Electric circuit arrangement for the input protection circuit of a switching power supply and a switching power supply

Abstract

The invention relates to an electric circuit arrangement for the input protection circuit of a switching power supply, having a surge protection circuit, which is contacted with a supply voltage on an input side and to which a current-compensated choke is connected as a suppression component, said current-compensated choke being connected to a rectifier circuit comprising an energy storage means on an output side. Via modifications to the circuit technology, such as using two varistors as surge protections, and by using suitable switching elements, such as silicon diodes as rectifier elements and ceramic capacitors as an energy storage means, the input protection circuit is designed such that the requirements, which an expanded input voltage range demands of a surge circuit, are fulfilled. Furthermore, the invention relates to a switching power supply having an electric circuit arrangement according to the invention for the input protection circuit.

Claims

1. An electric circuit arrangement (30) for an input protection circuit of a switching power supply, having a surge protection circuit (12), which is contacted with a supply voltage on an input side and to which a current-compensated choke is connected as a suppression component (14), said current-compensated choke being connected to a rectifier circuit (16) comprising an energy storage means (18) on an output side, characterized in that the surge protection circuit (12) is formed by a first and a second varistor (RV100, RV101), said first varistor (RV100) being arranged upstream of the current-compensated choke (LD100) and said second varistor (RV101) being arranged downstream of the current-compensated choke (LD100), in that the current-compensated choke (LD100) is dimensioned such that it has an ohmic resistance of 0.5 ohms to 1.0 ohms and an inductivity of 20 mH to 30 mH per spool, in that the rectifier circuit (16) comprises silicon diodes (D100 to D104) having an average forward current of at least 5 Amperes, in that the energy storage means (18) is realized as a ceramic capacitor (CK100, CK102), and in that conducting path fuses covered by a casting compound are integrated in a conductor plate as surge protection devices.

2. The switching power supply, characterized by the electric circuit arrangement for the input protection circuit according to claim 1.

3. The switching power supply according to claim 2, characterized by a power-factor-control control system for controlling a function sequence.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) Further advantageous features of embodiments can be derived from the following description and the drawings, which describe a preferred embodiment of the invention by means of an example. In the following,

(2) FIG. 1 illustrates an input protection circuit of a U1 power supply according to the state of the art,

(3) FIG. 2 illustrates an input protection circuit of a U2 power supply according to the state of the art, and

(4) FIG. 3 illustrates an electric circuit arrangement according to the invention for an input protection circuit of a wide-range power supply.

(5) FIG. 4 illustrates a schematic block diagram of a switching power supply.

DETAILED DESCRIPTION

(6) In FIG. 1, an electric circuit arrangement 10 is illustrated for the input protection circuit of a U1 power supply according to the state of the art.

(7) The circuit arrangement 10 essentially comprises four functional component groups which can be illustrated as circuits of consecutive signal processing steps starting from a mains voltage U.sub.n (input voltage of the circuit arrangement 10) contacted on an input side.

(8) On the input side, a surge protection circuit 12 is subjected to the mains voltage U.sub.n. The surge protection circuit 12 comprises a varistor R1 and, if required, further partially changeable resistances in order to attenuate transient surges in the mains voltage U.sub.n.

(9) A current-compensated choke L1 abuts thereto as a suppression component 14, high-frequency interference transmissions being mostly suppressed by means of said current-compensated choke L1.

(10) In the next signal processing step, a rectification occurs in a rectifier circuit 16 by means of a bridge rectifier which is equipped with Schottky diodes V1 to V4.

(11) The output voltage of the input protection circuit 10 is buffered by means of an energy storage means 18 which is realized as an electrolyte capacitor C5.

(12) FIG. 2 illustrates an electric circuit arrangement 20 for the input protection circuit of a U2 power supply according to the state of the art.

(13) This circuit arrangement 20 for a U2 power supply illustrates the same general layout as the circuit arrangement 10 for a U1 power supply, consisting of a surge protection circuit 12, a suppression component 14, a rectifier circuit 16 and an energy storage means 18.

(14) However, the circuit elements are subject to different marginal conditions relating to circuit technology due to the differing voltages and currents and are therefore dimensioned differently according to the requirements.

(15) FIG. 3 illustrates an electric circuit arrangement 30 according to the invention for the input protection circuit of a wide-range power supply.

(16) In this instance as well, the input protection circuit 30 is based on a surge protection circuit 12, a suppression component 14, a rectifier circuit 16 and an energy storage means 18, however, these functional component groups are modified regarding circuit technology and are provided with special circuit elements in order to enable a protection circuit for an input voltage range which is higher than the input voltage range of a U1 or a U2 power supply.

(17) Thus it can be seen in FIG. 3 that the surge protection circuit 12 is made of a first varistor RV100 and a second varistor RV101, said first varistor RV100 being disposed upstream of the current-compensated choke LD100 starting from the circuit input, i.e. as viewed from the in-contact mains voltage U.sub.n, and said second varistor RV101 being disposed down-stream of the current-compensated choke LD100.

(18) FIG. 4 shows a switching power supply 40 according to the invention comprising the electric circuit arrangement 30 and a power factor control system 42 for controlling the progress of the functions performed in the switching power supply 40.

(19) The current-compensated choke LD100 principally is targeted at suppressing common-mode interfering currents and consists of one highly permeable ring core, on which two windings are disposed, through which the current flows in opposite directions.

(20) Highly permeable manganese-zinc ferrites (material K7000) are preferably used as ring cores, as they can be operated in a frequency range ranging from 10 kHz to 1 MHz and have an outer diameter of 16 mm, an inner diameter of 9.6 mm and a height of 6.3 mm. The AL value (inductivity per winding number squared) of such a core is yielded at 4150 nH.

(21) Another longitudinal inductivity L100 is added for suppressing the differential-mode interference emissions which is switched at an output of the rectifier circuit 16 against mass.

(22) For this purpose, each of thesein total threespools comprises a winding having one ohmic resistance of 0.5 to 1 in each instance, as can be yielded from the following description.

(23) A switching power supply in the performance range to 20 W typically has an efficiency between 75 to 85%, i.e. the entire power loss is 15 to 25% of the input performance. The power loss in the input circuit should not surpass 5% and is therefore approx. of the entire power loss. Starting from a desired initial performance of the switching power supply of 10 W and an efficiency of 80%, an input performance of 12.5 W is therefore required, from which an input current I.sub.in of 0.625 A is yielded at an input voltage of 20 V (the input voltage is largest in small input voltages).

(24) The entire power loss P.sub.v is (12.5 W10 W)=2.5 W. From this, an overall ohmic resistance is calculated at R.sub.Cu=*P.sub.v/I.sub.in.sup.2=1.6. Divided onto a total of three required spools, an ohmic winding resistance of 0.53 per spool is yielded.

(25) The inductivity of the current-compensated choke LD100 consisting of two spools is preferably 20 mH to 30 mH per spool. The inductivity of the other longitudinal inductivity L100 is in the range of 1 mH.

(26) The bridge rectifier circuit 16 is made of 1000 V silicon diodes D100 to D104. In a intentional oversizing, said diodes have an average conducting current of 5 A in order to generate an as low as possible power loss.

(27) On the output side, two 450 V ceramic capacitors CK100 and CK102, each having 2.2 F, are installed for buffering the output voltage of the input protection circuit.

(28) On the input side, the circuit arrangement has two conductor path fuses as a surge protection device, which are integrated into a conductor plate and are covered by a casting compound. Said conductor path fuses are preferably realized as two 0.2 mm*5 mm galvanized solder paths in order to safely separate them when a short circuit occurs.