basic page 2 about the used Powersupplies    Page No.:D04-2
WARNING : At the following circuit diagrams i have marked up with light red shading the so called
                    "primary side" of the supply. In this areas there are voltages up to 400 Volt present!
Such voltages are lethal dangerous !
                    Never access this areas with present "live Voltage" ( i.e. supply "powered up" ) !
                    Red highlighted areas may only be accessed while powersupply is disconnected
                    from main powersource ( disconnected from powercord ) !
                    Never attempt this areas without ensuring the demanded precautions of safty !
                    Only experienced Users with advanced knowledge and successfully solved safty training
                    may work at this red highlighted areas !
                    Read red colored text with safty warnings ! Do not ignore this warnings !
                    Ignoring this warnings may cause electric schock with lethal results !

For security reasons in nearly all powersupplies it was common habit to have a kind of "separation method" to keep strict
the primary section apart from the secondary section. The 2 most common methods used have been using either a coil-
separation or a optocoupler, where the LED side was connected to secondary side while phototransistor was connected to
primary side. The picture below displays left side the coil method and right side the optocoupler method and picture of the
seperations units themselves.

The feedback path may be explained in simple functions:
Pick signal from secondary voltage path to be used as feedback signal,
clean that signal from disturbing dirt, maybe some small amplification for use at the seperator ( voltage level )
seperated transmission to isolated other primary side,
cleaning the feedback signal and amplification for use in primary side,
injection of the feedback signal to control/regulation circuit at the primary side.

For use as feedback signal there have been 2 variable parameters to take influence to the primary section and
thereby controlling the secondary section:
length of positive puls to control secondary amount of current ( i.e.  how much ampere )
and frequency used in transformer to control voltage level ( i.e. how many volts ).

Some feedback paths instead seperated "dirtsignal" from secondary section and pushed that signal back to primary section
targeting to eliminate the "dirtsignals" at secondary side ( similar to audio amplifiers ), by adding a inverted dirtsignal at the
primary section with pupose to "eliminate" dirtsignal by compensation. This kind of control was rather more rare and therefor
will not be explained here.

In generaal the first kind of feedback was used to keep control to the transmissionprocess from primary section to the secondary
section to avoid waste of power and keep amount of "powerconsumption" low ( not wasting unused power ).

Just to explain visually the previously explained example options of control by feedback by control of the
voltage switching by the powertransistor at the maintransformer:

In fact the range of control is ( not like in the picture above ) not that large..... the true range of variation to execute control
is limited to maximum of aproximatly only +/- 15% !

Now lets take a view to the details of a typical feedback path with an optocoupler:
In this plan the seperation circuit is a optocoupler NEC2501.  Weīll take our focus
to the secondary part of the feedback trail.
The LED part of nearly all optocouplers use the voltage and powerregulation chip
TL431 to ensure that the "basic setup" of the LED has a kind basic brightness and
lightemmision. The path A still contains a portion of squarewave signal taken from
the supplybranch at the transformer side E  before it passes the filtering coil ( choke ).
This squarewave portion will cause a kind of flickering at the LED in the frequency
used at the transformer in the secondary section.

After the choke at position F the supplyvoltage is cleaned from that portion of squarewave
voltage. The path B measures behind the resistor R2 the amount of ampere flowing along
the supplytrace to the connected device ( i.e. Mainboard ) and besides also adding the small
portion of AC "dirtvoltage" of the final voltagesupply to the compensation measurements
and also affecting the lightemmision of the LED , while the path C is used to
measure the voltage at that powertrace by taking a fixed portion of voltage between the
resistors R4 and R5 and adding that amount of voltage to the "base connector" of the TL431
and therefor slightly causing a variety in brightness of the LED above of the TL431.

The capacitor C9 blocks the DC voltage in the path C to the connection of the path B and
is only passed by AC "dirtvoltage" portion of the supply-voltage.

In this kind of feedback you will allways be able to identify the typ of feedback by the presence
of some kind of 6 pin device as optocoupler and in most cases added to that ( the transistor alike
looking ) 3 pin case of the IC TL431. The points that change from different powersupplies
are the components between the "transmission"unit consisting of the optocoupler and the TL431
and the components added in between that units and the measuring points at the traces picking
the voltages to be measured.


While path B measures amount of current (ampere) passing along the path of - 5 Volt, the path C measures voltage at - 5 Volt rail and path D measures the Voltage of + 5 Volt rail.
Now lets take a view to the details of a typical feedback path with a coil:

The voltage in Path A taken from +12 Volt path is regulated and therefor 
is only used for "pullup" of the base of Q5. The Q5 in
fact gets its signal from the output of the comperator 311 ( U2 ).
The one reference of the comparator is resulting from path of B
by the Path CR17 and R18 at the base of transistor Q2 and the emitter of Q2 with R15 setting up the defined voltage at the emitter and at the alternate variable path of B getting the
squarewaves from the - 5 Volt coil passing R12 and interacting with CR16 and C25 picking the small rest of the disturbing
"dirt-voltage" at the junction of R15 and CR16 and  adding that voltage up to the reference at the collector of Q2 to
the fixed reference made by the 2 diodes CR20 and CR21 together with C27. This is compared to the predefined voltage
at the output
of the 741 OPamp. The "setting" of the 741 OPamp is resulting from path C taken from the -5 Volt trace
behind the regulation along the R19 resistor, the trimming resistor R21, and the 2 remaining resistors R22 and R23. C25 is just blocking a portion of the DC voltage and passes part of the remaining frequent "dirt-voltage" to the Ground while other part of the measured voltage is taken from Path D by the resistor R24 to the "hot" end ( positive end ) of the trimming resistor R21.

later a powersupply became common that had additional regulation / adjustment section:

And more sophisticated the powersupply of the IIGS with quite complex feedback sections:

       due to european laws and german court decision:
 I hereby declare no responsibility to any "deep links" resulting from the links in this page. I have no influence to the pages linked hereby in this page and the
 contents in those pages. I therefor canīt take any kind of responsibility to contents in the pages, where these links direct the readers browser to nor to the
 contents resulting from following up links from those pages. The reference to contents by this links is dependent ro the status of the date when the links have
 been set ( April 2013 ) and it might occur that references and contents may change by the fact that domains may have been discontinued from their former owners.
 In such cases i canīt take any kind of responsibility to the changed contents. this is specialy valid to banners, advertisements or merchandising links in the targeted