JP2003284354A - H-bridge protective circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the puncture of an element caused by a short circuit in an H-bridge circuit. <P>SOLUTION: On a motor driving and controlling part, an FET monitoring function is provided that outputs short-time control signals one by one to switching elements Q1, Q2 and Q3 at a constant cycle time, and measures a current value in that instance via a current detecting part 1. For example, when a short circuit caused by the presence of water, iron particles or the like between the drain and the source or the gate and the source of Q2 brings Q2 in an 'ON' state, a pass-through current flows into the ground through Q1, Q2 when Q1 is turned on. The motor driving and controlling part detects this current to go into a start-stopping state and drives a displaying means like a buzzer, an LED, or the like to output an alarm. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an H-bridge protection circuit that prevents damage to the elements of an H-bridge circuit due to a short circuit.

[0002]

[Prior Art and Problems to be Solved by the Invention] FIG.
Shows an H bridge circuit in which P-type FETs Q1 and Q3, N-type FETs Q2 and Q4, and DC motor M are combined into an H-type, and as shown in Fig. 3, Q1 and Q3
When 4 is turned on, DC motor M rotates forward, and Q2, Q
When 3 is turned on, DC motor M rotates in reverse. When Q2 and Q4 are turned on, both terminals of the DC motor M are short-circuited and the DC motor M suddenly stops.

In an electric circuit, water or the like may adhere to circuit elements to cause a short circuit. In the H bridge circuit, the drain-source of FETs Q1, Q2, Q3, Q4 and When water or iron powder adheres between the gate and source and turns on, a through current flows and the FET is destroyed. For example, if Q1 and Q4 are turned on by the forward rotation drive operation when water is attached to Q3 and it is turned on,
A through current flows to ground through Q3 and Q4 connected in series as shown in 5, and Q3 and Q4 are destroyed. Further, when Q2 and Q3 are turned on by the reverse drive operation while Q1 is on, a through current flows through Q1 and Q2 as shown in FIG. 6, and Q1 and Q2 are destroyed. Such a damage accident is particularly likely to occur in a power tool or the like that is often exposed to wind and rain outdoors, and an object of the present invention is to prevent damage to the H-bridge circuit.

[0004]

The present invention is proposed in order to achieve the above-mentioned object, and a current detection circuit is connected to an H bridge circuit composed of four switching elements and a DC motor. Order control means for sequentially turning on the switching elements, means for comparing the current value when the switching elements are turned on and the reference current value, and the start / stop of the H-bridge circuit when the measured current value exceeds the reference current value. And an H-bridge protection circuit provided with control means for displaying a warning.

Further, a power supply voltage detection circuit is connected to an H-bridge circuit composed of four switching elements and a DC motor, and a sequence control means for sequentially turning on the four switching elements and an on-state of the switching elements by the sequence control means. The present invention provides an H-bridge protection circuit provided with control means for starting and stopping the H-bridge circuit and displaying a warning when the power supply voltage drops.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings. Fig. 1 shows P-type FET Q1, which is the same as Fig. 3.
Source grounded type H by Q3 and N type FET Q2, Q4 and DC motor M
A bridge circuit, D between Q1 and Q2 and between Q3 and Q4
C Motor M electrode terminal is connected. A current detection unit 1 for detecting a current flowing through the H bridge circuit is provided between the sources of Q2 and Q4 and the ground, and a current detection signal is input to a motor drive control unit (not shown).

In addition to the forward / reverse control function of outputting a control signal to the gates of Q1, Q4 or Q2, Q3 in response to the operation of the forward rotation switch or the reverse rotation switch, the motor drive control unit also performs a constant cycle by the FET monitoring program. Q1, Q2, Q3, in time
It is equipped with a protection function that sequentially outputs a control signal to Q4 to inspect the state of the H-bridge circuit. The FET monitoring program is continuously executed when the power of the motor drive control unit is on, and when Q1, Q2, Q3, and Q4 are normal, the FET monitoring program is executed according to the operation signal of the forward rotation switch or the reverse rotation switch. Performs interrupt processing that suspends temporarily, and then Q1, Q4 or Q2, Q3
The control signal is output to the gate of to drive the DC motor M, and the execution of the FET monitoring program is restarted after the motor is stopped. In addition, when abnormalities of Q1, Q2, Q3, and Q4 are detected, it does not respond to the operation signal of the forward rotation switch or the reverse rotation switch as the start / stop state and prevents the circuit from being destroyed.

