WO2008009196A1

WO2008009196A1 - A passive signal isolator with zero offset operation

Info

Publication number: WO2008009196A1
Application number: PCT/CN2007/001600
Authority: WO
Inventors: Xiangyang Yin; Dingmin Mo
Original assignee: ZHANG, Jiaoru
Priority date: 2006-07-11
Filing date: 2007-05-17
Publication date: 2008-01-24
Also published as: CN100392970C; CN1889348A

Abstract

A passive signal isolator with zero offset operation includes a self-oscillation circuit, a pair of complementary triodes, a DC offset circuit (10), a transformer (L1) and a rectifier circuit (20). One end (1) of the DC offset circuit is connected to the signal input end (Ii+) and the other end (2) and the output end of the self-oscillation circuit are connected to the bases of the complementary triodes. The DC offset circuit includes a capacitor (C103) and a reverse isolating element (D102) connected in series to the capacitor for isolating self-oscillation signals, one end of the capacitor is connected with the input of the current signals, the other end is connected to the positive pole of the reverse isolating element, and its reverse pole is connected to the bases of the complementary triodes.

Description

Passive signal isolator with zero bias operation

Technical field

The present invention relates to a current-type passive signal isolator, and more particularly to a passive signal isolator that operates with zero bias.

Background technique

As shown in FIG. 1, in the prior art, the passive signal isolator comprises a complementary three-pole pair and a DC-DC half-bridge circuit composed of a capacitor, and a half bridge mainly composed of a D101 (double diode series circuit) and a self-oscillating transformer. The self-excited oscillation circuit, the signal of 1:1 is combined with the rectifier circuit of the main transformer and the secondary of the main transformer, and the passive signal isolator chopping the input DC signal through the half bridge circuit and the half bridge self-excited oscillation circuit, so that It becomes an AC signal, and then the coupling of the main transformer is used to couple energy from the primary to the secondary, and finally the rectified output drives the load. The self-oscillating circuit of the traditional passive signal isolator is to divide a part of the current from the current loop by the resistor to maintain the starting and working of the oscillating circuit. As shown in the DC bias part of Figure 1, there is generally a shunt resistor, DC bias. One end of the set portion is connected to the signal input end, and the other end of the DC bias portion is connected to the base of the tube together with the output end of the self-oscillation circuit; this current is usually 10 microamperes or more. In the signal application requirements of a passive signal isolator with a range of 20 mA, a signal shunt of 10 microamperes will cause a signal error of 0.05%; this affects the transmission accuracy of the signal isolator to some extent.

Summary of the invention

It is an object of the present invention to provide a passive signal isolator capable of solving the problem that the self-excited oscillation circuit is deteriorated due to shunting from the current loop. The above object can be achieved by the following technical measures: a passive signal isolator with zero bias operation, including a self-oscillation circuit, a triode complementary pair tube, a DC bias circuit, a transformer and a rectifier circuit, wherein the DC bias portion One end is connected to the signal input end, and the other end of the DC bias part is connected with the output end of the self-oscillating circuit to the base of the complementary pair of tubes; the characteristic is that the DC bias circuit comprises a capacitor and is used for isolating the self-excited The reverse isolation component of the oscillating signal; the capacitor and the reverse isolation component are connected in series, one end of the capacitor is connected to the current signal input end, one end of the capacitor is connected to the forward pole of the reverse isolation component, and the reverse polarity of the reverse isolation component is connected to the complementary pair of the triode The base of the tube.

As a further improvement, the present invention adjusts the resistance in series between the capacitor and the reverse isolation element, thereby controlling the base current of the triode flowing into the half bridge circuit at the instant of starting, thereby making the circuit startup more stable.

As a further improvement, the present invention parallels the discharge resistors at both ends of the capacitor, so that when the signal input is deactivated or turned off, the capacitor can be discharged through the resistor to prepare for the next circuit start, making the next start more stable.

The reverse isolation element of the present invention is a diode or a triode.

The invention can also be realized by the following technical measures: a passive signal isolator with zero bias operation, including a self-oscillation circuit, a triode complementary pair tube, a DC bias circuit, a transformer and a rectifier circuit, wherein the DC bias portion One end is connected to the signal input end, and the other end of the DC bias part is connected to the base of the complementary pair of tubes together with the output end of the self-oscillating circuit; the DC bias circuit includes a capacitor, a discharge resistor and an adjustment resistor. The discharge resistor is connected at both ends of the parallel capacitor. One end of the capacitor is connected to the current signal input end, and the other end of the capacitor is connected in series with one end of the adjustment resistor, and the other end of the adjustment resistor is connected to the triode tube complementary to the tube. Base.

