JPH09331692A - Motor driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the time difference between the off-delays of MOSFETs, by connecting respectively the respective gate signals of a pair of P- and N- channel MOSFETs subjected to simultaneous energization with the emitter and collector sides of one PNP transistor. SOLUTION: Connecting respectively the outputs of an IC 2 for outputting the changeover signals of the energization directions of a motor coil 9 with low-frequency complying transistors(TRs) 31a, 31b, their outputs are connected respectively both with the bases of PNP small signal TRs 30a, 30b for driving the gates of MOSFETs and with the bases of TRs 32b, 32a to connect respectively the collectors of the TRs 32b, 32a with the bases of the TRs 30b, 30a. Also the emitters of the TRs 30a, 30b are connected respectively with the gates of P-channel MOSFETs 5a, 5b, and their collectors are connected respectively with the gates of N-channel MOSFETs 6a, 6b. Turning on or off alternately the TRs 30a, 30b by the IC 2, the time difference between the off-delays of the MOSFETs is reduced. By the on-off of the TRs 30a, 30b, the direction of the energization of a motor coil 9 is inverted. Thereby, a motor driving circuit is simplified to reduce its cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a DC brushless motor used in a fan or the like, and more particularly to a drive circuit having a MOSFET gate drive capable of effectively utilizing motor coil energy and a through current prevention. To do.

[0002]

2. Description of the Related Art FIG. 3 is a circuit showing a conventional example of bipolar current conduction by a MOSFET in a single-phase brushless DC motor coil. In FIG. 3, 1 is a Hall element for detecting the rotational position of a magnet rotor incorporated in the motor. Two
Is an IC for outputting a switching signal of the coil energizing direction, and 3 is a non-energizing time for preventing a power source short circuit phenomenon caused by a simultaneous turn-on of the upper and lower arm MOSFETs caused by a slight time lag of the signal transmission system when switching the energizing direction of the motor coil. Dead-time circuits that occur 4a, 4b are signal inversion circuits by transistors, 5a, 5b are P-channel MOS
In FET, the gate is connected to the collectors of the transistors 4a and 4b, 6a and 6b are N-channel MOS
FET 9 is a motor coil, 7a, 7b, 7c and 7d are diodes for bypassing the induced voltage generated from the motor coil when the motor coil energization direction is switched, and 8 is a capacitor for storing the induced energy.

FIG. 4 is a time chart showing signal waveforms at various parts in FIG. The operation of the circuit shown in FIG. 3 will be described with reference to FIG. During normal operation, the Hall element 1 outputs a waveform of 4-1 due to the rotation of the magnet rotor, and the position signal causes the IC 2 to output complementary signals such as 4-2a and 4-2b. The output of dead time circuit 3 is 4
-3a and 4-3b have a time delay of TD when they are on, and 4-5a and 4-5b show an off delay time of TL1 by the on and off times of the P-channel MOSFET.
Reference characters a and 4-6b indicate the ON delay time of the N-channel MOSFET and the OFF delay time of TL2. The OFF time of the P-channel MOSFET depends on the delay due to its own input capacitance and the gate drive NPN switching transistor 4.
The delay of the accumulation time due to the saturation regions of a and 4b is added and becomes large. Reference numeral 4-8 indicates a charge / discharge current of the capacitor, and the positive direction is a period during which the capacitor is charged with the induced energy of the motor coil as a current. In the negative direction, the charged energy is supplied from the capacitor to the motor coil as a discharge current. During this period, the current supply from the power supply is unnecessary and the efficiency is improved. The dead time circuit 3 includes resistors 22a and 22b and 2
A time delay circuit is formed by the capacitors 3a and 23b and compared by the comparators 24a and 24b to generate a dead time. Further, the transistors 21a and 21b are for extracting charges from the capacitors 23a and 23b.

