RU143748U1 - FAST KEY KEY PROTECTION DEVICE - Google Patents

Abstract

A high-speed power switch protection device comprising a power switch and a current sensor included in a primary circuit of an isolation transformer; a control device connected to the output of the current sensor, characterized in that it further comprises a switching unit connected between the control device and the control input of the power switch, and the switching unit is also connected to the output of the current sensor.

Description

Technical field

The utility model relates to electrical engineering and can be used in pulsed sources of secondary power supply (RES) as a circuit for the quick protection of the power switch of the RES in a short circuit mode (short circuit).

State of the art

When the converter is connected to a pulsed load, for example, to an energy-intensive processor system that has load fluctuations with a frequency much higher than the working frequency of the converter, a sharp surge or load shedding is possible, which can lead to significant surges in the output voltage of the converter, leading to processor system failures. To avoid such phenomena, storage capacities are installed near energy-intensive consumers, reaching values of several hundred thousand microfarads, which in turn requires a short-term operation in the short-circuit mode when power-consuming consumers are turned on, i.e. special requirements for converters appear.

One of these requirements is to protect the power switch from input current spikes in the short-circuit mode.

A device is known (patent US 6760203 "Switching power supply with overcurrent protection" with a priority date of June 27, 2002, IPC H02M 3/335, H02M 3/28) in which, in addition to the standard implementation of the gate control of the power transistor by feedback signals, a circuit is implemented shutdown of the control chip when overcurrent is detected, followed by a restart of the control chip. The current flowing through the key transistor 5 charges the capacitor 11, which opens the transistor 12 and thus helps to reduce the voltage level of the microcircuit with its subsequent shutdown.

The disadvantages of this device include the inability to limit the current flowing through the key transistor 5 in the short circuit mode in each conversion cycle.

A device is known (patent US 7015680 "Current-limiting circuitry", priority date 06/10/2004, IPC G05F 3/04, G05F 1/569, G05F 1/565), in which when the critical value of the current in the load 290 flowing is exceeded through the resistor RS2, a shutdown of the control output of the gate of the transistor Q282 is performed in each conversion cycle.

The disadvantages of this device include the presence of a special additional current input on the control chip 200, which is extremely rare in real PWM control chips.

A device is known (patent CN 202888788 "Overcurrent protection circuit and switching power supply", priority date 11/08/2012, IPC H02H 7/12, H02H 3/08), in which when the current exceeds a critical value, the voltage across the resistor increases to a value the breakdown voltage of the diode Z1, the transistor Q1 is opened and a trip signal is received at the input of the control microcircuit ICEN.

The disadvantages of this device include the inability to limit the current in the short circuit mode in each conversion cycle.

A device is known (application for utility model RU 2013138954 “Device with high-speed feedback”, priority date 08/08/2013, IPC H02M 3/335, H03K 17/689), in which the conversion of a high-speed total OS by input current and output voltage to reduce the duration of transients during load surge / discharge, as well as reducing the amplitude of the ripple of the output voltage while maintaining high accuracy of stabilization of the output voltage.

The disadvantages of the device include the lack of the possibility of short-term operation in the short circuit mode, required, for example, when the power source is operating at a significant reactive load.

This device is selected as a prototype.

Brief Description of the Drawings

In FIG. 1 is a diagram of the inventive device high-speed protection of the power key.

In FIG. 2 shows the timing diagrams of the operation of the high-speed power switch protection device in the normal mode and short circuit mode:

a) before the introduction of a limitation of the input current in each conversion cycle through the driver (1.4);

b) after the introduction of a limitation of the input current in each conversion step through the driver (1.4).

In FIG. Figures 3 and 4 show possible implementations of a high-speed power key protection device.

In FIG. Figure 5 shows graphs of the dependence of the output voltage on the output current with and without a power switch protection device.

In FIG. Figures 6 and 7 show the waveforms of the voltage of the drain-source of the power transistor and on the resistor of the current sensor in the short circuit mode without the power switch protection device and with it, respectively.

Utility Model Essence

The technical result, accelerated disconnection of the power switch in the short circuit mode, is achieved due to the fact that the current feedback signal is supplied to the switching unit bypassing the control device (PWM controller), and when a certain threshold value is reached, it disconnects the power switch from the control circuit.

