Kim T Dao

US Patent:

6407633, Jun 18, 2002

Filed:

Nov 16, 2001

Appl. No.:

09/992507

Inventors:

Kim Dao - Piedmont CA 94611-4326

International Classification:

H03F 136

US Classification:

330 86, 330282, 327554, 381121, 333174

Abstract:

An apparatus (Z) having controllable impedance is inserted from output ( ) to ground ( ) of an audio-signal amplifier ( ). Typically, the apparatus comprises a switch-chain ( ) having multiple switches ( and so on); the first switch ( ) is connected to one terminal ( ) of the apparatus. A capacitor ( and so on) is connected from each switch to a second terminal ( ). The network formed by the switch-chain ( ) and the capacitor network ( ) is called a matrix ( C). To bypass audio frequencies away from the chopping effect of the switches, an inductor ( ) parallels the matrix. To prevent shorting of audio signals to ground, a larger capacitor ( ) is in series with the inductor. An unstable voltage at output will see increasing capacitance as more switches are closed. The changing of capacitive impedance in relation to the amplitude of the unstable voltage is designed such that the unstable voltage cannot grow too large. More complex matrices further reduce voltage fluctuations.

US Patent:

51579421, Oct 27, 1992

Filed:

Jun 14, 1991

Appl. No.:

7/715565

Inventors:

Kim Dao - Piedmont CA

International Classification:

F25B 1500

US Classification:

62476

Abstract:

An improved regenerative absorption refrigeration cycle having a high COP and a commercially practicable pumping system. In the basic cycle, an ammonia/water solution is boiled in an externally-heated generator (11). The boiled-off ammonia vapor is cooled (14) in a regenerator (16), condensed (28), expanded to low pressure (32), and boiled in an evaporator (34) to extract heat from fluid circulating to and from a cooling load (41). The low-pressure liquid ammonia returns (46) to the regenerator (16) and is absorbed back into the low-pressure water from the generator. The solution is then cooled in a low-pressure absorber (50), pumped (53) to a high-pressure conduit (57) which is heated by the regenerator heat before going back to the generator 11. The improved cycle uses at least one intermediate absorber stage 60 to absorb more ammonia vapor (69, 71) into the solution coming from the lower pressure absorber (50) to produce a cooled solution of higher ammonia concentration. This higher concentration can be used to precool (87) the liquid refrigerant prior to expansion (32).

US Patent:

49215159, May 1, 1990

Filed:

Oct 20, 1988

Appl. No.:

7/260430

Inventors:

Kim Dao - Piedmont CA

International Classification:

F25B 700

US Classification:

62335

Abstract:

Multi-effect regenerative absorption cycles which provide a high coefficient of performance (COP) at relatively high input temperatures. An absorber-coupled double-effect regenerative cycle (ADR cycle) (10) is provided having a single-effect absorption cycle (SEA cycle) (11) as a topping subcycle and a single-effect regenerative absorption cycle (1R cycle) (12) as a bottoming subcycle. The SEA cycle (11) includes a boiler (13), a condenser (21), an expansion device (28), an evaporator (31), and an absorber (40), all operatively connected together. The 1R cycle (12) includes a multistage boiler (48), a multi-stage resorber (51), a multisection regenerator (49) and also uses the condenser (21), expansion device (28) and evaporator (31) of the SEA topping subcycle (11), all operatively connected together. External heat is applied to the SEA boiler (13) for operation up to about 500 degrees F. , with most of the high pressure vapor going to the condenser (21) and evaporator (31) being generated by the regenerator (49).