[0004]

As described above, in the bipolar conduction of the conventional single-phase brushless motor, the off time of the P-channel MOSFET is changed to the N-channel MOSFET.
Is longer than that of the motor coil energy during the time difference TL1-TL2.
It is circulated and consumed by the loop formed by a, the motor coil, and the diode 7b, and the circulating current does not contribute to the motor torque because it is generated at the switching position of energization. Further, the dead time TD is a non-energized time, and is determined in consideration of the variation of the off time of the P-channel MOSFET, but making it longer than necessary leads to a reduction in the motor output. An object of the present invention is to solve the above problems with a simplified circuit configuration.

[0005]

The present invention is a P channel M
The difference between the off delay times TL1 and TL2 between the OSFET and the N-channel MOSFET is minimized to reduce the motor coil circulating current and increase the amount of charge to the capacitor. In order to realize this with a simplified circuit, a pair of P-channel MOSFETs and N-channel MOSFEs that conduct electricity at the same time are provided.
Each of the gate signals of T is connected to a P-channel MOSFET on the emitter side and an N-channel MOSFET on the collector side of one PNP transistor, and the transistor is operated in the active region. The dead time is generated by delaying the off-time of the transistor by causing a large base current to flow in the transistor for relatively low-frequency amplification, which has a relatively large collector capacitance, as the conduction direction switching signal.

[0006]

[Operation] In the configuration described above, an inexpensive bipolar transistor is used for the MOSFET gate drive, but minority carriers are accumulated in the base during the saturation period of the collector current due to the switching operation, and it is discharged when it is off. There is an accumulation time during which the collector current continues to flow until it is removed. However, if used as an Emitter Follower, there is almost no delay when turned off. Also, in general, P
Since the channel MOSFET has a larger input capacitance and a longer switching delay time than the N-channel MOSFET, the P-channel MOSFET is driven faster by the emitter follower, and the N-channel MOSFET is driven slightly later by the collector connection to reduce the difference between the off times of the two. it can. Also, by the two energization switching signals from the IC,
The base current of each transistor is made to flow largely, and the off delay time of the transistor itself is generated for 30 to 40 μs. By connecting the base of the gate drive transistor of the above-mentioned MOSFET with that signal in a crossing manner with another transistor by that signal, a dead time is created for each phase switching by forcibly providing an off time and a power short circuit phenomenon due to the upper and lower arms. Does not occur.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIG.
1 is a Hall element that detects the rotational position of a magnet rotor built in the motor, and 2 is an IC that outputs a switching signal for the coil energization direction, which is the same as the circuit of the prior art shown in FIG. The outputs are connected to low frequency amplification transistors 31a and 31b, the outputs of the transistors 31a and 31b are connected to the bases of small signal transistors 30a and 30b of the PNP that drive the gates of the MOSFETs, and the outputs of the transistors 31a and 31b. The outputs are connected to the bases of the transistors 32b and 32a, respectively, and the collectors of the outputs are connected to the transistor 30b, respectively.
b, 30a, the small signal transistor 30a,
The emitter of 30b is a P-channel MOSFET 5a, 5
The gate of b, the collector is N-channel MOSFET6
IC2, which is connected to the gates of a and 6b, and outputs a switching signal for the motor coil energization direction,
The transistors 30a and 30b are alternately turned on and off.

When the transistor 30a is on, the MOS
The FETs 5a and 6a are turned on, the coil 9 is energized in the left to right direction, and when the transistor 30a is turned off, 30b is turned on, the MOSFETs 5b and 6b are turned on, and the motor coil 9 is energized in the opposite direction to the previous direction. To be done.

The off-time of the P-channel MOSFET is determined by its own input capacitance, and in this circuit the off-time delay TL1
Is about 20 μs, the delay of the PNP transistor is added to the N-channel MOSFET, and TL2 is about 15 μs, and the time difference is about 5 μs, which is less than half of the conventional value. To further reduce the time difference, a capacitor may be inserted in parallel with the collector resistance in the collector of the PNP transistor to delay the off time of the N-channel MOSFET. By reducing this time difference, the time of the circulating current to the motor coil is reduced, and the motor coil energy is effectively charged in the capacitor 8 via the diodes 7a and 7c or 7b and 7d connected in parallel to the MOSFET, Is supplied to the motor coil when the energizing direction is switched.

