JPH0333186Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Technical field The present invention relates to a drive circuit for a small motor driven by a DC power supply, and in particular, the output transistor provided in the drive circuit is affected by the kickback voltage when the power is turned off. This invention relates to a drive circuit that prevents wave damage.

(b) Background Art Conventionally, an output transistor that drives a small motor produces a kickback when the power switch connected between the small motor and the power supply is turned off.
back) voltage may be applied, leading to secondary breakdown.

In particular, when the small DC motor is locked, the current flowing through the output transistor may be 1A or more, and the kickback voltage is
If the voltage reaches 800V, the output transistor may be damaged.

Therefore, a diode was connected in parallel to the small motor, or a protective power transistor was provided on the base side of the output transistor. When the chip size increases, the chip area increases, leading to an increase in costs.

(c) Purpose of the present invention The present invention has a simple configuration and an integrated circuit (IC).
It is an object of the present invention to provide a small motor drive circuit that has a protection function for an output transistor provided in the small motor drive circuit, which is most suitable for small motor applications.

(d) Embodiment of the present invention The drawing shows a drive circuit for a small motor of the present invention.
In the drawing, 1 is a constant current source, 2 is a Zener diode as a reference voltage element, 3 is a comparator, 4 is a constant voltage transistor, 5, 5...5, 5 is an output transistor, 6 is a small motor as a load, 7 8 is a DC power source such as a built-in battery, 8 is a power switch, 9 is a DC resistor, 10 and 11 are resistors and variable resistors that constitute the voltage dividing stage 12, 13 is an IC block when integrated circuit (IC), 14 , 15, 16, 17 are external terminals led out from the IC block, 18 is a Zener diode for protection, 19, 19...1
9 and 19 are emitter resistors.

Next, a drive circuit for a small motor according to the present invention will be explained with reference to the drawings.

Now, the power switch 8 is closed, the DC voltage from the DC power supply 7 is applied to the small motor 6, the voltage across the small motor 6 is divided by the series resistor 9, the resistor 10, and the variable resistor 11, In addition, the comparator 3 compares the reference voltage applied via the Zener diode 2 to maintain a constant voltage across the small motor 6 and prevent fluctuations in its rotational speed. During such steady operation, when the voltage across the small motor 6 attempts to rise or fall, the input terminal voltage of the comparator 3 rises or falls as compared to the reference voltage. As a result, the output voltage of the comparator 3 changes to prevent the above fluctuation. At this time, the Zener diode 18 acts as a collector-base capacitor of the output transistors 5, 5, . . . 5, 5, and the oscillation stability is extremely high.

Next, when the power switch 8 is opened and turned off, the comparator 3 and the output transistors 5, 5, .
When a voltage equal to or higher than the secondary breakdown voltage occurs across the output transistors 5, 5, the Zener diode 18 turns on, turning on the output transistors 5, 5...5, 5, and only when the kickback voltage occurs, the Zener diode 18 turns on. turned on, the output transistor 5,
Since the transistors 5, 5, 5, 5 are turned on, the output transistors 5, 5, 5, 5 can be protected.

In this case, if the Zener voltage of the Zener diode 18 is V _Z and the base-emitter rise voltage of the output transistors 5, 5...5, 5 is V _BE , then V _Z +
The value of V _BE is set below the secondary breakdown voltage of the output transistors 5, 5, .

(e) Effects of the present invention The kick voltage that occurs at the moment the power switch is turned off is reduced to several hundred volts by turning on the output transistor by turning on the Zener diode, which would occur when the motor is locked as in the conventional case. It is possible to prevent damage to the output transistor due to the peak voltage that would otherwise reach this level.

[Brief explanation of the drawing]

The drawing shows an embodiment of the small motor drive circuit of the present invention. Explanation of main drawing numbers, 3...Comparator, 5...DC power supply, 6...Small motor, 7...DC power supply, 8...
Power switch, 9...Series resistor, 12...Voltage divider circuit, 18...Zener diode.

Claims (1)

[Scope of utility model registration request] A drive circuit for a small motor includes a comparator in which a constant current source and a reference voltage means are connected to a reference terminal, and a voltage dividing means for detecting the voltage across the small motor as a load of an output transistor is connected to an input terminal. A Zener diode is disposed between the collector and base of the output transistor so that the cathode is directly connected to the collector and the anode is directly connected to the base, and at least the constant current source, the reference voltage means, the output transistor, and the comparison vessel,
and the Zener diode is provided inside the IC,
By turning on the Zener diode when the power switch connected in series to the motor and the power source is turned off, destruction of the output transistor due to kickback voltage is prevented, and the Zener diode is used as a capacitor during normal operation. A drive circuit for a small motor, characterized in that the output transistor is thereby prevented from oscillating.