US Patent:

52555283, Oct 26, 1993

Filed:

Jun 3, 1992

Appl. No.:

7/894053

Inventors:

Kim Dao - Piedmont CA

International Classification:

F25B 1500

US Classification:

62101

Abstract:

The invention relates to an absorption system having a regenerator (17) wherein an absorption process of the absorption of low-pressure ammonia vapor into a weak liquid solution of ammonia-water is carried out in the shell (16) of the regenerator (17) with the heat of absorption being used in a generation process wherein a high-pressure ammonia water solution is boiled in a conduit (14) passing through the regenerator (17). A waste heat recovery conduit (40, 40', 40") is provided for concurrent flow of an ammonia-water solution and ammonia-water vapor, the flow being heated (46) to boil the solution. The heated vapor is then introduced into the absorption process in the shell (16) of the regenerator (17) with the heat (46) used to boil the solution in the waste heat recovery conduit (40) being recuperated in the regenerator as the hot vapor is absorbed into the ammonia-water solution therein. The heat (46) used to heat the waste heat recover conduit (40) can be waste heat in the flue gas (56), or waste heat in the cool end (61) of the regenerator (17), or waste heat in the high-temperature high-pressure vapor generated in the heating conduit (14) in the regenerator and/or in the externally-heated generator (18).

US Patent:

52188434, Jun 15, 1993

Filed:

Apr 10, 1992

Appl. No.:

7/866445

Inventors:

Kim Dao - Piedmont CA

International Classification:

F25B 1500

US Classification:

62476

Abstract:

An improved regenerative absorption cycle using a super-pressure boiler to achieve a high coefficient of performance (COP). In the basic cycle, an ammonia/water solution is boiled in high-pressure boiling conduit (66). Boiled-off high-pressure ammonia vapor is condensed (96), expanded to low-pressure (99), and boiled in evaporator (101) to extract heat from a refrigerating fluid going to cooling load (104). Low-pressure ammonia vapor from evaporator (101) returns to regenerator (28) and is absorbed back into low-pressure liquid. The low-pressure solution from regenerator (32) is then cooled in absorber (56) to reject heat from the cycle, and is then pumped (58) back to the high-pressure boiling conduit (66). In the present invention, the liquid solution from high-pressure boiling conduit (66) is pumped up to an externally-heated super-pressure boiler (11). Super-pressure ammonia vapor from boiler (11) is absorbed back into super-pressure liquid in absorption super-pressure conduit (26), which functions as an internal heat source to heat the high-pressure boiling super-pressure conduit (66).

US Patent:

6333674, Dec 25, 2001

Filed:

Mar 15, 2001

Appl. No.:

9/809395

Inventors:

Kim Dao - Piedmont CA

International Classification:

H03F 136

US Classification:

330 86

Abstract:

An apparatus (Z) having controllable impedance is inserted from output (22) to ground (23) of an audio-signal amplifier(20). Typically, the apparatus comprises a diode-chain (50) having multiple steps (52, 53, and so on); its first step (52) is connected to one terminal (62) of the apparatus. A capacitor (82, 84, and so on) is connected from each step to a second terminal (61). The network formed by the diode-chain (50) and the capacitor network (80) is called a matrix (60C). To bypass audio frequencies away from the chopping effect of the diodes, an inductor (31) parallels the matrix. To prevent shorting of audio signals to ground, a larger capacitor (30) is in series with the inductor. An unstable voltage at output will see increasing capacitance as it gradually breaks over more and more diodes. The changing of capacitive impedance in relation to the amplitude of the unstable voltage is designed such that the unstable voltage cannot grow too large.

US Patent:

46462201, Feb 24, 1987

Filed:

Jun 7, 1984

Appl. No.:

6/618219

Inventors:

Kim Dao - Piedmont CA

International Classification:

H02M 3315

US Classification:

363 28

Abstract:

A power supply 10 providing a DC output voltage comprises a voltage input circuit 11, a charge buildup and transfer circuit 14, a switch including SCR3 for selectively interconnecting the input circuit 11 and the charge buildup and transfer circuit 14, a trigger circuit including a unijunction transistor gating circuit 16 for triggering the SCR3, and a sensing circuit 22 including a current reference 26 for sensing the current output to the load 38 and comparing the output to current reference 26 while providing a comparison signal to the trigger circuit 16 so as to modify the triggering of SCR3 and thus the interconnection of the voltage input circuit 11 and the current buildup and transfer circuit 14.