Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-05-10
2001-04-17
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S284000, C323S276000, C363S056070
Reexamination Certificate
active
06218820
ABSTRACT:
TECHNICAL FIELD
The present invention refers to a frequency translator usable in a switching DC-DC converter of the type operating as a voltage regulator and as a battery charger, and to a method of frequency translation therefor.
BACKGROUND OF THE INVENTION
FIG. 1
illustrates, and indicates as a whole by the reference number
1
, a known step-down DC-DC converter usable as a voltage regulator. In particular, to provide an example, in
FIG. 1
a DC-DC converter is illustrated having a Buck circuit configuration; however, this should not be deemed limiting, in that considerations altogether similar to the ones that are made in what follows for this type of circuit configuration also apply to DC-DC converters having Boost and Flyback circuit configurations.
According to what is illustrated in
FIG. 1
, the DC-DC converter comprises an input terminal
2
, set, when in use, at an input voltage VIN, and an output terminal
4
supplying an output voltage VOUT lower than the input voltage VIN.
The DC-DC converter
1
comprises a first and a second switch
6
,
8
, typically formed of bipolar transistors or p-channel or n-channel MOSFET transistors, the opening and closing whereof are controlled in phase by a driving stage
10
. In particular, the first switch
6
presents a first terminal connected to the input terminal
2
of the DC-DC converter
1
, and a second terminal connected, via a diode
12
, to ground, whilst the second switch
8
presents a first terminal also connected to the input terminal
2
of the DC-DC converter
1
via a sense resistor
14
, and a second terminal connected, via the diode
12
, to ground.
The DC-DC converter
1
further comprises an inductor
16
connected between the second terminals of the switches
6
and
8
and the output terminal
4
; a capacitor
18
connected between the output terminal
4
and ground; and a voltage divider
20
formed of two resistors
22
,
24
connected between the output terminal
4
and ground and presenting an intermediate node
26
on which a division voltage VFB is present, which is proportional, through the division ratio, to the output voltage VOUT supplied by the DC-DC converter
1
.
The DC-DC converter
1
moreover comprises a differential voltage error amplifier (VEA)
28
presenting an inverting terminal connected to the intermediate node
26
of the voltage divider
20
and receiving from the latter the division voltage VFB, a non-inverting terminal receiving a reference voltage VREF, and an output terminal supplying an intermediate voltage VM and connected to a non-inverting terminal of a differential comparator
30
, known as PWM (Pulse Width Modulator) comparator, and hereinafter indicated by this name, which in turn presents an inverting terminal connected to the output terminal of an oscillator
32
supplying a comparison voltage VC presenting a sawtooth waveform and having a preset frequency upon which the switching frequency of the DC-DC converter
1
depends, and an output terminal connected to the input of the driving stage
10
of the switches
6
and
8
.
In particular, the PWM comparator
30
basically acts as a pulse width modulator and supplies at an output a voltage having a square waveform, the duty cycle whereof is a function of the voltage supplied by the voltage error amplifier
28
, and the frequency whereof depends upon the frequency of the comparison voltage VC supplied by the oscillator
32
.
Finally, the DC-DC converter
1
comprises a fixed threshold current limiting stage having the purpose of protecting the DC-DC converter
1
against current overloads and basically consisting of a differential comparator
34
, hereinafter indicated as CURL comparator, presenting an inverting terminal and a non-inverting terminal connected across the sense resistor
14
and an output terminal issuing a limiting signal VL supplied to the driving stage
10
; in particular, the CURL comparator
34
carries out the comparison between the voltage present across the sense resistor
14
and a preset reference voltage programmed inside it: if the voltage present across the sense resistor
14
is less than or equal to the reference voltage programmed inside it, then the limiting signal VL switches to a low logic level indicative of the absence of overloads, and the driving stage
10
continues to operate in a normal way, controlling opening and closing of the switches
6
and
8
at a nominal switching frequency correlated to the frequency of the comparison voltage VC supplied by the oscillator
32
, whereas if the voltage present across the sense resistor
14
is greater than the reference voltage programmed inside it, then the limiting signal VL switches to a high logic level indicative of the presence of overloads, and, in response to the switching of the limiting signal VL from the low logic level to the high logic level, the driving stage
10
controls opening of the switches
6
and
8
, so as to interrupt the current supplied to the DC-DC converter
1
.
The opening of the switch
8
causes the voltage across the sense resistor
14
to become zero, and thus causes the limiting signal VL generated by the CURL comparator
34
to switch again to the low logic level, and consequently the driving stage
10
to return to conditions of normal operating.
As a result, as long as the overload persists, the limiting signal VL supplied by the CURL comparator
34
continues to switch between the high and low logic levels, thus generating a pulse train which, when supplied to the driving stage
10
, causes switching of the operation of the DC-DC converter
1
between a normal operation, in which opening and closing of the switches
6
and
8
is controlled at a preset frequency correlated to that of the sawtooth voltage supplied by the PWM comparator
30
, and an current limitation operation, in which opening of the switches
6
and
8
is controlled in order to interrupt the current supplied to the DC-DC converter
1
.
The operation of the DC-DC converter
1
is in itself known and will here be referred to solely as regards the aspects necessary for understanding the problems lying at the basis of the present invention. In particular, the DC-DC converter
1
presents a single operating mode in which the voltage error amplifier
28
carries out regulation of the output voltage VOUT so that this remains constant as the current required by the load connected to the output terminal of the DC-DC converter
1
varies.
In
FIG. 2
there is illustrated and indicated by
40
a known step-down DC-DC converter usable as a battery charger, in which identical parts or parts equivalent to the ones of the DC-DC converter
1
are designated with the same reference numbers.
In particular, the DC-DC converter
40
differs from the DC-DC converter
1
by further comprising a sense resistor
42
connected in series to the inductor
16
and interposed between the inductor
16
and the output terminal
4
of the DC-DC converter
40
; a filtering stage
44
, made typically using an operational amplifier and presenting a first input terminal and a second input terminal connected across the sense resistor
42
, and an output terminal supplying a voltage equal to the filtered voltage VFR present across the sense resistor
42
; and a differential current error amplifier (CEA)
46
presenting an inverting terminal connected to the output terminal of the filtering stage
44
, a non-inverting terminal receiving a reference voltage VR, and an output terminal connected to the inverting terminal of the PWM comparator
30
through a decoupling diode
48
, which presents the anode terminal connected to the inverting terminal of the PWM comparator
30
and the cathode terminal connected to the output terminal of the current error amplifier
46
.
In particular, the reference voltage VR is generated by causing a constant current, supplied by a current generator
52
connected in series to a resistor
50
, to flow in the resistor
50
itself; the reference voltage thus obtained is then taken across the resistor
50
.
The operation of the DC-DC converter
Capici Salvatore
D'Arrigo Angelo
Marino Filippo
Pulvirenti Francesco
Galanthay Theodore E.
Han Jessica
Iannucci Robert
Seed IP Law Group PLLC
STMicroelectronics S.r.l.
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