CN213661445U

CN213661445U - Current limiting circuit

Info

Publication number: CN213661445U
Application number: CN202022090221.6U
Authority: CN
Inventors: 张建添; 申志鹏; 王小亮
Original assignee: Mornsun Guangzhou Science and Technology Ltd
Current assignee: Mornsun Guangzhou Science and Technology Ltd
Priority date: 2020-09-22
Filing date: 2020-09-22
Publication date: 2021-07-09
Anticipated expiration: 2030-09-22

Abstract

A current limiting circuit is used for a high-voltage-resistant overlapped flyback DC-DC converter and comprises at least one stage of current limiting unit, wherein each stage of current limiting unit comprises a diode, a resistor and a mutual inductor, the cathode of the diode is used for being connected with a current sampling pin of a control IC, the anode of the diode is connected with one end of the resistor and one end of a secondary circuit of the mutual inductor, the other end of the resistor is connected with the other end of the secondary circuit of the mutual inductor, and the connection point of the other end of the resistor and the other end of the secondary circuit of the; the primary windings of the mutual inductors of all levels are connected in series between the voltage-stabilizing connecting points and the winding connecting points with the same level as the primary windings of the mutual inductors of all levels. The utility model discloses utilize the mutual-inductor ingeniously, will restrict because of the too big former limit peak current that the switch tube switch is inconsistent, or the electric capacity is voltage-sharing produces, improve product efficiency.

Description

Current limiting circuit

Technical Field

The utility model relates to a flyback converter field, in particular to current limiting circuit.

Background

In recent years, technologies such as solar power generation, wind power generation, and hydroelectric power generation have become mature. In a power generation control system and power transmission, the input voltage of the system is higher and can reach several kilovolts. The voltage resistance of the switching semiconductor device is far from the application requirement of the system input voltage. In order to solve the problem of overhigh stress of the switching semiconductor, a topological structure that the converters are connected in series can be adopted.

Fig. 1 is a circuit structure of a known high-voltage tolerant overlap flyback DC-DC converter with an automatic voltage-equalizing function, and a double-overlap structure is explained in detail in "design of high-voltage tolerant overlap flyback DC-DC converter" in 5 th of 2001 in the journal of electrical technology "while fig. 1 is disclosed.

The circuit schematic diagram of the well-known high-voltage-resistant overlapped flyback DC-DC converter is shown in figure 1, and comprises an input circuit and an output circuit, wherein the input circuit comprises N (N is more than or equal to 2, and N also satisfies the value range) stages of identical primary winding units and voltage-sharing units which are connected in series, the primary winding unit of each stage is connected with the voltage-sharing unit in parallel, the primary winding units of each stage are connected in series, the connection point between the primary winding unit of N stage and the primary winding unit of the next stage is the winding connection point of N (N is more than or equal to 1 and less than or equal to N-1), the voltage-sharing unit of each stage is connected in series, the connection point between the voltage-sharing unit of N stage and the voltage-sharing unit of the next stage is the voltage-sharing connection point of N (N is more than or equal to 1 and less than or equal to N, and N satisfies the value range in the whole text), the voltage-sharing unit of N stage comprises a, the other end of the capacitor Cn (N is N) is used for grounding; the nth-stage primary winding unit comprises a primary winding Nn and a switching tube Qn, wherein one end of the primary winding Nn is used as the input end of the nth-stage primary winding unit, the other end of the primary winding Nn is connected with the conduction current inflow end of the switching tube Qn, the conduction current outflow end of the switching tube Qn is used as the output end of the nth-stage primary winding unit, the input end of the first-stage primary winding unit is used for being connected with a positive voltage end Vg of direct-current voltage, the nth-stage primary winding unit further comprises a resistor Rcs, one end of the resistor Rcs is connected with the output end of the nth-stage primary winding unit and is used for being connected with a current sampling pin of the control IC, and the other end of the resistor Rcs is used for being grounded. The control end of each switching tube applies synchronous drive signals, and the primary windings of all stages are controlled in phase and share a magnetic core.

