ATX Power Principle, Part 4: standby circuit type 2: In indirect

300Vdc power supply from the circuit bent / primary filter.

Effects components:

Rhv: limiting resistor, the output voltage follows it to about 270V.

R3, R5: Natural (each) for Q3.

Q3: standby power, here use Mosfet 2N60.

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R4: Creating negative feedback voltage, using voltage drop on R4 as a sensor to check the current through Q3, through which will be adjusted to Q3 stable operation.

ZD1: Voltage Stability foot G, in order to protect not to Q3 wide open, avoid for Q3 being punctured.

C34: Capacitor discouraged, Q3 protection no breakdown when subjected to large cathode voltage of the reverse scan period.

R9: Resistor distributed pressure, thereby stabilizing the (relatively) Q4 Q3 G and C foot.

L1: Load Q3. L2: Scroll feedback.

Q4: Warping differential pressure for the foot G Q3, acting commutation voltage feedback.

D5: Resetting the next in parallel adapter circuit to create a voltage (+) at the point A.

C8: Filter feedback voltage.

U1: from optical circuit, negative feedback voltage stability STB.

R17: improving low resistance, with the purpose of the feedback voltage disconnect to the foot B Q4 when the voltage dropped to ~ 2V.

C4, R6, D3: The reverse voltage, anti vibration breaks.

Principles:

300V voltage from circuit bent / Filter Primary through Rhv also ~ 270V supply for the circuit. This voltage is divided into two lines:

Route 1: At PN6, PN4 to the base D Q3.

Line 2: Over R3, R5 an R9 pressure rate of natural match for Q3, and Q4 (pin C). You notice Q4 with differential pressure for G Q3 should if saturated Q4, the voltage at G Q3 ~ 0, Q3 locked.

By natural (prey) by R3, R5 should Q3 open. The current passing from 270V through L1, the DS Q3 down mass, closed circuit. 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 shaped by D5 and filtered by C8 removed the voltage 1 dimensional is negative (+) at point A, is stable (relatively) R16, stability depends on the product of T = R16xC8 (time constant - the drainage area of ​​the circuit time constant RC)

The voltage at point A through CE U1 (over fiber) to pin B of Q4. Because the voltage is positive so it makes Q4 saturated. When Q4 saturated, the voltage at the foot C Q4 ~ 0, where C Q4 connected to the foot G Q3 UgQ3 ~ 0 for Q3 lock.

When the current through Q3 lock, lines through L1 lose, from school on L1 also lost makes 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.

So voltage the L2 loss should not take the pressure (+) at point A again. Yet for C8 was loaded (at first) so it makes discharge voltage at point A can not lose now, the C8 will discharge to maintain the (+) at the foot of B Q4 another first time and Q4 tieps on storm Republic, Q3 continue to lock. Until the voltage (+) by discharge C8 not enough to (≤ 2V), the R17 will interrupt the feedback voltage, B foot Q4 will reduce the O, Q4 course. When Q4 lock the natural voltage by R3, R5 and Q3 open recovery. A cycle open / locked started.

Oscillation frequency of the circuit:

Be determined by L2/C8/R16. This is the serial resonance occurs resonance, the voltage across L2 is max, then the voltage at point A is max enough to R17, Q4 saturated. If the voltage resonance is lost on L2 min, voltage point A min not enough to win the voltage drop on R17 to Q4, Q3 unlock (fixed) and the current through L1 is fixed not create from school do induced voltage on all the coils of the transformer STB lost. In other words, the oscillation frequency of the primary circuit by 1/2Πxsqrt (L2xC8R16).

Fact, when Q3 locked, 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-dimensional (-) in D 3, this 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:

Effect of C4, R6, D3 as direct feedback circuit.

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 / filtered by D9/C15 12V breeding range, amplified stimulated.

Line 2: Bending / filtered by D7/C13/C18 5V purple wire, high voltage through the resistor for PS-ON, raising circuit PG algorithm.

Stable voltage: Use OPTO U1.

If the output voltage increases (because the oscillation frequency changes), 5V output increases. Meanwhile source for extreme control of U1 (TL431) from 5V through R27 increased make 431 large opening.

Notice 431 connected in series with the diode of the OPTO, for 431 open large current through the diode (from 5V STB R30, through the diode, 431 down mass) increases, the light intensity of the diode increases affecting CE U1 as resistor RCE U1 reduced, this resistor in series from point A on the R17 should make the feedback voltage on B Q4 (through R17) increased, resulting in Q4 storm hoa/Q3 lock earlier than usual. In other words, the time to open Q3 small in 1 second will decrease the output voltage decreases.

If the output voltage is reduced (because the oscillation frequency change) 5V output decrease. Meanwhile source for extreme control of U1 (TL431) from 5V through R27 down to make 431 small opening.

Notice 431 connected in series with the diode of the OPTO, for 431 open large current through the diode (from 5V STB R30, through the diode, 431 down mass) down, the light intensity of the diode to reduce the impact to CE U1 to resistor RCE U1 increase, this resistor in series from point A on the R17 should make the feedback voltage on B Q4 (through R17) decreased, resulting in Q4 storm hoa/Q3 lock later than usual. In other words, the time to open Q3 in one small seconds will increase the output voltage increases.

Voltage stability: Using the negative feedback resistor R4 voltage.

If Q3 widening (high pressure), the flow through R4 increase. Voltage drop on R4 (in UR4 = IQ3 x R4) increased. To will find this pressure drop on leg B Q4 through R8 Ub Q4 up, Q4 saturation, Q3 lock earlier than usual. In other words, the time to open Q3 small in 1 second will decrease the output voltage decreases.

If Q3 small opening (low output voltage), the current through R4 reduced. Voltage drop on R4 (in UR4 = IQ3 x R4) down. To will find this pressure drop on leg B Q4 through R8 do Ub Q4 reduce, Q4 will be saturated, Q3 lock later than usual. In other words, the time to open Q3 in one small seconds will increase the output voltage increases.