Specialized chip series KA2S, form the basis of the power source monitor by SAMSUNG (400b, 500/500pM, CGM1706M) the chip KA2S0880/KA2S0680, CAN/CAN and others In the chip package is placed pulse width modulator control current pulse and high-voltage field-effect transistor. The chip is equipped with a soft start system and uses external synchronization. Pulse width modulator operates from a generator at a fixed frequency and has an internal protection circuit that blocks the chip at elevated or reduced voltage, overheating and critical modes of operation of the source.
The main devices of power sources, ensuring its operation are:
-rectifier voltage;
-circuit startup and synchronization;
-chain stabilization and protection;
-pulse rectifiers voltage
Typical operating circuit chip CAN applied to the power source monitor SAMSUNG CGM7607L, a schematic diagram of which is shown in here. The main circuit of the Converter shown in table. 1.
Table 1 The purpose of the chain Elements Rejection filter L601, S S… The network rectifier D601 . D604, TN, S, R606 Power circuit D605, R602, Of S608, S, T, D610, R604, Of S608, S Elements smooth run S, R605 The damping circuit D608, R603, S, S, R618, R619, D613 The stabilization circuit OR, IC602, ZD602, S, S Elements of the external clock T, S, D607, S, Q601, R615, R616, S, R664, D611
The rectifier voltage
The supply voltage of the AC plug IS601, F601 fuse-link, L601 supplied to rectifier D601…D604. Elements L601, S…S, BD601 form rejection filter that prevents the penetration in the electrical network of impulse noise generated by the power source during its operation. The rectifier bridge type based on discrete elements D601…D604, the negative terminal of which is connected to GND through a resistor R606. In the result, the capacitor C is charged to a voltage of +300 V via thermistor TN.
The device degaussing CRT monitor is connected via connector CN603, thermistor RT and contacts controlled relay RL601 connected to the output of the filter. The winding of the control relay RL601 included in the collector circuit transistor switch Q605 and operated by the DEGAUSS signal from the processor control modes.
The circuit startup and synchronization
The PWM power Converter circuits is performed by applying the appropriate voltage on pin 3 of IC IC601, which must be located within the required limits. For this purpose, the AC connected circuit consisting of the elements D605, R602, of s608. In that case, when the voltage on the capacitor of s608 will reach a magnitude of +15 V, which corresponds to the turn-on threshold of the comparator low voltage (UVLO) (Fig. 1), the comparator switches the chip is in its on position.
Fig. 1 is a Structural diagram CAN
To facilitate the startup mode Converter in the first moment of switching, when the feedback signals are absent and the mode of operation of the Converter close to the short circuit mode in the load mode is used for a smooth launch. Running in this mode provide external elements: the capacitor C and resistor R605, which is connected to pin 5 of the chip. The operation of the circuit is that during the charge of the capacitor C the PWM modulator generates control signals for the MOSFET as if the Converter operates with a zero error signal, the duration of the control signal at the output of the driver is small. When the capacitor CO is charged from an internal source voltage to the error of the soft start duration corresponding to this bug. As the charge voltage on the capacitor C reaches +5 V, the soft start circuit is disabled, and the duration of the control signal MOSFET increases, the voltage across the capacitor C is determined by the error signal generated by the feedback circuit.
In the steady state operation the power of the chip is supplied from the recharge circuit formed by the secondary winding of the transformer T (pin.6-9), elements D610, R604. The decrease in the voltage at the power supply pin of the chip (pin.W IC601) less than the value of threshold off UVLO comparator corresponding to +10 V, leads to the shutdown of the Converter.
When the current flows through the primary winding of the transformer T (pin. 2-5) in the power source the processes that contribute to its translation in steady-state mode of operation.
Elements T, S, D607 form a chain of external synchronization the internal oscillator of the chip pulses SYNC_P coming from the output of the cascade horizontal chain base of transistor Q601.
