Power Supply ATX, Mechanism and Operation. Part 1

7/28/2019 Power Supply ATX, Mechanism and Operation. Part 1

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Power Supply ATX, mechanism and operation.Part 1.

Repairand modernization

Since the power supply is an integral part of the PC, to know more details about it will be interesting to

everyone associated with the electronics and more. The quality of the power supply depends on the whole

work PC.

And so, I think that we should start with the basics for what purpose is the power supply:

the formation of the supply voltage components of a PC: +3.3 V +5 V +12 (extra-12V and-5V)

galvanic isolation between 220 and PC (to avoid hitting his shock, and there was no leakage current when

nterfacing components). A simple example is the galvanic isolation transformer. But for the PC power need

more power, and thus the larger transformer (comp would be a very great :), and transferred to his family

because of the considerable weight, but we passed it :).) For the construction of compact blocks are used in

high frequency power supply transformer, with the frequency order of the magnetic flux in the transformer be

minimal and is less than the cross section of the magnetic coils. Create a light and compact power supply

allows inflated in 1000 and once more frequency voltage transformer. basic principle of BP is the following, the

conversion AC line voltage (50 Hz) in the lane. voltage high frequency square wave (would oscilloscope would

show an example), which is reduced by a transformer, then rectified and filtered. Block Hema pulsed power

supply. 1. Block Converts AC 220V permanent. Composition of the unit: a diode bridge for rectifying the AC

Schematic diagrams for free Catalog of electrical circuits; articles on electronics,assistance on the forum.

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Power supplies from China In the online store. Huge selection of power supplies for asuper low price!

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voltage + f ilter for smoothing the rectified voltage. And also should be (in cheap PSU to save them vpaivaya

not, but I just recommend that when alteration or repair them put) filter voltage ripple from the pulse generator,

and thermistors smooth current surge when turned on. Pictured f ilter is indicated by a dotted line , which we

ound in almost any scheme PSU (but not always on board :)). 2. Block This block generates pulses of a certain

requency, which feeds the primary winding of the transformer. The frequency of generating pulses from

different manufacturers PSU is, somewhere in the 30-200kHz range. 3. The unit transformer is put on the

ollowing functions: - galvanic isolation; - reducing the voltage across the secondary windings to the required

evel. 4. Block This block converts the voltage obtained from block 3 into a DC. It consists of a rectifying diode

and a voltage ripple filter. Composition Filter: choke and a group of capacitors. Often saving capacitors pose a

small-small inductors and chokes. pulse generator in detail. circuit RF transmitter is a high-power transistors

hat operate in the mode key and pulse transformer. PD may represent a single-ended and push-pull converter:

single-cycle: open and close one transistor; - two stroke: alternately open and close the two transistors.

Enjoying picture. circuit elements: R1 - resistance that specifies the offset to the keys. You need to start the

process of a more stable oscillation in the converter. R2 - resistance that limits the base current of the

ransistors, it is necessary to protect the transistors from failure. TP1 - The transformer has three sets of

windings. The first generates the output voltage. The second is the load for the transistors. The third generates

a control voltage for transistors. When the first transistor circuit ajar just a little, because it is applied to the baseof a positive voltage across the resistor R1. In ajar transistor flows current that flows through the winding II. The

current creates a magnetic field. The magnetic field generates a voltage in the other windings. At the III coil

creates a positive voltage, the transistor that opens even more. Process until it happens, until the transistor will

not get in the saturation regime. Saturation mode is characterized in that when the control current applied to the

ransistor output current remains unchanged. only when the magnetic f ield generated by the voltage across the

windings, in the absence of the transistor changes as disappears and EMF in the windings of II and III . When

he voltage across winding III lost, then the opening of the transistor decreases and hence decrease the output

ransistor current and the magnetic f ield that will cause the voltage of opposite polarity. The negative voltage on

he winding III further closes the transistor. The process lasts as long as the magnetic field does not disappearcompletely. When the field is gone, gone negative voltage and the process will go around the circle again.

Push-pull converter works the same, but since there are two transistors, one by one, then such use increases

he eff iciency of the converter and improves its performance. Mainly used push-pull, but if you need low power

and size, as well as the simplicity, the single-cycle. discussed above converters have finished devices, but their

use is complicated by the spread of various parameters such as load output voltage, and temperature

ransducer. Key Management PWM controller (494). encoder consists of a transformer T1 and the transistor

