Power supply circuit » Car adapter http://apowersupply.com Sat, 04 Feb 2012 16:06:35 +0000 en hourly 1 http://wordpress.org/?v=3.1 3 volt car adapter http://apowersupply.com/3-volt-car-adapter-10.html http://apowersupply.com/3-volt-car-adapter-10.html#comments Sun, 08 Jan 2012 05:55:16 +0000 aPowerSupply.com http://apowersupply.com/?p=10 This 3 volts Car Adapter circuit is based on a standard LT1074CT switching regulator IC. The schematic shows the LT1074CT used as a positive step-down or ‘buck’ converter. The ‘switcher’ is used to convert a +12-volt car battery voltage down to +3 volts for use with the personal hi-fi’s and handheld games for the author’s two boisterous children on long car journeys. Note at under ten years of age, children will rarely be hi-fi aficionado’s and are generally not concerned with any noise generated by the ‘switcher ‘circuit.

3 volts car adapter circuit schematic

3 volt car adapter

The circuit is connected to the car +12-V system via the cigarette lighter socket — is advisable to use a fused version of the cigarette lighter plug. The +12-V arrives on the board via screw- terminal block J2. Diode D2 provides a reverse voltage protection, while C3 decouples the input to the switcher IC.

The LT1074CT briskly switches the supply voltage on and off in response to the signal applied to its F/B input, to the extent that the average output voltage is at the required level. The values of potential divider resistors R1-R3 have been chosen to attenuate the output voltage so that there is 2.5 V at the F/B pin. The difference between the attenuated output voltage and the internal 2.5-V reference is used to control the modulation effect of the switcher.

Components R2 and C2 provide frequency stabilisation for the feedback loop. Inductor L1 along with the LT1074CT form the main switching components, while C1 provides decoupling for the output load. The 3-V output voltage is taken from screw terminal J1. With this circuit built, boxed up and installed in your car, you can look forward to possibly your first ‘quiet’ long car journey.

]]> http://apowersupply.com/3-volt-car-adapter-10.html/feed/ 0 USB Power from Cigar Lighter Socket http://apowersupply.com/usb-power-from-cigar-lighter-socket-377.html http://apowersupply.com/usb-power-from-cigar-lighter-socket-377.html#comments Sun, 18 Dec 2011 22:25:21 +0000 aPowerSupply.com http://apowersupply.com/?p=377 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.

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.

USB Power Socket Circuit Diagram

usb power socket diagram

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