FIG. 2 is a time chart showing the signal waveform of each part of FIG. In the figure, 2-2a and 2b are output waveforms of the transistors 31a and 31b, t is a delay time of the transistor, and 2-3a and 3b are gate drive PNs.
The base signals of the P transistors 30a and 30b cause a dead time of TD, which is the same time as t. 2-5a,
5b indicates that the P-channel MOSFET is on. TL in off time
The OFF delay time of 1 is shorter than that of 4-5a and 5b in FIG. 2-6a and 6b are N-channel MOSFETs.
The off delay time of TL2 is the on-off time of 4-6 of FIG.
It is longer than a and 6b. As a result, the difference between TL1 and TL2 is as small as 2-8.

As described above in detail, according to the present invention, one P-channel MOSFET and one N-channel MOSFET, each of which is energized at the same time, has one P-channel at each gate terminal.
P channel MOSF on the emitter side of the NP transistor
By connecting an N-channel MOSFET to the collector side of ET, it is possible to reduce the difference in off delay time of the MOSFET and effectively use the motor coil energy. Further, a time constant circuit, a comparator, etc. are not required for the dead time circuit at the time of switching the energizing direction of the conventional method, and the circuit configuration can be simplified and low cost can be achieved.

[0011]

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a motor drive circuit according to the present invention.

FIG. 2 is an operation timing chart of the circuit of FIG. 1 which is an embodiment of the present invention and waveforms of respective parts.

FIG. 3 is a circuit configuration diagram of a drive circuit of a motor according to a conventional technique.

FIG. 4 is an operation timing chart of FIG. 3 and a waveform of each part of a circuit configuration diagram according to a conventional technique.

[Explanation of symbols]

 1 Hall element 2 IC 3 Dead time circuit 4a, 4b Transistor 5a, 5b P-channel MOSFET 6a, 6b N-channel MOSFET 7a, 7b, 7c, 7d Diode 8 Capacitor 9 Motor coil 10 Reference voltage 21a, 21b Transistor 22a, 22b Resistor 23a , 23b Capacitor 24a, 24b Comparator 30a, 30b Transistor 31a, 31b Transistor 32a, 32b Transistor 2-2a, 2b Output of transistor 31a, 31b 2-5a, 5b Output of P-channel MOSFET 5 2-6a, 6b Output of N-channel MOSFET 6 2-8 Current waveform of capacitor 8 4-1 Output voltage waveform of Hall element 1 4-2a, 2b Output waveform of IC2 4-3a, 3b Output of dead time circuit 3 -5a, 5b P-channel MOSFET5 output 4-6a, current waveform of the output 4-8 capacitor 8 of 6b N-channel MOSFET6

Claims (2)

[Claims] 1. An H-bridge circuit is constructed by arranging two P-channel field effect transistors (hereinafter referred to as MOSFETs) on the power source side and two N-channel MOSFETs on the zero potential side and connecting them in series. A coil of a single-phase brushless DC motor is connected to the intermediate connection point thereof, and a drive circuit of a motor in which the coil is bipolarly energized is provided with an energization stop (hereinafter referred to as dead time) circuit that operates every energization switching, A pair of P-channel MOSFETs and N-channel MOs that are simultaneously energized
One gate terminal of the SFET is driven by a PNP transistor, and the emitter side of the transistor is the P channel M
OSFET, the collector side is the N-channel MOSF
A motor drive circuit characterized by being connected to an ET. 2. The dead time circuit uses the base currents of two transistors that receive two conduction direction switching signals, which are complementary operations, as overdrive, delays the off time of the transistors, and delays the two signals by another transistor. The drive circuit for the motor according to claim 1, wherein the gate drive transistor is forcibly turned off for a delay time by connecting the gate drive crosswise.