JPH04130506A - Unified signal output device - Google Patents

Abstract

PURPOSE:To reduce power consumption and to suppress internal temp. rising so as to obtain highly reliable system by executing the switching operation of an output transistor. CONSTITUTION:A differential amplifier means OP1 amplifies the difference between an input signal Vin and a feed back signal Vs impressed via a return circuit FB and a PWM conversion means PM outputs a signal with the pulse width of a duty ratio corresponding to a differential signal from the differential amplifier means OP1 to execute the switching operation of an output transistor Q1. The charging and discharging of a condenser C1 is repeated corresponding to the ON/OFF of the output transistor Q1 and the voltage across the condenser, accordingly the voltage applied to a series circuit composed of a load RL and a reference resistance RS takes a value corresponding to an output current and the load RL. Thus, the power consumption can be reduced by the switching operation being conducted by the output transistor. Furthermore, the radiation amount of the output transistor can be suppressed and reliability can be improved.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention converts an input voltage signal such as 1 to 5 V or 0 to 2.5 V into a standardized unified signal such as 4 to 20 mA to The present invention relates to a unified signal output device that outputs signals to a computer, and more specifically, to a unified signal output device that can reduce power consumption and is effective when applied to controllers, signal conditioners, and the like.

<Prior Art> FIG. 3 is a block diagram showing an example of a conventional unified signal output device of this type.

Input signal Vin is amplified by amplifier OPI and applied to current control transistor Q1.

The emitter of transistor Q1 has a load RL and a reference resistance R.
8 are connected in series, and the voltage Vf generated across the reference resistor R8 is fed back to the input terminal of the amplifier OPI.

Here, the load RL is approximately 0 to 600Ω, and the input voltage Vin is, for example, 0.4 to 2. For Ov, the load RL
Convert the unified current output to, for example, 4 to 20 mA. In this case, the reference resistance R3 is, for example, 1
A 0Ω one is used.

<Problems to be Solved by the Invention> In a conventional device of this type having such a configuration, the voltage Vce between the collector and emitter of the output transistor Q1 is
It depends on the load resistance RL and the output current. For example, when the maximum output current is 20 mA flowing through the load and the power supply voltage Vcc = 15 V, the power consumption in the output circuit is 3.
00mW.

For this reason, in a system in which a plurality of devices of this type are used in response to a plurality of input signals, there is a problem that power consumption increases and internal temperature rises.

The present invention was made in consideration of such problems, and its purpose is to reduce power consumption by switching the output transistor, suppress internal temperature rise, and increase the reliability of the system. It is about providing.

<Means for Solving the Problems> The present invention for solving the above-mentioned problems includes: an amplification means for amplifying an input signal; and a PW for converting the signal from the amplification means into a pulse width signal.
M conversion means, an output transistor that is turned on and off by a pulse width signal from the PWM conversion means, a series circuit of an inductance element and a capacitor through which a current turned on and off by the output transistor flows, and a series circuit of an inductance element and a capacitor, which are connected to both ends of the capacitor. The obtained voltage is applied in parallel to the load and reference resistor, and to the series circuit of the inductance element and capacitor! #The device is configured to include a diode with a voltage drop and a feedback circuit means for negatively feeding back the voltage generated in the reference resistor to the input side of the amplification means.

Effect〉 Each of the above components performs the following operations.

The PWM conversion means outputs a pulse width signal with a duty ratio corresponding to the output voltage of the amplification means.

The output transistor performs a switching operation according to the duty ratio of the pulse width signal from the PWM conversion means.

Output transistor, inductance element, capacitor,
The diode constitutes a step-down chopper regulator, which applies a voltage to the load that corresponds to its output current and the value of the load resistance.

The feedback circuit means negatively feeds back the voltage generated at the reference resistor to the input side of the amplification means, and the amplification means outputs an error signal so that the input signal and this feedback signal are equal.

This allows a current corresponding to the input signal to flow through the load within a unified range.

<Example> Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 0, OPI is a differential amplifying means for amplifying an input signal Vin to be converted into a unified signal, and PM is a differential amplifying means for amplifying an input signal Vin to be converted into a unified signal. A PWM conversion means for converting a signal into a pulse width signal, Ql, is an output transistor that is turned on/off by a pulse width signal from the PWM conversion means.

RL is the load, R3 is a reference resistor connected in series with the load RL, C1 is a capacitor connected in parallel to the series circuit (load circuit) of the load RL and the reference resistor, and Ll is connected in series with the capacitor C1. The current turned on/off by the output transistor Q1 is
It flows to capacitor CI via this inductance element L1.

Dl is a diode connected in parallel to the series circuit of inductance element L1 and capacitor C1.

The output transistor Ql, the inductance element L1, the capacitor C1, and the diode D1 constitute a step-down chopper regulator CR, which applies a voltage corresponding to the output current and the value of the load resistance to the load RL.

FB converts the voltage VS generated across the reference resistor R3 to the differential amplification means O.
This is a feedback circuit means that feeds back to the other input terminal (+) of the PI.

The operation of the device configured in this way will be explained next. The differential amplification means OPI amplifies the difference between the input signal Vin applied to one input terminal (-) and the feedback voltage vS applied via the feedback circuit FB.

The PWM conversion means outputs a pulse width signal with a duty ratio corresponding to the error signal from the differential amplification means OPI, and causes the output transistor Q1 to perform a switching operation.

