JPH0514155A - Drive control circuit for n-channel fet - Google Patents

Abstract

PURPOSE:To drive an inexpensive N-channel FET with simple circuit configuration. CONSTITUTION:A drain of an N-channel FET10 is connected to a positive power supply and a load (piezoelectric element) L is connected to the source via a diode D10. A transistor(TR) TR1 as a switching element to switch the FET10 is connected to a gate of the FET10. A resistor R1 is connected to the collector of the TR1, and the other terminal of the resistor R1 is connected to a power supply E2 via a diode D20. Then a capacitor C is connected between the source of the FET10 and a connection section between the resistor R1 and the diode D20. Furthermore, a diode D30 (D40) is connected between the gate and source of the FET10 (between source of the FET10 and ground). When the TR1 is nonconductive, the FET10 is conductive by the charge stored in the capacitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control circuit for an N-channel field effect transistor (FET), and more particularly to an N-channel drive controllable by charge / discharge control between a gate and a source. The present invention relates to an FET drive control circuit.

[0002]

2. Description of the Related Art Conventionally, N-channel FETs have been used in place of bipolar transistors because of their high input impedance, excellent high-speed switching characteristics due to the absence of offset voltage, unlike bipolar transistors, and good noise characteristics. In many cases. Further, there is an advantage that it is cheaper than the P-channel type.

By the way, a circuit for driving and controlling the N-channel FET in a state where the source side thereof is not grounded is known as an example of a charge pump circuit or a bootstrap circuit. In these circuits, for example, the charge pump circuit, as shown in FIG. 3, when an ON / OFF signal is input to the control circuit 2 connected to the gate side of the N-channel FET 1, the oscillator 3 responds to the ON / OFF signal, and the charge pump circuit. The voltage controller 4 operates to apply an H or L gate voltage to the gate of the FET 1. Therefore, the drain and source of the FET1 are electrically connected or disconnected, and the voltage of the DC power supply VDD is F
It is configured to be applied to or disconnected from the load L via ET1. This circuit further includes FET2 and FET1 as switches for switching charge / discharge of the FET1 based on a command signal from the control circuit 2.
There is also a diode D1 for rectifying the gate and source of the device.

On the other hand, in the bootstrap circuit, as shown in FIG. 4, when the transistor TR is changed from the on state to the off state by the input signal, the FET 3 and the FET 4 are connected to the DC power source VS.
The current from the diode D2, reactance R and F
At the same time as flowing to the ground via ET3, the capacitor C
Is also charged. During that time, the FET 5 is in the cutoff state, and the voltage of the DC power source VS is not applied to the resistance load RL. On the other hand, if the transistor TR is switched on, the FET
3, the FET4 is turned off, but the electric charge stored in the capacitor C flows to the gate side of the FET5 and is discharged between the gate and source of the FET5 to make the drain and source of the FET5 conductive. As a result, the voltage of the DC power source VS is applied to the resistance load RL.

[0005]

However, both the charge pump circuit and the bootstrap circuit are complicated, the number of components is large, for example, many switching elements are used, and the reliability is low in order to turn on / off each switching element. Moreover, it was difficult to keep the cost and production cost low.

The present invention has been made in order to solve the above-mentioned problems, and is an N-channel type FE which has a reliable on / off drive control with an inexpensive and easy circuit configuration.
It is intended to provide a drive control circuit of T.

[0007]

In order to achieve this object, a drive control circuit for an N-channel type FET according to the present invention is an N-channel FET.
A drive control circuit for an N-channel FET, in which a load is applied to the source side of the channel FET, and a power supply voltage on the drain side is applied to or cut off from the load by conduction or interruption between the drain and source of the FET. And a capacitor for supplying an electric charge between the gate and the source of the FET, and a switching element for switching between charging and discharging of the capacitor and charging and discharging of the electric charge between the gate and the source. To do.

[0008]

The N-channel type F of the present invention having the above construction
According to the drive control circuit of ET, when the switching element is turned on, the electric charge is stored in the capacitor and the FE
The charge between the gate and the source of T is discharged. Therefore, the drain and source of the FET are cut off. on the other hand,
After that, when the switching element is turned off, the electric charge stored in the capacitor is supplied to the gate of the FET and discharged between the gate and the source of the FET. As a result, conduction is established between the drain and source of the FET, and the power supply voltage is applied to the load via the FET. In this way, the FET (which is also a switching element) is cut off and conducted in response to turning on and off of the switching element.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The circuit of this embodiment controls the driving of a switching element that applies or cuts off a voltage to a piezoelectric element which is a driving source of a piezoelectric dot printing apparatus, and as shown in FIG. Is connected to the anode side of the DC power supply E1 and the FE
The source side of T10 is connected to a load L such as the aforementioned piezoelectric element via a diode D10. The diode D10 is oriented in the forward direction from the source side of the FET 10 to the load L side. In the diode D10, the counter electromotive force generated when the load L includes the inductance component of the coil is generated in the diode D30 and the transistor TR described later.
Prevents flow to ground through 1. On the other hand, the FET
NP which is also a switching element on the gate side of 10
The collector side of the N-type transistor TR1 is connected and the emitter side of the transistor TR1 is grounded. Then, the TR is provided on the base side of the transistor TR1.
A transistor drive controller 50 for controlling ON / OFF of 1 is connected.

