A segmented drive and detection control circuit and method for power switching tubes

Abstract

The application discloses a segmented driving and detection control circuit and method of a power switch tube, and the control circuit comprises a freewheeling switch tube current detection circuit, a sample-and-hold circuit, a main switch tube current detection circuit, a main switch tube threshold voltage detection circuit and a main switch tube segmented driving control circuit; wherein the freewheeling switch tube current detection circuit is used for detecting the conduction current of the freewheeling switch tube; the sample-and-hold circuit is used for sampling and holding the current value when the freewheeling switch tube is turned off; the main switch tube current detection circuit is used for detecting the conduction current of the main switch tube; the main switch tube threshold voltage detection circuit is used for detecting the threshold voltage of the main switch tube; and the segmented driving control circuit is used for detecting the detection results of the above detection circuits. The application can effectively reduce the EMI and electric stress problems caused by the hard opening and hard closing of the power switch tube, and simultaneously realizes the fast switching control of the power switch tube.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, specifically to a segmented driving and detection control circuit and method for power switching transistors. Background Technology

[0002] In switching power supply circuits, EMI and electrical stress problems caused by the hard turn-on and hard turn-off of power switching transistors greatly affect the performance and reliability of the switching power supply circuits.

[0003] Traditional switching power supply drive control circuits, such as Figure 2 As shown, the PWM control signal is converted into power switch control signals ug and lg with strong driving capability through the ug_driver and lg_driver modules. A dead time control module is inserted between ug and lg to prevent M1 and M2 from being turned on simultaneously, thus preventing shoot-through current. In traditional switching power supply drive control circuits, the rising and falling edges of the drive control signals ug and lg have a fixed rate and are usually designed to be relatively steep to reduce the switching losses of the power switching transistors, improve conversion efficiency, and also ensure the reliability of the dead time.

[0004] However, this leads to serious EMI interference and electrical stress problems (power switching transistor withstand voltage, Where L is the package parasitic inductance of the power switch transistor. This refers to the rate of current change when the power switch is turned on or off. In some cases, this can even lead to the breakdown and damage of the power switch. To reduce the impact of EMI and switching electrical stress, it is necessary to control and reduce... This involves reducing the slope of the rising and falling edges of ug and lg, but this usually leads to a sharp increase in switching losses and makes the inserted small dead time unreliable (overwhelmed by the slow rising and falling edges of ug / lg). In some high-frequency applications, it even limits the switching frequency of the power switch. Therefore, a segmented drive and detection control circuit for the power switch is needed to effectively reduce EMI and electrical stress problems caused by hard turn-on and hard turn-off of the power switch, while achieving fast switching control of the power switch. Summary of the Invention

[0005] The purpose of this invention is to provide a segmented driving and detection control circuit and method for power switching transistors to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a segmented driving and detection control circuit for a power switch, comprising a freewheeling switch current detection circuit, a sample-and-hold circuit, a main switch current detection circuit, a main switch threshold voltage detection circuit, and a main switch segmented driving control circuit; wherein, the freewheeling switch current detection circuit is used to detect the on-state current of the freewheeling switch; the sample-and-hold circuit is used to sample and hold the current value when the freewheeling switch is turned off; the main switch current detection circuit is used to detect the on-state current of the main switch; the main switch threshold voltage detection circuit is used to detect the threshold voltage of the main switch; and the segmented driving control circuit is used to drive the main switch power transistor to turn on or off in segments at different rates according to the detection results of the above detection circuits.

[0007] Preferably, the sample-and-hold circuit is used to sample and hold the current value when the continuous current switch is turned off, and this current value is used to indicate whether the main switch is fully turned on or off.

[0008] Preferably, the main switch threshold voltage detection circuit indicates the minimum voltage when the main switch is turned on or off.

[0009] Preferably, the segmented drive control circuit determines whether the main switch has been turned on or off based on the detection results of the detection circuit. Before the main switch is turned on, it is driven to turn on slowly at a lower rate. After the main switch is turned on, it is driven to turn on quickly and fully at a higher rate. When the main switch is turned off, it is driven to turn off quickly at a higher rate. When the main switch enters the turn-off process, it is driven to turn off slowly at a lower rate.

