WO2003009455A2

WO2003009455A2 - Circuit breaker

Info

Publication number: WO2003009455A2
Application number: PCT/AT2002/000208
Authority: WO
Inventors: Harald Schweigert; Stefan Gut
Original assignee: Siemens Ag Österreich
Priority date: 2001-07-16
Filing date: 2002-07-15
Publication date: 2003-01-30
Also published as: WO2003009455A3; AT411945B; EP1407530A2; ATA11042001A

Abstract

The invention relates to a switch converter with a primary winding of a transformer (UET) in series with a switch console (T, S), comprising a self-conducting semiconductor switch (S) and an auxiliary semiconductor switch (T). The longitudinal voltage (USD) of the auxiliary switch is supplied to a control circuit (AST) as operating voltage (UB) at least at the start and the output thereof is applied to control elements of the auxiliary switch.

Description

SWITCHING DEVICE

The invention relates to a switching device consisting of a controlled by a drive circuit switch, via which a load circuit to an input voltage can be laid, from which at least temporarily an operating voltage for the drive circuit is derived, the controlled switch is in cascade with an auxiliary semiconductor switch, wherein the Output of the drive circuit is guided to the control electrode of the auxiliary switch, the control voltage of the switch is equal to the longitudinal voltage of the auxiliary switch and this longitudinal voltage of the drive circuit is supplied as the operating voltage.

Likewise, the invention relates to a switching converter having a transformer with a primary winding and at least one secondary winding, wherein the primary winding is connected in series with a controlled switch to an input voltage and with a drive circuit which supplies drive pulses for the switch, wherein from the input voltage at least temporarily, an operating voltage for the drive circuit is derived, the controlled switch is cascoded with an auxiliary semiconductor switch, wherein the output of the drive circuit is guided to the control electrode of the auxiliary switch and the control voltage of the switch is equal to the longitudinal voltage of the auxiliary switch, and this longitudinal voltage) of the drive circuit as Operating voltage is supplied.

In many fields of electrical engineering, such as power engineering, power supplies, etc., there is a desire to switch high voltages by means of semiconductor switches or timed to a load to thereby lower down, for example, the contact wire voltage of electrical paths to avoid, or to From heavy power frequency transformers to be able to move to much smaller and lighter transformers, for example, operate at 20 kHz or more.

The supply voltage for the drive circuit is expediently derived from a secondary voltage of a switching converter or derived with the aid of series resistors from the high input voltage. The former solution is inherent to the problem that a switching converter must be tarnished in the first place in order to generate a secondary voltage and that switching pulses of the drive circuit are also required for the starting process. At least large delays occur between switching on an input voltage and providing a secondary voltage. In the second-mentioned solution, ie the use of a series resistor, there are high losses in the resistors, since a voltage of, for example, 600 volts must be reduced to one of 12 volts. Because of these losses must also be provided for a special heat dissipation of the series resistor for the supply voltage of the drive circuit.

In one of the US 5,602,724 A become known circuit of the type specified, a cascode circuit of the controlled switch is used with an auxiliary switch and it is mentioned that the drive circuit can also be supplied by the drain voltage of the auxiliary semiconductor switch. However, the mentioned disadvantage of increased losses remains, since the gate of the controlled switch is supplied via a voltage divider from the input voltage.

There are also solutions known to wegzuschalten such series resistors after the startup of a switching converter and then to gain this operating voltage of the drive circuit of a secondary voltage of the switching converter. This naturally leads to a further component complexity.

Another solution for supplying the drive circuit is the use of an auxiliary power supply with a mains frequency driven transformer or the use of its own switching converter whose input is connected to the input voltage. In all cases, the component cost is high, for example, in view of the required insulation of the windings of small supply transformers, which are at a high input voltage.

An object of the invention is therefore to provide a switching device that is particularly suitable for switching high voltages and in which a simple and secure way a power supply of the drive circuit is guaranteed at least during startup. In particular, the supply voltage should not fail even at idle or parallel operation and idle and the power loss should be as low as possible.

The stated object is achieved with a switching device of the type mentioned, in which the controlled switch is a self-conducting semiconductor switch, which is in cascode with an auxiliary semiconductor switch, wherein the output of the drive circuit is guided to the control electrode of the auxiliary switch, the control voltage of the switch equal the longitudinal voltage of the auxiliary switch and this longitudinal voltage is supplied via a rectifier of the drive circuit as the operating voltage. In the solution according to the invention, the longitudinal voltage of the auxiliary switch is rectified and is available as the operating voltage of the drive circuit, whereby a defined voltage is present in a usable range. Despite a high input voltage increases in the selected cascode circuit, the voltage at the auxiliary switch not higher than z. As the pinch-off voltage of the (main) switch, which is responsible for switching the actual high voltage.

Advantageously, the longitudinal voltage of the auxiliary switch of the drive circuit is supplied via a decoupling diode.

In an advantageous embodiment, it is provided that in series with the coupling-out diode is a protective resistor, which can also be dimensioned by its load capacity so that it acts as a burn-off fuse in the event of a short circuit.

It is particularly advantageous to use the invention if the controlled switch is a SiC JFET. For applications with such a switch particularly high input voltages can be switched, in which a supply of the drive circuit by conventional means is even more difficult or more expensive than household power voltages.

It is also advantageous if the auxiliary switch is an IGFET, since this is well suited in combination with a controlled switch of high dielectric strength in a cascode.

The switching device according to the invention has particular advantages when the load branch is a primary winding of a transformer in a switching converter.

The specified solution is also suitable in connection with a switching converter of the type specified above to solve the problems mentioned. Especially with switching converters, the problems mentioned are of particular importance. Again, there may be a protective resistor in series with the coupling-out diode, the controlled switch may be a SiC-JFET, or the auxiliary switch may be an IGFET.

In an advantageous variant, it is provided that a continuous operating voltage source is provided and this continuous operating voltage is applied to the operating voltage input of the drive circuit using a circuit breaker. These solutions are in terms of switching off the available during start-up operating voltage of the above solution with a series resistor, but here eliminates the unnecessary power consumption in the series resistor. If the continuous operating voltage is higher than the operating voltage during startup, a diode can be used as a disconnector, in the simplest case, the decoupling diode, which is provided anyway. If the continuous operating voltage is lower than the operating voltage obtained in accordance with the invention, a controlled switch can be provided for switching off the operating open-circuit. As a source for the Dauerwetriebsspannxmg may also be provided a separate transformer with nachgespeichertem rectifier.

In view of the not insignificant within the scope of the invention question of high input voltage and withstand voltage of the controlled switch, it is particularly advantageous if the transformer has a protective winding, which - opposite to the Primärwicklung- via a protective diode to the input voltage.

The invention together with further advantages is explained below with reference to exemplary embodiments with reference to the drawings. In this show

• Figure 1 shows a basic circuit for a switching device according to the invention, and

2 shows a switching converter according to the invention, which uses a switching device according to FIG.

1, which is generally intended to explain the principle of the invention, is an input voltage UZK via a controlled switch T to a load LAS. The switch T is to be controlled by a drive circuit AST, which supplies switching pulses. Usually duty cycle and / or frequency of the switching pulse can be changed. In the present case, the control of the switch T is not directly, but via an auxiliary switch S, the (main) switch T and / or auxiliary switch S are in a known cascade circuit, which is explained in more detail below using example switching types.

The controlled switch T is in the embodiment of Fig. 1, an n-channel SiC-JFET, ie, a junction field effect transistor in silicon carbide technology. Such a FET, which is self-conducting, offers various advantages over a silicon FET, in particular a much higher dielectric strength in the order of 1500 volts, an approximately 3 times higher thermal conductivity of the base material silicon carbide, higher operating temperatures of 300-400 ° C and a much better switching performance compared to Si MOSFETs in the same power range. The switch T conducts when its gate-source voltage UGS is zero, and it turns off when its gate-source voltage U _G S has reached the so-called pinch-off voltage Up. This pinch-off voltage is about 20 to 40 volts for a SiC JFET. For driving the switch T is with this the auxiliary transistor S in series, in the example, an n-channel IGFET / E, thus a self-locking insulating layer field effect transistor. The gate of the switch T is connected to the source of the auxiliary switch S, the source of the switch T to the drain of the auxiliary switch S, and the source of the auxiliary switch S is here at the negative pole of the input voltage UZK. Drive pulses of the drive circuit AST are supplied to the gate of the auxiliary switch S.

When the auxiliary switch S is turned on, the source potential of the switch T is pulled to "minus", whereby the switch T begins to conduct when the potential difference between its gate and source falls below the pinch-off.

When switching off the auxiliary switch S opens the potential connection between the source and gate of the switch T, which is above the auxiliary switch, d. H. between whose drain and source a voltage builds up, which now causes the switching off of the switch T as soon as its value has reached the pinch-off voltage.

It is essential that the drain-source voltage of the auxiliary switch, which is equal to the gate-source voltage of the (main) switch T, never be greater than the pinch-off voltage ("pinch off" voltage), so that when open Switches T and S is the voltage to be switched minus the pinch-off voltage to the voltage-resistant switch T. The auxiliary switch S must therefore have only a low withstand voltage of, for example, 50 volts.

The lying at the auxiliary switch S longitudinal voltage UDS is supplied via a coupling diode Dl and a smoothing capacitor G of the drive circuit AST as the operating voltage UB, whereby immediately when switching on the input voltage in the start-up phase, the power supply for the drive circuit is ensured. After starting, the longitudinal voltage UDS of the auxiliary switch S is a square wave voltage corresponding to the AnSteuerimpulsen, which can be used after rectification and screening as a continuous operating voltage for the drive circuit AST, if you do not resort to a different Spannungsversorgimg in this case, which will be discussed below in connection with Fig. 2 is explained. In Fig. 2, an application of the switching device according to the invention or an inventive switching converter is shown. An input AC voltage U _E is rectified by means of a rectifier GLR and smoothed using a capacitor CZK. At this capacitor is a Zwischenkreissparmung or input voltage UZK, which can be placed on the in Fig. 1 explained in more detail switching circuit code T + S to a primary winding Li of a transformer UET. This primary winding Li thus represents the load according to FIG. 1. The current flowing through the switching cascode S + T is measured in the present example with the aid of a measuring resistor Ri.

The voltage occurring at a secondary winding L ₂ is rectified with the aid of a rectifier T ₂ and smoothed on a capacitor C ₂ , so that a secondary output DC voltage UA is formed. The output current can be detected by means of a measuring resistor Rs.

Again, a drive circuit AST is provided which provides drive pulses for the auxiliary switch S. The operating voltage UB of the drive circuit AST is obtained analogously to FIG. 1, but here is still a protective resistor RT connected in series with the output diode Dl. This protective resistor can also be dimensioned so that in the case of a short circuit of the operating voltage Ü _B intentional burning of the resistor takes place in the sense of a backup.

In the embodiment according to FIG. 2, an auxiliary winding LH of the transformer UET is furthermore provided, which can generate a continuous operating voltage UB 'for the drive circuit with the aid of a rectifier DH and a smoothing capacitor C _H. It is then provided a means to turn off the start of the entire circuit according to the invention generated operating voltage Ü _B. If the auxiliary operating voltage UB 'is greater than the operating voltage UB, the function of the switch can be taken over by the decoupling diode Dl, which is shown in the present case. Alternatively, what is likewise indicated in FIG. 2, a controlled switch SWI ensures the switching off of the operating voltage UB generated according to the invention after the circuit has started up. The switch SWI could be opened by a simple control circuit, for example, as soon as the auxiliary operating voltage UB 'has reached a certain value. In this case, it would even be possible to dispense with the decoupling diode D1.

The pulse generated by the drive circuit AST changes in the present case its duty cycle, optionally also the frequency, in dependence on supplied variables, in particular the output voltage UA and the associated output current. These quantities are fed to an evaluation circuit AWS and usually via an optocoupler OKO forwarded as input to the drive circuit AST. In this way, regulation or limitation of output voltage and / or current can be carried out in a manner known to the person skilled in the art. Likewise, it is well known to those skilled in the art that the current through the primary winding Li, here measured at the resistor Ri, is supplied as an input to the drive circuit AST, for example, to determine the end of the type control pulses.

Since the invention proves to a particular extent in the presence of high input voltages UZK, it is also expedient if, as in the present case, a protective winding Ls of the transformer UET is provided which is opposite to the primary winding Li via a protective diode Ds to the input voltage UE. In this way, the voltage generated at the primary winding Li during demagnetization can be limited to a maximum of twice the input voltage.

