Analysis of ATX power control current - Power Circuit - Circuit Diagram

MOS power IC full range

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

inductance

SMD aluminum electrolytic capacitor

Offline detection of ATX power, first measure the PS-ON and PW-OK signals in the standby state, the former is high level, the latter is low level, the plug 9 pin output +5V, the other has no output. The second is to wake up the ATX power supply, use a wire to short the ATX plug 14 pin PS-ON signal to any of the ground terminals 3, 5, 7, 13, 15, 16, 17 and connect the ATX power supply to the electrode. The state wakes up to start the controlled state. At this time, the PS-ON signal is low level, the +5VSB and PW-OK signals are high level, the ATX tap +3.3V, ±5VSB signal is high level, and the ATX plug +3.3V, ±5V, ±12V has output. The switching power supply fan rotates, and the above operation can also be used as an offline power verification method for the optional ATX switching power supply.

Second, the work of ATX switching power supply control current

1. Auxiliary power circuit

As long as there is power loss input, the ATX auxiliary power supply is always working, providing the working voltage for the switching power supply control circuit, and the power loss is rectified by high voltage. Filtering, outputting about 300V DC ripple voltage. One way through R72, R76 to the auxiliary power switch Q15 base, the other through the T3 switch transformer's primary winding is added to the Q15 collector, so that Q15 is turned on. The induced potential of T3 feedback winding (upper positive and negative) is applied to the base of Q15 through positive feedback branches C44 and R74 to make Q15 saturate and conduct. The feedback current charges capacitor C44 through R74, R78 and Q15. As the C44 charging voltage increases, the base current flowing through Q15 gradually decreases. The induced potential of the T3 feedback winding is reversed (upper negative and positive), and the C44 voltage is superimposed on the base of Q15, causing the base potential of Q15 to become negative. Closed quickly.

When Q15 is turned off, ZD6, D30, C41, and R70 form the Q15 base negative bias cut-off circuit, and the positive end of the feedback winding induced potential forms a charging loop through C41, R70, and D41 to the negative end of the induced potential. The negative electrode of C41 is a negative voltage, and the base potential of Q15 is turned on by D30 and ZD6, and the lead position is at a negative potential higher than the negative voltage of C41 by about 6.8V (diode voltage drop and voltage regulation value). At the same time, the charging voltage of the positive feedback branch C44 passes through the T3 feedback winding, V78, Q15, and R74 to form a discharge loop. As the C41 charging current gradually decreases, the Ub potential rises, and when Ub turns on again, it enters the oscillation of the next cycle.

During Q15 saturation, the induced potential of the T3 secondary winding output is negative, the rectifier is turned off, and the conduction current flowing through the primary winding is stored in the T3 auxiliary power transformer with magnetic energy. When Q15 turns from saturation to cutoff, the induced potential of the two output ends of the secondary winding is positive, and the magnetic energy stored by T3 is converted into electric energy and is rectified by BD5 and BD6. The voltage of the BD5 rectified output is for the Q16 three-terminal regulator 7805, the Q16 output +5VSB rectified output voltage is supplied to the ICI pulse width to the 12-pin power input terminal of the TL494. The 14-pin output voltage regulator is 5V, and the ATX switching power supply control is provided. The operating voltage of all components of the current.

2, PS-ON and PW-OK signal circuit

During standby, the main board turns off the electronic switch of the control circuit. The PS-ON signal is 3.6V high. The Ur potential of the IC10 precision voltage regulator circuit WL431 rises, the Uk potential drops, and Q7 turns on. The regulated 5V is sent to the 4 pin of the ICI through Q7, V80, D25 and D40. When the voltage of the 4 pin exceeds 3V, the 8 and 11 pins are blocked to the pulse width output, so that the T2 and T1 transformers are stopped and there is no output voltage. After the controlled start, the PS-ON signal is grounded, the Ur of the IC10 is zero potential, the Uk potential is raised to +5V, the Q7 is cut off, the ICI4 pin is low, the 8 and 11 feet output the pulse width modulation signal, and the ICI output mode control terminal 13 Connect the foot to 5V. The pulse width adjuster is a parallel push-pull output, and the 8 and 11 feet output a pulse width modulation control signal with a phase difference of 180°, controlling the excitation oscillation of the T2 primary winding, and the T1 main power source under the induced potential generated by the T2 primary. The secondary winding induced potential of the switching transformer is rectified to form a voltage of +3.3V, 5V, and 12V. The PW-OK generation circuit is composed of IC5 voltage comparators LM393, Q21, C60 and its peripheral components. During standby, ICI's feedback control terminal 3 is low level, Q21 is saturated, and IC5's 3 pin inputs low level, Q21 is saturated, IC5's pin outputs low level, PW-OK outputs zero level to the host. The power supply self-test signal, the host stops working in standby state. After the controlled start, the potential of the 3 pin of ICI rises, Q21 enters the amplified state from saturation conduction, 5V charges C60 through R104, the control level of IC5's 3-pin gradually rises, and IC51 pin outputs high-level PW-OK signal. The host detects that the PW-OK power supply is intact and starts the system.

3, automatic voltage regulation control circuit

ICI's 1 and 2 pin voltage sampling amplifiers have positive and negative input terminals. The sampling resistors R31, R32 and R33 form a +5V, +12V automatic voltage regulator circuit. When the output voltage rises (+5V or +12V), the sampling voltage is taken from R13. ICI's 1 pin and 2 pin reference voltage comparison, the output error voltage and the oscillation pulse of the chip sawtooth wave generating circuit are compared and amplified in the PWM comparison, so that the output pulse width of the 8 and 11 pin is reduced, and the output voltage falls back to the standard range; Conversely, the voltage regulation control process is reversed, thereby stabilizing the switching power supply output voltage.