JPS627554B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit, and more particularly to a semiconductor circuit using a voltage control element suitable for driving a capacitive element, such as a plasma display panel (PDP) element, with a high voltage pulse. .

FIG. 1 shows a conventional drive circuit for driving a capacitive load CL. In the same circuit, capacitive load
When charging CL, after applying a high voltage pulse to the terminal Vin, if a negative or zero level input signal is applied to the base of the control transistor TR1, the control transistor TR1 turns off, so the resistor R1 is connected from the Vin terminal to the base of the control transistor TR1. Transistor TR for charging through
2 base current flows, charging transistor TR
2 is turned on. Therefore, a charging current I _E flows from the terminal Vin to the charging transistor TR2 to charge the capacitive load.

When stopping charging, the control transistor
Set the base potential of TR1 to high level. Then, since the control transistor TR1 is turned on, the base potential of the charging transistor TR2 is lowered and the charging transistor is turned off, and charging to the capacitive load CL is stopped, and the remaining power in the capacitive load CL is The charge generated is discharged through the resistor R2, the diode D1, and the control transistor TR1.

By the way, in the above conventional circuit, when charging the capacitive load CL, it is desirable to reduce the value of the resistor R1 to effectively flow the charging current _IE . However, if the value of the resistor R1 is too small, when the control transistor TR1 is turned on, this resistor R
The current flowing through the control transistor TR1 through the control transistor TR1 becomes large, which may destroy the control transistor TR1.
Even if TR1 is not destroyed, a large amount of invalid current flows when charging is stopped. For this reason, for example, when constructing a drive circuit for the PDP element, a large number of drive circuits are used, resulting in a significant increase in power consumption. Therefore, it was necessary to take a certain compromise value for the value of the resistor R1.

The present invention provides a capacitive load drive circuit that allows the value of the resistor R1 to be almost zero when charging the capacitive load, and to a value close to infinity when charging is stopped. The aim is to improve the conventional drawbacks.

For that purpose, the present invention provides a drive circuit that controls a charging transistor to charge a capacitive load by turning on and off a control transistor connected to a base circuit of the charging transistor. The present invention provides a drive circuit characterized in that a voltage-dependent variable resistor whose resistance value increases as the voltage increases is inserted into a base circuit of a charging transistor. Examples will be described in detail below with reference to the drawings.

FIG. 2 is a circuit diagram showing one embodiment of a drive circuit according to the present invention. In the figure, Z is a voltage-dependent variable resistor, and D2 is a surge absorption diode. In FIG. 2, the same parts as in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

In Figure 2, when the control transistor TR1 is turned off to charge the capacitive load CL,
When the collector potential of the transistor TR1 rises and the voltage applied to both ends of the variable resistor Z becomes smaller, this resistance value becomes smaller, so that the charging current I _E expressed by the formula below, which charges the capacitive load, flows effectively. .

I _E =Vin-(Vout+VBE _(TR2) / _R1 /
(1+h _FE )+R2 Also, in a steady state where a high voltage is applied to the terminal Vin, when turning on the control transistor TR1 to clamp the voltage applied to the terminal Vin, the voltage applied to both ends of the variable resistor Z is Voltage VR _Z
VR _Z =Vin-V _CES(TR1) , and approximately the same voltage as the high voltage applied to the terminal Vin is applied. Therefore, the resistance value of variable resistor Z becomes very large, and the control transistor
The current flowing through TR1 becomes very small.

FIG. 3 is a partial sectional view showing a state in which a variable resistor Z is disposed on a part of a silicon semiconductor substrate on which a drive circuit for driving a capacitive load is integrated. Third
In the figure, 1 is a P-type silicon semiconductor substrate, 2
is an N ⁺ type buried layer, 3, 4, and 5 are isolation regions made of an insulator such as silicon dioxide or a P type region, and 6 is a control transistor TR1.
7 is the collector region, 7 is the base region, and 8 is the emitter region. Further, 9 is an insulating layer made of silicon dioxide, 10 is an N ⁺ type buried layer formed on the surface of the silicon semiconductor substrate 1, and 11 is the N ⁺ type buried layer 1.
N ^- type epitaxial layer provided on 0, 12
is a P ⁻ layer provided in the N ⁻ layer 11, and serves as a resistor of the variable resistor Z. 13 to 16 are aluminum wiring layers, and 17 to 21 are electrode windows.

In the structure shown in FIG. 3, when a high voltage is applied to the aluminum wiring layer 13 and the control transistor TR1 is off, the potential of the aluminum wiring layer 14 remains the same as the potential of the aluminum wiring layer 13. Therefore, since the potential between the N ^- layer 11 and the P ^- layer 12, which are at the same potential as the aluminum wiring layer 13, is zero, the depletion layer generated at these PN junctions is small. Therefore, the resistance value between electrode windows 17 and 18 becomes extremely small.

On the other hand, when a high voltage is applied to the aluminum wiring layer 13 and the control transistor TR1 is turned on, the potential of the aluminum wiring layer 14 becomes approximately the ground potential. Therefore, P ^- in the vicinity directly below the electrode window 18
A large reverse bias voltage is applied to the PN junction between layer 12 and N ^- layer 11. Therefore, the depletion layer greatly spreads into the P ^- layer 12, where the impurity concentration is lower than that of the N ^- layer 11, and the area between the electrode windows 17 and 18 approaches a pinch-off state, and the resistance value between the two electrode windows becomes Increased.

As explained in detail above, according to the present invention,
When charging a capacitive load, it is possible to reduce the resistance value of the resistor that supplies the base current of the charging transistor, which allows the charging current to flow more effectively than before, and also allows charging by turning on the control transistor. When the applied voltage is stopped and the applied voltage is clamped, the value of the resistor connected to the collector of the control transistor increases, so the power supply current flowing through the control transistor can be reduced.
Therefore, the amount of power consumed during operation of the control transistor can be reduced, and destruction of the control transistor can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional drive circuit, Fig. 2 is a circuit diagram showing an embodiment of the present invention, and Fig. 3 is a part of a silicon semiconductor substrate on which a drive circuit for driving a capacitive load is integrated. FIG. 3 is a partial cross-sectional view showing an embodiment in which a variable resistor is provided. In the figure, TR1 is a control transistor, TR2 is a charging transistor, Z is a variable resistor, 1 is a silicon semiconductor substrate, 3, 4, and 5 are isolation regions, 11 is an N ^- layer, and 12 is a P ^- layer. be.

Claims (1)

[Claims] 1. In a drive circuit that controls a charging transistor to charge a capacitive load by turning on and off a control transistor connected to the base circuit of the charging transistor, the resistance value increases as the applied voltage increases. A drive circuit characterized in that a voltage-dependent variable resistor that increases the voltage is inserted into the base circuit of a charging transistor.