DC Power Supply: A-D-A

Thread Starter


Joined May 7, 2007
Greetings everyone:

I am a new member, and currently a college student about to graduate in less than two weeks. Although my degree is in chemistry, I recently decided that I really didn't want to do organic chemistry research for the rest of my life, so I decided to try out some new fields. I am taking my first real course in electronics this semester, in which I have a final exam tomorrow (don't worry, I'm not asking for exam help).

Anyway, frequently throughout class, my professor made the remark that in his experience with electronics, a good portion of the problems and failures occur in the DC power supply. He also said that there have been very few technological advances with regard to power supplies in the last 30 years, such as that used by a laptop computer. Also, in that lecture, he pointed out how there is significant energy loss in the transformer coils, rectifiers, and filters, much of which causes heating.

This got me thinking about an alternate method of producing DC voltage from AC mains. Basically, I was thinking of a method that would
1. Digitize the incoming mains AC signal using an ADC.
2. Convert the sinusoidal digitalsignal into a flat digital signal through some sort of logic circuit.
3. Convert the flat digital signal into DC using a DAC.

At this point in my education, I would not know how to accomplish step 2, but I'd be surprised if it couldn't be done, given what humanity has accomplished with digital logic circuits.

Anyway, I am curious to know what research has been done in this area (I'm sure someone came up with this idea before me), and how the energy efficiencies of this method compare to energy efficiencies of existing power supplies.


Joined Apr 2, 2007
are u talking about transmission of power using dc
form what i know,
the steps described by u are some what similar to conversion of analog signal
to digital, but when you talk of power supplies a lot more practical complications
are involved.
first, there is no need for exact d/a conversion according to signal as no data is being transferred we only want to transfer power there is a great deal of difference between the two.
also d/a conversion is different in the sense that data transmission is
of importance here and power supply is used to amplify or even encode or decode the signal like in opamp .
in general the power associated with supplies is so high that digital ckts wont
even last against it. the heat dissipation wud easily burn away the whole ckt.
i believe the voltage drops across these circuit wud be much more than
what we have with conventional methods.

try reading abt smps for some development in this field.
btw ac transmission and distribution is far more advantageous than dc.

btw organic chemistry is one of the most conceptual and beatiful subjects i have ever learned,
reaction mechanism is the best (isnt it interesting to be able to predict product of any 'never seen before reactants")


Joined Jan 10, 2006
Most variable speed drives do this.
They convert AC to DC, then recreate an AC sinewave of variable frequency using PWM and filters.


Joined Apr 2, 2007
Most variable speed drives do this.
They convert AC to DC, then recreate an AC sinewave of variable frequency using PWM and filters.
my knowledge is limited in this case,
wud u plz care to elaborate a little as to why and how,
is it conversion of ac to dc power, if so why is it required?

John Luciani

Joined Apr 3, 2007
Your professor is correct about the unreliability of the power
supply. Next on the list is the fan.

He is not correct about the advances in power supply technology.
Power supplies have evolved quite a bit in the last 30 years. Check
out the DC-DC converters at www.vicr.com. Check out the various power
supply controllers at Linear Technology, TI and OnSemi. I have a small
switching power PCB layout with three converters at
My designs use the LTC and OnSemi controllers.

The power supply in your PC is not advanced since one of the
main design goals is price. The laptop is more advanced since
two of the main design goals are efficiency and size. The laptop
supply will trade-off price since laptop users are willing
to pay for a smaller machine with longer battery life.

The problem with using ADCs and DACs and logic is that all of those
devices were not designed to process power efficiently. One of the
most efficient ways to get to DC from AC is a bridge rectifier and a
capacitor. To get an isolated low voltage DC you would convert your
rectified AC input to high frequency AC signal. The AC signal would be
connected to a step-down transformer and rectified to a low voltage

(* jcl *)