An integrated circuit contains the gate drivers and the control components for constructing a DC power supply in any of the most popular converter topologies. Multi-function elements in the control circuit minimize the area of the chip. The integrated circuit drives both the upper and lower switches of a half-bridge converter and separately regulates two power supply output voltages, one by pulse width modulation and the other by frequency modulation.

Integrated circuit for controlling power converter by frequency modulation and pulse width modulation

In a self-oscillating type switching power supply in which an input source, a primary winding of a transformer, and a switching element are connected in series, and a constant output is supplied to a load from a secondary winding of the transformer by the operation of the switching element, in order to obtain a signal to turn off the switching element, a sense circuit for detecting the output of the switching power supply is provided, and the analog signal from the sense circuit is inputted to one winding of a saturable reactor, and at a time point when the switching element is to be turned off, the analog input signal is converted into a pulse signal insulated from the analog input signal, and the pulse signal is outputted from another winding of the saturable reactor. By such a system, a switching power supply having a very simple circuit arrangement and high output voltage precision can be achieved.

Switching power supply using a saturable reactor to control a switching element

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DC-DC converters are the heart of any switched mode power supply (SMPS) system. Rather than using multiple number of DC-DC converters for regulating voltage of each of the outputs in a multi-output SMPS, the reliability and cost-effectiveness can be improved if a single DC-DC converter is used and viable control technique is employed to regulate the voltages effectively. This paper deals with such a multi-output SMPS of 175W rating, typically used in a personal computers (PCs), using forward boost converter. An effort is made to improve the input power quality also at the utility interface by employing average current control mode. The effect of load variation and input supply variation on SMPS is studied to demonstrate the performance and effectiveness of this converter in regulating the outputs in the wide range of mains voltage.

Power quality improvement in multi-output forward boost converter

When the power source voltage is charged to a capacitor between the source side of a MOSFET and a saturation reactor at the time of starting, the gate voltage of the MOSFET is caused to rise. When this charging voltage or the gate voltage exceeds the threshold voltage, the MOSFET is energized. The energization of this MOSFET induces a voltage in the tertiary self-excited oscillation winding through the primary winding, and a part of the induced voltage is applied to the gate of the MOSFET while some other part is applied to the reactor. This causes the magnetic flux of the saturation reactor to be set to the direction opposite that which had been set before. When the product of the voltages applied to the saturation reactor has reached the level for the allowable saturation magnetic flux density the saturation reactor is saturated and the gate voltage is discharged to turn off the MOSFET. When the MOSFET is energized once, the setting and resetting of the saturation reactor is repeated alternately due to the actions of the primary winding and the tertiary self-excited winding to enter the state of stable operation.

Starting circuit of self-excited inverter

A ringing choke converter using a single core saturable reactor in the control circuit is described. Besides the few components, simplicity and small size usually found in self-oscillating converters, this converter features a saturable reactor protective functions for overcurrent through the main transistor switch and for magnetic saturation of the power transformer, and good isolation of output from input.

A Saturable Reactor Controlled Ringing Choke Converter

This thesis pertains to a forward converter consisting only of primary-side control circuits for regulating the output voltage. Control circuits in a conventional forward converter for regulating the output voltage control the on and off times of primary-side switching transistor by comparing the output voltage directly with the reference voltage. To isolate the primary from the secondary, the converter must contain not only the main transformer but also insulated transformers in control circuit power supply and transistor driver circuits. Since the forward converter described in this thesis converts output voltage to primary-side voltage proportioned to the output voltage by the main transformer, all control circuits in the converter can be configured on the primary side; to isolate the primary side from the secondary side, only the main transformer need be insulated. The converter generates a fly-back voltage from energy stored in the main transformer by turning a transistor on and cramps the voltage at a level proportional to the output voltage. This thesis describes how this forward converter produces stable output.

Simplified Isolated Forward Converter

This paper introduces a DC-to-DC converter which simultaneously regulates two output voltages individually by turning a transistor switch on and off to give good regulation and high conversion efficiency. The converter combines a buck and a buck-boost converter through one transistor switch; the buck circuit operates in the continuous inductor current mode, and the buck-boost circuit operates in the discontinuous inductor current mode. Together they can regulate two output voltages by controlling the duty ratio and operating frequency of the switching operation.

M. Kohno

Papers

A Saturable Reactor Controlled Ringing Choke Converter

Simplified Isolated Forward Converter

Single-Ended DC-to-DC Converter with Two Individually Controlled Outputs