초록 ▼

Inrush currents in the dc intermediate circuit of a motor controller necessitate the incorporation of protection circuits. These circuits usually take the form of a resistor inserted in series with the intermediate circuit, and the resistor is short-circuited after completion of inrush by a switch p

Inrush currents in the dc intermediate circuit of a motor controller necessitate the incorporation of protection circuits. These circuits usually take the form of a resistor inserted in series with the intermediate circuit, and the resistor is short-circuited after completion of inrush by a switch positioned in parallel with the resistor. To reduce cable-transmitted electrical noise an earthed noise-decoupling capacitor is added to the intermediate circuit, but it also requires protection against inrush currents. To minimise the number of components, a protection circuit is described which combines noise filtration and inrush protection. According to the invention, the inrush resistor has the form of a resistor network and is connected to a switch which via a controller alters the resistance of the resistor network, so that when the switch is open, the resistance to a differential current is greater than the resistance to a common mode current, and when the switch is closed, there is greater resistance to a common mode current than to the differential current.

대표청구항 ▼

What is claimed is: 1. An electronic circuit for protection against inrush currents, the circuit comprising: an inrush resistor; a switch, which is controlled by a controller; and a noise-decoupling capacitor which diverts noise currents to earth; wherein the circuit is arranged in a DC intermediat

What is claimed is: 1. An electronic circuit for protection against inrush currents, the circuit comprising: an inrush resistor; a switch, which is controlled by a controller; and a noise-decoupling capacitor which diverts noise currents to earth; wherein the circuit is arranged in a DC intermediate circuit and inserted in series with an intermediate capacitor, the inrush resistor having the form of a resistor network connected to the switch, and wherein the controller via the switch alters the resistance of the resistor network, so that when the switch is open, the resistance to a differential current is greater than the resistance to a common mode current, and when the switch is closed, there is greater resistance to a common mode current than to the differential current. 2. The electronic circuit according to claim 1, wherein the circuit acts as both a noise filter and inrush protection when the switch is open, but as a noise filter only when the switch is closed . 3. The electronic circuit according to claim 2, wherein the circuit incorporates only one switch, and the switch is connected to the intermediate capacitor. 4. The electronic circuit according to claim 3, wherein the switch is connected in series between a first intermediate capacitor and a second intermediate capacitor, and that the resistor network is connected in parallel with the switch. 5. The electronic circuit according to claim 4, wherein the resistor network comprises two resistors connected in series and the noise-decoupling capacitor is connected between a midpoint common to the two resistors and earth. 6. The electronic circuit according to claim 1, wherein the resistance of the resistor network to the common mode current when the switch is closed, is lower than the resistance when the switch is open. 7. The electronic circuit according to claim 6, wherein one or more resistors in the resistor network are negative temperature coefficient resistors. 8. The electronic circuit according to claim 1, wherein the controller doses the switch immediately after the intermediate capacitor is charged. 9. The electronic circuit according to claim 1, further comprising: a further noise-decoupling capacitor connected to earth from a positive conductor of the intermediate circuit. 10. The electronic circuit according to claim 1, the circuit further comprising: an initial noise-decoupling capacitor placed prior to a rectifier; and a second noise-decoupling capacitor, which is connected to the initial noise-decoupling capacitor and to a supply line; wherein in parallel with the initial noise-decoupling capacitor a second switch is connected, which second switch is controlled by the controller. 11. The electronic circuit according to claim 1, wherein the switch is a relay or a transistor.