The known circuit structure is different from a general single-ended flyback converter (for example, N is 2), the primary winding of the high-voltage tolerant overlap flyback DC-DC converter is divided into two identical parts, namely a primary winding N1 and a primary winding N2, the primary winding N1 and the primary winding N2 are respectively controlled to be on and off by a switching tube Q1 and a switching tube Q2, and synchronous driving signals are applied to gates of the switching tube Q1 and the switching tube Q2. Therefore, under ideal working conditions, the switching tube Q1 and the switching tube Q2 are simultaneously turned on and off, and the potential of the voltage-sharing connection point A is shared due to the consistency of the primary winding N1 and the primary winding N2. Although the circuit can solve the problem of overhigh voltage stress of the switching tube, when the circuit is actually applied to a product, a plurality of reliability problems exist. Because the turn-on voltages of the two switching tubes and the driving signals of the two switching tubes cannot be perfectly consistent, there are many uncontrollable differences, which will inevitably cause the turn-on and turn-off of the switching tube Q1 and the switching tube Q2 in the circuit structure to be asynchronous, and once the on and off of the switching tube Q1 and the switching tube Q2 are asynchronous, there will be the following problems:

as shown in fig. 2, when the switching tubes are not turned on consistently, assuming that the switching tube Q1 is turned on first, at this time, the terminal voltage Vc1 of the capacitor C1 is still greater than the terminal voltage Vc2 of the capacitor C2, because the switching tube Q2 is not turned on yet, at this time, the polarity of the primary winding N2 is positive and negative, the forward voltage V2 induced by the primary winding N2 is greater than Vc2, the forward voltage V2 charges the capacitor C2 through the body diode of the switching tube Q2, at this time, the forward current increases, a large negative voltage is generated on the resistor Rcs, which affects the normal sampling of the control IC of the product. Because the negative voltage on the resistor Rcs cannot reach the current sampling turn-off voltage of the control IC, the control IC still provides drive, and the primary side peak current of the period is overlarge.

In the prior art, there is a method for solving the above problem, still taking a circuit with N being 2 as an example, as shown in fig. 3, a resistor Rx is connected in series between the voltage-sharing connection point a and the winding connection point, when the switching tubes are not uniformly turned on or the input capacitors are not voltage-sharing, as shown in fig. 4, the forward voltage induced by the primary winding that is turned on later charges the capacitors through the resistor Rx, the resistor Rx plays a role in current limiting, and the larger the resistance of the resistor Rx is, the better the resistance is. However, the resistor Rx can only reduce the forward current, the voltage on the resistor Rcs is still negative, and the current sampling pin of the control IC in the switching period still cannot sample a signal to turn off the driving, so that the primary peak current is too large, and the transformer core is saturated to cause the switch tube damage in a severe case.

Interpretation of terms:

n (N is more than or equal to 1 and less than or equal to N-1) level winding connection points: and the connection point between the n-stage primary winding unit and the next-stage primary winding unit.

N (N is more than or equal to 1 and less than or equal to N-1) level voltage-sharing connection points: and a connection point between the n-stage voltage-sharing unit and the next-stage voltage-sharing unit.

The control end of the switch tube: a port for controlling the switch to be switched on and off, for example, for an MOS transistor, a grid electrode of the MOS transistor is referred to; for a triode, the base of the triode is referred to.

The conduction current inflow end of the switching tube is as follows: after the switch is turned on, a port into which current flows, for example, for a P-MOS tube, refers to a source electrode of the P-MOS tube, and when the switch is turned on, the current flows from a source electrode with high voltage to a drain electrode with low voltage; for PNP transistors, the emitter of the transistor is referred to, and when conducting, current flows from the emitter with high voltage to the collector with low voltage.

Conduction current outflow end of the switching tube: after the switch is switched on, the port where the current flows out, such as for a P-MOS tube, refers to the drain electrode of the P-MOS tube; for PNP transistors, the collector of the transistor is referred to.