The invention makes the triode have a certain current DC offset when the circuit is started. The DC bias current is derived from the shunt of the current loop, and automatically cuts off the DC bias loop when the startup is completed. After the startup is completed, the driving energy of the triode is controlled by the current loop. The oscillating circuit is provided, thereby avoiding the loss of the current signal and improving the signal transmission accuracy of the isolator.

DRAWINGS

Figure 1 is a schematic circuit diagram of a passive signal isolator;

Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 are schematic diagrams of various implementations of the DC biasing section in a passive signal isolator.

Figure 8 and Figure 9 are circuit diagrams of the single-sided bias of the tube in the passive signal isolator.

detailed description

As shown in Figure 1 and Figure 2, Ii+ is the positive terminal of the signal input by the current signal, and Π - is the negative terminal of the signal input by the current signal. Q100 is a complementary pair of NPN and PNP transistors. Q100 and capacitors C104 and C105 form a typical DC-DC half-bridge circuit. Capacitors C100, C101, C102 and D101 (dual diode series circuit) and transformer L2 form a self-oscillating circuit of the half bridge. L1 is a 1: 1 signal coupling transformer. The secondary connection of the transformer L1 is connected to the rectifier circuit. The DC bias circuit comprises a capacitor C103 and a diode D102 for isolating the self-excited oscillation signal; one end of the capacitor C103 is connected to the current signal input end, one end of the capacitor C103 is connected to the anode of the diode D102, and the cathode of the diode D102 is connected to the triode complementary tube. The base of the medium NPN tube.

The working principle of the circuit is as follows: When the current signal is connected to the Ii+ and Ii- terminals, the capacitor C103 and the diode D102 form a DC bias to the transistor of the transistor Q100, and the NPN tube of the Q100 is turned on, the capacitor Feet. Then there is a current flowing through the 2 and 1 pins of the transformer L2, flowing through the 3 and 2 feet of the D101, flowing through the 2 and 1 legs of the Q100, and returning to the 2 pin of the transformer L2 to form a loop. At this time, the PNP tube of Q100 is turned on, causing the current to flow through 6+ through the pins 6 and 1 of Q100, flowing through pins 2 and 3 of transformer L2, flowing through pins 2 and 1 of transformer L1, flowing through capacitor C105 back to Ii- A loop is formed to complete the positive chopping of the DC signal. Due to the relationship of the transformer with the same name, for the transformer L2, the current flows through the 2 and 3 feet and the current is increasing, which causes the current flowing through the 2 and 1 pins of the Q100 to increase, which further aggravates the 2 and 1 feet flowing through the transformer L1. The positive feedback of the current, which forms the current, also causes the core of the transformer L2 to quickly reach saturation. The current in the two loops then decreases. The current flowing through the transformer L2 is reduced, causing the inversion of the base drive voltage of the L2 to the triode, and causing the current to be inverted. When the inverted voltage reaches a certain value, the PNP tube is turned on, and the NPN tube is turned off, and the two loops The current is inverted, and the reverse chopping of the DC signal is completed in the same way. The forward and reverse chopping signals are coupled via transformer L1 and output by Io+, Io- after secondary rectification.

In this embodiment, the capacitor C103 and the diode D102 are DC biased to the NPN tube of the Q100. At the instant of starting, the capacitor C103 is equivalent to a short circuit, and has a DC bias of a certain current, which helps the self-oscillating circuit to start. The current flows from the positive pole of the signal input, flows through the capacitor C103, flows forward through the diode D102, flows into a base of the transistor pair, flows into the emitter of the transistor, and finally flows into the negative pole through the input of other circuits, thereby forming a circuit starting instant. Offset. During the startup process, the bias current is charged to the capacitor C103. When the capacitor C103 is fully charged, the voltage across the capacitor C103 is equal to the signal input voltage. At this time, the self-oscillation of the circuit is completed, the bias current is reduced to zero, and the base drive current of the transistor is Provided by the energy of the self-oscillating circuit. The self-oscillating circuit is connected in series in a circuit composed of a triode, which does not cause shunting of the current main circuit; and the reverse action of the diode D102 makes the capacitor C103 not repeatable and fast. Charge and discharge to affect the driving of the base of the triode. At this time, the current signal in the circuit is completely chopped by the transformer L1, and there is no other shunt, so that the high-precision isolation transmission of the current signal can be realized.