VT1. Mains voltage through a network filter (SF) is applied to the network rectifier (NE) diode bridge, f ilter

capacitor Cf and through the winding W1 is applied to the collector of the transistor VT1. When applied to the

base of transistor rectangular pulse, it is opened and through which the current flows increases Ik. The same

current flowing through the primary winding and the transformer T1 causes that increase the magnetic flux in the

ransformer core and the self-inductance voltage is induced in the secondary winding W2. As a result, the

diode VD appear positive voltage. By increasing the pulse duration on the base of the transistor VT1, will

ncrease the voltage in the secondary circuit, and if the duration of the decrease, the voltage will decrease. By

varying the pulse width on the base of the transistor, we change the output voltage to the winding W1 T1, and

provide stabilization of the output voltages of the power supply. Need a pulse-forming network run and manage

heir duration (latitude). This scheme uses a PWM (pulse - width modulation) controller. PWM controller

consists of: - the driving pulse generator (which determines the frequency of the converter) - control scheme; -

a logic circuit, which controls the pulse duration; - protection scheme. This is a topic for another article. To

stabilize the output voltage of power supply, the circuit PWM controller should " know "the value of the output

voltage. It uses a feedback circuit (or circuit monitoring), performed by optocouplers U1 and resistor R2.

ncreasing the voltage in the secondary circuit of the transformer T1 will increase the intensity LEDs, and

herefore reduce the transition resistance phototransistor (members of the optocoupler U1). This leads to the


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esistor R2 connected in series to increase the phototransistor voltage drop and reduce the voltage at the 1

Shimko. Reducing stress causes the logic circuit component of the PWM pulse width to increase until the

voltage on the 1 st output does not match the specified parameters. The process of reverse when the voltage

decreases. there are two implementations of feedback loops: - "immediate" in the diagram above, the

eedback is removed directly from the secondary rectifier - "indirect" is removed directly from the auxiliary

winding W3 (see figure below), change the voltage on the secondary winding will change it on the winding W3,

which is transmitted through R2 to 1 output Shimka. Below is a diagram of a real PD. 1. The unit is rectified

and filtered AC voltage, and there is a filter on the noise being produced by BP. 2. Block This block forms the

+5 VSB (Standby power), and feeds the PWM controller. 3. The block on the third block (PWM - Controller

494) put the following functions: - control transistor switches; - the stabilization of output voltages; - protection

against short circuits. 4. Unit The structure of this unit comprises two transformers and two groups of transistor

switches. transformer generates a first control voltage for the output transistors. one group of transistors

amplifies the signal generated TL494 and transmits it to the first transformer. transistor group 2 is loaded on

he main transformer, where the main voltages generated supply. 5. The block structure in this block are

Schottky diodes for rectifying the output voltage of the transformer and the low pass filter. The composition

ncludes LPF big capacitors (depending on the manufacturer PD) and inductors, and resistors to discharge

hese capacitors in switched power supply. Some of duty room. differences between standard units of PSUATX standard AT that the ATX power supply source are standard standby power supply. 9-pin (20 pin, purple

wire) terminal voltage is produced +5 VSB which goes to the mat board to power the control circuit power

supply. This circuit provides a signal PS-ON (14 pin connector, green wire.) In this scheme, the converter

operates at a frequency determined by the parameters in the main transformer T3 and nominal values of

elements in the base circuit of the transistor key Q5 - capacity of the capacitor C28 and the initial resistance of

he resistor offset R48 [1]. Positive feedback on the base of the transistor Q5 comes with an auxiliary winding

of the transformer T2 through the elements of C28 and R51. The negative voltage from the same winding after

ectifier elements D29 and C27, if it exceeds the zener voltage of ZD1 (in this case 16) is also fed to the base

of Q5, inhibiting operation of the converter. In this way, control is performed for the output voltage level. Powersupply from mains rectifier to the inverter f lows through the current limiting resistor R45, which, when it fails, you

can replace the fuse current of 500 mA or eliminate altogether. In the circuit of Fig.1 resistor R56 0.5 ohms

nominal included in the emitter of transistor Q5 is a current sensor for excess current of transistor Q5 above

he permissible voltage across the resistor R54 has applied to the base of transistor Q9 type 2SC945 opening

t, and thereby disabling operation Q5 . Similarly, the Q5 is an additional protection and primary winding T3.

R47C29 chain serves to protect the transistor Q5 Surge. As a key transistor Q5 in this model of PD used

ransistors KSC5027. In my previous article, BP was similar elements (duty room.) Now consider the

PD live. 1. Filter elements of network interference generated by the PSU. 2. The diode bridge rectifies AC

220V. 3. Filter capacitance-voltage network. 4. The radiator for the transmitter output transistors and transistor

nverter duty room. 5. The main transformer: isolation from the network and the formation of all the stress. 6.

Transformer for generating a control voltage output transistors. 7. Transformer inverter-duty forming voltage. 8.

The radiator for the Schottky diode. 9. Chip PWM - Controller. 10. Filters output voltages (electrolytic

capacitors). 11. Chokes f ilter output voltages.At this until stop. Thank you al l for such a long note. I hope at

east someone benefited :) Waiting for comments and suggestions on the amendment. Extension will be ...
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Power Supply ATX, Mechanism and Operation. Part 1

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