![Automotive 12V to 5V USB charger assembled PCB]
This project presents a nominally 12V to 5V step down power adapter for use in a motor vehicle to supply 5V at up to 2A from a USB socket.
It is intended to be plugged into a cigar lighter socket in a car or other vehicle and can be used with any device that is normally charged from a 5V USB power outlet at up to 1.8A.
Although most recent cars already have built in USB sockets suitable for such use, some may not be capable of supplying enough current to charge devices such as tablets and smartphones. Many cars designed before about 2010 may not have USB outlets at all.
However, most vehicles have cigar lighter outlets allowing a high current connection directly into the vehicle 12V supply. This is clearly unsuitable for use to directly charge 5V input devices so some form of voltage reduction and - due to the noisy and very roughly regulated battery voltage behaviour - voltage regulation is required.
Many of the designs for 12V to 5V adapters already freely available on the web use linear regulation, which will dissipate somewhere in the region of 15W to 20W at a 2A load at maximum alternator output and so require significant heat sinking.
Most do not provide any form of input over-voltage protection against alternator load dump (See: https://en.wikipedia.org/wiki/Load_dump) or input reverse polarity connection.
Most do not provide any form of output over-voltage protection in the event of a short circuit failure of the series voltage regulation element, which could result in the connection of the 12V input supply directly to the 5V output.
It is not clear what level of protection is provided by commercially available devices offered for sale.
**A review of many of the designs and products offered on the web did not inspire confidence in the safety of connecting an expensive, high-end tablet or smartphone to any of them.**
**This project presents a design offering clearly defined protection of both input and output connections.**
**1) Input voltage**
8V to 55V DC
**2) Load Dump and input reverse polarity protection:**
The input side is designed to operate from the nominal 12V vehicle supply but is able to withstand transients, including - in the event of accidental or intermittent vehicle battery disconnection - alternator load dump, up to 55V. It is also protected against accidental reverse polarity connection of the input supply.
**3) EMI filtering:**
The input side also has low pass filtering to reduce noise being imported into the regulator from the vehicle supply.
The same filtering reduces switching noise being exported from the regulator into the vehicle supply to minimise the possibility of interference with other vehicular equipment.
The filtering is also designed to ensure the stability of the input to the regulator at all input voltages.
**4) Output short circuit and over-voltage protection:**
The 5V output is protected against output short circuit faults.
The 5V output is also protected against device failure that could result in the 12V input being imposed directly onto the 5V output, such as a series switch transistor failure in the step down regulator chip. In the event of such a failure, the instantaneous voltage imposed on the 5V output is clamped to just below 5.7V. A few milliseconds after the output over-voltage is clamped to 5.7V, a series 2A fuse blows, providing a permanent disconnection from the vehicle supply.
The presence of input and output voltages are indicated by separate green (input) and red (output) LEDs.
**5) Output voltage and current:**
5V+/-0.25V at up to 1.8A (limited by the rating of the output side USB connector, the regulator chip can supply up to 2A with an up-rated connector).
* Please note however, that this is not a cheap project to build for two reasons.
a) the L4978 switch mode regulator is one of the few through hole parts available that meet the 8V to 55V input voltage range requirement. Whilst there are cheaper devices available in surface mount packaging, in the interests of making this project accessible to the widest range of users, it was decided to avoid the need for any specialist soldering skills or equipment;
b) The design uses high quality components that are specified and sourced to meet strict design requirements. As is the rule for any switch mode power supply design, it is strongly recommended to build this project using only the specified components or alternatives of known equivalent specifications.
