Snubber circuit

Details Snubber circuit Snubber circuit

2002-03-28

2003-09-09

Sircus, Brian (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

High voltage dissipation

C361S119000

Reexamination Certificate

active

06618235

ABSTRACT:

BACKGROUND OF THE INVENTION
Switching-induced transient overvoltages are a common problem in high-speed, high power switching circuits, such as switching power converters and pulse modulators. Rapid current or voltage changes during commutation generate transient voltages because of the energy stored in circuit inductances and capacitances. In modern high-power switching circuits where current and voltage slew rates can reach 1 kA/ &mgr;s and 10 kV/ &mgr;s, transient voltage spikes can be quite severe. A number of voltage transient suppression circuits and devices have been developed in an attempt to solve this problem.
It is known to use a capacitive “snubber” as a voltage transient suppression circuit. A “snubber circuit” is shown in
FIG. 1
generally at
10
(comprising a resistor
12
and capacitor
14
wired in series) in parallel with a switching power semiconductor
16
. The resistor
12
and the capacitor
14
together form the snubber circuit
10
, which is used in many different applications to limit the voltage overshoot and the rate of change in the voltage when a transient occurs in the system. A sudden rise in voltage across a switching power semiconductor
16
opening will be tempered by the charging action of capacitor
14
(the capacitor
14
opposing the increase in voltage by drawing current). During ON/OFF transition, the capacitor
14
is being charged by absorbing the energy stored in circuit inductance
17
. The resistor
12
limits the amount of current that the capacitor
14
will discharge through the switching power semiconductor
16
when it closes again. The capacitor
14
is discharged during the ON state of the switching power semiconductor
16
. Stored energy in capacitor
14
dissipates during the next ON period in resistor
12
and in the switching power semiconductor
16
. Although the operation of each of the various snubbers differs slightly from the others, the method employed by all of the snubbers to suppress transient voltage is similar.
These snubber circuits, while generally able to limit voltage transients to a desirable level, have several disadvantages. For example, one disadvantage of this snubber circuit is that, due to the typical nature of its function, the resistor is sized such that it can withstand the power applied when the capacitor is working properly, but the resistor would have significantly more than its rated power applied to it if the capacitor fails or is shorted. In a typical circuit, when the capacitor shorts, the resistor power dissipation can be 100 times higher than its rating. Consequently, if the capacitor fails, the resistor will fail catastrophically shortly afterward. It is usually undesirable to select the resistor power rating to continuously withstand shorted capacitor conditions due to cost and mechanical constraints. Also, in many applications, a mechanism to detect capacitor failure and remove power cannot act quickly enough to protect the resistor. Attempts to implement a faster detection circuit often result in false triggers due to noise, which adversely impact the equipments reliability. Thus, there is a desire to eliminate the possibility of catastrophic resistor failure should the capacitor fail in a snubber circuit, while still providing a reliable, cost effective, and mechanically practical power circuit design.
SUMMARY OF THE INVENTION
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a voltage transient suppression circuit for power electronic circuits comprising: a snubber circuit having a resistor and a first and second capacitive element connected in series with a resistive circuit element; and a sensing logic device connected in parallel with the snubber circuit. The logic circuit is configured to receive voltage signals indicative of said first and second capacitive elements of the snubber circuit, and said logic circuit utilizes said voltage signals to determine if a component failure has occurred.


REFERENCES:
patent: 4502085 (1985-02-01), Morrison et al.
patent: 4554500 (1985-11-01), Sokira
patent: 4709318 (1987-11-01), Gephart et al.
patent: 5115415 (1992-05-01), Mumby et al.
patent: 6043636 (2000-03-01), Gaudreau et al.

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