Circuit stabilization and protection
The feedback circuit formed by the optocoupler OR and chip low-power adjustable stabilizer permanent tension parallel type IC602. To the control electrode of the IC IC602 the information supplied on the output voltage from the divider formed by the elements R612, R610, VR601 connected to the channel +195 V. When reducing the output voltage decreases, the current through the photocell optocoupler OR, and thus the output current in the circuit of the collector-emitter of the phototransistor OR connected to the input of the error signal (pin. 4 IC601). This leads to an increase in the duration of a control pulse MOSFET and to a corresponding increase in the output voltage to the required value. So the Converter is implemented, the control error of the output voltage.
The output voltage regulation is performed by the resistor VR601 canal +195 V. the Voltage higher than +7.5 V at the input of the error signal (pin. 4 IC601), leads to the cessation of operation of the chip triggering of the comparator reset voltage. Elements R611, S are designed to reduce transients in the chip, the photosensor of the opto-coupler is supplied with the voltage of +14 In(2).
Mode control current regulator (primary winding T pin. 5-8) implemented the internal circuits of the chip as a way of regulating the output voltage by increasing the current to the load with one hand, and on the other as an element of protection against the maximum current in the load circuit. At maximum currents in the load of this circuit turns off the output MOSFET transistor until the next start cycle.
Chip IC601 power source has a function restart without disconnecting from the mains. The period between successive runs when congestion is determined by the charging time of the capacitor C from internal sources 1 mA and 5 mA. In the long-term overload the inverter is turned off completely using the built-in comparator turn off the power.
The snubber circuit D602, S, R609 and S, D604, R610, R623 protect the MOSFET transistor from switching pulses caused by the inductance of the windings of pulse transformer from exceeding the instantaneous power at the drain.
The pulse power rectifiers
The pulse rectifiers voltage of the secondary power supplies are collected by the half-wave rectification circuit. The main elements of the circuits of the secondary rectifiers are shown in table. 2.
Table 2
Rectifier Source The composition + 195 In T pin. 11-12 D631, S, S, BD631, R631 +80 In T pin. 13-1 D633, S, R635, BD632 40 In T pin. 10-1 D640, S + 14V(1) T pin. 17-14 D634, S, BD613 +14(2) T pin. 17-14 D636, S +8 In T pin. 16-14 D638, R621, S, R622, Q602, 0604, Q603, R620, R623 -12V T pin. 18-14 D639, S + 12V + 14 V(1) IC632, Q610, S, S, R625 -14 B_AUDIO T pin. 1-2 D612, S, BD605 + 14 BJJSB T pin. 1-2 D641, S +5V + 14(2) IC633, S, S, S, R617Signals SUSPEND and OFF the power source is transferred to the low consumption of electricity. The SUSPEND command is blocked +12 V voltage using a transistor switch Q610, and the team OFF voltage +8 V.
Typical fault
Blows the mains fuse FH601.
In this case, when you unplugged the monitor, it is necessary to check the serviceability of the elements of the barrier filter and rectifier network (L601, S…S, D601…D604), check the operation of the chip (pin. 1,2) IC601, and elements of the damping circuit (D608, R603, S).
The output voltages of the power module are missing.
To verify the presence of voltage of +300 V To the capacitor C. In his absence, check the operation of the network elements of the rectifier D601…D604, TN. When the monitor to check the presence of the supply voltage of the chip IC601 +16 V between pins 2 and 3. In his absence, check the operation of the elements D605, R6O2, SO, D610, R604. If voltage is less power +10 V (power supply off), it should be ascertained in the absence of faults in the load of the secondary rectifiers, health themselves secondary rectifiers and circuit elements of the feedback OR, IC6O2. In the case of proper operation to replace the chip IC601.
Output voltage is above or below the norm and are not regulated by the variable resistor VR601.
To check the serviceability of the elements OR, IC602, S, ZD602 and S.
Publication: www.radioradar.net