Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
2001-08-16
2003-07-22
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C323S225000, C323S272000
Reexamination Certificate
active
06597155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to DC-DC power converters. In particular, the present invention relates to a self-oscillating DC-DC power converter and circuit, and a method of self-oscillating a DC voltage.
2. Description of the Prior Art
Generally, a control IC is used to control a DC-DC power converter to convert an input DC voltage into a desired output DC voltage (either higher or lower than the input DC voltage).
FIG. 1
is a schematic diagram of a circuit for a DC-DC converter controlled by an ASIC UC3842 to convert input DC voltage V
in
into output DC voltage V
o
. This particular design circuit has some shortcomings. First, when the input voltage is lower than 5V, a DC-DC converter which utilizes an IC for a controller cannot be used because IC's do not work properly in low voltage input situations. Also, the use of an IC to control the circuit increases the overall cost of the circuit.
To overcome the above-mentioned drawbacks, a self-oscillation DC-DC converter (i.e., a BUCK DC-DC converter) has been proposed by the Chinese Patent No. 99108088.2. This BUCK DC-DC converter is shown in FIG.
2
. As shown therein, the DC-DC converter includes a PNP transistor Q
1
, a primary turn L
1
, a diode D
1
and a capacitor C
2
. An auxiliary turn L
2
connects the base of transistor Q
1
to the emitter of transistor Q
1
through a capacitor C
1
and a resistor R
3
. The circuit also includes a transistor Q
2
which has its emitter and collector connected to the emitter and base of transistor Q
1
to conduct a part of the base current for transistor Q
1
. Transistor Q
2
decides whether transistor Q
1
is on or off according to the change of output voltage. Therefore, this DC-DC converter keeps the output voltage steady via the use of transistor Q
2
.
This BUCK DC-DC converter does not adopt the use of an IC controller and is effective for use with a low input DC voltage. Further, since an IC is not used, it costs less to manufacture than that of the ASIC circuit of FIG.
1
. However, this BUCK DC-DC converter has a few drawbacks. First, this BUCK DC-DC converter is only suitable with PNP transistors. This DC-DC converter is also only suitable for use where the output voltage is always lower than the input voltage, and cannot be applied for use as a BOOST DC-DC converter wherein the output voltage is higher than the input voltage. Moreover, because this BUCK DC-DC converter requires an auxiliary turn L
2
to start oscillation, it requires numerous components and is difficult to manufacture.
Accordingly, there remains a need for a simple DC-DC converter which is self-oscillating and can be used effectively as a BOOST DC-DC converter.
SUMMARY OF THE INVENTION
The present invention is a self-oscillation DC-DC converter which utilizes a single turn inductor L
1
. In the circuit of the present invention, the input positive terminal of the DC source is connected to a terminal of the inductor L
1
. The other terminal of the inductor L
1
is connected to the collector of a transistor Q
1
and the anode of a diode D
1
. One terminal of a capacitor C
1
is connected to the output positive terminal V
o+
and the other terminal of capacitor C
1
is connected to the output negative terminal V
o−
. The input negative terminal of the DC source is directly connected to the output negative terminal. The base of transistor Q
1
is connected to the input positive terminal of the DC source through a resistor R
1
. The emitter of the transistor Q
1
is connected to the input negative terminal of the DC source. A second transistor Q
2
is also provided. The collector of transistor Q
2
is connected to the base of transistor Q
1
and the emitter of second transistor Q
2
is connected to the emitter of transistor Q
1
. The base of transistor Q
2
is connected to the collector of transistor Q
1
through a resistor R
2
.
The self-oscillation DC-DC converter circuit described herein does not use an auxiliary turn, thereby allowing the use of NPN transistors. Positive feedback is achieved by a voltage change V
ce1
of the transistor Q
1
from a saturation state to a non-saturation state. In the non-saturation state, the transistor Q
2
is turned on, the transistor Q
1
is turned off and self-oscillation is achieved. The self-oscillation DC-DC converter according to the present invention operates normally when the input voltage is lower than 5V
dc
. Also, the use of fewer components lowers the overall cost of the circuit and enables a decreased size circuit to be produced.
The self-oscillation DC-DC converter circuit of the present invention uses relatively few components, thereby decreasing the cost to manufacture and decreasing the overall size required of the circuit. Moreover, the self-oscillation DC-DC converter works when the input voltage is lower than 5V
dc
.
A further embodiment is also disclosed wherein power loss is reduced and overall efficiency of the circuit is increased by the addition of a power amplifier driver circuit and a power stage to create a self-oscillation BOOST DC-DC converter.
The power amplifier driver circuit added in the further embodiment of the present invention preferably comprises an NPN transistor Q
3
, resistors R
4
, R
5
and a capacitor C
2
. The power stage of the self-oscillation BOOST DC-DC converter includes a high power transistor Q
4
, an inductor L
2
, a diode D
2
and a capacitor C
3
. The power amplifier driver circuit amplifies the power of the voltage (pulse signal V
ce1
) from the collector to the emitter of transistor Q
1
to drive the high power transistor Q
4
. Resistor R
4
and capacitor C
2
trim the pulse signal V
ce1
. Transistor Q
4
boosts the input voltage to a higher output voltage. When transistor Q
4
is turned on, inductor L
2
is charged. When transistor Q
4
is turned off, the charge stored in inductor L
2
is discharged to output. The high power transistor Q
4
is preferably a power MOSFET and reduces power dissipation.
With the addition of the power amplifier driver circuit and the high power transistor, the self-oscillation DC-DC converter of the present invention is adapted to be a self-oscillation BOOST DC-DC converter. Accordingly, a highly efficient self-oscillation BOOST DC-DC converter is achieved.
REFERENCES:
patent: 3974439 (1976-08-01), Holland
patent: 4510400 (1985-04-01), Kitely
patent: 4514679 (1985-04-01), Schierjott
patent: 4999566 (1991-03-01), Kuehn
patent: 5233287 (1993-08-01), Lenk
patent: 5406471 (1995-04-01), Yamanaka
patent: 5844399 (1998-12-01), Stuart
patent: 5949222 (1999-09-01), Buono
patent: 6215286 (2001-04-01), Scoones et al.
patent: 6236191 (2001-05-01), Chaffai
patent: 6252383 (2001-06-01), Wittenbreder
patent: 99108088.2 (1999-12-01), None
Chen Yi
Huang Minchao
Bel Fuse Inc.
Ostrolenk Faber Gerb & Soffen, LLP
Sterrett Jeffrey
LandOfFree
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