JPH0385014A - Pwm/dc voltage conversion circuit - Google Patents

Abstract

PURPOSE:To attain PWM/DC voltage conversion with less power consumption and load fluctuation by switching a flowing-in current source and a flowing-out current source based on a PWM signal so as to act the result on a capacitor and extracting the capacitor voltage. CONSTITUTION:A flowing-in current source 1 and a flowing-out current source 2 connect to a capacitor C alternatively with a changeover switch 3 and the changeover of the changeover switch 3 is controlled with a PWM signal given through a terminal 4. The constant currents I1, I2 of the flowing-in current source 1 and the flowing-out current source 2 are made identical to each other. By switching the flowing-in current source 1 and the flowing-out current source 2 with respect to the capacitor C by using a PWM signal, a DC voltage proportional to a time ratio of the connection to the flowing-in current source 1 and the flowing-out current source 2 and the constant current 1 and inversely proportional to the capacitance of the capacitor C is led out at an output terminal 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a PWM/DC voltage conversion circuit that converts a PWM (pulse width modulation) signal into a DC (direct current) voltage.

BACKGROUND OF THE INVENTION Such a PWM/DC voltage conversion circuit is used in a circuit (for example, a channel selection circuit of a television set) that controls a DC voltage using a PWM signal output from a microcomputer.

As shown in Figure 6, a conventional PWM/DC voltage conversion circuit amplifies a PWM signal given from a microcomputer using a transistor (QIO), and then passes it through a low-pass filter (
11) into a DC voltage, and the output is sent to an operational amplifier (1
0) is supplied to the negative input terminal (-). The circuit shown in Fig. 6 functions as a part of the channel selection circuit, and the operational amplifier (10) divides the 33V power supply voltage to its positive input terminal (+) with a resistor (+2&) (R?). The obtained voltage is input through a resistor (R6), and a tuning voltage is generated at the output. The low pass filter (
II) is a resistor (1? (R4) and a capacitor (C+)
It is composed of.

As mentioned above, in order to widen the voltage control range (tuning voltage range) in the conventional PWM/Dc1 pressure conversion circuit, which amplifies the PWM signal and converts it to DC using a low-pass filter, The collector of the transistor (Q,.) and the power supply (33V
) must be made small. However, when the value of the resistance (Rg) is reduced in this way, a relatively large current flows, resulting in a drawback that power consumption cannot be reduced. Moreover, since the current includes ON33/Ih fluctuations, the load fluctuations become large.

The present invention has been made in view of these points, and it is an object of the present invention to provide a PWM/DC voltage conversion circuit with low power consumption and low load fluctuation.

The PWM/DC voltage conversion circuit of the present invention includes a capacitor, an inflow current source and an outflow current source for the capacitor, and an inflow current source and an outflow current source for the capacitor. and switching means for switching the outflow current source to act on the capacitor, and means for taking out the voltage of the capacitor.

According to this configuration, the capacitor is charged and discharged by switching between the outflow current source and the inflow current source by the switching means. The switching is performed based on a PWM signal. Therefore, the charging time and discharging time change depending on the pulse width of the PWM signal, and the voltage of the capacitor changes.

Large” L-fuel Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, (1) is an outflow current source for providing a charging current to the capacitor (C), and (2) is an inflow current source that also provides a discharging current. These current sources (1)
(2) is alternatively connected to the capacitor (C) by a changeover switch (3) to perform its function.

The switching of the changeover switch (3) is controlled by a PWM signal applied through the terminal (4). For example, PW
During the low level period of the M signal, the changeover switch (3) is set to the contact (3a) side, and during the high level period, the changeover switch (3) is set to the contact (3b) side.
) side. Here, the constant current 1. of the outflow current source (1) and the inflow current source (2). , 1. are the same as each other (1+ =
1! −1), but these constant currents 1+, I
t does not necessarily have to be the same.

