6. 6.5V, 12V, 19V power supply circuit required for small signal processing circuit operation
The circuit of 6.5V, 12V and 19V is shown in Figure 3. The circuit is mainly composed of green current mode pulse width modulator U101 (FAN7601MX, working frequency up to 300kHz), field effect power switch tube Q103, switching transformer T101 and its peripheral circuits. The functions of each pin of U101 (FAN7601 MX) are shown in Table 4. The 400V DC voltage output by the PFC circuit is divided into two input switching power supply circuits, one is connected to the drain D of the field effect switch Q103 via the 5-2 winding of T101; the other is passed through the voltage of R121, R104~R107, Q101 (e pole) U510 provides 15V voltage), U102 composed of voltage regulator circuit voltage regulation, output 12V voltage to U101 (FAN7601 MX) 7 pin external capacitor C113 charging, when the voltage across C113 rises to 11V, U101 internal oscillation circuit starts to oscillate The output pulse is output from pin 6 and is applied to the gate of Q103 through D101, R114, and R115 to control the turn-on and turn-off time of Q103. During the conduction of the switch Q103, the windings of the T101 store energy, and there is no rectified and filtered voltage output; during the off period of the switch Q103, the induced potential generated by each winding of the T101 passes through the respective rectifying and filtering systems, and outputs corresponding operating voltages. The induced potential generated by the winding of T1017-6 is filtered by D206, filtered by C202 and C211, and the output voltage is 6.5V. The induced potential generated by the winding of T1019-8 is filtered by D203, filtered by C208 and C222, and output 12V voltage; T1019-10 The induced potential generated by the winding is rectified by D204 and filtered by C210, and the output voltage is about 26V. This voltage is regulated by the 19V series voltage regulator circuit composed of Q204-Q206, ZD240 and other components. The voltage of the D pole of Q205 is 19V. . D103, C114 and R116 of the D pole of Q103 form a spike absorbing circuit for protecting the field effect switch Q103. In the circuit, U102 is used as a PFC low-voltage detection shutdown control circuit. When the voltage of the PFC sent to the U102 control terminal through the sampling component is lower than 2.5V, U102 is not turned on, so that Q101 stops working, U101 cannot receive power supply, and the whole machine stops working.
7. The voltage regulator control circuit voltage control circuit is mainly composed of U101, optocoupler PC150, precision voltage regulator U203 (KA431 S) and sampling resistors R228, R229 (monitoring 12V voltage), R230, 8231 (monitoring 6.5V voltage) and R243, etc. composition. When the output voltage of 12V or 6.5V rises, the potential of the R terminal of U203 is increased by the voltage divider of the sampling resistor, and the voltage of the K terminal of U203 is lowered, so that the current flowing through the photodiode inside the photocoupler PC 150 increases. The brightness of the light-emitting tube is enhanced, the conduction level of the phototransistor is enhanced, and finally the current of the 2-pin current flowing into the U101 is increased, and the internal oscillation circuit reduces the duty ratio of the output driving pulse, so that the on-time of the field effect switching transistor Q103 is shortened, and the output voltage is lowered. If the output voltage is reduced, the control process is reversed as described above, thus keeping the output voltage stable. In order to ensure the safety of the rear-end equipment, the voltage-stabilizing sampling circuit of the power supply is also unique. At the same time, the two sets of output voltages are sampled, and the sampling resistors are precision chip resistors, which avoids the disadvantages caused by the adjustable resistors, which is also different from Other circuits.
Typical fault 1: The power indicator flashes, but the whole machine has no display. The fault is caused by the leakage of the filter capacitor C206 (2200μF/10V) of the 6.5V power supply line, causing the 6.5V voltage to drop to 0.5~2V. Replace the C206. The machine resumes working normally.
Typical fault 2: The power indicator light is red, but the whole machine has no display. The fault is caused by the ce pole of Q1 01 (KST2907A), which causes the U1017 pin to run out of power, causing the internal oscillation circuit of U101 to stop working. Replace Q101. The machine resumes working normally.
8. Backlight power supply circuit (or backlight circuit)
The circuit is mainly composed of input interface circuit (backlight lighting control, brightness control circuit), modulator (PWM) U301 (LX1691AIPW, operating frequency range 30kHz ~ 200kHz), high voltage half bridge gate driver integrated circuit U701 (FAN7382MX), high voltage half The components of the bridge power amplifying circuits Q706, Q707 and T701, and the lamp power supply sampling feedback circuit are shown in Fig. 4.
The working process of the circuit is as follows: INV-CTRL (inverter control signal or backlight lighting signal) output by the microprocessor is high (about 4.3V) and is added to the b pole of Q318 via D318, and Q318 and Q317 are sequentially saturated and turned on. The 12V voltage Q317 is connected to the U303 input pin. After being regulated by U303 (KIA78L05F), it outputs 5V voltage, and is sent to U301 (LX1691AIPW) 16 pin via R318. The other channel is divided by R319 and R320 and sent to U3019 ( Enable terminal), once the U301 16 pin has 5V working voltage, and the 9-pin enable terminal voltage is greater than 3V, its internal oscillation circuit starts to work, the oscillation signal is output from U3012, 3 feet, after being transformed by the isolation transformer T702, The low and high side drive signals are output from T7025, 4 feet, T7025, and 6 pins respectively. The low-side drive signal is push-pull-amplified by Q703 and Q704 and added to the U7013 pin. The high-side drive signal is push-pull-amplified by Q701 and Q702 and added to the U7012 pin. The U3012 / 3 pin is the excitation pulse output, and the two have opposite phase and phase delay characteristics. U3019 foot ENA (Enable) lighting enable end, this pin is the enable end of U301 running or not, or the control end of the lamp lighting, see Figure 4. If the pin is high 4V or so, all functions are enabled, U301 starts to run, and the lamp is lit; if it is low, U301 internal power supply is disconnected from VDDP pin, disable all functions, U301 stops working, lamp The tube is extinguished. U30115 pin VDDA (Reference) 3V reference voltage output, this pin is a 3V reference voltage output by U301 16-pin VCC power supply through internal voltage regulation, for U301 internal and external circuit work, U301 protection when the pin has no output. U301 13-pin 0V-SNS is the lamp over-voltage detection input. The T701 secondary induced voltage is input to a high-voltage voltage-divided capacitor sampling circuit, and a full-wave AC voltage proportional to the voltage of the lamp at the midpoint is input. The 0V_SNS input signal is a voltage sampled by the lamp and then full-wave rectified and sent to the digital comparator of the 2V reference voltage inside U301. The input signal frequency of this pin ranges from 10 kHz to 500 kHz. During normal operation, the voltage of the pin is less than ±2V. When the signal voltage of the detection input is greater than ±2V, the internal digital comparator is turned over, the protection circuit is controlled, U301 is disabled, and the lamp is extinguished. U301 14-pin OC-SNS overcurrent sensing input This pin is the overcurrent detection input. After the current sampling circuit, input a full-wave AC voltage OC_SNS proportional to the current of the secondary winding of the high-voltage transformer, and then add it to the comparator with a reference voltage of 2V inside U301; if the voltage continues to be greater than 2V , the internal comparator output is flipped and an overcurrent shutdown will occur. The functions of each pin of U301 (LX1691AIPW) are shown in Table 5.
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