1, LED commonly used constant current chip: LM2623, MAX5033, NCP3063, TPS61042, FSDM311, NCP1027, NCP1216.
2, the constant current source is composed of signal source and voltage control current source (VCCS). The sinusoidal signal source adopts direct digital frequency synthesis (DDS) technology, that is, the sinusoidal sampling data is continuously read from EPROM at A certain frequency, and the sinusoidal signal required by EIT is generated after D\/A conversion and filtering. The system uses DDS integrated chip AD9830, which has two 12-bit phase registers and two 32-bit frequency registers. Under the control of the single chip microcomputer, the corresponding register can be easily obtained below 2MHz arbitrary frequency and phase output, in which the frequency accuracy is 1\/2 32, the phase resolution is 2π\/ 212, the output amplitude can also be adjusted within a certain range, so it can meet the requirements of the system multi-frequency excitation (10kHz ~ 1MHz).