A frequency converter with a rectifier on an input side and a backup capacitor arranged downstream of the rectifier. Input-side phases of the rectifier feed the backup capacitor via multiple half-bridges of the rectifier. The input-side phases are connected to grid-side phases of a multiphase supply grid via a pre-circuit. Each grid-side phase is connected to an input-side phase within the pre-circuit via a phase capacitor. Each grid-side phase is additionally directly connected to another input-side phase within the pre-circuit via a switch and the grid-side phases are short-circuited with the input-side phases when the switches are closed. Each phase capacitor connects two grid-side phases or two input-side phases together. The frequency converter has a control apparatus which keeps the switches open when pre-charging the backup capacitor and closes the switches when a specified charge state of the backup capacitor is reached.

A power conversion apparatus includes a rectifier circuit, an inverse conversion circuit, and a capacitor. The rectifier circuit rectifies alternating current power of the alternating current power supply. The inverse conversion circuit inversely converts a voltage Vdc rectified by the rectifier circuit into an alternating current voltage having a certain frequency and applies the alternating current voltage to a motor whose maximum power consumption Pmax is 2 kW or larger. The capacitor is provided between the rectifier circuit and the inverse conversion circuit and has a capacitance C that satisfies a condition of a following expression in relation to an alternating current voltage Vac of the alternating current power supply and the maximum power consumption Pmax. $\begin{array}{cc}C\le 350\times {10}^{-6}\frac{P\max }{{\mathrm{Vac}}^2}.& \left(1\right)\end{array}$

A power train is described herein comprising a load, a first power supply for providing power to the load, a DC-link capacitor connected to the load, a main converter configured to convert DC power to AC power for powering the load; and pre-charge circuitry. The pre-charge circuitry comprises pre-charge means configured to, during a first, pre-charge phase, prevent said power from being provided to said load but provide power to said DC-link capacitor to charge said DC-link capacitor, and, further configured to, during a second, post-charge phase, allow said power to be provided from said first power supply to said load. A method for providing power to the load is also described herein.

An improved electric circuit structure for short circuit protection is applicable to examining a device under test, comprising a circuit breaking element, a thermistor, a filtering and rectifying module and a capacitor. A first end of the circuit breaking element is connected to a power source. The filtering and rectifying module is connected to a second end of the circuit breaking element, a ground, a first end of the thermistor and a first end of the capacitor. A second end of the capacitor is connected to a second end of the thermistor. The capacitor is connected in parallel with the device under test. The circuit breaking element disclosed in the present invention is a ceramic tube fuse and forms an open circuit when the device under test forms a short circuit. Meanwhile, the ceramic tube fuse withstands voltage between its first and second end without generating any physical damage.

In a power converter, an inductance L of a reactor and a capacitance C of a capacitor satisfy a condition of the expression (1) below. In the power converter, a current-limiting circuit between an AC power source and the capacitor is unnecessary. Herein, αm ([A.Math.s]) is a value of a ratio of a maximum rated current squared time product to a maximum rated output current of diodes of a rectifier circuit, Pmax is a maximum power consumption of the motor, Vac is a voltage value of a three-phase AC voltage, and a value of a constant a is 4.3

[00001]$\begin{array}{cc}a.C.\sqrt{\frac{C}{L}}.Math.\frac{{\mathrm{Vac}}^3}{P_{\max }}\le {\alpha }_m.& \left(1\right)\end{array}$

Disclosed herein is a AC direct LED driving apparatus. The light emitting diode (LED) driving apparatus includes: a rectifier configured to receive and rectify an alternating current (AC) voltage; an LED configured to emit light based on a rectified voltage received from the rectifier; a capacitor connected to a first terminal of the LED, and configured to drive the LED while alternating between charging and discharging sections according to a preset cycle; a first current driver connected to a second terminal of the LED and configured to control a path of current flowing in the LED and the capacitor based on different input voltage levels; a second current driver configured to control charging and discharging of the capacitor; and a first diode connected onto a current path of the capacitor and the second current driver, and configured to form a discharging path for driving the LED based on a charged voltage of the capacitor.

In order to restrain damage of a component due to rush current, a main relay in a power source circuit is not turned on and does not conduct a power source line even when a heat source microcomputer is activated with a capacitor not sufficiently charged. This configuration avoids start of charging the capacitor without current limitation, to restrain damage of the component due to rush current.

A voltage converter includes a circuit formed by a parallel association, connected between first and second nodes, of a first branch and a second branch. The first branch includes a first controlled rectifying element having a first impedance. The second branch includes a resistor associated in series with a second rectifying element having a second impedance substantially equal to the first impedance. The second rectifying element may, for example, be a triac having its gate coupled to receive a signal from an intermediate node in the series association of the second branch. Alternatively, the second rectifying element may be a thyristor having its gate coupled to receive a signal at the anode of the thyristor.

An improved electric circuit structure for short circuit protection is applicable to examining a device under test, comprising a circuit breaking element, a thermistor, a filtering and rectifying module and a capacitor. A first end of the circuit breaking element is connected to a power source. The filtering and rectifying module is connected to a second end of the circuit breaking element, a ground, a first end of the thermistor and a first end of the capacitor. A second end of the capacitor is connected to a second end of the thermistor. The capacitor is connected in parallel with the device under test. The circuit breaking element disclosed in the present invention is a ceramic tube fuse and forms an open circuit when the device under test forms a short circuit. Meanwhile, the ceramic tube fuse withstands voltage between its first and second end without generating any physical damage.

A voltage converter delivers an output voltage between a first and a second node. The voltage converter includes a capacitor series-coupled with a resistor between the first and second nodes. The resistor is coupled in parallel with a bidirectional switch receiving at its control terminal a positive bias voltage referenced to the second node.