Venus C6458 power supply

Venus C6458 uses it's excited switching power supply, and the oscillation circuit uses TEA2261.

Oscillation process:
The 220V alternating current is reduced by R804 and TH803 and stabilized by ZD801 to obtain a voltage of about 12V. It is sent to pin (16) of IC801 through D806 and R806 as the oscillation starting voltage of IC801. When the voltage at pin (16) is greater than 10.3 When V, the circuit starts to oscillate, and the excitation pulse is output from pin (14), which is added to the base of switching tube Q801 through D817, D819~D821, and a positive 300V DC voltage is applied to pin (1) of the switching transformer. The collector of Q801 is connected An AC pulse voltage is generated between pins (3) and (1) and (3) of the switching transformer. In this way, each winding of the switching transformer begins to output voltage.

Voltage stabilization process:
1. Standby state:
The output voltage of TEA2261 in standby state is affected by the following two aspects: First, the voltage sent to pin (6) via D811 and R816. There is a voltage comparator inside pin (6) of TEA2261. The reference voltage of the comparator is 2.49V. When the input voltage of pin (6) is greater than 2.49V, the comparator outputs a negative voltage. On the contrary, when the input voltage of pin (6) is less than 2.49V, the comparator outputs a positive voltage; in addition, TEA2261 The (10) and (11) pins and the external R810 and C815 form an RC oscillation circuit. The voltage output by the comparator and the sawtooth wave output by the RC oscillator are added to the internal pulse modulator. The voltage output by the comparator can be controlled The pulse width output by the pulse modulator controls the pulse output by pin (14), which also controls the output voltage of the switching power supply.
On the other hand, the voltage output by D811 is divided by R816, R818 and VR810 and sent to the base of Q801. After being amplified by Q801, it is connected to pin (11) of IC801 to control the oscillator frequency of the RC oscillator. Adjust VR810 to The frequency of output pulses from pin (14) can be adjusted, thus controlling the output voltage.

2. Power-on state
In the power-on state, the oscillation frequency of TEA2261 is determined by the pulse input from pin (2). In the power-on state, pin (58) of the CPU outputs a high level. This high level is added to the base of Q851. Q851 is saturated and turned on, and Q852 is also turned on. A 12V voltage is output from the collector of Q852. This 12V voltage is On the one hand, it is sent to pin (40) of TA8659 as the row oscillation starting voltage, and the row scanning circuit starts to work. On the other hand, it is added to pin (2) of IC802 through R869, and IC802 starts to work.
There is a voltage comparator inside pins (5) and (6) of IC802. The reference voltage of the comparator is 2V. The main power supply voltage of the switching power supply +B (130V) is divided by VR851, R852 and R853 and then added to the IC802 (5) Pin, after comparing with the reference voltage of the comparator, outputs a control voltage. There is a sawtooth wave oscillator inside pins (7) and (8) of IC802. The horizontal pulse obtained from the filament winding is sent to pin (8) of IC802 through R859, C859 and D858, so that (8) and (9) The oscillation frequency of the oscillator inside the pin is equal to the horizontal frequency. After the sawtooth wave output by the oscillator is transformed by the pulse width controller and logic, a square wave signal is output from pin (3). The control voltage output by the voltage comparator can control pin (3). The width of the output square wave signal, so the output voltage can be adjusted by adjusting VR851.
The square wave signal output by IC802 is isolated by T802 and sent to pin (2) of IC801 to control the pulse width output by pin (14) of IC801, that is, to control the output voltage of the switching power supply.

Protection circuit:
1. Overvoltage protection:
The voltage of pin (16) of TEA2261 cannot be greater than 15.7V. When the power supply voltage output is too high, the voltage output by the windings of switching transformer (8) and (9) must also increase. When the voltage When the voltage obtained after rectification by D811 and filtering by C811 is greater than 15.7V, the pulse output by TEA2261 (14) pin is turned off, and the switching power supply has no voltage output. At this time, even if the voltage of pin (16) drops below 15.7V, pin (14) still has no pulse output. Be sure to turn off the power supply, and then check the voltage of pin (16) again after restarting. If it is less than 15.7V, the power supply will Back to work.

2. Under-voltage protection:
When the voltage of pin (16) of TEA2261 is less than 7.4V, the internal under-voltage protection circuit operates, and the pulse output by pin (14) is turned off. When restarting, the voltage of pin (16) is detected again, such as It will work again only when the power supply is greater than 7.4V.

3. Overcurrent protection:
The emitter of the switch tube is connected with R822 and R832 as current sampling resistors. The current flowing through the emitter generates a sampling voltage on R822 and R832. This voltage is divided by R812 and R831 and then sent to the At pin (3) of TEA2261, TEA2261 has two thresholds at this time:
the first threshold is when the voltage of pin (3) is greater than 0.6V, the external capacitor C816 of pin (8) is charged, and when the voltage on C816 is charged to 2.25 When V, the internal overcurrent protection operates, the pulse output from pin (14) is turned off, and the switching power supply has no voltage output. However, if the voltage on C816 has not been charged to 2.25V, the voltage at pin (3) drops below 0.6V. , then C816 will release the charged voltage, and protection will not occur. This is mainly to prevent the malfunction of the protection circuit caused by excessive charging current of the switch tube at the moment of power-on.
The second threshold is when the voltage of pin (3) is greater than