[0010] The above-mentioned method for segmented driving and detection control of power switching transistors includes the following steps:

[0011] S1: First, detect and maintain the current of the freewheeling switch, which serves as the basis for determining whether the main switch is fully turned on or off. Combined with the threshold voltage of the main switch, the final determination is made as to whether the main switch is turned on or off.

[0012] S2: When the main switch is turned on, it is first turned on slowly at a low rate. If its on-current exceeds the current value of the sampled and held freewheeling switch, and the gate drive control signal of the main switch also exceeds the threshold voltage of the main switch, it is determined that the main switch has been turned on, and the process is switched to turn on quickly and fully at a higher rate. When the main switch is turned off, it is first turned off quickly at a higher rate. If its on-current is lower than the current value of the sampled and held freewheeling switch, or the drive control signal of the main switch is lower than the threshold voltage of the main switch, it is determined that the main switch has entered the turn-off process, and the process is switched to turn off slowly at a lower rate.

[0013] Preferably, in the above method, the current value of the freewheeling switch is the current value corresponding to the freewheeling switch being turned off, and this current value serves as the basis for determining whether the main switch is fully turned on.

[0014] Preferably, in the above method, the threshold voltage of the main switch is the minimum voltage at which the main switch is turned on or off.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] This invention achieves precise control over the rate of change of the power switch current by accurately determining when the power switch is turned on and off. At the same time, it accelerates the entire turn-on and turn-off speed of the power switch, thereby suppressing EMI interference and reducing switching electrical stress while ensuring low switching losses and reliable dead time. Attached Figure Description

[0017] Figure 1 This is a circuit diagram of the present invention;

[0018] Figure 2 The background diagram shows a traditional power switch drive control circuit. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1 This invention provides a technical solution: a segmented driving and detection control circuit for power switching transistors. This embodiment takes a half-bridge driving circuit composed of M1 and M2 as an example to illustrate the basic control principle of this invention. It is assumed that M1 is the main switching power transistor of the half-bridge driving circuit and M2 is a synchronous freewheeling switching power transistor (buck circuit).

[0021] The circuit of this invention includes: a low-side current sensing circuit for a synchronous freewheeling switch (M2), a sample and hold circuit (S&H), a high-side current sensing circuit for a main switch (M1), a high-side power MOS voltage sensing circuit for a main switch, and a segmented drive control circuit composed of IG1 to IG4, wherein current sources IG1 and IG2 are directly controlled by a PWM control signal, and IG3 and IG4 are also controlled by the switch detection circuit. The circuit includes: a current detection circuit for the synchronous freewheeling switch to detect its on-state current; a sample-and-hold circuit to sample and hold the current value when the synchronous freewheeling switch is turned off; a current detection circuit for the main switch to detect its on-state current and compare it with the current value when the synchronous freewheeling switch is turned off to determine whether the main switch is fully turned on or off; a threshold voltage detection circuit for the main switch to detect its threshold voltage and compare it with the gate drive control signal ug of the main switch to provide another basis for determining whether the main power switch is turned on or off; and two detection and comparison circuits jointly control IG3 and IG4 of the segmented drive control circuit to determine whether to drive the main power switch at a higher rate (IG3 and IG4 connected) or at a lower rate (IG3 and IG4 disconnected).

[0022] The above control circuit works as follows: First, the current value when the synchronous freewheeling tube is turned off is detected, sampled and held. This current value is used to indicate whether the main switch is fully turned on. When the main switch enters the turn-on process, the main switch is slowly turned on at a small rate. At this time, the drive current corresponding to the gate of the main switch is provided by IG1.

[0023] When the on-current of the main switch transistor reaches and exceeds the current value when the freewheeling transistor is turned off, and the ug drive signal also exceeds the threshold of the main switch transistor, the segmented drive control circuit connects IG3, allowing the main switch transistor to be turned on quickly and fully at a larger rate.

