JPH0412790Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a flyback type switching regulator, and more specifically, a signal transmission circuit that enables good signal transmission between primary and secondary. The present invention relates to a switching regulator.

(Prior Art) FIG. 6 is a connection diagram of a flyback type switching regulator. This switching regulator switches (on/off) the DC voltage Vin by a transistor Q functioning as a switching element, and switches the primary winding N of the main transformer T.
In addition to 1, this causes current IC to flow through the primary winding to store energy in the transformer, and transistor Q
is turned off, the current ID is supplied to the secondary winding of the main transformer T, and it is rectified and smoothed by a rectifying and smoothing circuit consisting of a diode and a capacitor C to obtain a DC voltage Vo. has been done. The DC output voltage Vo is determined by the turns ratio n:1 of the main transformer T and the on/off state of the transistor Q, as shown in equation (1).
This corresponds to the off time ratio Ton/Toff.

Vo=Vin・(IC/ID)・(Ton/Toff)...(1) Therefore, although not shown here, there is a control circuit for controlling the on/off time ratio of transistor Q, and this control circuit. Signal transmission for isolating signals related to DC voltage Vo (or error signals between DC voltage and reference voltage) and providing them as feedback signals, which are necessary to keep (stabilize) DC voltage Vo in the circuit. A circuit is provided.

By the way, in a flyback switching regulator with such a configuration, the DC voltage Vo
Conventionally, a signal transmission circuit for giving a signal related to the control circuit as a feedback signal is
It was common to use photokatsupura.
The reason for this is that it has advantages such as easy signal isolation and relatively simple configuration.

(Problems that the invention aims to solve) However, the signal transmission method using the photo coupler may not have enough withstand voltage, and when transmitting analog voltage in an open loop, the light emitting efficiency of the light emitting element in the photo coupler may deteriorate. There were problems such as a compensating circuit being required and the configuration becoming complicated.

The present invention was devised in view of the problems in the prior art, and its purpose is to provide a structure with a signal transmission circuit between the primary and secondary circuits that has a high withstand voltage and is less susceptible to temperature changes and changes over time. This is an attempt to realize a simple switching regulator.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, stores energy in the primary winding of the main transformer by passing current through the primary winding of the main transformer when the switch element is on, and when the switch element is off. In a flyback switching regulator that operates to supply current to the secondary winding of the main transformer, there is a transformer for signal transmission and a transformer connected in series to the primary winding of this transmission transformer for transmission. an impedance element whose impedance changes depending on a signal; and a drive signal applying means for applying a winding voltage of the main transformer as a drive signal of the transmission transformer to a series circuit of the primary winding of the transmission transformer and the impedance element. The present invention is characterized by being provided with a rectifying and smoothing circuit that rectifies and smoothes the voltage generated in the secondary winding of the transmission transformer to obtain a DC voltage corresponding to the signal to be transmitted.

(Example) FIG. 1 is a connection diagram showing an example of a device according to the present invention. In this figure, FC is a flyback converter section, and parts corresponding to those in FIG. 6 are given the same reference numerals. _N3
is an auxiliary winding wound around the main transformer T, and _D2 is a diode that rectifies the voltage generated in the auxiliary winding _N3 . IS is a signal transmission circuit attached to converter FC.

The signal transmission circuit IS assumes that the signal to be transmitted is, for example, a feedback signal for providing a signal related to a DC voltage (Vo) applied to a load to a control circuit (not shown). T1 is a signal transmission transformer, and R1 is an impedance element that is connected in series to the primary winding N11 of the transmission transformer T1 and whose resistance (impedance) changes depending on the signal to be transmitted (feedback signal related to the output voltage). resistance. As this impedance element, a transistor is used, for example, and its impedance is configured to change in relation to the output voltage or an error signal between the output voltage and the reference voltage.

The series circuit of the primary winding N11 of the transmission transformer T1 and the resistor R1 as an impedance element includes an auxiliary winding N3 provided in the main transformer T described above.
A voltage eA obtained at is applied via a rectifier diode D2, and the transmission transformer T1 is driven by this voltage eA.

D3 and C2 are the secondary winding N of the transmission transformer T1
This is a rectifying and smoothing circuit that rectifies and smoothes the voltage ec generated at the terminal 12 to obtain a DC voltage eD corresponding to the signal to be transmitted. The DC voltage eD obtained here is
It is applied to a control circuit for turning on/off the switching element Q. The control circuit inputs the obtained DC voltage eD to the rectifying and smoothing circuit, and controls the on/off period of the switch element Q so that it becomes a constant value (or zero if it is an error signal). Thereby, the output voltage Vo applied to the load RL is controlled so as to be always maintained at a constant value.

Note that RS is the secondary winding N of the transmission transformer T1.
This is a reset circuit for the transformer T1 connected in parallel to the transformer T12, and may be omitted.

