Method to increase the efficiency of a power switching device

Details Method to increase the efficiency of a power switching device Method to increase the efficiency of a power switching device

2000-02-28

2002-04-30

Wong, Peter S. (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S222000, C323S908000, C323S301000, C361S018000, C361S094000

Reexamination Certificate

active

06380722

ABSTRACT:

FIELD
The invention relates to a method for limiting the switching current of a switching device and therefore limiting the power dissipated by the switching device at turn-on time, and further returning energy to a power receiving circuit when the switching device disconnects from the power source.
BACKGROUND
During the turn-on time for a switching device, which may include, but is not limited to, an FET or bipolar transistor, wasteful transition power is dissipated during a transition turn-on time. Thus, the longer the transition turn-on time lasts, the more wasteful power is dissipated.
FIG. 1
shows, for example, a MOSFET switching device
10
which switches a voltage from
+
V to the input of inductor
20
in a simple buck regulator. It is known to provide a buck regulator, which includes an inductor
20
, capacitor
30
and freewheel diode
50
and switching device
10
for producing a first regulated output voltage across the capacitor
30
from a pulsed input supply. Controller
60
is provided to control the duty cycle of the switching device
10
. During the transition turn-on time required for the switching device
10
(which may be, but is not limited to, an FET or bipolar transistor), transition power is dissipated, and the longer the transition, in relation to the repetition period of the transition, the more power is dissipated, as further illustrated in this example.
More particularly, the disadvantageous example embodiment of
FIG. 1
shows a buck regulator which utilizes a switching device
10
, which is used to switch the input of inductor
20
to the input voltage
+
V for a period of time, and then to disconnect inductor
20
from
+
V for a subsequent period of time. If switching device
10
has to switch
15
A (i.e., 15 amps), the power being switched will be given by the formula 15×
+
V. If
+
V were 20V, then the power switched would be 300 watts, since (15A)(20V)=300watts. That is, as an example, when 15A are transmitted from source
+
V, and when transistor
10
is turned on, the left side of inductor
20
charges up to
+
V, which is the voltage level from the power source. Current begins to increase through inductor
20
and capacitor
30
is charged up. In a stable state, the charge on capacitor
30
rises above the output voltage and then back down below the output voltage, producing a ripple. In this example, then, the transistor
10
would be immediately switching 15A at turn-on time, and therefore would be wasting a significant amount of power during turn-on transition time.
SUMMARY
According to the invention, a method, including the steps of limiting a current sent from a power source to a switching device, and system are provided for limiting a switching current in a switching device during the transition turn-on time of the switching device by disposing an inductor device in series between the power source and the switching device, and returning flux energy stored in the inductor device to a power receiving circuit at a turn-off time of the switching device.


REFERENCES:
patent: 5420780 (1995-05-01), Bernstein et al.
patent: 5929614 (1999-07-01), Copple
patent: 6091615 (2000-07-01), Inoshita et al.

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