1 city power rectifier circuit work exception protection

Normal main switching power supply, power rectifier circuit, filter capacitor c818, C819 intermediate node voltage should be for half of the output voltage of rectifier, that is, when the city electricity is AC220V, c818 cathode rectifier voltage should be around for 270V. C818 anode should make an appointment for 135V. At this time IC801 feet should be 21.2V. Due to the protection function monitoring pipe q805 emission electrode is connected with the 21.2V (i.e. IC801 fifthly, feet), base the r837 and D827 pick in c818, C819 center nodes in the (+135V), at this time due to D827 anti bias cut-off and enable q805 in cut-off state, do not affect the power of the normal work.

D827, Q805,, OV,, C819, C818, and other causes of failure, such as C819, are caused by the failure of the open circuit. So the Q805 collector output high voltage, and two outputs: the first road to the Q803 base, Q803 saturation conduction, 21.2V high voltage IC801 5 feet by Q803 beam through the guide pole, D822, equivalent resistance R846 to the IC801 pin, internal protection circuit control, main switch power source for forced oscillation the circuit to stop vibration and stop work; second way to voltage protection tube D821 cathode, D821 Zener conduction, the conduction current flowing through the R843 to the D819 photosensitive diode, the photosensitive triode collector emitter equivalent resistance for photosensitive diode conduction current surge and drop, the photosensitive triode conduction current surge, the Q852 base drive current is shorted to ground, the Q852 cutoff, reset relay RL801 lost in the off state, the electricity is cut off, so that the main power switch to stop working.

2 power switching rectifier circuit output voltage over-voltage protection

D820, R818, R817, D819, D821 and so on. When the mains input voltage is higher than 160V, if commutation mode automatic conversion circuit misoperation, it will cause the voltage of the output end of the rectifier is too high and breakdown of the main switching power supply and load on the circuit components. Therefore the machine set rectifier output over-voltage protection circuit, the in the overvoltage phenomenon. Due to the abnormal increase in C819 cathode voltage, the high voltage after the r817 and r818 partial pressure by the added to the voltage regulator tube the D820 Yin extreme, the D820 Zener conduction, and then to Q803 have been saturated conduction, so IC801 due to internal Overcurrent protection circuit control and stop work; also caused d821 and D819 have conduction, so Q852 due to the base drive current is short circuited in cut-off state, the RL801 disconnect, forced switch power supply to stop working, to protect switch power supply and load circuit components to avoid overvoltage damage to.

3 over voltage protection of +B output terminal for switching power supply

, R831 and R830, Q856 and D832, etc.. When some reason caused by output voltage of + B (normal is 140V) abnormal rise, after partial pressure resistance R830, R831 partial pressure, at both ends of the R831 of overvoltage monitoring sampling voltage will increase accordingly. The sampling voltage more than 10.4V and d832 zener diode conduction, the Q856 saturated conduction, so Q852 due to the base drive current is short circuited and in cut-off state, RL801 lost power on reset switch power supply stops working, to protect the main switching power supply load circuit is protected from overvoltage damage.

4 line output circuit overcurrent protection

By Q590, D591, R557 and other components of the protection function of the monitoring circuit, which is the R557 is over current sampling resistor and line output circuit DC power supply current limiting resistor. When some reason caused by line output circuit over-current, R557 (0.22) at both ends of the DC voltage drop would be too big and the current protection, monitoring and control Q590 saturated conduction, D591 Zener conduction, D591 pass current through socket DLL 4 feet sent to Q856 base, the Q856 saturated conduction, so Q852 was forced to stop. The RL801 power fail reset force power switch stop working.

 

5 field output circuit overcurrent protection

The protection function monitoring circuit is composed of D459, D451, and so on. When some causes field output circuit working current is too large or field output coupling capacitors C454 leakage, shunt resistance R454, R482 at both ends of the DC voltage drop will increase, so d459, Kun positive guide pass, the Q856 conduction, the shoot pole conduction current will make the base of the Q852 drive current is shunted to stop Q852, RL801 lost power on reset, forcing the switch power supply and field output circuit are to stop working, thereby protecting field output integrated from over-current damage.

