Design of Power Supply Scheme for Constant Voltage Small Household Appliances Non Isolated Driving P

The drive chip sm7055-12 is a power switch chip with current mode PWM control mode and integrated high voltage starting circuit

And 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 appliances

Product 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 current

。 Is proportional to ID:

ID   = GID ? IS

From the above figure: (i s I FB)? R2 ? 0.23V

Main characteristics of drive power management chip sm7055-12:

Topology support: low cost buck, buck-boost and other schemes

730v single chip integration process is adopted

85vac 265vac wide voltage input

Standby power consumption is less than 120mW@220Vac

Integrated high voltage starting circuit

Integrated high voltage power switch

60KHZ fixed switching frequency

Built in frequency buffeting technology to improve EMC performance

Current mode PWM control mode

Built in over-temperature, over-current, over-voltage, under voltage and other protection functions

Built in soft start

Built in intelligent soft drive technology (improved)

EMC (performance)

Package form: to252-2, DIP8

Application fields of sm7055 driver power management chip:

Power supply for small household appliances such as rice cookers and electric pressure cookers

Drain source breakdown voltage

Drain end off state leakage current

Source drain on resistance

Hvdd on voltage

Hvdd off voltage

Hvdd hysteresis threshold voltage

Hvdd operating current

Chip charging current

It 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 IFB

Current 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 board

Some GND feet.

The figure above shows a typical sm7055-12 drive power management icbuck-boost circuit, in which C1, C2 and L1 form π filter, which is beneficial to improve EMI characteristics

Sex; 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 chip

Capacity C3 charging, when

When 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 system

Restart, 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.