FIG. 2 shows a routine of the FET monitoring program. When the motor drive control unit is powered on (S1), the motor drive control unit sequentially outputs control signals to Q1, Q2, Q3 and Q4 for a short time (tens of μsec). The following) is output, and the current flowing through the current detection unit 1 to the ground is measured each time. The current value when Q1, Q2, Q3, and Q4 are turned on is the reference current value (Q1, Q2, Q
3), which is slightly higher than the leakage current rating of Q4), repeat steps S2 to S9 to repeat Q1, Q2, Q
Repeat the test of 3, Q4.

On the other hand, for example, when Q2 is in the ON state due to water or iron powder or the like being attached between the drain and the source of Q2 or between the gate and the source of Q2, when Q1 is turned on, Q1 is turned on. , A through current flows to the ground through Q2,
Based on the result of comparison (S3) between this current and the reference current value, the motor drive control unit enters a start / stop state and drives a display means such as a buzzer or an LED to display a warning (S1).
0). As described above, the control signal output time to Q1, Q2, Q3, and Q4 is controlled to be extremely short so that the switching element is not destroyed by the through current.

When Q1 is on, a through current flows through Q1 and Q2 when Q2 is turned on, and the process proceeds from S5 to S10 to start and stop and display a warning. If Q4 is on,
When Q3 is turned on, a through current flows in Q3 and Q4, causing S7 to S1.
Go to 0, and if Q3 is on, turn on Q4 when Q4 is on.
3, shoot-through current flows in Q4 and progresses from S9 to S10, and Q1, Q2, Q3,
When any of Q4 shows an abnormality, the operation of the H bridge circuit is stopped to prevent the switching element from being broken.
If a warning is displayed, turn off the power, inspect the circuit board, remove the cause of the element short circuit, and turn on the power again.
If the motor drive control unit is reset and the FET monitoring program is executed and the H bridge circuit returns to normal, the DC motor can be driven in the forward and reverse directions.

In addition to the FET monitoring program, when the DC motor M is overloaded during normal operation and an overcurrent flows through the H-bridge circuit, this is detected via the current detector 1 and Q1, By cutting off the control signal to Q2, Q3, Q4 and stopping the operation of the H bridge circuit, Q1, Q2, Q3, Q4
Prevents the DC motor M from burning.

In the above-mentioned embodiment, the short circuit of the FET is detected by the current value. However, Q1, Q2, Q3, Q4 are sequentially turned on, the voltage change at that time is monitored by the power supply voltage detection circuit, and the FET is
It may be configured to detect the power supply voltage drop due to the through current when a short circuit occurs and stop the operation of the H bridge circuit and perform the warning operation.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the technical scope of the present invention, and it goes without saying that the present invention extends to those modifications. is there.

[0014]

As described above, in the H-bridge protection circuit of the present invention, the four switching elements forming the bridge are sequentially energized for a short period of time to measure the current value or the power supply voltage, and the switching element is short-circuited. Since the control means for stopping the activation of the H-bridge circuit when the through current flows is provided, the through current does not flow through the switching element even if the activation operation is performed at the time of short circuit, and the destruction of the switching element can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention in which a current detection unit is added to an H bridge circuit.

FIG. 2 is a flowchart of a FET monitoring program.

FIG. 3 is a circuit diagram of an H bridge circuit.

FIG. 4 is a circuit diagram of an H bridge circuit.

FIG. 5 is a circuit diagram of an H bridge circuit.

FIG. 6 is a circuit diagram of an H bridge circuit.

[Explanation of symbols]

Q1, Q2, Q3, Q4 FET M DC motor 1 Current detector

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichi Okubo             6-6 Hakozakicho, Nihonbashi, Chuo-ku, Tokyo             Cos Co., Ltd. F-term (reference) 5H007 AA12 BB06 CA02 CB02 CB05                       DB13 DC02 FA03 FA06 FA13                       GA08 GA11

Claims (2)

[Claims] 1. A current detection circuit is connected to an H-bridge circuit composed of four switching elements and a DC motor,
Sequence control means for sequentially turning on the switching elements, means for comparing the current value when the switching elements are turned on with the reference current value, and activation of the H-bridge circuit when the measured current value exceeds the reference current value. An H-bridge protection circuit provided with control means for stopping and displaying a warning. 2. A sequence control means for connecting a power supply voltage detection circuit to an H-bridge circuit composed of four switching elements and a DC motor to sequentially turn on the four switching elements, and an on-state of the switching elements by the sequence control means. An H-bridge protection circuit provided with control means for starting and stopping the H-bridge circuit and displaying a warning when the power supply voltage drops at times.