DE202016004285U1 - Active inrush current limit - Google Patents

Abstract

Current limiting device for electronic or electrical consumers, comprising: - means (5) for connection to the feeding network, and - a means (15) for connection to the load side, and - a Graetz rectification stage (1), and - means for active regulated current limit ((7), (8), (11) and (12)) characterized in that in the current path between the mains input voltage (4) and output voltage (6) a Graetz rectifier bridge (1) is connected in series, said Connection to the AC voltage inputs takes place and on whose DC output side a current-limiting, actively regulating current path consisting of (8) and (12) is provided in connection with a reference voltage source.

Description

Electrical and electronic circuits often have an interference suppression capacitor and / or a rectification stage in their input region, which in many cases is implemented in combination with an input capacitor. The purpose of the input capacitor is to store and dispense energy when the energy demand of the electronic circuit is greater at certain times than the energy that can be provided by the feeding network at all times. For energetic reasons, attempts are made to dispense with ohmic resistances in the input circuit, which at the moment of switching on could limit the current to the input capacitance of the load. However, if there is no series resistance, the current is limited only by the line resistance of the supplying connecting lines and parasitic resistances of the rectification stage and the input capacitance. This results in short-term charging current peaks, which can be some 10 amps in practice for consumers whose rated current is, for example, only 100 milliamperes. Furthermore, modern power supplies with clocked switches on the input side often equipped with noise suppression capacitors, which can also lead to high charging current peaks.

These inrush surges can cause the triggering of upstream protection elements, such as fuses. This undesirable effect gets in practice of considerable importance when several consumers of this property are operated together on a circuit breaker. The mismatch between inrush current on the one hand and the rated current on the other hand leads to the fundamental difficulty in the design of the security system. If this is based on the nominal current, then in practice an undesirable triggering of the safety device at the moment of switching on is often observed. If the fuse system is designed for the inrush current peak, the detection of impermissibly high rated currents, which are not due to inrush current, becomes difficult.

State of the art

This problem has been known for decades and is solved on the one hand by a high variance of security elements as well as by different circuit variants. So it is state of the art that an ohmic series resistance is bridged after the end of the charging of the input capacitor with a switch. Another common option is to switch the load in the zero crossing of the input voltage, so that there is no voltage difference between the input capacitance and the mains input at the moment of switching on, so that no current flows at the moment of switch-on.

Both methods have disadvantages in principle. Thus, the use of a switch to bridge an ohmic resistance in the input circuit for a relatively expensive and leads when using a mechanical switch to a significant limitation of the life of the product. Arrangements that switch in the voltage zero crossing of the input load, have the fundamental disadvantage that they remain ineffective when switching from constant voltages. Their principal disadvantage is that they are based on recognizing when a switch-on is as smooth as possible, but do not limit the input current flow: detecting and switching at the zero crossing prevents - and this is due to their effect - switching at high input voltage to a voltage-free input capacitance , Missing in the input circuit but a current-limiting component, such as an ohmic resistance, it also comes to high charging currents, which are significantly higher than the rated current of the product, in the first few half-waves of the input voltage supply. This case is particularly relevant when, for example, DC voltages are used to supply electronic consumers, here such an arrangement remains in principle ineffective. Practical relevance has this, if z. B. in DC emergency power supplies battery voltages are switched to consumers.

This problem is solved with the features listed in the protection claim 1.

With the invention it is achieved that high inrush current peaks are avoided in consumers. Thus, it limits the input current to a well-defined level, and can be used for both input AC voltages and DC input voltages. As consumers, those with high input capacitance can be used for energy storage, but also consumers such as lamps with glow wire coil, which cause a high current flow at the moment of switching.

1 shows the basic input circuitry that is found in many electronic devices. The input voltage ( 4 ) is generated by a Graetz rectification stage ( 1 ) rectified and the input capacitance ( 3 ) via a resistor ( 2 ). Is the resistance missing ( 2 ) are rectifying stage ( 1 ) and input capacity ( 3 ) directly connected. In this case, the described very high current flow occurs until the input capacitance is charged. The current flow is undefined and is only defined by supply and parasitic resistances. One too undefined current flow is due to the often provided to ensure the electromagnetic compatibility on the input side noise suppression capacitors ( 18 ).

The 2 shows how the problem of limiting the inrush current peaks is achieved according to the invention. For this purpose, the circuit arrangement 2 with the clamps ( 5 ) to the supplying network and via the terminals ( 15 ) connected to the consumer whose inrush currents are to be limited.