Further, the collector side of the transistor TR1 is connected to the anode side of the DC power source E2 for applying the gate voltage of the FET 10 via the diode D20 and the resistor R1. The diode D20 is oriented in the forward direction from the DC power source E2 side toward the collector side of the transistor TR1.
Further, a capacitor C1 and a diode D30 are provided in parallel with the resistor R1. The direction of the diode D30 is also forward toward the collector side of the transistor TR1. On the other hand, the power source E of the capacitor C1
The terminal on the side opposite to the 2 side is connected to the source side of the FET 10. The cathode side of the diode D40 is connected to the connecting line, and the anode side of the diode D40 is grounded. The diode D40 is for forming a closed circuit for the current flowing through the transistor TR1 to the ground.

Next, the operation of the drive control circuit for the N-channel FET will be described. Now transistor TR1
The transistor T is driven by an input signal from the drive controller 50.
A base voltage VBE is generated between the base and emitter of R1 and TR
Suppose 1 is turned on. Then, the current from the DC power source E2 flows through the diode D20 and the resistor R1 to the transistor TR1. At this time, the transistor TR1 is conductive and its emitter is grounded, so that the gate and source of the FET10 are kept discharged. , The drain and source of the FET 10 are cut off. Therefore, the voltage of the DC power source E1 is not applied to the load L. The current from the DC power source E2 also flows to the capacitor C1 via the diode D20, and the capacitor C1 is charged. On the other hand, it is assumed that the transistor TR1 is turned off in this state. Then, a part of the electric charge stored in the capacitor C1 flows to the gate of the FET 10 through the resistor R1 and is discharged between the gate and the source. Therefore, FET1
Since electric charge is charged between the gate and source of 0 to cause a potential difference, the drain and source of the FET 10 become conductive. Therefore, the voltage of the DC power source E1 is applied to the load L via the FET 10 and the diode D10. When the transistor TR1 is turned on in this way, the FET1
0 is cut off, and when the transistor TR1 is cut off, the FET 10 is turned on.

FIG. 2 shows how the potential difference between both terminals of the capacitor C1 changes by switching the ON / OFF drive control signal of the transistor TR1 and how the voltage between the gate and source of the FET 10 changes at that time. It shows whether to do. As shown in the figure, when the transistor TR3 is turned on, the capacitor C1 is stored, and the voltage between the gate and source of the FET 10 is in the off state during that time, while when the transistor TR1 is turned off, the capacitor C1 is discharged. The FET 10 is on. Therefore, the electricity of the DC power source E is FET
It flows between the drain and source of 10 and flows to the load L through the diode D10, and drives the load L.

[0013]

As is apparent from the above description, according to the present invention, ON / OFF driving of the N-channel FET is performed by discharge control between the gate and the source, and the source potential and the drain potential are trapped. It can be controlled without using it. Therefore, it has a simpler structure than the conventional device,
The number of parts can be reduced, the reliability can be improved, and the cost can be kept low. Therefore, it is very useful to apply this drive control circuit, for example, to drive the piezoelectric element of the piezoelectric dot printing apparatus.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an ON / OFF drive control signal for a switching element, a potential difference across a capacitor, and a G-S of FET 1 according to the present invention.
It is a figure showing the correspondence of the change with a voltage.

FIG. 3 is a charge pump circuit diagram shown as a conventional example.

FIG. 4 is a bootstrap type circuit diagram also shown as a conventional example.

[Explanation of symbols]

 FET10 N-channel FET C1 Capacitor TR1 Bipolar transistor E1 DC power supply for load drive E2 Power supply for gate voltage application

Claims (1)

Claim: What is claimed is: 1. A load is applied to the source side of an N-channel type FET, and a power supply voltage on the drain side is applied to the load by turning on or off the drain-source of the FET. N-channel type FET
And a capacitor for supplying electric charge between the gate and source of the FET, and a switching element for switching between charging and discharging of the capacitor and charging and discharging of electric charge between the gate and source. A drive control circuit for an N-channel FET, which is characterized in that: