DE1789158B1

DE1789158B1 - Overvoltage protection circuit for a thyristor

Info

Publication number: DE1789158B1
Application number: DE19661789158
Authority: DE
Inventors: Manfred Dipl-Ing Liska; Ulrich Dipl-Ing Michael; Herbert Poppinger
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1966-04-26
Filing date: 1966-04-26
Publication date: 1974-09-26

Description

lanchediode η 4. Diese Avalanchediode η 4 liegt mit einem Widerstand r S und einer Entkopplungsdiode η 3 in Serie. Über diesen Zweig ist die Shockleydiode ρ 2 mit der Anode des Thyristors ρ 1 verbunden. Der Auslösepunkt bzw. die Auslösespannung dieser Anordnung wird bestimmt durch die Grenzspannung der Avalanchediode η 4 — die auch eine Zenerdiode sein kann —, bei der der Stromfluß über diesen Zweig stark zunimmt. Da zum Zünden der Shockleydiode ρ 2 nur der Schaltstrom erforderlich ist, der kleiner als 200 uA ist, kann der Strom über die Avalanchediode η 4 durch den Widerstand r 5 soweit begrenzt werden, daß auch über einen längeren Zeitraum die Diode η 4 nicht durch hohe Verlustleistung gefährdet wird.lanchediode η 4. This avalanche diode η 4 lies with a resistor R s and a decoupling diode η 3 in series. The Shockley diode ρ 2 is connected to the anode of the thyristor ρ 1 via this branch. The trigger point or the trigger voltage of this arrangement is determined by the limit voltage of the avalanche diode η 4 - which can also be a Zener diode - at which the current flow through this branch increases sharply. As for igniting the Shockleydiode only the switching current ρ 2 is required, which is less than 200 uA, the current can η about the avalanche diode 4 r through the resistor 5 are limited to the extent that even over a longer period, the diode does not η 4 by high Power loss is endangered.

Der eigentliche Zündstrom für den Thyristor ρ 1 wird dem Kondensator c 2 entnommen, sobald die Spannung an der Shockleydiode ρ 2 die Spannung an der Zenerdiode η 5 unterschreitet. Durch den Kondensator c 1 wird im wesentlichen sichergestellt, daß beim Zuschalten der Netzspannung die Überspannungsschutzschaltung sofort betriebsbereit ist.The actual ignition current for the thyristor ρ 1 is taken from the capacitor c 2 as soon as the voltage at the Shockley diode ρ 2 falls below the voltage at the Zener diode η 5. The capacitor c 1 essentially ensures that the overvoltage protection circuit is immediately ready for operation when the mains voltage is switched on.

Hierzu 1 Blatt Zeichnungen1 sheet of drawings

Claims

1 - 21 - 2

depends. In addition, there are only Shockley diodes

Claim: a reverse voltage of a maximum of 200 to 300 V. Es

would therefore have to have several such diodes in series

Overvoltage protection circuit can be switched for a Thy-. But this creates the ristor again, with a problem connected in parallel with the thyristor, for a uniform potential distribution th RC element, whose capacitor has to be provided via one.

Shockley diode of the control path of the thyristor It has also been proposed in place of the

is parallel, whereby the resistor of the RC- mentioned diode use a small auxiliary thyristor to link another capacitor connected in parallel and ignite this overhead. The tet is characterized in that the ignition timing depends not only on the capacitor (c2) of the AC element (c 2, rl) on the absolute value, but also on a Zener diode (nS) connected in parallel that the Differential quotient of the voltage. One between the anode of the thyristor (p 1) and the further uncertainty lies in the strong Temperaturi? C element a diode (n 1) is connected, that dependence of the tipping point, which is also of copy between the tap of the .RC element and the 15 can have very different values for each specimen. Shockley diode (p 2) a decoupling diode (n 2) A common feature of all protective circuits mentioned is that the control electrode of the thyristor has a further disadvantage in that the shockley diode and another decoupling response point of the protective circuit are not free-lungs diode (n 3) and an avalanche diode (η 4). selected and adapted to the thyristor to be protected is connected to the anode of the thyristor and can be 2 °, but of the available diodes that the zener diode is dimensioned so that the or auxiliary thyristors depends.
Voltage on the capacitor lying parallel to it. An overvoltage protection circuit of the input

(c 2) for igniting the Shockley diode not mentioned type is sufficient for example from the lit. raturstelle »Hitachi-Hyoron (Hitachi-Rundschau)«,

25 Volume 46 (March 1964), issue 3, page 533, image 4,

--- known. With this circuit are some of the on

problems shown overcome. It does occur, however

The invention relates to an overvoltage protection circuit for a thyristor in this known overvoltage protection circuit, with an i? C element connected in parallel with the Thy- difficulties in dimensioning the Bauristor, its condensate 30 elements, in particular in the dimensioning of the sator via a Shockley diode of the control path of the resistor and the capacitor of the .RC element thyristor is parallel, the resistance of the due to the frequency response of the i? C element on,
i? C element a further capacitor connected in parallel- It is the task of an overvoltage

is tet. protective circuit of the type mentioned at the beginning

An overvoltage protection for thyristors seems to make it possible that difficulties in the dimensioning are not necessary at first sight, since it is possible to avoid components,
yes belongs to the essence of such a component, according to the invention this task is thereby

that it also triggers the conductive state that the capacitor of the RC element flips when the applied voltage is connected in parallel to a certain Zener diode that exceeds the limit value between th. This also applies to the 4 ° anode of the thyristor and the RC element a diode if no control current is supplied to the thyristor that is between the tap of the RC- . The limit voltage required for tilting the limb and the Shockley diode decoupling is correspondingly higher. It is said in the diode that the control electrode of the thyristor is "overhead" in the case of an igniter. via the Shockley diode and another decoupling

It has now been shown that such an overhead diode and an avalanche diode ignite with the anode in power thyristors is definitely connected to the thyristor and that the Zener diode must be avoided, since such components remain, is dimensioned so that the voltage at the same time you can take the damage. In order to prevent the lying capacitor to ignite the one between the anode and the control path Shockley diode is not enough,
a power thyristor via a resistor a 50 In the following, the over-Shockley diode or Zener diode according to the invention is switched (SCR voltage protection circuit exemplarily with reference to the manual, publisher General Electric, 3rd edition, figure explained in more detail.

Pp. 34-35). These diodes must be designed in such a way, In the figure, the thyristor to be protected is ρ 1

that a current flow is only possible when the designated. Its anode-cathode route is the maximum permissible operating voltage at the thyri-55 via a valve η 1 an ÄC element, consisting of the disturbance is reached. But then a relatively high resistance r 1 and the capacitor c 2 must be able to flow in parallel so that the thyristor is also switched. Parallel to the resistance r 1 there is a white safety blown. terer capacitor c 1 and parallel to the capacitor

Circuits, the ER, the conditions indicated c2 is a Zener diode η 5. The control path of the fill, are serious drawbacks with behaf- ^6o thyristor ρ 1 is a tet via a resistor R. 3 For example, with regard to the four-layer diode ρ 2, usually called a Shockley diode, a relatively high, maximum permissible operating diode and a decoupling diode η 2 had to be connected to a Zener diode with an RC element to tap the voltage of the thyristors. The Zener diode η 5 is so high a breakdown voltage and a corresponding measure that the voltage on the capacitor2 high power dissipation can be used. The second part of the Shockley diode to ignite the Shockley diode can be seen in the fact that its ρ 2 required limit value can be reached. The breakdown voltage of an ava-