Design of Power Supply Scheme for Constant Voltage Small Household Appliances Non Isolated Driving P
12v300ma scheme design non isolated constant voltage driving power supply icsm7055 replaces cytThe drive chip sm7055-12 is a power switch chip with current mode PWM control mode and integrated high voltage starting circuitAnd high-voltage power tube, which can realize the solution of low-cost and cost-effective switching power supply system.The chip is applied to buck and buck-boost system schemes, supports 12V output voltage, and is conveniently applied to small household appliancesProduct area. It also provides perfect protection functions such as over temperature, over-current, over-voltage and under voltage to ensure the reliability of the system.The current ID through the high voltage MOS is divided into two parts, one of which is the chip sampling currentã Is proportional to ID:ID Â = GID ? ISFrom the above figure: (i s I FB)? R2 ? 0.23VMain characteristics of drive power management chip sm7055-12:Topology support: low cost buck, buck-boost and other schemes730v single chip integration process is adopted85vac 265vac wide voltage inputStandby power consumption is less than 120mW@220VacIntegrated high voltage starting circuitIntegrated high voltage power switch60KHZ fixed switching frequencyBuilt in frequency buffeting technology to improve EMC performanceCurrent mode PWM control modeBuilt in over-temperature, over-current, over-voltage, under voltage and other protection functionsBuilt in soft startBuilt in intelligent soft drive technology (improved)EMC (performance)Package form: to252-2, DIP8Application fields of sm7055 driver power management chip:Power supply for small household appliances such as rice cookers and electric pressure cookersDrain source breakdown voltageDrain end off state leakage currentSource drain on resistanceHvdd on voltageHvdd off voltageHvdd hysteresis threshold voltageHvdd operating currentChip charging currentIt can be seen from the above formula that if the IFB current is large, the ID current is small; If the IFB current is small, the ID current is large. When IFBCurrent greater than (0.23V / r2)When, the chip will turn off PWM, and the chip will automatically enter burst mode.Note (1): the chip shall be welded to the PCB board with 200mm2 copper foil for heat dissipation. The thickness of the copper foil is 35um, and the copper foil is connected to the PCB boardSome GND feet.The figure above shows a typical sm7055-12 drive power management icbuck-boost circuit, in which C1, C2 and L1 form Ï filter, which is beneficial to improve EMI characteristicsSex; R1 resistor is surge suppression element; D1 is a rectifier diode, forming a half wave rectifier circuit.When the switching power supply is started, the voltage on the C2 capacitor will be powered to the chip hvdd through the high voltage start MOS tube inside the chipCapacity C3 charging, whenWhen the C3 capacitor voltage reaches 11.5V, the internal high voltage starts, the MOS tube is closed, and the PWM is turned on, and the system starts to work.When the C3 capacitor voltage drops below 9V, turn off the PWM signal, and the chip will generate a reset signal to make the systemRestart, this is undervoltage protection.Slots shall be cut between the drain pin of IC and GND and hvdd to meet the requirements of safety regulations.The routing distance between the primary loop and the test loop shall be as thick and short as possible, so that it is easier to pass the EMC test.