Controlling high side devices without using level shift...

Details Controlling high side devices without using level shift... Controlling high side devices without using level shift...

2001-04-24

2003-02-18

Wells, Kenneth B. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Current driver

C326S083000

Reexamination Certificate

active

06522178

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of communicating between a high side device driver and a low side controller without using a level shift circuit.
2. Brief Description of the Prior Art
Most circuits in power processing applications use a “high side device” that needs to be controlled (i.e., turned on or off at predetermined times) to process the power. These devices (IGBTs, FETs, bipolars and other devices) utilize a “driver IC” that raises its gate above its source to turn it on. As during the turn on process, the source/emitter also rises substantially above the -ve rail of the DC bus (to which the main controller is typically referenced). This causes the driver to “float up” with the device source voltage. Consequently, high voltage ICs (HVICs) with internal level shifting switches typically are used to communicate the “on/off” signals to the driver of the gate. A typical prior art circuit is illustrated in FIG.
1
.
Referring to
FIG. 1
, a controller
2
communicates with a power switching circuit
4
by way of HVIC
6
. The switching circuit includes high side switch
8
and low side switch
10
. A high side driver
12
and a low side driver
14
of the HVIC
6
are associated with the high and low side switches
8
,
10
, respectively. The two switches are connected in series between a high voltage rail and ground. The high voltage rail typically carries hundreds of volts. In contrast the controller
2
typically operates in the 5 volt range. Consequently, in order for the controller
2
to communicate with high side switch
8
, a level shift circuit
16
is incorporated in HVIC
6
to communicate the low voltage signal from controller
2
to the high side driver
12
. The circuits operate to generate a signal at output
18
. Typically, the controller alternates opening and closing the two switches to generate a high voltage square wave, for example.
In some cases, the high side driver also performs “fault protection.” This involves sensing a parameter in the high side switching device, such as current or voltage, for example, and turning off the device to protect it from failure in the event that the parameter exceeds a certain value. The decision is then communicated to the controller by means of a level shift down device. An example of such a prior art circuit is shown in FIG.
2
.
Referring to
FIG. 2
, a controller
20
communicates with a power switching circuit
22
by way of HVIC
24
. The switching circuit includes high side switch
26
and low side switch
28
. A high side driver
30
and a low side driver
32
of the HVIC
24
are associated with the high and low side switches
30
,
32
, respectively. The controller
20
communicates with high side switch
26
by way of a level shift up circuit
34
, similar to the circuit shown in FIG.
1
. Fault protection information generated by protection circuitry in driver
30
is communicated back to controller
20
by way of a level shift down circuit
36
.
Accordingly, the need exists for a technique for communicating between a high side driver circuit and a low voltage controller without requiring level shifting circuitry.
SUMMARY OF THE INVENTION
The present invention provides analog and digital methods of achieving communication with the high side driver without requiring an HVIC with an internal level shift circuit.
A preferred circuit according to the present invention includes a low voltage controller with time coding circuitry generating an output, such as a voltage, a current, or a digital signal. A driver includes circuitry for decoding the output and controlling a high voltage switch. Circuitry for communicating between the controller and the driver is provided which does not require level shift circuitry. The driver decodes the signals received from the controller to generate on and off time pulses for controlling the switch.


REFERENCES:
patent: 4733342 (1988-03-01), Mueller et al.
patent: 6232803 (2001-05-01), Nguyen

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