.3 x Rt x Ct

where Rt = R2 +P1 (in Ohms)

Ct = C1 (in Farads)

Parts List

Resistors, All 1/4 watt 5%

2M2 = 1
22K - 1
10K = 1
1M = 1
120 ohms = 1
1M pot= 1
5K pot = 1

Capacitors
1uF/50V non-polar = 4
0.33uF = 1
470uF/25V = 1
1uF/25V electrolytic = 1

Diodes, 1N4007 = 5
Transistor, BC557 = 1
IC, LM338 = 1

Relay,12V/400 ohm = 1
Push button = 1

Transformer = 0-12V/5 amp

Output resistors as per the given formula

SHARING IS CARING!


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!



34 thoughts on “Timer Based Cell Phone Charger Circuit”


  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. Sir Good Morning!! could i ask you a image or schematics on what to do with unconnected pin of any IC?
    thank you very much Sir, im sorry to ask because i cant understand when you say it has to be connected to a logic level.

    • jindro, the inputs of a CMOS IC such as which start with 74XX or, 40XX or 4XXX consist of logic gates in them, for example nand gate, NOT gates etc. When one of these gates are not used or are unconnected, their input pins should be terminated either to the positive line or to the negative supply line…in order to keep them stable.

    • the indicated transformer/switch wires will become the inputs for the 220V AC, and a 3rd earthing pin could be included which could be connected with the chassis or the enclosure if a metal enclosure is used, or simply with the body of the transformer.

  3. Hello mr. Swagatam,
    Hope you are doing well.
    Would you kindly provide me with a software that I could use to design this circuit.

    Regards.

    • Hello Saad,

      Do you mean PCB? Sorry I am not practically familiar with any PCB designing software that I can recommend, although you could find plenty if you search online

  4. hi swag.i have a rechargeable flahlight with capacitor of 584J 400V .it always puff up.it has no resistor across it.what value should i use.

    • Hi Dennis, It is happening simply because the capacitor is a bad quality capacitor, change it with a good quality one, preferably from some reputed brand. because if it is rated at 400V it can never puff up. the resistor is not compulsory, it may be included to discharge the cap while it is unplugged from mians, to avoid a discharge shock to the user in case he touches the plug pins accidentally.

  5. thanx .hope u don’t mind me asking for electronic circuits because you are such a BIG HELP . i’m just starting to hook in electronics.till next request.god bless.

    • Hi Dennis, it may be any related item but still it will require a lot of accuracy and calculations to build it…
      by the way I have seen that whenever I sit beside my wifi 4G device it becomes faster…it seems my body acts a like an antenna.

  6. hi swag.thanx for fast response.i just opened my email now since my last message to you. can you help me decide what is the best soldering iron wattage and soldering lead diameter to use
    in pcb’s.thanx

  7. gud day swagatam.can u help me provide:
    1. a circuit for rechargeable battery operated soldering iron like ISOTIP with adjustable current to vary wattage from 30w to 60w with digital wattage display using 4.2v lithiun or 3.7v 18650 if possible.
    2.circuit for adjustable current to vary wattage soldering iron with digital watts display directly on 220 v. thanx

    • Good day Dennis, you can accomplish it with a simple IC 555 PW circuit as shown below:

      https://homemade-circuits.com/2012/05/make-this-pwm-based-dc-motor-speed.html

      you can replace the motor with your soldering.

      I do not have a digital watt meter circuit at the moment, however you can use a digital ammeter which will allow you to get reading equivalent to watts…you can calibrate the meter range into watts…so basically it will show amps but the modified calibration will enable it to convert the readings into watts…as per my assumption.

    • Saad, you will have to practically check and identify which pinout of IC 4060 gives the required pulses equivalent to seconds or minutes…but before that you will need to build the 4033 counter circuit successfully….

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