[0024] When the main switch enters the turn-off process, the segmented drive control circuit first controls the main switch to turn off at a relatively high rate. At this time, the drive current corresponding to the gate of the main switch is provided by IG2 and IG4.

[0025] When the on-current of the main switch is detected to be lower than the current value when the freewheeling tube is turned off, or the ug drive signal voltage is lower than the threshold voltage of the main switch, the segmented drive control circuit will disconnect IG4, allowing the main switch to turn off slowly at a smaller rate (IG2); thereby achieving segmented and precise control of the turn-on and turn-off rates of the power switch.

[0026] It is worth noting that the basic principle remains the same for different switching power supply topologies: sampling the current value of the freewheeling transistor (soft-switching transistor) as the basis for determining the turn-on and turn-off of the main switch transistor, and combining this with the threshold voltage of the main switch transistor to ultimately achieve precise segmented drive control of the main switch transistor. For example, in the boost topology, M2 is the main switch transistor and M1 is the freewheeling transistor.

[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A segmented driving and detection control circuit for a power switching transistor, characterized in that, It includes a freewheeling switch current detection circuit, a sample-and-hold circuit, a main switch current detection circuit, a main switch threshold voltage detection circuit, and a main switch segmented drive control circuit. The freewheeling switch current detection circuit detects the on-state current of the freewheeling switch; the sample-and-hold circuit samples and holds the current value when the freewheeling switch is off; the main switch current detection circuit detects the on-state current of the main switch; the main switch threshold voltage detection circuit detects the threshold voltage of the main switch; and the segmented drive control circuit drives the main switch power transistor to turn on or off in segments at different rates based on the detection results from the above detection circuits. The segmented drive control circuit determines whether the main switch has been turned on or off based on the detection results of the detection circuit. Before the main switch is turned on, it is driven to turn on slowly at a lower rate. After the main switch is turned on, it is driven to turn on quickly and fully at a higher rate. When the main switch is turned off, it is driven to turn off quickly at a higher rate. When the main switch enters the turn-off process, it is driven to turn off slowly at a lower rate.

2. The segmented driving and detection control circuit for a power switching transistor according to claim 1, characterized in that: The sample-and-hold circuit is used to sample and hold the current value when the continuous current switch is turned off, and this current value is used to indicate whether the main switch is fully turned on or off.

3. The segmented driving and detection control circuit for a power switching transistor according to claim 1, characterized in that: The main switch threshold voltage detection circuit indicates the minimum voltage at which the main switch is turned on or off.

4. A method for segmented driving and detection control of a power switching transistor according to any one of claims 1-3, characterized in that: Including the following steps: S1: First, detect and maintain the current of the freewheeling switch, which serves as the basis for determining whether the main switch is fully turned on or off. Combined with the threshold voltage of the main switch, the final determination is made as to whether the main switch is turned on or off. S2: When the main switch is turned on, it is first turned on slowly at a low rate. If its on-current exceeds the current value of the sampled and held freewheeling switch, and the gate drive control signal of the main switch also exceeds the threshold voltage of the main switch, it is determined that the main switch has been turned on, and the process is switched to turn on quickly and fully at a higher rate. When the main switch is turned off, it is first turned off quickly at a higher rate. If its on-current is lower than the current value of the sampled and held freewheeling switch, or the drive control signal of the main switch is lower than the threshold voltage of the main switch, it is determined that the main switch has entered the turn-off process, and the process is switched to turn off slowly at a lower rate.

5. The method for segmented driving and detection control of a power switching transistor according to claim 4, characterized in that: The current value of the freewheeling switch is the current value corresponding to the freewheeling switch being turned off, and this current value serves as the basis for determining whether the main switch is fully turned on.

6. The method for segmented driving and detection control of a power switching transistor according to claim 5, characterized in that: The threshold voltage of the main switch is the minimum voltage at which the main switch is turned on or off.

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