Zhixin Solution｜Smart plugs make electrical appliances smarter

In terms of power supply, Toshiba has launched a small chip-type LDO voltage regulator according to the different application environments of smart plugs and the different working voltages required by internal components. The LDO voltage regulator has nine series, including four characteristics, which can Outputting a variety of voltages and currents can not only meet the DC power needs of smart plugs, but also quickly promote the process of product miniaturization.

In terms of relay control, Toshiba has proposed four solutions based on the size of the control current, including AC switching circuits for mechanical relays, AC switching circuits for photorelays (less than 0.3A), and AC switches for photovoltaic output optocouplers and MOSFETs. circuit (approximately 0.3A to 1A) with a triac and a triac output photocoupler for AC switching circuits (1A or above) . Commonly used are mechanical relay AC switching circuits.

As we all know, relay control requires current drive, because the current output by ordinary controllers generally cannot directly drive relays. At the same time, the internal structure of relays is generally composed of coils, armatures and metal contacts, etc., which drive its work. A self-induced electromotive force will appear when the circuit is running. If it is not protected by a freewheeling diode, it will easily damage the control circuit and cause irreparable losses. Toshiba has done enough homework on the drive relay and circuit protection of this solution. In terms of driving, it is recommended to use small signal N-channel MOSEFT to drive the relay. Here Toshiba recommends using SSM3K36FS or SSM3K56FS . The MOSEFT packages are all SOT-416 packages, V dss supports a maximum of 20V, and the conduction current is 0.5A and 0.8A respectively. The power dissipation is 0.15W. At 4.5V, the maximum R DS(ON) values ​​are 0.66Ω and 0.235Ω respectively. In terms of circuit protection, Toshiba recommends the use of CRS series Schottky diodes CRS03 and CRS13. Both diodes use smaller S-FLAT ^™ , which helps reduce the PCB footprint. The maximum reverse peak voltage of CRS03 is 30V and is suitable for application in circuits below 30V. The maximum reverse peak voltage of CRS13 is 60V and is suitable for application in circuits below 60V. The maximum forward average current of both can reach 1A, which can well solve the problem of the relay's self-induced electromotive force damaging the circuit.

In terms of small current AC switching circuits, Toshiba also has plans for its reference. When controlling electrical equipment with AC less than 0.3A, Toshiba's self-developed photorelay TLP3549 can be used . It is packaged in DIP8 and has good heat dissipation conditions. It also has a maximum conduction current of 0.6A and a maximum control current of 25mA. It is isolated. The voltage is 2500V, which can better protect the subsequent circuit from being damaged by strong electricity.

When controlling 0.3A-1A AC electrical appliances, you can refer to the AC control circuit implemented by a combination of optocoupler and MOS launched by Toshiba. Here Toshiba recommends using TLP series optocouplers TLP3906 and TLP3910 . TLP3906 is packaged in SO6, and TLP3910 is packaged in SO6L, both of which can reduce PCB size. At the same time, their maximum control current is 30mA, but the power consumption is as low as 12μA. In terms of isolation, the maximum isolation voltage of TLP3906 can reach 3750V and the minimum creepage distance can reach 5mm, while the maximum isolation voltage of TLP3910 can reach 5000V and the minimum creepage distance can reach 8mm.

When controlling current above 1A, the AC switching circuit control realized by Toshiba triac output optocoupler can be used. Triac output optocouplers can use TLP265J , TLP266J , TLP267J and TLP268J . These four thyristor output optocouplers are all in 4-pin SO6 packaging, which not only reduces the size of the PCB, but also supports pin compatibility. The V DRM is 600V, the maximum I FT of TLP265J and TLP266J is 10mA, the maximum I FT of TLP267J and TLP268J is 10mA, the I T (RMS) is 70mA, and the isolation voltage is 3750V.

In terms of circuit protection, since smart plugs need to be touched by people, they will inevitably encounter the effects of static electricity. Toshiba has been very considerate in this aspect of circuit protection and provides customers with TVS diodes with a variety of parameters to achieve different circuits. Protection plan for their reference.

Here Toshiba mainly recommends using DF2B series TVS diodes, the specific models are: DF2B7ASL , DF2B5M4SL , DF2B6M4SL and DF2B6M4BSL . This series of diodes is available in a small SOD-962 package, with four ESD voltage protection levels and two reverse operating peak voltages of 3.6V and 5.5V. The minimum junction capacitance is only 0.2pF, which can reduce the impact on signal transmission of the protection circuit.