U.S. patent application number 09/833411 was filed with the patent office on 2002-04-25 for switching arrangement.
This patent application is currently assigned to U.S. PHILIPS CORPORATION. Invention is credited to Zwerver, Hendrik Jan.
Application Number | 20020047600 09/833411 |
Document ID | / |
Family ID | 8171544 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020047600 |
Kind Code |
A1 |
Zwerver, Hendrik Jan |
April 25, 2002 |
Switching arrangement
Abstract
Switching arrangement for igniting and operating of a
high-pressure discharge lamp which is provided with: input
terminals for connecting a power source, output terminals for
connecting the lamp which is ignited and operated by the
arrangement, a flyback converter having a semiconductor switching
element and a transformer of which a primary coil is electrically
connected to one of the input terminals and a secondary coil having
a secondary coil voltage is connected to one of the output
terminals, a control circuit for generating a switching signal for
control of the semiconductor switching element in a conducting or a
non-conducting switching state, means M for generating a control
signal S intended for the control circuit, which signal S depends
on the secondary coil voltage and on a current through the
secondary coil.
Inventors: |
Zwerver, Hendrik Jan;
(Elindhoven, NL) |
Correspondence
Address: |
Jack E. Haken
U.S. Philips Corporation
580 White Plains Road
Tarrytown
NY
10591
US
|
Assignee: |
U.S. PHILIPS CORPORATION
|
Family ID: |
8171544 |
Appl. No.: |
09/833411 |
Filed: |
April 12, 2001 |
Current U.S.
Class: |
315/224 ;
315/291 |
Current CPC
Class: |
H02M 3/33507
20130101 |
Class at
Publication: |
315/224 ;
315/291 |
International
Class: |
H05B 037/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 24, 2000 |
EP |
00201842.2 |
Claims
1. A switching arrangement for igniting and operating a
high-pressure discharge lamp, the switching arrangement comprising:
input terminals for connection of a power supply source, output
terminals for connection of the lamp to be operated, a flyback
converter comprising a semiconductor switching element and a
transformer, a primary winding of which is electrically connected
to one of the input terminals and a secondary winding having a
secondary winding voltage is electrically connected to one of the
output terminals, a control circuit for generating a switching
signal to control the semiconductor switching element in a
conducting or a non-conducting switching state, means M for
generating a control signal S for the control circuit in dependence
upon the secondary winding voltage and a current through the
secondary winding.
2. A switching arrangement as claimed in claim 1, characterized in
that the means M comprise a sense circuit for generating a signal
S1 in dependence upon the secondary winding voltage.
3. A switching arrangement as claimed in claim 1 or 2,
characterized in that the means M comprise a current-sense circuit
for detecting a current through the secondary winding.
4. A switching arrangement as claimed in claim 3, characterized in
that the current-sense circuit is connected to an output of the
sense circuit by means of a sample & hold switching
circuit.
5. A switching arrangement as claimed in claim 4, characterized in
that the sample & hold switching circuit comprises a switching
element which is alternately switched to a conducting and a
non-conducting state by means of an inverted switching signal of
the control circuit.
6. A switching arrangement as claimed in claim 1, characterized in
that the sense circuit comprises a capacitive sense element which
is connected to the secondary winding by means of an impedance.
7. A switching arrangement as claimed in claims 5 and 6,
characterized in that a main electrode of the switching element is
connected between the capacitive sense element and the
impedance.
8. A switching arrangement as claimed in claim 1, characterized in
that the control circuit for generating a switching signal for
controlling the semiconductor switching element comprises means for
maximizing, with respect to time, a switching state of the
semiconductor switching element.
Description
[0001] The invention relates to a switching arrangement for
igniting and operating a high-pressure discharge lamp, the
switching arrangement comprising:
[0002] input terminals for connecting a power supply source,
[0003] output terminals for connecting the lamp to be operated,
[0004] a flyback converter comprising a semiconductor switching
element and a transformer, a primary winding of which is
electrically connected to one of the input terminals and a
secondary winding having a secondary winding voltage is
electrically connected to one of the output terminals,
[0005] a control circuit for generating a switching signal for
controlling the semiconductor switching element in a conducting or
a non-conducting switching state.
[0006] A switching arrangement of the type described in the opening
paragraph is known from EP 0 746 186. The known switching
arrangement is suitable for igniting and operating a car headlamp.
The lamp may be directly connected to the output terminals.
However, the lamp is usually incorporated in a commutation network
in the form of, for example, a bridge circuit which in its turn is
connected to the output terminals.
[0007] The switching arrangement comprises means for detecting the
lamp current and the lamp voltage. The power consumption of the
lamp is determined by means of the signals thus detected and is
subsequently used as a control signal for controlling the
semiconductor switching element of the flyback converter. The lamp
is thus power-controlled.
[0008] The known switching arrangement has the drawback that
information about the current through the primary winding of the
transformer is obtained by means of a separate measuring resistor
in series with the semiconductor switching element. This leads to
large losses. Another way of detecting the current through the
primary winding is the use of a current transformer. This has the
drawback that a transformer is relatively large and impedes the
miniaturization of the switching arrangement.
[0009] It is an object of the invention to provide a measure
eliminating the drawback described.
[0010] According to the invention, the switching arrangement of the
type described in the opening paragraph is characterized in that it
comprises means M for generating a control signal S for the control
circuit in dependence upon the secondary winding voltage and a
current through the secondary winding.