In preparation for the next circuit start, it is more stable at the next startup. Parallel discharge resistor R100 (see Figure 3) is connected across the capacitor C103 so that when the signal input is deactivated or de-energized, capacitor C103 can pass through resistor R100. Discharge. If the circuit is turned off after the circuit starts to work normally, the capacitor C103 has no power bleeder circuit, so that the capacitor C103 is not fully discharged, and the circuit starts unstable. At this time, the base current of the transistor is large. . In addition, the resistance R100 is usually very large, reaching about 10M. The voltage across the capacitor C103 is equal to the signal input voltage. When the self-oscillation of the circuit is completed, the resistor R100 replaces the capacitor C103 to form a bias loop, but the bias current is very small. Think of zero.

In order to control the base current of the triode flowing into the half-bridge circuit at the moment of startup, the circuit startup is more stable, and the resistor R101 is connected in series between the capacitor C103 and the diode D102 (Fig. 4).

As shown in FIG. 5, the resistor R100, the capacitor C103, the resistor R101 and the diode D102 form a DC bias portion, the resistor R100 is connected in parallel with the capacitor C103, a parallel connection of the resistor R100 and the capacitor C103 is connected to the positive pole of the signal input, and the resistors R100 and C103 are Another parallel connection is connected to one of the legs of the resistor R101, the other end of the resistor R101 is connected to the anode of the diode D102, and the cathode of the diode D102 is connected to the base of the NPN transistor, so as to control the base of the transistor flowing into the half bridge circuit at the moment of adjustment initiation. The current can discharge the capacitor and make the circuit work more stable.

As shown in Fig. 6, the diode D101 is used instead of the diode D102 shown in Fig. 5. The transistor can be either NPN type or PNP type, and the base limiting current resistance of the triode is increased. R102, this circuit can also have the same effect.

As shown in Figure 7, the DC bias circuit consists of capacitor C103, discharge resistor R100 and regulation resistor R101, discharge resistor R100 is connected across the capacitor C103, one end of capacitor C103 is connected to the current signal input terminal, and the other end of capacitor C103 is connected to the regulation resistor. One end of the R101 is connected in series, and the other end of the adjusting resistor R101 is connected to the base of the NPN tube in the complementary pair of the transistor. The circuit can still make the circuit work normally, but the DC bias signal is easily superimposed on the oscillating drive signal of the half-bridge circuit, which affects the stability of the circuit operation.

As shown in FIG. 8, the above-mentioned DC bias loop can be set for the PNP tube in the complementary pair tube of the triode, or the DC bias loop is set for the PNP tube and the NPN tube in the complementary pair tube of the triode as shown in FIG. 9 , principle and effect the same.

Claims

Rights request

1. A passive signal isolator operating at zero bias, comprising a self-oscillating circuit, a triode complementary pair tube, a DC bias circuit, a transformer and a rectifying circuit, wherein one end of the DC biasing portion is connected to the signal input end, DC bias The other end of the portion is coupled to the output of the self-oscillating circuit to the base of the complementary pair of tubes; wherein: the DC bias circuit includes a capacitor and a reverse isolation element for isolating the self-oscillation signal; In series with the reverse isolation component, one end of the capacitor is connected to the current signal input terminal, one end of the capacitor is connected to the forward pole of the reverse isolation component, and the reverse pole of the reverse isolation component is connected to the base of the complementary diode of the transistor.

2. The zero-biased passive signal isolator of claim 1 wherein: a triode base current regulating resistor is provided in series between the capacitor and the reverse isolating element for controlling a transient instant flow into the half bridge circuit. .

3. A zero-biased passive signal isolator according to claim 1 or 2, characterized in that: a discharge resistor is connected in parallel across the capacitor.

4. A zero-biased passive signal isolator according to claim 1 or 2, wherein: said reverse isolation element is a diode or a triode.

5. A passive signal isolator with zero bias operation, comprising a self-oscillating circuit, a triode complementary pair tube, a DC bias circuit, a transformer and a rectifying circuit, wherein one end of the DC biasing portion is connected to the signal input end, and the DC bias The other end of the portion is connected to the base of the complementary pair of tubes with the output of the self-oscillating circuit; wherein: the DC bias circuit comprises a capacitor, a discharge resistor and a regulating resistor, and the two ends of the discharge resistor are connected in parallel. One end of the capacitor is connected to the current signal input end, and the other end of the capacitor is connected in series with one end of the adjusting resistor, and the other end of the adjusting resistor is connected to the base of the complementary diode of the transistor.