ATX Power Principle, Part 3: standby circuit type 1: In the direct

3.2.Standby circuits using blocking oscillator
Type 1: In direct (illustrated by circuit stabdby source LC-200)

300Vdc power supply from the circuit bent / primary filter.
Effects components:
Q12: blocking oscillator, and standby power.
R55/R56: the natural Q12, resistor acts as a "primer"
D23: Resetting feedback to maintain oscillation, the output voltage in Anode D28 is negative (-).
C19: Filter leveled voltage feedback.
R57: Distribution, preliminary steady voltage feedback.
ZD2: Cut when feedback voltage (-) from point A voltage less than the voltage of it.
C3/L2: parallel RC frame resonance, the resonant frequency of this framework which is calculated by the formula: f = 1/2Πxsqrt (L2xC3). You may wonder about this, but for an AC signal (+) and mass sources considered as short (through the filter capacitor) so for AC shall R55/C3 regarded as parallel with L2.
L1: Download Q12.
L2: Coil voltage feedback with the task of creating the effects Lenz used to maintain oscillation.
R58/C23/D32: Removal reverse voltage, anti vibration breaks.

Principles:
Voltage 300V through R55/R56 natural vacuum B Q12, the voltage at the base of B ~ 2V (measuring DC when interrupts feedback) makes saturation Q12 open always.
When Q12 saturation current through it as follows: (+) 300V L1 → C leg EC Q12 → Q12 → mass. Since this line passes through L1, according to the characteristics of the coil (always generate line against the line through it on the phenomenon of electromagnetic induction) should flow through the L1 does not reach saturation increased from from. So the magnetic field in the transformer core STB cun increased gradually (from school).
According to induction Lenz's law, the magnetic field increases slowly on STB transformer core will rise above all the windings of the transformer 1 touch power productivity.
Induced voltage on L2 is bent by D28 and of C19 removed dienap filtration one-dimensional negative polarity (-) at point A, is stable (relatively) by R57, stability depends on the product of T = R57xC19 (time constant - the drainage area of ​​the circuit time constant RC)
The voltage at point A via ZD2 to the B leg of Q12. As a negative voltage pulse it with the positive voltage due to natural R55/56 taken to, the result is 2 voltage trng mixed together making B Q12 leg voltage to 0, the current through L1, Q12 loss .
When the through L1, Q12 loss from school on it also lost to the magnetic field in the transformer core = 0 leads to the induced voltage on the transformer windings STB = 0. Of course, the induced voltage on the coil L2 loss.
Because the voltage across L2 loss, D28 does not give negative voltage. Still because C19 has loaded (before), so now it makes discharge voltage at point A can not lose now, the C19 discharge will maintain the sound level at the foot of B Q12 adding 1 more time, Q12 continues to lock. Go when negative voltage discharge by the C19 is not large enough to open ZD2 ZD2 will break, not negative voltage to B leg Q12, this time B leg only positive pressure by R55/56 brought to and it opened saturation. A saturated cycle / lock begins.

Oscillation frequency of the circuit:
Determined L2/C3. Since this is a parallel resonance when the resonance line through L2 is max, then the feedback is max enough ZD2 open, Q12 will lock when the resonance is lost. In other words, the oscillation frequency of the primary circuit by 1/2Πxsqrt (L2xC3).
Fact, when Q12 lock, line L1 through not lost immediately due to the magnetic field in the transformer core is still (small) rise to the induced voltage on the L1 direction (+) C Q12, voltage exists in the very short time (like a reverse sweep in the performance of the TV, CRT) should be of great value (~ 800V source of new life) give rise to two consequences:
- Q12 can be punctured by pressure too great to overcome, the Q12 is designed using high voltage.
- Q12 leakage current due to large voltage, resulting current through L1 is maintained, the induced voltage on L1 maintenance makes the voltage negative (-) B Q12 maintaining and not recoverable voltage natural (+) and so the cycle saturation / lock not implemented. In other words, the range loss.
FIX: When high pressure foot C Q12 will launch D32 neutral voltage on C23. If you calculated the value will see the voltage at the base of C Q12 and the voltage across C32 is in the opposite direction, neutralize each other. R58 resistor is increased to neutralize a very short time, eliminate the phenomenon Q12, recovery cycle fluctuations.

Note: To understand that you review the theory of operation mode of BJT (mode A, B, C) and the principle of the resonant circuit, the parameters resonance.
Induced voltage on L3 generated by the magnetic field change due to continuous Q2 saturation / lock. This voltage is shaped / standby voltage filter removed.
Line 1: Resetting by D30 12V feed variations, amplified stimulated.
Line 2: Resetting by D29, C23 filter and voltage regulator IC 7805 5V removed for purple wire, high voltage through the resistor for PS-ON, raising circuit PG algorithm.

The damage:
Phenomenon 1: Explosion fuse, replace it.
- Chap Q12, or Q12 replaced by low voltage BJT, plugged in always. For this source, the oscillation frequency of 13kHz, the Q12 can be used C2335, 13007 is OK.
Note: The source of life, the frequency of 19Khz not use the C2335 too (because UCE max voltage of the low-C2335)

The phenomenon of 2: standby voltage loss.
Loss of oscillation by:
- Cut resistance all (R5/56).
- End D28 feedback loss.
- Dry, lost, foot rot C19 not, smoothing filter, feedback pulse ZD2 lock.
- Terminate or change the wrong value feedback ZD2 loss.

Phenomenon 3: Loss 5V STB
- Off the D29, 7805
- Short-C23

Phenomenon 4: Apply standby loss
-, Diode leakage bent.
- Dry filter capacitor.