[0011] The switching arrangement according to the invention has the
surprising advantage that a direct current measurement by the
primary winding can be dispensed with. In an advantageous
embodiment of the switching arrangement, the means M comprise a
sense circuit for generating a signal S1 in dependence upon the
secondary winding voltage. The means M preferably also comprise a
current-sense circuit for detecting a current through the secondary
winding. It is then advantageous if the current-sense circuit is
connected to an output of the sense circuit by means of a sample
& hold switching circuit. It is thus relatively easily possible
to correct the signal S1 for the occurrence of a DC voltage across
the secondary winding. In an advantageous embodiment, this is
realized in that the switching arrangement comprises a switching
element which is alternately switched to a conducting and a
non-conducting state by means of an inverted switching signal of
the control circuit.
[0012] An advantageous embodiment of the sense circuit is
constituted by a capacitive sense element which is connected to the
secondary winding by means of an impedance. A main electrode of the
switching element is preferably connected between the capacitive
sense element and the impedance. In this way, the desired control
signal is formed by means of a relatively simple construction of
the means M. This contributes to the miniaturization of the
switching arrangement.
[0013] In an advantageous embodiment of the switching arrangement
according to the invention, the control circuit for generating a
switching signal for controlling the semiconductor switching
element comprises means for maximizing, with respect to time, a
switching state of the semiconductor switching element. It is
thereby achieved that the time during which the semiconductor
switching element is in the conducting or non-conducting state is
limited under circumstances of, for example, a very low lamp
voltage or a relatively low power supply voltage.
[0014] These and other aspects of the invention are apparent from
and will be elucidated with reference to the embodiments described
hereinafter.
[0015] In the drawings,
[0016] FIG. 1 is a circuit diagram of a switching arrangement
according to the invention,
[0017] FIG. 2 shows, in detail, a flyback converter of the
arrangement shown in FIG. 1, and
[0018] FIG. 3 shows means M in detail.
[0019] In FIG. 1, the reference numerals 1, 2 denote input
terminals for connecting a power supply source, and 3, 4 denote
output terminals for connecting the lamp L to be operated. The
reference I denotes a flyback converter which is shown in greater
detail in FIG. 2. The switching arrangement also comprises a
control circuit CC and means M for generating a control signal S
for the control circuit CC. In the embodiment described, the lamp
is incorporated in a bridge circuit BC which is connected to the
output terminals 3,4.
[0020] In FIG. 2, TR denotes a transformer of the flyback converter
I, a primary winding PW of which is electrically connected to one
of the input terminals 1, and a secondary winding SW having a
secondary winding voltage is electrically connected to one of the
output terminals 4.
[0021] A semiconductor switching element of the flyback converter I
is denoted by T1. The semiconductor switching element T1 is
alternately switched to a conducting and a non-conducting state by
means of a switching signal SS which is generated in the control
circuit CC. The flyback converter also comprises a diode D and a
buffer capacitor C.
[0022] In FIGS. 2 and 3, the means M are shown in greater detail.
They comprise a sense circuit II for generating a signal S1 at an
output 5 in dependence upon the secondary winding voltage, and a
current-sense circuit III for detecting a current through the
secondary winding SW. At point B, the sense circuit II is connected
to one end of the secondary winding. At point E, the current-sense
circuit III is connected to the other end of the secondary winding
and is connected to the sense circuit by means of a sample &
hold switching circuit constituted by switching element T2. A
control electrode g2 of the sample & hold switching element T2
is electrically connected via an inverter circuit IV to the
switching signal SS of the control circuit CC for alternately
switching to a conducting and a non-conducting state by means of an
inverted switching signal {overscore (S)} {overscore (S)} of the
control circuit.
[0023] In the embodiment described, the sense circuit II comprises
a capacitive sense element, in the form of a capacitor CS, which is
connected to the secondary winding SW by means of an impedance, in
the form of a resistor RS. Resistor RS and the capacitor CS thus
form a series circuit. The value of the resistor RS determines the
value of the voltage across the capacitor CS. For a considerably
linear relation between the voltage across the capacitor CS and the
secondary winding voltage, the capacitor voltage is relatively
small and is preferably not more than 10% of the secondary winding
voltage. Point A constitutes the junction point between resistor RS
and capacitor CS and also the junction point with the output 5.
Point A is also connected to a main electrode d2 of the switching
element T2, which functions as a sample & hold switching
circuit and forms part of the current-sense circuit YIN. The
current-sense circuit further comprises a measuring impedance RIS
in series with the secondary winding SW. A relatively low value of
the voltage across the capacitor CS also results in a small
dissipation in the measuring impedance RIS. A high-frequency filter
in the form of, for example, an RC combination R1,C1 may be
used.
[0024] In the embodiment of the means M shown in FIG. 3, a
switching element T3 is arranged between point A and output 5 in
the sense circuit II, which switching element has a gate electrode
g3 connected to the switching signal SS of the control circuit CC
for alternately switching the switching element T3 to a conducting
and a non-conducting state. Output 5 is also connected to ground by
means of a resistor R2. Use of the switching element T3 together
with the resistor R2 has the advantage that the signal formed at
the output 5 is a true image of the variation of the current
through the primary winding PW of the transformer TR. To reduce
dissipation, the resistor R2 may be replaced by a switching element
T4 (connections shown by means of broken lines in the Figure) which
is switched with the inverted switching signal {overscore (S)}
{overscore (S)} of the control circuit.
[0025] The control circuit CC also comprises means in the form of
two timers by which the time during which the semiconductor
switching element is conducting and the time during which it is
non-conducting is limited to a maximum.
[0026] The switching elements T2, T3 and T4 can be joined with
parts of the control circuit CC to form an integrated circuit.
[0027] A practical realization of the embodiment described is
suitable for igniting and operating a car headlamp comprising a
high-pressure discharge lamp of the types D2R and D2S, manufactured
by Philips and having a nominal power of 35 W.
* * * * *