UC3846 is a current pulse width modulation chip introduced by Unitorde. The modulation chip has double-ended output and can directly drive bipolar power tube or field effect transistor (MOSFET). Its main advantages are full-featured, automatic feedforward compensation, and powerful band. Load response characteristics, undervoltage protection, soft start, terminal lock protection. The peripheral control circuit is simple, and the operating frequency is up to 500kHz. It is suitable for the 100~3OOW regulated power supply, the highest input voltage is 40V, and it has self-protection function. The internal block diagram is shown in Figure 1. The internal circuit of UC3846 mainly includes: oscillator circuit, current measuring amplifier, error feedback amplifier, reference voltage source, overvoltage protection circuit and undervoltage lockout circuit. UC3846 pin and its The functions are shown in Table 1.
Figure 1 Internal structure of UC3846
Table 1 UC3846 pin function table
System block diagram shown in Figure 2, the vehicle power supply 24V, after the input filter circuit, isolation transformer, power converter, rectifier filter circuit, and finally get 24V output voltage. Figure 3 is a block diagram of the control system of the system. The system uses a double loop of current and voltage. The feedback voltage and the reference voltage are generated by the comparator. The error voltage Ue of the outer loop output is calculated by the PI controller. The result is used as the inner loop PI controller. Benchmark, dual closed loop improves the performance of isolated power supplies.
Figure 2 Block diagram of isolated power system
Figure 3 Double closed-loop control block diagram of isolated power supply
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