6 picture tube filament power supply over-voltage protection

By r569, R568, D566, Q858 etc. the protection function of the monitoring circuit and the sampling voltage of the overvoltage protection and monitoring is by R581, d565, C572 components such as the line output transformer T501 - 4 feet winding induction of inverse pulse rectifier and filter formed. When some reason caused by line output stage formed retrace pulse voltage is too high, T501 and output picture tube filament power supply voltage is too high, the voltage by d565, C572 rectifier filter and r569, R568 pressure and sampling voltage generated at both ends of the R568 corresponding too large, Yu Shiwen pressure pipe D566 Zener conduction, Q858 saturated conduction, forced Q852 for base drive current is short circuited the deadline, RL801 power fail reset, is main switching power supply stop work, so as to achieve the protection tube is protected from overvoltage damage. And because line retrace pulse voltage is too high, caused by CRT anode voltage is too high, by tube X-ray intensity is too large, the to the viewers is unfavorable, so the protection function monitoring circuit also plays X-ray protective effect.

7 line output circuit over-voltage protection

The protection function of the control circuit is composed of ot-c555, C567, D554, d859, Q856 and microprocessor IC1213 is 6 foot internal protection circuit and the standby control circuit, with dual overvoltage protection function.

The reverse pulse voltage of the Q552 collector of the output tube is formed by C555 and C567, and the voltage is formed at both ends of the C567. When in normal work, the inverse range capacitance C567 formed at both ends of the inverse process of the pulse amplitude was lower than D554 zener voltage threshold, D554 non conduction, to the normal work of the whole circuit without effect. If for some reason caused high + B (140V) power supply or other reasons caused by the inverse process of pulse amplitude anomaly increases, C567 at both ends of the pulse voltage also increased, forcing D554 Zener conduction and the conduction current through the D553 R839, both ends of the R839 produce higher DC voltage, the electric voltage of two output:

Path through a socket A1 II feet, R1103 sent to the IC1213 is 6 feet, make the internal protection circuit control (which is actually the microprocessor internal data latch). The 33 foot output shutdown low level control signal, and the standby control tube cut-off Q852, RL801 lost power on reset and forced to switch the power to stop working, to protect the line output and the load circuit is protected from overvoltage damage.

Another path R865, R859, d859 added to Q856 base, the Q856 saturated conduction, forced Q852 due to the base current is short circuited in cut-off state, RL801 lost power on reset to double line output circuit and an overvoltage protection function.

8 switching power supply +12V and +25V output voltage or loss of voltage protection

Consists of the D861, D863, Q861, D862, Q856 and the IC1213 is foot internal protection circuit and standby control circuit etc., with dual overvoltage protection function. Q861 emitter is connected with the formation of remote power approximately 9V DC voltage, at the base of the Q861 respectively connected 12V, +25V undervoltage or loss of pressure monitoring and protection components D863, D861, together to form a dual NAND circuit, in normal working two diodes are reverse cut-off, the Q861 in an off state, on the normal operation of the whole circuit has no effect.

When some reason (such as its corresponding load circuit over-current) cause +25V or + 12V output voltage is reduced to below approximately 7V or ov, D861 D863 positively conduction the Q861 saturated conduction, the collector output high voltage after R864 D862 divided into two output: Luke to the IC1213 is 6 feet, the microprocessor executes protection shutdown, under the protection of the standby; another way at the same time the R865, R859, d859 added to Q856 base, Q856 saturated conduction, Q852 deadline to allow the RL801 release, the main switching power supply due to power outages and stop work.

9 standby reset protection circuit

The microprocessor control protection circuit, reset circuit in order to avoid misoperation, standby reset protection circuit composed of Q857, the protection principle is: when some causes relay driver protection circuit connected to the Q852 base outside the control tube, because the base drive current is short circuited at low potential, so in IC1213 (33 feet) high level output during the boot command, because the launch of Q857 junction and conduction, the collector output high voltage, R865, A1, R1103 to the back foot IC1213 6 feet, the internal circuit processing, the standby control output shutdown low level control signal, to ensure that the main switch power supply stop at this time, in the standby state.

Obviously the microprocessor with power on self-test function, it is through the test of the 6 foot with and without high level input signal to determine the main switch power supply part integrated standby protection circuit is controlled. That when the machine when the computer is turned on, the first detection IC1213 is the pin voltage is low level ov, if not, main switch power supply and load circuit failure, and to 0.5 seconds from the IC1213 is the output high level control signal controls the operating condition of the Q1003 (refer to figure 1