200w Atx PC Power Supply
200w Atx PC Power Supply
200w Atx PC Power Supply
Introduction
Here I bring you wiring diagram of PCs power supply of DTK company. This power
supply has ATX design and 200W performance. I was drawed diagram, when I repaired
this power supply.
Schematics diagram
Circuit description
This power supply circuit uses chip TL494. Similar circuit is used in the most power
supplies with output power about 200W. Device use push-pull transistor circuit with
regulation of output voltage.
Line voltage goes through input filter circuit (C1, R1, T1, C4, T5) to the bridge rectifier.
When voltage is switched from 230V to 115V, then rectifier works like a doubler.
Varistors Z1 and Z2 have overvoltage protect function on the line input. Thermistor
NTCR1 limits input current until capacitors C5 and C6 are charged. R2 and R3 are only
for discharge capacitors after disconnecting power supply. When power supply is
connected to the line voltage, then at first are charged capacitors C5 and C6 together
for about 300V. Then take a run secondary power supply controlled by transistor Q12
and on his output will be voltage. Behind the voltage regulator IC3 will be voltage 5V,
which goes in to the motherboard and it is necessary for turn-on logic and for "Wake on
something" functions. Next unstabilized voltage goes through diode D30 to the main
control chip IC1 and control transistors Q3 and Q4. When main power supply is running,
then this voltage goes from +12V output through diode D.
Stand-By mode
In stand-by mode is main power supply blocked by positive voltage on the PS-ON pin
through resistor R23 from secondary power supply. Because of this voltage is opened
transistor Q10, which opens Q1, which applies reference voltage +5V from pin 14 IO1 to
pin 4 IO1. Switched circuit is totally blocked. Tranzistors Q3 and Q4 are both opened
and short-circuit winding of auxiliary transformer T2. Due to short-circuit is no voltage
on the power circuit. By voltage on pin 4 we can drive maximum pulse-width on the IO1
output. Zero voltage means the highest pulse-width. +5V means that pulse disappear.
Start of supply
Somebody pushes the power button on computer. Motherboard logic put to ground input
pin PS-ON. Transistor Q10 closes and next Q1 closes. Capacitor C15 begins his charging
through R15 and on the pin 4 IC1 begins decrease voltage to zero thanks to R17. Due to
this voltage is maximum pulse-width continuosly increased and main power supply
smoothly goes run.
Normal operation
Output voltages +5V and +12V are measured by R25 and R26 and their output goes to
the IC1. Other voltages are not stabilised and they are justified by winding number and
diode polarity. On the output is necessary reactance coil due to high frequency
interference. This voltage is rated from voltage before coil, pulse-width and duration
cycle. On the output behind the rectifier diodes is a common coil for all voltages. When
we keep direction of windings and winding number corresponding to output voltages,
then coil works like a transformer and we have compensation for irregular load of
individual voltages. In a common practise are voltage deviations to 10% from rated
value. From the internal 5V reference regulator (pin 14 IC1) goes reference voltage
through the voltage divider R24/R19 to inverting input(pin 2) of error amplifier. From the
output of power supply comes voltage through divider R25,R26/R20,R21 to the non
inverting input (pin 1). Feedback C1, R18 provides stability of regulator. Voltage from
error amplifier is compared to the ramp voltage across capacitor C11. When the output
voltage is decreased, then voltage on the error amplifier is too decreased. Exciting
pulse is longer, power transistors Q1 and Q2 are longer opened, width of pulse before
output coil is grater and output power is increased. The second error amplifier is
blocked by voltage on the pin 15 IC1.
PowerGood
Mainboard needs "PowerGood" signal. When all output voltages goes to stable, then
PowerGood signal goes to +5V (logical one). PowerGood signal is usually connected to
the RESET signal.
Look at circuit connected to output voltage +3.3V. This circuit makes additional voltage
stabilisation due to loss of voltage on cables. There are one auxiliary wire from
connector for measure 3.3V voltage on motherboard.
Overvoltage circuit
This circuit is composed from Q5, Q6 and many discrete components. Circuit guards all
of output voltages and when the some limit is exceeded, power supply is stopped.
For example when I by mistake short-circuit -5V with +5V, then positive voltage goes
across D10, R28, D9 to the base Q6. This transistor is now opened and opens Q5. +5V
from pin 14 IC1 comes across diode D11 to the pin 4 IC1 and power supply is blocked.
Beyond that goes voltage again to base Q6. Power supply is still blocked, until he is
disconnected from power line input.
Links
Pi
Signal Color 1 Color 2 Pin Signal Color 1 Color 2
n
1 3.3V orange violet 11 3.3V orange violet
2 3.3V orange violet 12 -12V blue blue
3 GND black black 13 GND black black
4 5V red red 14 PS_ON green grey
5 GND black black 15 GND black black
6 5V red red 16 GND black black
7 GND black black 17 GND black black
8 PW_OK grey orange 18 -5V white white
9 5V_SB violet brown 19 5V red red
10 12V yellow yellow 20 5V red red