The operation of the apparatus configured as described above will now be described with reference to the operational waveform diagram of FIG. 2.

In FIG. 2, A is the waveform of the voltage _eA generated in the auxiliary winding _N3 , which changes in a rectangular waveform depending on whether the transistor Q is turned on or off. this voltage
e _A is rectified by diode D ₂ and applied to the series circuit of transformer T ₁ primary winding N ₁₁ and resistor R ₁ . As a result, the sum of the secondary side load and excitation impedance of the transformer _T1 and the voltage e _B divided by the resistor _R1 are applied to the primary winding _N11 of the transformer _T1 . B is the waveform of the voltage e _B applied to the primary winding N ₁₁ , and the amplitude of this voltage is
Varies depending on the size of _R1 . ha, trance
This is the waveform of the voltage _eC generated in the secondary winding _N12 of _T1 , and is almost the same as the signal waveform in (b), with an amplitude proportional to the turns ratio of the transformer _T1 .

The voltage e _C generated in this secondary winding N ₁₂ is rectified by a diode D ₃ and smoothed by a capacitor C ₂ .
D is the waveform of the voltage e _D obtained across the resistor R ₂ ,
Its value corresponds to the value of resistor _R1 , and becomes a DC voltage isolated from the primary side.

3 to 5 are main part connection diagrams of other embodiments of the present invention.

In the embodiment of FIG. 3, in _FIG.
Instead, a transistor Q ₂ is connected in series with the primary winding N ₁₁ of the transformer T ₁ .

In the embodiment shown in FIG. 4, _the auxiliary winding N ₃ provided in _the transformer T in FIG _. The voltage is applied to a series circuit consisting of the primary winding of R1 and a resistor _R1 .

The embodiment shown in FIG. 5 assumes that the signal to be transmitted is an overvoltage detection signal (a status signal that indicates its state with high/low levels).

If an excessive voltage is applied to the load from the switching regulator, it is necessary to take measures such as stopping the switching operation to protect the load. Normally, this type of switching regulator is equipped with a means to detect excessive voltage applied to the load, and the excessive voltage detection signal (status signal) is sent to the switching element side (primary side of the main transformer T). It is designed to be transmitted insulated.

In this embodiment, such an overvoltage detection signal is caused by an impedance change represented by a resistor R1, and is passed through a transmission transformer T1 to a secondary winding N12.
The configuration is such that the output is used to turn on/off the transistor Q3. When an excessive voltage occurs, the smoothing circuit of capacitor C2 and resistor R2 receives a status signal indicating this, and upon receiving the status signal, the control circuit immediately stops the switching operation. That will happen.

In each of the above embodiments, the case where the resistor R ₁ is connected in series with the primary winding N ₁₁ of the transformer T ₂ is exemplified, but instead of the resistor R ₁ , its value can be changed depending on the signal to be transmitted, for example. An impedance element whose impedance changes may be used.

(Effects of the invention) As explained above, according to the invention, the main signals required in the switching regulator, such as the feedback signal related to the output voltage applied to the load and the overvoltage detection signal, For signal transmission between the primary and secondary sides of the transformer, a transmission transformer whose drive signal is the voltage obtained from the main transformer T is used, and a flyback period during which the peak value of the voltage obtained from the main transformer T is constant is established. This method is used to transmit signals while insulating them.

Therefore, according to the present invention, compared to conventionally used photocups, the device is equipped with a signal transmission circuit that has a higher withstand voltage and is less susceptible to temperature changes and aging.
A switching regulator with a simple configuration can be realized.

[Brief explanation of the drawing]

Figure 1 is a connection diagram showing an example of the device of the present invention, Figure 2 is its operating waveform diagram, Figures 3 to 5 are connection diagrams of main parts of other embodiments of the invention, and Figure 6 is a known device. FIG. 2 is a connection diagram of a flyback type switching regulator. FC...converter part, IS...signal transmission circuit,
T...Main transformer, Q...Switch element, _T1 ...
…signal transmission transformer, R ₁ …resistance.

Claims (1)

[Claims for Utility Model Registration] When the switch element is on, current is passed through the primary winding of the main transformer and energy is stored in the transformer.
In a flyback type switching regulator that operates to supply current to the secondary winding of the main transformer when the switch element is off, a signal is connected in series to the signal transmission transformer and the primary winding of this transmission transformer. an impedance element whose impedance changes depending on the signal to be transmitted; and a series circuit of the primary winding of the transmission transformer and the impedance element; the winding voltage of the main transformer is applied as a drive signal of the transmission transformer; The present invention is characterized in that the transmission transformer is provided with a drive signal applying means and a rectifying and smoothing circuit that rectifies and smoothes the voltage generated in the secondary winding of the transmission transformer to obtain a DC voltage corresponding to the signal to be transmitted. Switching regulator.