JPS63182913A - Driving circuit for field effect transistor - Google Patents

Abstract

PURPOSE:To reduce the current drive capability of a transistor (TR) and to decrease the heat and current consumption of a boosting circuit by using a current source for a component deciding its charge mobility in moving an electric charge charged in the 1st capacitor into the 2nd capacitor at its discharge. CONSTITUTION:A current source 15 is used for a component deciding the mobility of an electric charge from a capacitor C1 to C2 in the boosting circuit and a voltage VF extracted at a connecting point F is fed to a gate of a field effect transistor FET. When a transistor (TR) Q1 is switched by a B signal of a square wave oscillator 1 and the TR Q1 is turned on, the potential at a connecting point C is decreased up to the GND level and the capacitor C1 is charged. When the TR Q1 is turned off, the potential at the connecting point C is increased up to a potential at a connecting point D and the capacitor C2 is boosted to a voltage higher than the power voltage VD. Since the same current continues flow from the IS to the capacitor C2 in this way, the current source IS is set small to reduce the current consumption and heat.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a circuit for driving a field effect transistor using a booster circuit.

(b) Background of the Invention A drive circuit for the above-mentioned field effect transistor has conventionally been constructed as shown in FIG.

That is, when a rectangular wave signal as shown in FIG. 2B generated by a relaxation oscillator is input to the input terminal B of the booster circuit, the transistor Q1 turns ON, and the potential at the connection point C decreases. Diode D due to power supply voltage VD
1.

Next, by turning OFF the transistor Q1, the potential at the 0 point rises to the potential at the D point, the charge stored in the capacitor C2 is discharged, and the capacitor C2 is connected to the power supply voltage VD.
It is charged to a higher voltage, and connection points E and F are connected accordingly.
The potential of the capacitor C is also boosted by the amount of the power supply voltage VD, and the potential of the capacitor C
The voltage VF boosted to 2 is twice the power supply voltage VD and is applied to the gate of a field effect transistor that requires a high gate voltage.

However, in the above circuit, the ability to transfer charge from capacitor C1 to C2 is determined by resistor R1, so in order to increase the ability, the value of resistor R1 must be reduced, resulting in a large current consumption. The amount of heat generated increases.

It is necessary to use a transistor with a large current driving capability as the O transistor Q1.

This caused problems such as:

(C) Purpose of the Invention The object of the present invention is to provide a field effect transistor drive circuit that solves the problem described in t by using a current source in place of a resistor for transferring charges in a capacitor.

(D) Structure of the Invention This invention provides a field effect transistor that uses a current source as an element that determines the charge transfer ability of a first capacitor in order to avoid transferring the charge charged in a first capacitor to a second capacitor during discharge. It is characterized by being a drive circuit.

(E) Effect of the Invention According to this invention, when the electric charge of the first capacitor is transferred to the second capacitor by the OFF operation of the transistor, the transfer ability is determined by the current source.
During movement, current flows without being affected by the resistance value, and the value of the current source can be set small.

(f) Effects of the invention Therefore, compared to the conventional circuit, the current consumption of the booster circuit is reduced,
There will be no problem with heat generation.

The current driving capability of the O transistor can be reduced.

Since it does not depend on the temperature characteristics of the O resistance, the temperature characteristics of the boosted voltage value can be made small.

It is possible to achieve the following effects.

(g) Examples of the invention An embodiment of the present invention will be described below with reference to the drawings.

In the circuit shown in Fig. 1, the circuit portion surrounded by the broken line constitutes a square wave oscillator 2 for controlling ON/OFF switching of the transistor Q1, and connects the output end of the operational amplifier OPI to the resistors Rt1, Rt2, and the capacitor Ct. A square wave signal (C in Figure 2) is created from the reference voltage by applying feedback to the non-inverting input of the operational amplifier using a time constant circuit, and this is applied to the base of transistor Q1 of the booster circuit, that is, input terminal B is being applied. Incidentally, FIG. 2 shows the signal waveform of the first country name part.

In addition, in the booster circuit, a current source IS is used in place of the resistor R1 in the conventional circuit shown in FIG. The voltage is applied to the gate of FET.

The resistor RF is a load resistor for driving the field effect transistor FET, and Q2 is a bridriver transistor for switching the field effect transistor FET.

Next, to explain the step-up operation, when the transistor Q1 is switched by the signal shown in FIG.
As is clear from Figure C, the voltage drops to GND, and the capacitor C1 is charged via the diode D1.

Next, when the transistor Q1 goes 0F-F, the potential at the connection point C rises to the potential at the connection point, and the charge charged in the capacitor C1 moves along the path of current source IS → capacitor C1 → diode D2 → capacitor C2. , capacitor C
2 is boosted to a voltage higher than the power supply voltage VD. - As an example, if a 7.2-inch battery 1 is used as the power supply voltage yb, the voltage F boosted by the capacitor C2 will be approximately 11.5V.

On the other hand, due to the current consumption of the load resistor RF, the value of the voltage VF decreases while the transistor Q1 is ON, but if the transistor Q1 is continuously switched at a fast cycle as shown in FIG. Since the voltage VF is always maintained near the boosted voltage value of 11.5V, it is maintained at a voltage that can drive the field effect transistor FET.

Therefore, when transistor Q2 for the driver is turned on, the potential at the connection point G drops to GND, and gate voltage is no longer applied to the field effect transistor FET, turning it off.However, when transistor Q2 is turned on, gate voltage is applied to field effect transistor FET. Since the field effect transistor FET is turned on, the field effect transistor FET can be switched by turning ON/OFF the transistor Q2.

In this way, when boosting the power supply voltage VD to a voltage VF such as IL5V and applying it to the base of the field effect transistor FET, an element that determines the ability to transfer the charge of the capacitor C1 to the capacitor C2 for the above boosting is used. Since the current source Is is used as the current source Is, the same current continues to flow from Is to the capacitor C2 via the capacitor C1 and diode D1 without depending on the change in the charge at the connection point C. Therefore, the value of the current source Is is set small to reduce the current consumption. It can be expected to reduce the temperature and suppress heat generation.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a driving circuit diagram of a field effect transistor, FIG. 2 is a signal waveform diagram of a first overlapping section, and FIG. 3 is a circuit diagram of a main part of a conventional circuit. Ql, C2...Transistor FET...Field effect transistor C1, C2...Capacitor Is...Current source

Claims (1)

[Claims] 1. Charge and discharge the first capacitor by ON/OFF switching of the transistor, transfer the charge to the second capacitor, and apply a voltage higher than the power supply voltage to the gate of the field effect transistor. A driving circuit for a field effect transistor, the circuit having a step-up circuit that uses a current source as an element that determines charge transfer ability from the first capacitor to the second capacitor.