USB DC Power Supply from Cigar Lighter Socket

The diagram shows the circuit of a versatile USB power socket that safely converts the 12V battery voltage into stable 5V. This circuit makes it possible to power/recharge any USB power-operated device, using in-dash board cigar lighter socket of your car.

The DC supply available from the cigar lighter socket is fed to an adjustable, three-pin regulator LM317L (IC1). Capacitor C1 buffers any disorder in the input supply. Resistors R1 and R2 regulate the output of IC1 to steady 5V, which is available at the ‘A’ type female USB socket. Red LED1 indicates the output status and zener diode ZD1 acts as a protector against high voltage.

USB Power Socket Circuit Diagram:


USB Power Socket Circuit Diagram

Assemble the circuit on a general-purpose PCB and enclose in a slim plastic cabinet along with the indicator and USB socket. While wiring the USB outlet, ensure correct polarity of the supply. For interconnection between the cigar plug pin and the device, use a long coil cord as shown in Fig. 2. Pin configuration of LM317L is shown in Fig. 3.


Author by: P. MARIAN Source By: EFY



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USB Reading Lamp

Light your table top with this cool White LED Lamp. It is powered from the USB port and is ideal to take notes while browsing internet. The USB port can provide 5 volts and 100 mA current which is sufficient to light the LED lamp.

USB Reading Lamp Circuit diagram:

USB Reading Lamp Circuit diagram

Power to the circuit is derived from the USB port using the standard A type plug. To give continuous regulated power, Zener regulation is employed. Resistor R1 restricts base current to T1 so that output will be current regulated. Since White LED requires minimum 3.6 volts, 4.7 volt Zener is used to provide constant 4.7 volts to LEDs. Resistor R2 restricts LED current to around 20 mA, so that they will not be damaged. Connect the power lines to USB plug observing correct polarity. Use a reflector for LEDs to get maximum illumination.

 Pin out of SL 100

Pin out of SL 100

Author: D. MOHANKUMAR


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Sealed Lead Acid Battery Charger Using LT3755

This Sealed Lead Acid Battery Charger is deigned using the LT3755 DC DC controller. The LT3755 is a DC DC controller designed to operate as a constant-current source and supports a wide input voltage range from 4.5 up to 40 volts and a can provide a maximum output voltage of 70 volts.

Sealed Lead Acid Battery Charger Circuit Diagram:

Charger Circuit Diagram

Also the LT3755 is a DC/DC controller can be used for any other applications where is needed a high efficiency ( like LED drivers ).

The main features of this Sealed Lead Acid (SLA) Battery Charger circuit are : adjustable frequency 100kHz to 1MHz ,low shutdown current:

The Sealed Lead Acid (SLA) Battery Charger based on the LT3755 require an input voltage between 8V to 40V and has VFLOAT = 13.5V and VCHARGE.

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USB-Chargeable Emergency Inspection Light

Described is one USB-chargeable Emergency Inspection Light for in-lab use, wired around a hi-efficiency 5mm-white LED. The power-bank of this circuit is a 1F/5.5v (yes, 1 Farad!) super capacitor. Just connect your finished circuit to an active usb port, and push switch S1 when necessary. The result is a short-time white light from LED1, generated by the charge stored in C1. Fuse F1 in the circuit is added for usb port protection, and diode D1 works as a “one-way” switch. Resistor R1 limits the current (and hence the light output) through LED1.

USB-chargeable Emergency Inspection Light Circuit Diagram:

Light Circuit Diagram


In the prototype, 1F/5.5V super capacitor took up from an old video cassette recorder was used. If you are using the commonly-available 1F/2.5v type super capacitor, you should connect two of them in series as shown here. Note that, this reduces the total capacitance, but doubles the voltage rating. Only one drawback of this idea is the undepicted price of the super capacitor; 1F/2.5v super capacitor in an Indian online store costs about 300 Indian Rupee (~ $5)!

Inspection Light Circuit Diagram

(author’s prototype realized using cannibalized parts)

 Emergency Inspection Light Circuit Diagram


(1 farad super capacitor)

Note: Super capacitor is a special capacitor (electrochemical double layer capacitor) offers ultra-high capacitance and ultra-low equivalent series resistance. Super capacitors hold up power for long duration, and that’s why the LED in our circuit works for a finite duration even after it’s unplugged from the USB port.

Author: T.K. HAREENDRAN


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Digital-DC Step-Down DC-DC Converter with ZL2106

The ZL2106 is an innovative power conversion and management IC that combines an integrated synchronous step-down DC/DC converter with key power management functions. The power supply circuit build around the ZL2106 IC can provide an output voltage from 0.54 volts up to 5.5 volts  from an input voltage range between 4.5 volts and 14 volts.

Digital-DC Step-Down DC-DC Converter Circuit Diagram:

Converter Circuit Diagram

DC-DC Converter Circuit Diagram


Internal low RDS(ON) synchronous power MOSFETs enable the ZL2106 to deliver continuous loads up to 6A with high efficiency. The ZL2106 also supports phase spreading to reduce system input capacitance. This power supply circuit diagram will provide a 3.3 volts output from an 12volts input.

Main features of this converter are:Integrated MOSFET switches, 6A continuous output current, ±1% output voltage accuracy, Snapshot™ parametric capture, I2C/SMBus interface, PMBus compatible, Internal non-volatile memory (NVM).


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