Adjustable non-dissipative voltage boosting snubber network
This disclosure describes a non-dissipative snubber circuit configured to boost a voltage applied to a load after the load's impedance rises rapidly. The voltage boost can thereby cause more rapid current ramping after a decrease in power delivery to the load which results from the load impedance rise. In particular, the snubber can comprise a combination of a unidirectional switch, a voltage multiplier, and a current limiter. In some cases, these components can be a diode, voltage doubler, and an inductor, respectively.
1. A power system comprising:
a DC power supply supplying DC power to first and second rails having a voltage between the first and second rails;
a switching circuit receiving the DC power via the first and second rails and converting the DC power to a pulsed DC voltage, the pulsed DC voltage configured for application to a plasma load; and
a snubber circuit coupled to the first and second rails such that the voltage between the first and second rails falls across the snubber circuit, the snubber circuit comprising:
a first unidirectional switch configured to allow current to pass from the first rail;
a voltage multiplier coupled between the first unidirectional switch and the second rail, and configured to:
absorb and store energy from the DC power supply via the first unidirectional switch when an impedance seen by the switching circuit increases;
boost the voltage between the first and second rails by virtue of absorbing and storing the energy from the DC power supply;
then apply at least a portion of the stored energy to the switching circuit when the impedance seen by the switching circuit decreases and thereby decrease the voltage between the first and second rails; and
an electrical node between the first unidirectional switch and the voltage multiplier; and
a current limiter coupled between the electrical node and the first rail and limiting rises in current that the voltage multiplier discharges to the switching circuit.
2. The power system of claim 1 , wherein the snubber circuit further comprises a second unidirectional switch having an anode coupled to the inductive circuit and a cathode coupled to the first rail.
3. The power system of claim 1 , wherein the first unidirectional switch includes a diode.
4. The power system of claim 1 , wherein the inductive circuit includes an inductor.
5. The power system of claim 4 , wherein the voltage multiplier includes two capacitors in parallel.
6. The power system of claim 5 , wherein the two capacitors charge in series and discharge in parallel.
7. The power system of claim 6 , wherein the voltage multiplier includes at least two diodes.
8. The power system of claim 1 , wherein the voltage multiplier increases the voltage on the first rail by a factor of two.
9. The power system of claim 1 , wherein the voltage multiplier increases the voltage on the first rail by a factor of between one and two.
10. The power system of claim 1 , wherein the inductive circuit limits a rise in current provided to the plasma load when one or more plasma arcs occur.
11. The power system of claim 1 , further comprising a first switch coupled between the cathode of the first unidirectional switch and the inductive circuit, the first switch configured to create an open circuit between the first unidirectional switch and the inductor when one or more plasma arcs occur.
12. The power system of claim 11 , wherein current passing through the inductive circuit adds energy to the voltage multiplier when the first switch is open, and this energy is delivered to the plasma load through the inductive circuit when the first switch is then closed.
13. The power system of claim 11 , further comprising a unidirectional switch coupled between the second rail and an electrical node coupling the first switch and the inductive circuit, the unidirectional switch preventing a voltage spike in the inductive circuit when the first switch opens.
14. The power system of claim 11 , further comprising a voltage multiplier modifier that provides a variable control over the increase in the voltage of the DC pulses for the first portion of each pulse.
15. The power system of claim 11 , wherein the switch closes at the start of each pulse and remains closed for a first portion of each pulse, and opens for a second portion of each pulse.
16. The power system of claim 11 , wherein the switch is an IGBT.
17. The power system of claim 1 , wherein the DC power supply has an output that is limited to slow current changes.
18. The power system of claim 17 , wherein the DC power supply is a current source.