There is disclosed a diode snubber for the voltage transients generated in the parasitic inductance of a switched resistor when current therethrough is interrupted. Also disclosed is the use of such a diode snubber in: a series switched resistor regulator; a shunt switched resistor regulator; a hybrid switched resistor regulator and a passbank switched resistor regulator. Also disclosed is the use of a linear dissipative regulator in all these forms of switched resistor regulators to maximize the effiency of power delivery to the load.
RELATED APPLICATIONS
This application is a continuation-in-part application of a U.S. patent application entitled "Switched Resistor Regulator With Linear Dissipative Regulator," Ser. No. 945,924 filed Dec. 23, 1986 now U.S. Pat. No. 4,719,404, which was a continuation-in-part application of a U.S. patent application entitled "Switched Resistor Regulator," Ser. No. 754,036, filed July 11, 1985, now U.S. Pat. No. 4,668,906, both of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention relates generally to power supplies, and, more specifically, to regulated power supplies using switched resistors having parasitic inductance.
One particular application for regulated power supplies is supplying power to ion lasers. Important factors for such power supplies are weight, speed, simplicity, reliability and radio frequency emissions.
U.S. patent application Ser. No. 754,036, filed July 11, 1985, now U.S. Pat. No. 4,668,906, describes a dissipative switched resistor regulator in which current flow through a resistor which is electrically connected to a load is controlled by varying the duty cycle of a switch which switches the resistor into and out of the circuit between a power source and the load; the resistor may be in series with or in parallel with the load. However, since there is always a series resistance between the source and the load when the switch is closed (for the series switched resistor regulator configurations), there is a minimum voltage drop which cannot be avoided even when the duty cycle is 100%. This unwanted lost power in the switched resistor results in poor efficiency. Also, the full source voltage cannot be applied to the load because of the voltage drop across the switched resistor when the duty cycle is 100%. The problem cannot be solved merely by decreasing the series resistance since this results in increased peak current through the switch which may exceed the capability of the switch to dissipate power. Also, decreased switched resistor resistance results in increased capacitor ripple currents.
The related U.S. patent application entitled, "Switched Resistor Regulator with Linear Dissipative Regulator", Ser. No. 945,924, filed Dec. 23, 1986, now U.S. Pat. No. 4,719,404, teaches a solution to this problem. The solution taught there is a linear dissipative regulator which bypasses the resistor and switch combination with a low resistance path when the duty cycle of the switch is 100%. This minimizes the power lost in the switched resistor during intervals when the duty cycle is 100%.
It has been found that the wire-wound resistors used for the switched resistor in some switched resistor regulator power supplies have parasitic inductance. This parasitic inductance causes voltage transients when current through the resistor is cut off. These voltage transients take the form of large voltage spikes which can damage switching transistors used to switch the resistors in and out of the circuit. Unless these voltage spikes are "snubbed", they can damage the switching transistors.
Designs for snubbers are well known. A simple design for a snubber is a capacitor which shunts the switching transistor. The capacitor acts as an initial short in passing the current of the voltage transient around the switch until the capacitor charges up. Such a design has the problem that the snubber capacitor charges up with the current in the transient spike. This charge must be bled off the snubber capacitor before the next cycle of the switch or the snubber capacitor will not be effective to snub the next transient. This bleeding off of charge occurs through the switch the next time the switch is turned on. This increases the electrical stress on the switch.
A lone capacitor cannot be used for the snubber without an additional series resistor. This is because the capacitor and the parasitic inductance together act as a tuned circuit and can oscillate or "ring". The addition of a series resistance sufficient to critically damp the circuit is necessary to suppress this ringing. However, this additional series resistance also slows down the process of charging and discharging the snubber capacitor. The slower charging tends to mitigate somewhat the effectiveness of the snubber. To regain the snubbing effectiveness, a diode is placed in parallel with the resistor such that the voltage transient will be of the proper polarity to forward bias the diode and charge the snubber capacitor through the diode. To protect the diode from being destroyed by excessive current, a small current-limiting resistor is placed in series with the diode. However, the diode is reverse biased during the discharge cycle to ready the snubber capacitor for the next transient, so discharging must occur through the series resistor. This slows the discharge rate and places a limitation on the maximum rate at which the switch may be operated since the next cycle cannot start until the snubber capacitor is fully discharged. A further disadvantage of the above-described prior art snubber design is that it is too complicated and expensive since it involves many components and many interconnections between them.
