12V to 16V 2A DC-DC inverter

[complete picture]
A DC-DC inverter able to convert unregulated 12V DC input to 16V DC at a rated 1.6A. With a heatsink it seems to cope fine driving loads at up to 2.1A.

I originally built this little inverter to power/charge my VAIO PCG-C1X Picturebook laptop from the 12V supply of my motorcycle. It's also been useful for extending the otherwise woeful battery life of the VAIO itself when used in conjunction with a decent lead-acid battery.

I take no responsibility for what you do to your VAIO, blah blah blah...

parts list

power plugs

[the power widget] Because I couldn't find a source for the weird Sony DC power plug, I chopped the one off my AC adaptor, leaving about 10cm of cable, and soldered a pair of male/female inline DC connectors to the chopped cable ends. The inverter could then be connected via the resulting widget.

Since then, I've received this info from the C1-Forum mailing list (thanks to Bob Hawbaker) :

Date: Mon, 26 Jun 2000 11:34:12 -0500
From: "Terry J. Neville" 
Organization: Lind Electronics, Inc.
Subject: Re: Power Supply for Sony C1X/505

We obtain our pre-molded cable and connector from a company in the far east.
It's called a #MP205 connector. I have not seen it sold in local retails
either. If someone wishes to purchase one of our premolded cables we can make
them available by calling #800-659-5956 at $6.00 each plus shipping. Please
note that the newer #PCG-C1X Sonys now use a rectangular connector and we have
not been able to source that one yet.     Thanks, Terry Neville


I soldered the components to a generic prototyping PCB, with wires or the component legs themselves forming interconnections. I used rigid solder pins to terminate the input and output leads, tying a knot to prevent stress.

The whole PCB fit snugly into a small plastic bulkhead mounting case with wire inlets that I found locally at Jaycar.

Refer to the photos and the schematic diagram below for construction details. Note the small aluminium plate bolted between the regulator tab and the case, forming a heatsink. The bolt holds the entire circuit inside the case.

[construction pics]

how it works

The circuit is a boost step-up regulator based around an LM2577-ADJ (pdf, 896k) voltage regulator chip and a few other discrete components. Resistors R1 and R2 set the regulated output voltage.


A switch inside the voltage regulator closes between pins 4 and 3, causing current to flow through the inductor to ground. When the switch is released a few microseconds later, a back-EMF 'kick' is produced by the inductor, resulting in a positive pulse with respect to the input voltage. This pulse charges the output capacitor via the schottky diode, which tends towards an equilibrium voltage.

The switch continues to oscillate, the diode preventing the switch from shorting the output capacitor during the 'on' phase. The output voltage is monitored via the voltage divider R1/R2, causing the duty cycle of the switch oscillator to be continuously regulated in order to maintain a constant output voltage under varying loads.