In Fig. 1, by switching between the outflow current source (1) and the inflow current source (2) for the capacitor (C) using a PWM signal, the time period during which the outflow current source (1) and the inflow current source (2) are connected is determined. A DC voltage proportional to the ratio and the constant current ■ and inversely proportional to the capacitance of the capacitor (C) is derived to the output terminal (5). Note that (R) (R) is a resistance selected to have a relatively large value.

Next, FIG. 2, which embodies the configuration of FIG. 1, will be explained. In the same figure, a transistor (Qs) constitutes a current mirror-connected outflow current source (1), and (Q4
) (Qs) (Qt) (Ql) similarly constitutes an inflow current source (2) of current mirror connection. The input terminals of these current sources (1) and (2) are respectively connected to the collectors of transistors (Ql) (Q). 6) constitutes a differential amplifier (7),
The base of the transistor (Q) is connected to a constant voltage source (8), and the base of the transistor (Q) is connected to a PWM signal input terminal (9).

Next, the operation of the circuit shown in FIG. 2 will be explained with reference to the signal waveform diagram shown in FIG. Differential amplifier (7) is a transistor (Ql)
The constant voltage (V th) applied to the base of the transistor (0□) is compared with the PWM signal applied to the base of the transistor (0
The transistor (portion l) is OFF at the part higher than h)
The transistor (Q2) turns on, and the inflow current source (2
) operates to discharge the capacitor (C) with a constant current ■. This discharge current flows to the ground point through the transistor (O6). At this time, the outflow current source (1) does not operate because the transistor (Q, ) is OFF, and the transistor (
Ql) (口, ) is the cutoff.

Conversely, when the PWM signal is lower than the constant voltage (Vth), the transistor (Ql) is ON and the transistor (Q2
) is turned off, the outflow current source (1) and inflow current source (2) are switched, the outflow current source (1) is activated and the inflow current source (2) is inactivated. For this reason, the capacitor (
C) is charged with a constant current I through the transistor (06).

In FIG. 3, (b) shows the discharging current caused by the inflow current source (2), and (C) shows the charging current caused by the outflow current source (1). Moreover, (d) shows the voltage of the capacitor (C). The discharge period (T) of the PWM signal (
As the ratio between T1) and the charging period (T2) changes, the voltage of the capacitor (C) also changes.

Figure 4 shows the duty b (T I
/T x 100) and the output voltage (DC).
When the inflow current (discharge current) T2 is the same and large, (
(b) represents the characteristics when + + > I t, and (c) represents the characteristics when h is T2.

Figure 5 shows an example of a channel selection circuit using the circuit shown in Figure 2, in which the output of the capacitor (C) is connected to the performance amplifier (10
) to the negative input terminal (-) of the terminal. The same circuit as the conventional example shown in FIG. 6 is connected to the plus input terminal (+) of the operational amplifier (10).

According to the present invention, it is possible to widen the output DC voltage range with less current consumption (therefore, less power consumption). In addition, since the current consumption can be reduced in this way,
It is possible to eliminate load fluctuations in the power supply. Furthermore, the circuit of the present invention is also suitable for tC conversion, as can be seen from the above implementation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a PWM/DC voltage conversion circuit implementing the present invention, and FIG. 2 is a circuit diagram showing its specific configuration.
FIG. 3 is a signal waveform diagram for explaining FIG. 2, and FIG. 4 is a characteristic diagram for explaining the relationship between the PWM signal and the output voltage. FIG. 5 is a circuit diagram when the circuit shown in FIG. 2 is used as a channel selection circuit. FIG. 6 is a circuit diagram showing a conventional example. (1) - Outflow current source, (2) - - Inflow current source. (3) - Selector switch, (5) - Output terminal. (7)...Differential amplifier, (C)...-capacitor.

Claims (1)

[Claims] (1) A capacitor, an inflow current source and an outflow current source for the capacitor, switching means for switching the inflow current source and outflow current source to act on the capacitor based on a PWM signal, and means for extracting the voltage of the capacitor. and,
PWM/DC voltage conversion circuit consisting of.