Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2003-07-18
2004-10-19
Berhane, Adolf (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S901000
Reexamination Certificate
active
06806694
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a switching regulator and a drive circuit therefore. The drive circuit taps off an intermediate circuit input voltage of the switching regulator, an output voltage of the switching regulator available at an intermediate circuit capacitor, and an output current thereof at a current measuring element of the switching regulator and controls at least the electrical output parameters and the power factor of the switching regulator in accordance with an adjustable desired value by controlling the duty ratio of a power switch. The power switch is connected in parallel with the intermediate circuit capacitor through a diode and controls the charging current of the intermediate circuit capacitor.
A switching regulator of this type and a drive circuit of this type are disclosed in Siemens Components 1/86, pages 9 to 13, titled “Application Note; Active Harmonic Filtering for Line Rectifiers of Higher Output Power”.
Generally, power supplies for various applications, for example for personal computers, charging units, plug-in power supply units, etc., are usually configured as pulsed switching regulators. Connected to such switching regulators is a drive circuit by which a number of functions of the switching regulator are realized, such as e.g.:
a) a control of the electrical parameters of the output of the switching regulator;
b) a control of some electrical parameters of the input of the switching regulator, in particular the power factor;
c) realization of a soft start of the switching regulator;
d) realization of various protection functions, such as overvoltage protection, overcurrent protection, undervoltage shutdown, etc.; and
e) changeover of the switching regulator to various operating states, such as sleep mode, standby mode, protection mode, normal mode, startup mode, hick-up mode etc.
FIG. 1
schematically shows a switching regulator which is disclosed in the document mentioned above and whose intermediate circuit, containing a power switch T
1
, an inductor L
1
, a resistor R
1
, a diode D
1
, a diode D
11
bridging the inductor L
1
and the diode D
1
, and also an intermediate circuit capacitor C
1
, is used by way of example for the subject matter of the present application. A drive circuit
100
illustrated as a block in the lower part of
FIG. 1
taps off the intermediate circuit output voltage Vout at the intermediate circuit capacitor C
1
, a voltage level indicating the present output current level at the resistor R
1
connected in series in the intermediate circuit, and an input voltage level at the inductor L
1
and generates. At least on the basis of these quantities, pulses are derived for controlling a duty ratio of the power switch T
1
acting on the control gate.
The circuit configuration shown in
FIG. 2
shows details of the drive circuit
100
disclosed in the above-mentioned document (with the exception of the circuit blocks
110
and
111
that are part of the invention of the instant application).
The drive circuit
100
shown in
FIG. 2
contains, in so far as it is disclosed in the above document, a first control amplifier
101
, which receives the output voltage Vout of the switching regulator and a desired voltage Vout, desired for the output voltage of the switching regulator at its inputs and generates, from these input signals, a first control voltage VR
1
at its output. The first control voltage VR
1
is fed to a multiplier
102
, which receives, at a second input, the rectified input voltage |vin| present at the intermediate circuit and generates, from these input quantities, a desired current level I
desired
at its output designated by A. In the drive circuit
100
which can be gathered from the above document, the point A is connected to the point B. Furthermore, the drive circuit
100
contains a second control amplifier
103
, which receives, at one of its inputs, a signal derived from the desired current level I
desired
at the output of the multiplier
102
and a signal derived from the actual output current level Iout of the switching regulator and generates therefrom a second control voltage which is output at its output. The second control voltage is fed to a PWM block
104
and, through a summation element
105
, to a driver
107
, which applies drive pulses to the control gate of the power switch T
1
. The drive circuit
100
also contains a current limiting device in the form of a third control amplifier
106
, which receives the actual output current level Iout of the switching regulator at one of its inputs and a reference signal Ref
2
at the other input and whose output is fed to the summation element
105
. The function of the third control amplifier
106
is explained below.
The known drive circuit described above forms a so-called active harmonic filter circuit, the function of which, in combination with the switching regulator illustrated in
FIG. 1
, leads to optimized efficiency and power factor values. The behavior of the switching regulator and the function of the drive circuit during the start of the switching regulator will be considered in greater detail below.
Before the switch-on of the power supply, i.e. before the application of the input voltage |Vin| to the rectifier of the switching regulator, all energy stores, the inductances and capacitors are empty. In the event of the switch-on of the power supply, the grid voltage is suddenly connected to the system. This leads to large current surges during the charging of the capacitors (here of the intermediate circuit capacitor C
1
). The current surges can destroy components, principally the semiconductors, such as the power switch T
1
and the diode D
1
. The initial charging of the relatively large intermediate circuit capacitor C
1
in the event of the switch-on of the power supply effects a current surge (“inrush”) which may exceed the maximum acceptable peak current intensity of the diode D
1
, which is a very fast diode. Likewise, the current surge may exceed the maximum current-carrying capacity of the input bridge rectifier.
The diode D
11
, which is connected in parallel with the inductor L
1
and with the diode D
1
and is a customary silicon diode, avoids the high current loading by initially charging the intermediate circuit capacitor C
1
from the grid voltage (Vin) rectified by the bridge rectifier.
Another possible way of avoiding the high current surge in the event of switch-on consists in initially connecting a resistor in series with the intermediate circuit capacitor C
1
.
A soft start function to be realized by the drive circuit
100
is intended to protect the system components, principally the semiconductors, in the event of the switch-on of the power supply.
A known and widespread soft start solution is based on limiting the duty ratio (duty cycle) for the power switch T
1
of the intermediate circuit, which is also known as a power factor correction (PFC) circuit. The duty ratio for the power switch is initially kept very low and increases with time until the control acts. This function is illustrated in the accompanying graphical representation of
FIG. 3A
, in which the curve d(T
1
) depicted by dashes represents the duty ratio d of the power switch T
1
and the solid curve d(D
1
) represents the duty ratio at the diode D
1
for 25 ms after the switch-on. Since the diode D
1
carries the current during the rest of the switching period of the power switch T
1
, that is to say while the latter is switched off, a very large duty ratio is established for the diode D
1
during the start, as is illustrated in
FIG. 3A
by the profile of the curve d(D
1
). At the same time, the maximum peak current in the power switch T
1
and in the diode D
1
will also reach very large values. This is illustrated by the curves I
max
(T
1
) and I
max
(D
1
) in the graphical representation of
FIG. 3B
(the peak values of these two currents are always identical).
The graphical representation of
FIG. 3C
shows the profile of the output voltage Vout (dashed curv
Herfurth Michael
Rupp Roland
Zverev Ilia
Berhane Adolf
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Stemer Werner H.
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