Type-c ultrasonic cutting knife

Preface:

After multiple versions of testing and modification, it can now work normally, but it seems that the efficiency is not high, and there is high room for optimization.

I designed a pulse transformer for the first time, and it can work normally after debugging but the efficiency is not high, and I hope that the relevant industry leaders can make suggestions or optimize the design. Beginners are not recommended to reproduce!

Type-c integrated ultrasonic cutting knife

Open source license: CC-BY-NC-SA-4.0 is strictly forbidden for any form of commercial use

Basic parameters:

Voltage: 20V (power supply needs to support PD/QC 20V output)

Current: 0.3~1A

Power: 6~20W (MAX:25W)

Operating frequency: 40KHz (measured 38.9KHz)

Operate:

Press the button to turn on and turn off with two clicks.

Red light: The power supply is abnormal, the voltage is insufficient, and it cannot be started (the power supply does not support fast charging will also cause a red light)

Green light: The power is OK and the job is ready.

Blue light: power output, normal working state.

Application Scenarios:

The 3D printed parts are supported for cutting, and the paper is cut in batches.

Circuit Section:

Measured: R45 short D5 NC.

UCC27517 may not have enough drive capacity for AON7544, and in the case of >10W, the AON7544 heat is greater.

Subsequent designs should focus on strengthening the power bridge drive capability, although this may also be related to the improper design of the transformer.

The power supply uses CH224 to communicate with the charger to trick 20V.

Program Section:

MCU Model: STC8H1K08 QFN-20 Program Download Clock: 30MHz

The gate transformer drive signal is output by STC8H hardware PWM, and the source code refers to STC8H official hardware PWM driver.

The first two versions here are intended to be bridged outputs, so in fact, the program is to output PWM signals with dead time complementarity.

The third version is changed to a single tube, and the PWM signal output is positive.

Tested here 30M clock ARRH=0X03 The output effect is the best The measured output PWM frequency is 38.9KHz.

PWMA_DTR=0X00~0XFF Dead time control registers that can be used to adjust the output PWM duty cycle.

The lower the value, the higher the PWM output duty cycle, and the higher the value, the lower the PWM output duty cycle.

The best value for this transformer test is 0xBF.

PWMA_ARRH change the PWM output frequency, in the case of 30MHz clock, the PWMA_ARRH=0x03 PWM output frequency is 38.9KHz.

According to the data sheet, the actual oscillation frequency difference of +-3KHz meets the working conditions.

Pulse Transformers:

The transformer is a leadless ferrite tank transformer.

Core model: GU-18 core cross-sectional area 43.8mm2.

Primary: single strand diameter 0.23mm four-wire and winding 28T

Secondary: single strand diameter 0.05mm single wire 420T

The secondary is wound on the inner side, and the primary is wound on the outer side (transformers are wound by hand)

Commissioning & Testing:

MOS gate drive signal

The transformer outputs a resonant signal.

The ultrasonic transducer is bonded to the housing with 704 silicone rubber.

Interior Simulation:

Housing assembly:

The shell is printed with JLC3D laser sintered nylon, and the accuracy and feel are OK, but the material is soft.

The keys are printed using transparent lithography 8001 translucent resin.

The modeling documents are attached as follows:

Note: The key also acts as a light guide function, due to the limitation of the actual key batch model error, shell printing error, etc., the height of the key needs to be adjusted according to the actual situation, here is to polish the upper surface of the key in order to adapt to the actual height of the PCB button.

Screw selection M2*10MM countersunk head screw *8.

Ultrasonic Transducer Model: H-CSD-OD15-66.5-40K Ultrasonic Knife Transducer (see attachment for technical data and modeling)

https://item.taobao.com/item.htm?_u=i20292vc2rfe37&id=771352524068&spm=a1z09.2.0.0.33392e8dwQNbUU

Housing fixed washer: 1.9*11mm washer

Instructions:

1. The power supply is abnormal, the voltage is insufficient, and it cannot be started (the power supply does not support fast charging and will also cause a red light)

Green light: The power is OK and the job is ready.

Blue light: power output, normal working state.

Development Process:

2024.10.26-V1.0 The scheme adopts BOOST boost + 2 times voltage to reach 400V through bridge inverter output.

Test results: the boost limit voltage is 268V, the bridge drive is not working properly, and the LDO power supply is seriously heated.

2024.11.15-V2.0 The solution uses BOOST + 3 times the voltage to reach 400V, and the power supply is replaced with DC-DC.

Test results: the bridge drive is abnormal, the boost cannot be loaded, the heat is large, and the overall volume is too large.

2024.12.18-V3.0 Single-tube drive pulse transformer for step-up.

The high-power load efficiency is low, and the power tube heats up greatly.

The follow-up improvement direction is to optimize the pulse transformer design and gate drive scheme to reduce heat generation.

Test Video:

https://www.bilibili.com/video/BV1HekKYAEHR/?vd_source=f2ecf6d07c56387a85d94b5338693a63

It is estimated that the effective conversion power of the actual transducer may only be more than 10W, and the paper can be cut continuously, but it cannot cut coarse plastic or metal materials, and the ultrasonic head cutting 6061 aluminum blade will rub against the aluminum to produce high temperature and sparks, but it cannot be cut.

Note: There will be high-frequency electromagnetic interference when the ultrasonic transducer is working, try not to use it near sensitive electronic products.