JPS61164471A - Output circuit of integrated circuit - Google Patents

Abstract

PURPOSE:To reduce wasteful power consumption by driving the transistor of output stage by a current source. CONSTITUTION:With a constant-current source X as a reference a current source 4 for driving Tr Q5 of output stage is formed of a mirror circuit Y made of transistors (Tr) Q6-Q9. Thus, when Tr Q4 is turned OFF by the output of a timer having a capacitor Ct and a voltage comparator CP, a drive current is supplied to the Tr Q5 by a mirror circuit Y to turn ON it. When Tr Q4 is turned ON, Tr Q5 is turned OFF. Thus, since the consumed power becomes constant by a constant-current source X, even if the power voltage of used DC power source E is largely varied, it can be stably operated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an output circuit of an integrated circuit that controls an inverter circuit or the like of a fluorescent lamp lighting device.

[Background Art] Conventionally, as shown in FIG.
, a pair of secondary windings 1tlA N 21L, N zb and a feedback winding N, an oscillation transformer OT having a pair of secondary windings 1tlA N 21L, N zb and a feedback winding N, a resonance capacitor C, a resistor R,, R2, and a current limiting inductance L0, and two large windings #i. N 21Lt N z
In a fluorescent lamp lighting device using an inverter circuit 1 whose b output is passed through a current-limiting and DC blocking capacitor C0, a lighting control circuit co that controls DC preheating of the filaments 3a and 3b of the fluorescent lamp 2 has a As shown in Figure 4,
A timer circuit formed by a time constant circuit consisting of a resistor Rt and a capacitor Ct, a reference voltage generation circuit consisting of voltage dividing resistors Ra and Rb, and a voltage comparison circuit CP that compares the voltage Ve across the capacitor Ct and the reference voltage Vd. 6 and resistance R
It is formed of a drive circuit consisting of e, Rd and a transistor Q4, and an output transistor Q driven by the collector output of the transistor Q4. ) 3a and 3b are preheated with a DC power source E, and after a certain period of time, the transistor Q is turned on to operate the inverter circuit 1 and apply a high voltage to the fluorescent lamp 2 to turn it on. This lighting control circuit co is formed of an integrated circuit. By the way, in such a conventional example, the transistor Q at the output stage of the lighting control circuit CO made up of an integrated circuit was driven by a voltage source made up of the transistor Q, the load resistor Rd, and so on. Even when transistor Q is off, transistor Q does not require a drive.

This means that current is flowing to the load resistance Rd via
There is a problem that the power consumption due to the load resistance Rd of the drive circuit becomes larger than necessary, resulting in wasted power consumption.In particular, when the power supply voltage range used is wide, there is also the problem of reliability. there were.

[Objective of the Invention 1 The present invention has been made in view of the above-mentioned points, and its purpose is to reduce wasteful power consumption and to provide a system which can be used over a wide voltage range. Another object of the present invention is to provide an output circuit of an integrated circuit that operates stably without causing problems in reliability.

[Disclosure of the Invention 1 (Embodiment 1) Fig. 1 shows an embodiment of the present invention, in which a transistor Q in the output stage is driven by a mirror circuit consisting of transistors Q6 to Q with a constant current source X as a reference. A current source 4 is formed to drive the output stage transistor Q5.

Now, when transistor Q is turned off, current is reflected in mirror circuit Y, and a drive current is supplied to transistor Q, turning on transistor Q. On the other hand, transistor Q4 is turned on. When turned on, no current is reflected in the mirror circuit Y, and the output stage transistor Q is turned off. In this case, the current source 4 outputs the output stage transistor Q.
5, it is possible to reduce wasted power consumption due to the load resistance Rd of the drive circuit in the conventional example, and the consumed power is made constant by the constant current source X. Therefore, even if the power supply voltage of the DC power supply E used changes significantly, stable operation can be achieved without any reliability problems.

(Embodiment 2) Figure 2 shows another embodiment, and shows a circuit example in which the constant current source X of the current source 4 that drives the output stage transistor Q is configured to be negative. The other configurations and operations are the same as in the first embodiment.

[Effects of the Invention] As described above, the present invention drives the output stage transistor with a current source, and can reduce unnecessary power consumption due to the load resistance of the drive circuit in the conventional example. Even in the case of a wide voltage range, there is an effect that stable operation can be performed without causing problems in reliability.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional example. Q is an output transistor, and 4 is a current source as shown in Figure 1.

Claims (1)

[Claims] (1) An output circuit of an integrated circuit characterized in that a transistor in an output stage is driven by a current source.