A classification scheme is used to categorize tapped-inductor switched-mode power supplies. This new scheme allows the many possible circuit variants to be displayed in a logical manner and analyzed for practicality and performance. The scheme offers a way of ensuring that no tapped inductor converter circuit is neglected when a tapped-inductor circuit is to be chosen for any particular application.

Synthesis of Tapped-Inductor Switched-Mode Converters

A pulse width modulated DC motor operating system is disclosed which reduces the communication back to the power supply of transient spikes caused by the switching characteristics of the freewheeling diode. The switched current path comprises, in series, a DC power supply, a low pass filter including charge storage means, a DC motor armature, a FET and a resistor. A freewheeling diode is connected across the motor armature. PWM signal generating apparatus switches the FET to control average motor armature current. A capacitor is connected across the FET and diode with minimal lead length to reduce stray inductance. The capacitor is effective to communicate voltage shifts across the resistor with FET switching to the cathode of the diode and thus serve as a source of supplemental current flow through the diode during diode switching partially in preference to the charge storage means of the low pass filter, whereby the diode switching voltage spikes communicated through the low pass filter to the DC power supply are reduced in amplitude and frequency and RFI is reduced. The resistor, along with another low pass filter, also provides an average motor armature current signal for current limiting apparatus and thus serves a dual function in the circuit.

PWM motor operating system with RFI suppression

An electric-discharge-machining power source in an electric discharge machine, which is capable of generating machining pulses each having a large peak value and a small pulse width, thereby attaining an improved machining speed. In the electric-discharge-machining power source, when supply of a power source voltage in between a workpiece (W) and a tool electrode (P) is prohibited by transistors (T1, T2), a generated return current attributable to energy accumulated in stray inductances (L1, L2) is returned to a high-voltage smoothing capacitor (C2) through return diodes (D1, D2). This allows the capacitor to be charged up to a voltage exceeding the power source voltage. As a result, the return current falls rapidly. In response to an output from a comparator (1) generated when a divided voltage (VH) corresponding to the capacitor charge voltage exceeds a reference voltage (VL), a transistor (T3) is rendered to be conductive. This allows the electric charge accumulated in the capacitor to be returned to a power-source-voltage smoothing capacitor (C1) through the transistor and an impedance (Z).

Electric discharge machining power source

A system for converting three-phase AC to DC voltage employs three separate converter circuits having their outputs connected in parallel to reduce current harmonics. Each converter circuit includes a full wave rectifier feeding a pulse width current modulator which modulates the DC current flow to the load in a manner to maintain the magnitude of the DC current proportional to the instantaneous magnitude of the DC voltage. The current modulators act as substantially resistive loads to reduce source current harmonics and correct the power factor. The modulators include a pair of transistors connected in a push-pull circuit which are controlled by an oscillator circuit to modulate the DC current at a frequency which is many orders of magnitude greater than the line frequency of the AC source. The DC current outputs of the modulators are coupled through DC/DC isolation transformers to the load.

Three-phase ac to dc power converter with power factor correction

Disclosed is a new single-phase passive harmonic filter for one or more nonlinear loads. The filter improves the total system performance by drastically reducing the line side current harmonics generated by nonlinear loads. The filter includes single-phase integrated inductances with an appropriately placed tap across which is connected a tuning capacitor. The combination of the inductance up to the tap position and the tuning capacitor form a series tuned filter configuration while the remainder of the integrated inductance is used for harmonic attenuation. A shunt capacitor is employed for shunting higher order harmonic components. A single-phase passive voltage regulator provides the needed voltage bucking to prevent over voltage at the load terminals of the filter. The filter provides an alternate path for the harmonic currents generated by nonlinear loads. The over voltage caused by the increased capacitive reactance is controlled by either capacitor switching or by the use of the passive voltage regulator or a combination of the two. Capacitor switching is dependent upon load conditions.

Single-phase harmonic filter system

Current spikes in a buck power converter due to commutating diode turn-off time is eliminated by using a tapped inductor in the converter with the tap connected to the switching transistor, without the commutating diode in the usual place, and instead connected to conduct current from one end of the tapped inductor remote from the load during the interval in which the transistor is not conducting. In the case of a converter having a center-tapped (primary and secondary) transformer between two switching power transistors operated in a push-pull mode and two rectifying diodes in the secondary circuit, current spikes due to transformer saturation are also eliminated by using a tapped inductor in the converter with the tap connected to the rectifying diodes and a diode connected to conduct current from one end of the tapped inductor remote from the load during the interval in which the transistors are not conducting.

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William T. McLyman

Papers

Elimination of current spikes in buck power converters