Fig. 1 has shown a representative application of the invention using the example of a switching converter, but it should be understood that other applications, such as boosters, step-down converters or inverters in general, are also possible. For example, the inventive generation of the operating voltage in a drive circuit of double-H bridges with six switches for generating a three-phase AC voltage, the supply of the floating gate drive circuits take over. In fact, such converters have a particular problem in that their own gate supply power supply units must be provided with elaborate, electrically isolated output voltages, with starting of the drive circuits being necessary in time before the power unit. Here, by applying the invention and by optical transmission of the drive pulses, the overall circuit can be made much simpler.

Furthermore, the invention of particular advantage in the series connection of a larger number of power semiconductors, z. B. for DC power transmission, be, in which the drive pulses are transmitted via optical fibers. In such applications, of course, the construction of its own auxiliary power supplies for supplying the drive circuits is particularly complex.

Claims

1. switching device consisting of one of a drive circuit (AST) controlled switch, via which a load circuit (LAS; Li) to an input voltage (UZK) can be laid, from which at least temporarily an operating voltage (UB) is derived for the drive circuit, the controlled Switch (T) is in cascode with an auxiliary semiconductor switch (S), wherein the output of the drive circuit (AST) is guided to the control electrode of the auxiliary switch, the Steuerspannimg (Ugs) of the switch (T) equal to the longitudinal voltage (USD) of the auxiliary switch (S ) and this longitudinal voltage of the drive circuit is supplied as operating voltage (ÜB), characterized in that the controlled switch (T) is a self-conducting semiconductor switch.

2. Switching device according to claim 1, characterized in that the longitudinal voltage (U _SD ) of the auxiliary switch (S) of the drive circuit (AST) via a coupling diode (Dl) is supplied

3. Switching device according to claim 2, characterized in that in series with the coupling diode (Dl) is a protective resistor (Dl).

4. Switching device according to one of claims 1 to 3, characterized in that the controlled switch (T) is a SiC-JFET.

5. Switching device according to one of claims 1 to 4, characterized in that the auxiliary switch (S) is an IGFET.

6. Switching device according to one of claims 1 to 5, characterized in that the load branch is a primary winding (LI) of a transformer (UET) in a switching converter.

7. Switching converter with a transformer (UET) having a primary winding (Li) and at least one secondary winding (L ₂ ), wherein the primary winding in series with a controlled switch (T) to an input voltage (UZK) and with a drive circuit (AST ), which supplies drive pulses for the switch, wherein at least temporarily an operating voltage (UB) for the drive circuit is derived from the input voltage, the controlled switch (T) in cascode connection with a Auxiliary semiconductor switch (S) is located, wherein the output of the drive circuit (AST) is guided to the control electrode of the auxiliary switch and the control voltage (Ugs) of the switch (T) equal to the longitudinal voltage (USD) of the auxiliary switch, and this longitudinal voltage) of the Ansteuerschalrung as the operating voltage (UB), characterized in that the controlled switch (T) is a normally-on semiconductor switch.

8. Switching converter according to claim 7, characterized in that the longitudinal voltage (USD) of the auxiliary switch (S) of the drive circuit (AST) via a coupling diode (Dl) is supplied.

9. Switching converter according to claim 8, characterized in that in series with the coupling diode (Dl) is a protective resistor (RT).

10. Switching converter according to one of claims 7 to 9, characterized in that the controlled switch (T) is a SiC-JFET.

11. Switching converter according to one of claims 7 to 10, characterized in that the auxiliary switch (S) is an IGFET.

12. Switching converter according to one of claims 7 to 11, characterized in that a continuous operating voltage source is provided and this continuous operating voltage (ÜB) using a circuit breaker (SWI, Dl) to the operating voltage input of the drive circuit (AST) is set.

13. Switching converter according to claim 12, characterized in that the transformer (UET) has an auxiliary winding (LH) for generating a continuous operating voltage (Ü _B ') by means of a downstream rectifier (DH) and smoothing capacitor (CH).

14. Switching converter according to one of claims 7 to 13, characterized in that the transformer (UET) has a protective winding (Ls) - opposite pole to the primary winding (Li) - via a protective diode (Ds) to the Eingangspannimg (UE).