***Buying cheap parts of unknown specifications can result in damage to the adapter, the load on charge and possibly to the user through unexpected overheating and consequential risk of fire and even explosion.***
* L4978 Datasheet:
* Applications Note:
AN1061: Designing with L4978, 2A high efficiency DC-DC convertery:
* The SMPS stage is designed according to ST.com Applications Note: AN1061
DESIGNING WITH L4978, 2A HIGH EFFICIENCY DC-DC CONVERTERY
based on the specification given in:
4.1 Electrical Specification
Input Voltage range: 8V-55V
Output Voltage: 5.1V ±3% (Line, Load and Temperature)
Output ripple: 34mV
Output Current range: 1mA-2A
Max Output Ripple current: 20% Iomax
Current limit: 3A
Switching frequency: 100kHz
Target Efficiency: 85%@2A Vin = 55V, firstname.lastname@example.orgA Vin = 12V
The 555 timer could possibly be one of the most commonly used IC in DIY electronics projects. You can find many circuits and applications based on 555 Timer IC that have already been designed and published in [EasyEDA open source community] by our users, You can simply open any free design, edit it and get ideas from these open source designs.
Here we list some simple and interesting circuits projects and applications, tutorials and books for beginners and advanced engineers. With these resources you will learn how the 555 works and will have the experience to build some of the circuits below.
##Simple 555 Timer Circuits and Applications##
There are many applications of 555 timers. Here as an example we will discuss 555 Timers used in Lamp Dimmer, Wiper Speed control,Timer Switch,Variable duty cycle fixed frequency 555 oscillator etc. You can open any of these circuits and edit it to you want.
NE555 is configured in astable (bistable) mode, due to the pin 3 of the IC is a coupled MOSFET or (if you want,it can also be a power transistor that matches the pins of the MOSFET), you can connect a bigger load such as DC motors or 12VDC bulbs to adjust the light intensity or speed of rotation by potentiometer.
**2.[Lamp Dimmer using NE555]**
This project is about simple lamp dimmer project using NE555 timer IC. PWM method is used for controlling the brightness of the lamp. This method is very power efficient and low cost compared to linear power control circuits. In PWM method the load is driven using a high frequency square wave and the duty cycle of this square wave is varied for controlling the power delivered to the load. The efficiency of this circuit was found to be 95.5% when tested in the lab. The same circuit can be also used to control the speed of DC motors.
**3.[Wiper Speed control using NE555]**
This project is about a simple automobile wiper speed control. The speed of the automobile wiper can be adjusted using a potentiometer using this circuit. The circuit operates from 12V DC and can be fitted to any automobile operating on 12V electrical system. With slight modification, the same circuit can be made to operate on 24V systems also.
![wiper speed control]
**4.[Timer Switch using 555 and relay]**
A simple circuit that powers a led strip when the momentary switch is pressed, then shuts it down automatically after XX seconds. There is a potentiometer to adjust the length of the delay but I need the light to be ON for at least 30 seconds. You can change the values of capacitor C1 and resistor R1 to what you need. A 100uF capacitor and a 500K potentiometer should give an adjustable delay of near 0 seconds to 55 seconds.
![Timer switch schematic]
**5.[Variable duty cycle fixed frequency 555 oscillator]**
A fixed frequency variable duty cycle oscillator based on a 555 timer and using the push-pull output to drive the RC timing through two routing diodes, a pot and a series resistor to limit the min/max duty cycle to something sensible at around 9%/91%.
![Variable duty cycle fixed frequency 555 oscillator]
###How 555 timer works###
There are three modes of output with the 555 timer – monostable, bistable, and astable. Each mode has different characteristics, and will determine how the 555 timer outputs current. The following articles well explained the three modes of the 555 timer.
part 1, [555 Timer Basics – Monostable Mode]
part 2: [555 Timer Basics – Bistable Mode]
part 3: [555 Timer Basics – Astable Mode].
###555 Timer Circuits Site###
The [555 Timer Circuits] site contains lots of the electronics info you need to know about the 555 Timer. With over 80 different electronic circuits that you can build.
###Book to learn 555 Timer Circuits and Projects###
If you want to learn more about the 555 timer, you should read, understand and do things on your own with 555 IC. the book [Timer, Op Amp, and Optoelectronic Circuits and Projects Book Vol. 1 By Forrest Mims] is a great resource to have on your bench. The book has lots of information about the 555 timer, OpAmps, and other IC’s too.
![555 Timer Book]