Small and beautiful electric hot water cup dismantling: the legendary “back killer”

The IQ tax has been paid a bit more recently. It feels very practical if I don’t start with this electric hot water cup. I really don’t know which scenes are suitable for this thing when I get it? After all, it is called a travel electric hot water cup. The scene of no travel, but the biggest impact of the current new crown epidemic is travel. This water cup was born at an untimely time and met its nemesis. To put it bluntly, it is a miniature version of the electric kettle. In the current situation, there are not many usage scenarios. Now that the boat is done, then make the best use of it and dismantle it.

dismantling

After dismantling, I divided the hardware solution into 3 parts: AC to DC power supply part, heating module part and MCU control part.

AC to DC power supply section

The AC to DC part is also the function of the strong current board. We can know from here that the board finally outputs 5V DC to supply power to the MCU.

First, the 220V power supply enters from the input interface, then passes through the fuse, and then passes through the Π filter network. When it comes to how to convert high-voltage alternating current into low-voltage direct current, the Circuit scheme is a bit strange, or rather interesting. It does not have a transformer, so how does it convert 220V alternating current into 5V direct current?

The answer is on the back of the board. There is a Lishengmei high-voltage step-down converter (LN8K05) on the back, which is a current-mode power switch controller with integrated PWM and PFM hybrid control circuit, which can directly convert AC power into 5V output without a transformer of direct current.

A typical circuit design is as follows:

heating module part

The heating module part contains electric heating tubes and ceramic fuses.

The above picture can clearly see that the electric heating tube (red) and the bottom of the water cup are welded together at high temperature, so basically if they are broken, they will be broken and cannot be replaced, but generally speaking, the electric heating tube is not easy to break.

The green part is a ceramic fuse, which can also be understood as a thermal fuse, which is used for overheat protection and cut off the power supply.

The yellow part should also be a protection device, but unfortunately I can’t see the model.

MCU control part

Finally, let’s look at the MCU control part. The functions on this small board include touch function, LED indicators, NTC temperature detection and heating control (the latter two are actually reflected on the power board).

The indicators include heating and keep warm indicators (yellow). The design of the touch key is more thoughtful, and it is connected to the casing (red) through a spring-like structure.

If NTC is detected, it is connected to the bottom of the water cup through the above (red) interface.

The heating control part is controlled by this triac (model: BTA06, green) on the power board. You can understand it as an AC switch device that controls the heating and shutdown of the water cup.

It is a pity that the MCU on the small board cannot see the model, but it is speculated that domestic devices are still used.

After reading the disassembly, it is not difficult for us to speculate on its hardware circuit scheme.

Main device BOM form:

Model Description

LN8K05 High Voltage Buck Converter

RH230 ceramic fuse

BTA06 Bidirectional Silicon Controlled Rectifier

Summarize

The appearance of the Yunmi electric hot water cup is still good, but it is heavy and not portable enough. Moreover, the water cup is only 400ml, and half of the volume is occupied by the circuit module. Secondly, after opening the lid, you can see that the combination of the cup body and the shell has There are leaks, and with a strong plastic smell, the core of the cup is not well polished. There are a lot of unsatisfactory places. It seems that I want everything on this product, but I have no choice but to take care of everything.

This may be the common problem of many new Internet companies making products at present. After finally thinking of an idea, they want to rush to the market, but because of the details, they hand over a good idea, which is a pity. As a hardware engineer, I feel the urge to bring my creative inspiration to the market, and I also think that such a small and beautiful idea of ​​an electric hot water cup can meet the rigid needs of some people. After all, foreigners will not understand Traditional Chinese love for a sip of warm water.