The functional core of the circuit arrangement is the rectifier ( 1 ) in conjunction with a current limiting arrangement consisting of the resistor ( 7 ), the transistor ( 8th ), the resistance ( 12 ) and the zener diode ( 11 ) is formed. This circuit arrangement consisting of the components ( 7 ) 8th ) 11 ) and ( 12 ) has been known for decades and described in the basic literature in terms of their functionality. The current through the resistor R2 is determined by the by the gate-source voltage of the transistor ( 8th ) reduced zener voltage of the Zener diode ( 11 ) divided by the resistance of the resistor ( 12 ). An increase in the current through the transistor 8th would increase the voltage across the resistor ( 12 ) cause. However, since the Zener diode voltage is constant, this voltage increase would lead to a reduction of the gate-source voltage and thus again to a reduction of the transistor current. In this way it is ensured that the current through the transistor Q1 can never become larger than through the zener diode voltage, the gate-source voltage of the transistor ( 8th ) and the resistance of the resistor ( 12 ).

Of course, the current limiting function can also be implemented using P-channel field-effect transistors or else using NPN or PNP bipolar transistors. According to the invention, the protective circuit when using the components ( 1 ) 7 ) 8th ) 11 ) and ( 12 ) functioning. Of course, on the elements ( 7 ) and ( 11 ) can be omitted if another voltage reference is provided.

A particular advantage of the invention is the simplicity and scalability of the device. If larger inrush currents are desired, then the elements ( 8th ) and ( 12 ) connect additional transistor resistor pairs in parallel. In the whole 2 you realize that it is with the couples ( 9 ) and ( 13 ) such as ( 10 ) and ( 14 ) There are two more current-carrying component pairs. The circuit arrangement thus limits the current in the consumer to the current sum resulting from the individual currents through the transistors ( 8th ) 9 ) and ( 10 ) as well as the ten-diode current through resistor R1.

3 shows that the circuit arrangement is particularly flexible in that in the current paths of the transistors ( 8th ) 9 ) or ( 10 ) Switch ( 16 ) and ( 17 ) are placed, to ensure the function at least one switch must be closed. It is understood that these switches can be placed in each branch, but need not. In this way, application-specific maximum inrush currents can be easily defined. To cover a large current limit variation range, the resistors ( 12 ) 13 ) and ( 14 ). For example, it is conceivable to determine the size of the current flow in resistors ( 12 ) 13 ) and ( 14 ) by a factor of 2.

Of course, the transistor resistor pairs do not have to work with a common zener diode reference voltage but rather the individual transistor resistor pairs (( 8th ) 12 ) and ( 9 ) 13 ) and ( 12 ) 14 )) are each made up of separate reference voltages - in With ( 7 ) and ( 11 ) numbered - fed. In this case, the switch can be located above the Zener diode ( 11 ), where you can use a very low-cost low-power switch. This eliminates the placement of the switch in the respective sub-circuit of the transistors ( 8th ) 9 ) and ( 10 ).

Of course, any number of current-limiting components can simply be switched in parallel, so that the circuit can be scaled arbitrarily.

4 shows, by way of example, an arrangement in which 6 current-limiting paths are connected in parallel, wherein all but the first path can be arbitrarily switched on and off.

LIST OF REFERENCE NUMBERS

1

Graetz rectifier stage

2

resistance

3

input capacitor

4

input voltage

5

Input terminals or input cable of the circuit arrangement

6

Output voltage of the circuit arrangement

7

resistance

8th

transistor

9

transistor

10

transistor

11

Zener diode

12

resistance

13

resistance

14

resistance

15

Output terminals or output cable of the circuit arrangement

16

Switch (jumper)

17

Switch (jumper)

18

Störschutzkondensator

Claims (8)

Current limiting device for electronic or electrical consumers, comprising: - a means ( 5 ) for connection to the feeding network, and - a means ( 15 ) for connection to the load side, and - a Graetz rectification stage ( 1 ), and - means for actively controlled current limitation (( 7 ) 8th ) 11 ) and ( 12 )), characterized in that in the current path between mains input voltage ( 4 ) and output voltage ( 6 ) a Graetz rectifier bridge ( 1 ) is connected in series, wherein this connection takes place at the AC voltage inputs and on whose DC voltage output side a current-limiting, actively regulating current path consisting of ( 8th ) and ( 12 ) is provided in connection with a reference voltage source. Current limiting device according to claim 1, characterized in that at least one further is connected in parallel with the first current path. Current limiting device according to claim 2, characterized in that the individual current paths can be switched on and off by means of switches. Current limiting device according to claim 1, characterized in that the resistors determining the current in the individual paths have equal resistance values. Current limiting device according to claim 1, characterized in that of the resistances determining the currents in the individual paths at least one has a different resistance value Current limiting device according to claim 1, characterized in that a Zener diode is used as a voltage reference. Current limiting device according to claim 1, characterized in that a voltage reference ( 11 ) is used for all current path combinations of transistor and resistor. Current limiting device according to claim 1, characterized in that at least one second voltage reference ( 11 ) is used so that there are at least two different reference voltages that are separately connected to the control inputs of the transistors grouped in this way. Current limiting device according to claim 8, characterized in that in all but one switch arranged in parallel, the voltage references ( 11 ) can be bridged.

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