In this example, the output transistor Q1 is of PNP type, and is turned on when the pulse width signal from the PWM conversion means PM is at a low level, and turned off when it is at a high level. When the output transistor Q1 turns on,
The current 'f4 flows from the electric current 211f V c (to the capacitor C1 via the inductance element L1, and the capacitor C
I is charged. Furthermore, when the output transistor Q1 is turned off, the charge stored in the capacitor C1 is transferred to the contribution RL
, discharges through the reference resistor R8. Therefore, the capacitor C1 is repeatedly charged and discharged according to the on/off state of the output transistor Q1, and the voltage across the capacitor C1, and therefore the voltage applied to the series circuit of the load RL and the reference resistor R3, is equal to the output current and the load RL. The value corresponds to

The voltage S generated across the reference resistor R8 is connected to the feedback circuit FB.
The signal is negatively fed back to the input terminal of the differential amplification means OPI.

Now, when the input signal Vin increases, the differential amplification means OP
The output signal of 1 decreases, and as a result, the deinity ratio of the pulse width signal from the PWM conversion means PM decreases. In this case, the time during which the output transistor Q1 is on increases, and the value of the voltage applied to the load RL increases. As a result, the feedback voltage VS obtained across the reference resistor R8 also increases. As the feedback voltage vS increases, the input signal V in and the feedback voltage VS eventually become equal (VS=V
ine, the operation is stable, and a current corresponding to the input signal Vin can be caused to flow through the load RL.

The range of change (span) of the current flowing through the load is determined by the reference resistance R.
It can be changed by adjusting the value of 3.

The outfit configured like this! According to the output transistor Q
1 performs a switching operation, so power consumption here can be reduced.

FIG. 2 is a configuration block diagram showing another embodiment of the present invention.

In this embodiment, the PWM conversion means PM includes a triangular wave signal generator SG and a comparator O for comparing the triangular wave signal from the triangular wave signal generator with the signal from the amplification means OPI.
It is composed of P2. Here, the triangular wave signal generator SG is composed of an operational amplifier OP3 that inputs the reference voltage obtained to the Zener diode D3, and an integrator INT that integrates the output of the operational amplifier OP3, and outputs a triangular wave signal with a constant period. is configured to do so.

The output transistor Q1 is connected to two transistors Q2. Q
3 connected by Darlington is used. In the series circuit of the reference resistor R3 and the load RL, one end of the load RL is connected to the common line, and the reference resistor R3
is floating from the common line. For this reason, a differential amplifier OP5 is provided, and the feedback voltage VS generated at the reference resistor R3 is
The output of the differential amplifier OP5 is fed back to the input terminal of the amplifying means OP1 via the period circuit FB.

Note that an offset resistor Rof and a diode D2 are inserted and connected between the reference resistor R3 and the load RL.

This diode D2 and offset resistance Rof are the load R
This is to generate a small voltage across the capacitor C1 when the value of L is 0Ω, thereby stabilizing the regulation operation. Also, load RL
It has a function of converting the ripple voltage generated across the reference resistor R3 into a common mode when the value of R3 is small, thereby increasing the accuracy of current detection.

According to this embodiment, the triangular wave signal from the triangular wave signal generator SG is output to the PWM signal of another unified signal output circuit (not shown).
The conversion means can be used in common and can be connected to the -jlf common line of the load RL, so it can be used to convert multiple input signals into a unified current signal and supply it to multiple loads. It is effective in some cases.

<Effects of the Invention> As explained in detail above, the present invention controls switching of the voltage applied to the load according to the load condition (resistance size) and the output current. tt force efficiency can be improved. Furthermore, since the internal loss caused by the output transistor is reduced, the amount of heat generated can be suppressed and reliability can be improved.

The following table shows experimental data showing the power consumption (m W >) inside the device depending on the load value and the output current value in the example circuit of FIG. 2 when the power supply voltage Vcc is 24V.

In the case of the conventional circuit shown in Figure 3, regardless of the load value,
For example, when the output current is 20mA, the power consumption inside the device is 580mW.The smaller the load, the higher the percentage of power consumption inside the device.With a load of 0Ω (load or short), all of the 580mW (100%) The power consumption of the product to which the present invention is applied is a maximum of 312 mW, which is a considerable reduction in internal power consumption compared to conventional products, and heat generation can be suppressed. I understand.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a configuration block diagram showing one embodiment of the present invention;
This figure is a block diagram showing another embodiment of the present invention, and FIG. 3 is a block diagram showing an example of a conventional unified signal output device of this type. OPI...Amplification means, PM...PWM conversion means, Q
l...Output transistor R1-...Load, R3...Reference resistance, CI...
...Capacitor, Ll...Inductance element Dl...Diode, FB...Feedback circuit means

Claims (1)

[Claims] Amplifying means for amplifying an input signal, and a PW for converting the signal from the amplifying means into a pulse width signal.
M conversion means, an output transistor that is turned on and off by a pulse width signal from the PWM conversion means, a series circuit of an inductance element and a capacitor through which a current turned on and off by the output transistor flows, and a series circuit of an inductance element and a capacitor, which are connected to both ends of the capacitor. A load and a reference resistor to which the obtained voltage is applied, a diode connected in parallel to the series circuit of the inductance element and the capacitor, and a feedback circuit that negatively feeds back the voltage generated at the reference resistor to the input side of the amplifying means. A unified signal output device comprising means.