The high-speed power switch protection device (Fig. 1) contains: a power switch (1.1) and a current sensor (1.3) included in the primary circuit of the isolation transformer (1); a control device (1.2) connected to the output of the current sensor (1.3) characterized in that it further comprises a switching unit (1.4) connected between the control device (1.2) and the control input of the power switch (1.1), and the switching unit (1.4) is also connected to the output of the current sensor (1.3).

Comparative analysis with the prototype shows that the inventive high-speed power key protection device is characterized by the presence of a switching unit, connected between the control device and the control output of the power key and having an output connected to the output of the current sensor. Thus, the claimed device meets the criterion of "novelty."

The device implements high-speed protection of the power switch in each conversion cycle from overcurrent during short-term operation of the power supply in short-circuit mode, for example, when working on a reactive load. This is achieved due to the accelerated shutdown of the power switch (1.1) by supplying the feedback signal of the current sensor (1.3) not only to the control device (1.2), but also to the switching unit (1.4), which disconnects the power switch (1.1) before the control device ( 1.2). This eliminates the internal delays of the control device (PWM controller), affecting the delay time for turning off the power switch in each conversion cycle.

Such a high-speed protection with limited pulse current of the power switch allows to reduce its peak pulse power, to avoid overheating of the transistor crystal, thereby increasing its reliability.

Timing diagrams of the operation of the IVE before and after the introduction of the input current limitation in each conversion cycle are shown in FIG. 2a and 2b, respectively, where: I ₀ - current protection threshold in the control device (PWM controller), I ₁ - current through the power switch in short circuit mode, I ₂ - current through the power switch in normal mode, t _ass - current protection delay time.

Timing diagrams (Fig. 2a, 2b) explain that the use of high-speed protection of the power switch (1.1) leads to a sharp decrease in the current I ₁ through the power switch in each conversion cycle in the short circuit mode and does not affect the operation of the power supply in normal mode (current I ₂ through a power switch).

An example of a possible implementation of a high-speed power key protection device with the execution of a switching unit on a microcircuit, for example, an LM5112SD driver microcircuit, and using a current transformer (transformer T1, diode VD1, resistors R4, R5) or a resistive sensor (resistor R4) as a current sensor (1.3) shown in FIG. 3 and 4, respectively.

The signal from the current sensor is fed to the current feedback input (CS) of the PWM controller microcircuit (PWM) through the integrating circuit (resistor R1, capacitor C1), which serves to suppress pulsed noise and to the additional inverse input of the INB driver chip through the voltage divider across the resistors R2, R3 and filter capacitor C2.

In the normal state, when the signal level from the current sensor at the INB input is less than the threshold value, the driver operates in the operating mode. If the threshold value of the voltage at the input INB is exceeded, the output signal of the power transistor is formed at the output of the driver microcircuit and, accordingly, the power transistor VT1 closes. In this case, the division coefficient (divider R2, R3) is selected in such a way as to ensure the fast turn-off of the power transistor on the one hand and, on the other hand, to provide sufficient time for the PWM controller to respond to an excess of the input current.

An experimental verification confirmed the effectiveness of the claimed power key protection device. So, for example, for a 100 W module, with the implementation of a power switch protection device in accordance with FIG. 3, at an input voltage of 75 V, the output short-circuit current after the introduction of the power switch protection device decreased from 86 A to 38 A, i.e. 2.3 times (Fig. 5) and, accordingly, the pulsed current through the power transistor decreased 2.2 times. A decrease in the pulse current through the power transistor leads to a decrease in the overheating of the crystal of the transistor and thereby to increase its reliability. The voltage diagrams of the current sensor and drain-source of the transistor VT1 before and after using the power switch protection device are shown in FIG. 6 and 7, respectively.

The proposed device high-speed protection of the power switch is made of standard elements that are commercially available from industry. It is assembled by typical installation operations using standard equipment and does not require adjustment, which is especially important in serial production. Therefore, the proposed device meets the criterion of "industrial applicability".

Claims (1)

A high-speed power switch protection device comprising a power switch and a current sensor included in a primary circuit of an isolation transformer; a control device connected to the output of the current sensor, characterized in that it further comprises a switching unit connected between the control device and the control input of the power switch, and the switching unit is also connected to the output of the current sensor.