SUMMERY OF THE UTILITY MODEL

In view of this, the to-be-solved technical problem of the utility model is to provide a current-limiting circuit, be applicable to high pressure resistant eclipsed form and flyback DC-DC converter, solve high pressure resistant eclipsed form and flyback DC-DC converter because the switch is asynchronous or electric capacity is not voltage-sharing, produce forward current, cause control IC current sampling mistake, arouse that primary peak current is too big and cause the problem that the switch tube damaged.

In order to solve the technical problem, the utility model discloses a following technical measure realizes:

a current limiting circuit is suitable for a high-voltage-resistant overlapped flyback DC-DC converter and comprises at least one stage of current limiting unit, wherein each stage of current limiting unit comprises a diode Dn, a resistor Rn and a transformer TRn, the cathode of the diode Dn is used for being connected with the output end of a final stage primary winding unit, the anode of the diode Dn is connected with one end of the resistor Rn and one end of a transformer TRn secondary side circuit, and the other end of the resistor Rn and the other end of the transformer TRn secondary side circuit are connected to the ground.

The primary circuits of the mutual inductors TRn of all stages are connected in series between the voltage-stabilizing connecting points and the winding connecting points with the same number of stages.

In the scheme, N satisfies N is more than or equal to 1 and less than or equal to N-1.

Compared with the prior art, the utility model discloses following beneficial effect has:

1. the primary side current of the transformer TR1 can be increased due to the fact that the switch tubes are inconsistent or capacitors are not voltage-sharing, and meanwhile, after the current induced by the secondary side winding of the transformer TR1 is converted into voltage through the resistor R1, the voltage rectified through the D1 can also be increased. When the voltage rectified by the secondary winding of the TR1 reaches the protection voltage, the IC is turned off, the MOS is turned off, no current flows through the primary side, and the peak current of the primary side is limited in a safety range. Therefore, when the sampling of the resistor Rcs fails, the mutual inductor TR1 can effectively sample the current on the primary side and feed back the current to the chip, and after the set current is reached, the IC is turned off to drive the switching tube to be turned off, so as to limit the peak current on the primary side, ensure that the power device on the primary side works in a reliable range, and increase the reliability of the product.

2. The utility model relates to a current-limiting circuit increases the device few, and is with low costs, and easily design, and the reliability is high.

Drawings

FIG. 1 is a schematic circuit diagram of a prior art high voltage tolerant overlap flyback DC-DC converter;

FIG. 2 is a current loop diagram of a high voltage tolerant overlap flyback DC-DC converter in the prior art when the switching tubes are not turned on consistently and the capacitors are not voltage-sharing;

FIG. 3 is a schematic circuit diagram of a prior art improved high voltage tolerant overlapping flyback DC-DC converter;

FIG. 4 is a current loop diagram of a prior art improved high voltage tolerant overlap flyback DC-DC converter when the switching tubes are not turned on consistently;

fig. 5 is a schematic circuit diagram of the current limiting circuit including the second-stage current limiting unit applied to the three-stage high voltage tolerant overlapped flyback DC-DC converter.

Detailed Description

In order to make the present invention more clearly understood, the present invention will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

First embodiment

Fig. 5 shows a schematic circuit diagram of a current limiting circuit applied to a three-level high voltage tolerant overlapped flyback DC-DC converter, where the current limiting circuit includes two stages of current limiting units.

The first stage current limiting unit comprises a diode D1, a resistor R1 and a transformer TR1, and the second stage current limiting unit comprises a diode D2, a resistor R2 and a transformer TR 2.

The cathode of the diode D1 is connected with the output end of the final primary winding unit, the anode of the diode D1 is connected with one end of the resistor R1 and one end of the secondary side circuit of the transformer TR1, and the other end of the resistor R1 is connected with the other end of the secondary side circuit of the transformer TR1 to the ground. The primary circuit of the transformer TR1 is connected in series between the primary voltage stabilizing connection point and the primary winding connection point.

The connection of the elements of the second-stage current limiting unit is the same as that of the corresponding elements in the first-stage current limiting unit, but the primary circuit of the mutual inductor TR2 is connected in series between the secondary voltage stabilizing connection point and the secondary winding connection point.