Accordingly, a need has arisen for a snubber design which is simple, effective, and inexpensive.
SUMMARY OF THE INVENTION
According to the teachings of the invention, there is taught the use of a diode snubber which is coupled across the switched resistor and its parasitic inductance. This flies in the face of teachings in the prior art to the effect that a diode cannot be used to snub an inductor. The reason for, this is that the average voltage across a pure inductor must be zero and this cannot be true when a diode is placed across the inductor. Current would rise to infinite levels since L di/dt must be non-zero if the average voltage across the inductor is not zero. This would be the case with a diode snubber.
In a system built according to the teachings of the invention, the snubber diode is placed in a shunt connection across the switched resistor and its intrinsic parasitic inductance. The switched resistor resistive component limits the rise of current to infinite levels which would otherwise tend to occur if the switched resistor resistive component were not present.
A high frequency voltage generator (10) produces a high positive voltage and a high negative voltage. A parallel connected coil (26) and diode (30) are connected between the high voltage supply and a target (44) of an x-ray tube (40). A second parallel connected coil (28) and diode (32) are connected between the negative voltage and an electron source (42) of the x-ray tube. The coils are preferably a multiple pancake design (FIG. 3 ). When the tube starts to arc, the sudden increase in current flow through the coil is converted and stored in a magnetic field leaving only a small current to contribute to arcing. The coils are sized such that the current which passes to the x-ray tube is sufficiently small that the arcing is usually extinguished without an avalanche phenomenon occurring. The diodes permit the energy stored in the magnetic field to be converted into a current flow through the coil and diode such that the energy is dissipated as heat by the inherent electrical resistance of the coil with only a minimal amount of the energy passing over time to the x-ray tube.
A dynamic sensor regulator that provides a mechanism for introducing desirable tonal artifacts in component-based guitar amplifier systems by inducing voltage fluctuations into the power supply of a preamplifier. The dynamic sensor regulator comprises a regulator circuit, connected to an amplifier that is connected to a converter circuit that is connected to a variable control circuit. The amplifier includes a floating bias circuit that dynamically adjusts the bias state of an output driving amplifier in response to signal fluctuations of the regulator output signal. A transformer is connected to the amplifier output and once the transformer's saturation point has been reached, the saturation of the transformer increases proportionally with the amplifier's input signal while the regulated output signal remains constant, emulating amplifier overload and saturation.
A pulse width modulation apparatus includes a load circuit, a signal switch, a shunt switch, and a resistor. The signal switch isolates the load circuit from a voltage source along a signal path. The shunt switch is connected to the signal path at a point between the signal switch and the load circuit. The shunt switch isolates the signal path from a ground voltage. A resistor is connected in series between the signal switch and the shunt switch.
An electrical switching device having a plurality of parallel coupled IGBTs is provided. The electrical switching device balances electrical currents in each of the IGBTs that are supplied to a load.
An improved power supply for converting any of various standard national AC network voltages to low-voltage DC power suitable for driving a 1 or 2-watt device, such as a fan, features a semiconductor control circuit (18, FET 46) which chops each half-wave of a rectified voltage and uses the low-voltage portions to feed charging current pulses to a storage capacitor. The voltage on the capacitor (14) is used by other portions of the circuit to regulate rotation speed of the fan or other consuming device (40) to a value set on a variable resistor. The use of the low-voltage portions of the input signal reduces power losses and increases efficiency.
