Multiple output bootstrapped gate drive circuit

Details Multiple output bootstrapped gate drive circuit Multiple output bootstrapped gate drive circuit

2000-08-10

2001-07-03

Nguyen, Matthew (Department: 2838)

Electric power conversion systems

Current conversion

Using semiconductor-type converter

C307S077000

Reexamination Certificate

active

06256215

ABSTRACT:

TECHNICAL FIELD
This invention relates to a low cost bootstrapped gate drive circuit for driving bridge transistors of multiple power supply bridge circuits.
BACKGROUND OF THE INVENTION
Various circuits, including many power supply and motor control circuits, utilize transistor bridge arrangements to selectively couple a load to a power supply. In general, one terminal of the power supply is designated as the circuit common or ground, and transistors that couple a load to the circuit ground are referred to as low-side switches, whereas transistors that couple a load to the other terminal of the power supply or an intermediate potential are referred to as high-side switches. Since the emitter or source of a low-side transistor is referenced to circuit ground, its gate drive circuit may also be referenced to ground, and a simple and inexpensive circuit design may be used. However, the emitter or source of a high-side transistor floats with respect to ground, and its gate drive circuit must therefore be isolated from ground. One technique commonly employed with insulated gate transistor bridges utilizes a capacitor and diode to create a floating power supply for the gate drive of the high-side transistor. This technique, illustrated in
FIG. 1
, is referred to as bootstrapping, and eliminates the need for expensive transformer isolated power supplies. Referring to
FIG. 1
, a Low Level Controller
10
generates control signals L
1
and H
1
for biasing low-side and high-side bridge transistors Q
1
and Q
2
alternately on and off to alternately couple an electrical load LOAD
1
to a ground potential defined by the negative terminal of battery
12
and a source potential VS defined by the positive terminal of battery
12
. The Low Level Controller
10
is powered by Logic Level Power Supply
14
, which develops a logic level voltage Va, such as 5 VDC. The control signal L
1
is applied to gate drive amplifier U
1
, which switches the gate of low-side transistor Q
1
between the logic level voltage Va and ground potential, according to the logic state of the control signal L
1
. Similarly, the control signal H
1
controls the operation of gate drive amplifier U
2
for high-side transistor Q
2
, but in this case a level shifter (LS)
16
is needed since the source of high-side transistor Q
2
floats at load potential VL
1
. A by-pass capacitor C
1
supplies a gate drive potential Vb relative to the source of high-side transistor Q
2
, and Logic Level Power Supply
14
charges capacitor C
1
substantially to voltage Va through diode D
1
during on periods of low-side transistor Q
1
. If desired, a by-pass capacitor C
2
may also be used to establish a gate drive potential for gate drive amplifier U
1
, as shown. The drive circuit for high-side transistor Q
2
is said to be bootstrapped because its gate drive potential Vb shifts upward with the load potential VL
1
when low-side transistor Q
1
transitions from on to off. At such point, the gate drive potential Vb is higher than the logic level voltage Va, and the diode D
1
is reverse biased. When control signal H
1
changes states to turn on high side transistor Q
2
, the by-pass capacitor C
1
supplies the required gate drive energy.
While conventional bootstrapping can be advantageously used in single power supply bridge circuits such as shown in
FIG. 1
, it can only be used in multiple power supply bridge circuits by providing separate logic level voltages for each power supply, which of course, entails significant expense. Accordingly, what is needed is a simple and inexpensive gate driver circuit having multiple outputs for driving bridge transistors of multiple power supply bridge circuits.
SUMMARY OF THE INVENTION
The present invention is directed to an improved low-cost gate drive circuit for driving the bridge transistors of a multiple power supply bridge circuit with a single logic level voltage. In general, the single logic level voltage is referenced to one of the power supplies (referred to herein as the first power supply) and provides gate drive voltages for bridge transistors associated with all of the power supplies. The logic level voltage is bootstrapped to a first by-pass capacitor to provide a first gate drive voltage for a high-side transistor associated with the first power supply, and the charge on the first by-pass capacitor is consecutively bootstrapped to additional by-pass capacitors to provide multiple gate drive voltages for bridge transistors associated with the other power supplies.


REFERENCES:
patent: 4316243 (1982-02-01), Archer
patent: 6043618 (2000-03-01), Kawagoshi
patent: 6151222 (1982-02-01), Barrett

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