The current limiting circuit of the present embodiment operates as follows:

as shown in fig. 5, when the driving timing sequence of the switching tube is inconsistent due to circuit parasitic parameters, the voltage balance on the primary winding units of each stage is ensured, the automatic coupling adjustment is performed by using the primary windings N1, N2 and N3 with the common magnetic core, and the voltage on the voltage equalizing units of each stage is further stabilized according to the mutual inductance current balance principle on the primary windings N1, N2 and N3. In order to avoid the phenomenon of mutual current inductance generated among the primary windings N1, N2 and N3 in the dynamic process, the current sampling and continuous driving of the control IC are influenced, the switching tube is not closed, and finally the primary side current is overlarge to damage the switching tube. The utility model discloses the current on the three winding is sampled simultaneously through mutual-inductor TR1, TR2 and resistance Rcs to the circuit. When the voltage of the capacitor C1 is higher than that of the capacitor C2 or the capacitor C3, or the switch tube Q1 is conducted earlier than that of the switch tube Q2 or the switch tube Q3, forward currents are induced by the primary windings N2 and N3, energy on the capacitor C1 is transmitted to the capacitor C2 and the capacitor C3 through the forward relation of the primary windings N1, N2 and N3, so that the current flowing through the primary winding of the transformer TR1 is increased, and meanwhile, the rectified voltage of the secondary winding of the transformer TR1 is also increased. When the rectified voltage of the secondary winding of the transformer TR1 exceeds the protection voltage of the current sampling pin of the control IC, the control IC is turned off to drive, the switching tube is turned off, no current exists in the primary windings N1, N2 and N3, and the peak current of the primary side is limited within a safety range. Similarly, when the voltage of the capacitor C2 is larger than that of the capacitor C1 or the capacitor C3, the current flowing through the primary side of the transformer TR2 increases, and the rectified voltage of the secondary side winding of the transformer TR2 also increases. When the voltage rectified by the secondary winding of the transformer TR2 exceeds the protection voltage of the current sampling pin of the control IC, the control IC is turned off to drive, when the voltage of the capacitor C3 is larger than that of the capacitor C1 or the capacitor C2, the voltage on the resistor Rcs is also increased, and when the voltage of the resistor Rcs exceeds the protection voltage of the current sampling pin of the control IC, the control IC is turned off to drive. Therefore, no matter which capacitor among the 3 capacitors is not voltage-sharing, the current limiting circuit can ensure that the primary side peak current is within a set value, and the power device works within a reliable range.

The embodiments of the present invention are not limited to the above, and according to the above-mentioned contents of the present invention, the common technical knowledge and the conventional means in the field are utilized, without departing from the basic technical idea of the present invention, the specific implementation circuit of the present invention can also make other modifications, replacements or changes in various forms, all falling within the scope of the present invention.

Claims

1. A current limiting circuit is used for a high-voltage-resistant overlapped flyback DC-DC converter, and is characterized in that:

the current limiting device comprises at least one stage of current limiting unit, wherein each stage of current limiting unit comprises a diode, a resistor and a mutual inductor;

the connection relationship of each stage of current limiting units is as follows: the primary winding of the mutual inductor is used for being connected between a voltage-sharing connection point and a winding connection point of the corresponding stage of the overlapped flyback DC-DC converter circuit in series; one end of a secondary winding of the mutual inductor is used for being grounded and is simultaneously connected with one end of a resistor, the other end of the secondary winding of the mutual inductor is simultaneously connected with the other end of the resistor and the anode of a diode, and the cathode of the diode is used for being connected with a current sampling pin of a control IC of the overlapped flyback DC-DC converter.

2. A current limiting circuit is used for a high-voltage-resistant overlapped flyback DC-DC converter, and is characterized in that:

the current limiting unit comprises a current limiting unit with one less stage than the circuit stage of the heavier stacked flyback DC-DC converter, wherein each stage of current limiting unit comprises a diode, a resistor and a mutual inductor;