A Low-Power Constant-Current Converter with HIC Techniques and its Circuit Simplification

A low-power constant-current converter that is required to be small and inexpensive, is developed. The most effective means for size and cost reduction is to introduce hybrid IC (HIC) techniques and to mount as large a number of circuit elements as possible on the HIC substrate. Application of a circuit with a simple configuration is important for the HIC techniques. A flyback type converter that has a small number of parts is utilized, and circuit simplification techniques are developed. The driving transformer for isolation between the input and output in the control loop is replaced by a photocoupler, and the power supply for the transformer secondary circuit is improved to miniaturize the converter. A control circuit to compensate for phase-lag in the photocoupler is studied and a simple method is proposed. Both a method for simplifying the circuits and the analysis and design of the phase-compensation circuit for the constant-current converter are described. The converter is miniaturized to 9.2 cm³/W by application of the HIC technique. The size of the converter corresponding to one subscriber can be reduced to 1/5 compared with that of the conventional multi-output converter.