JPH04105556A - Circuit for controlling the secondary side of dc/dc converter - Google Patents

Abstract

PURPOSE:To improve output voltage characteristics and make it possible to operate at frequency by providing a transistor, which shorts the gate and the source of a field effect transistor when a base current is given, and controlling the base current of the transistor according to the output voltage of load, and controlling the conduction time of the field effect transistor. CONSTITUTION:In the condition that a transistor Tr1 is off, an FET2 is in ON condition, and the voltage V1 of the secondary winding of a transformer T1 is given approximately intact to a rectifying circuit through the FET2. When the transistor Tr1 is turned on, the FET2 is turned off losing the bias voltage between the source and the gate, and the input voltage of the rectifying circuit is interrupted. And by controlling the on time of the transistor Tr1 in a control circuit 2, the conduction time of the FET2 is controlled, and the output voltage E0 in load R1 is stabilized. What is more, B, which shows the voltage generated in the load R1 during control, is approximately equal to C, which represents the output voltage when it does not have the FET2, and the power loss becomes approximately zero.

Description

[Detailed Description of the Invention] [Summary] To provide a secondary side control circuit for a DC/DC converter, which has good output voltage characteristics and is capable of increasing the frequency. When the switching field effect transistor connected in series with the primary winding of the transformer is turned on, the voltage generated in the secondary winding is rectified through a rectifier diode and a choke coil, and when it is turned off, it is stored in the choke coil. In a DC/DC converter, the source and drain are connected between one end of the secondary winding and the rectifier diode, and the gate is connected through a resistor. A field effect transistor to which a bias voltage is applied, a transistor provided to short-circuit the gate and source of this field effect transistor when a base current is applied, and a base current of the transistor that changes depending on the output voltage of the load. The present invention is constructed by providing a control circuit that controls and changes the current flow time of the switching field effect transistor to stabilize the output voltage.

[Industrial application field]

The present invention relates to a secondary side control circuit of a DC/DC converter, and in particular, a DC/DC converter that improves output voltage characteristics and enables higher frequencies by using FET as a control element.
/DC converter secondary side control circuit.

In the secondary side control circuit of the DC/DC converter, the output voltage is stabilized by controlling the flow time of the output current using a current control element.

Thus, in the secondary side control circuit of the C/DC converter, it is desired to improve the output voltage characteristics and increase the operating frequency.

[Conventional technology]

FIG. 10 shows a secondary side control circuit of a conventional DC/DC converter, and exemplifies a circuit using a saturable reactor as a current control element.

In FIG. 10, T1 represents a transformer, and N1 and N2 are a primary winding and a secondary winding, respectively.

For example, L is a saturable reactor using an amorphous core, L is a choke coil, FET is a switching field effect transistor, D,,D! .

D is a diode, CI is a capacitor, RL is a load resistance, and E is a power supply. Further, 1 is a drive circuit for the FET, and 2 is a control circuit.

The circuit shown in Figure 10 is a forward type DC/DC
A converter circuit is formed, and when the FET is turned on, current flows from the human power supply voltage E to the primary winding N1 of the transformer TI. This causes the secondary winding N! Voltage generated at ■1
Accordingly, saturable reactor Ls, rectifier diode D
Power is supplied to load R4 via I and choke coil L.

When the FET is off, power is supplied to the load RL via the commutation diode D2 by the energy stored in the choke coil L. Capacitor CI is load R4
to produce an output voltage Eo, which produces an output current of 1°. At this time, the drive circuit 1 controls ON/OFF of the FET at a constant cycle.

A saturable reactor has a large impedance when the secondary current starts to flow, thus blocking the output current, but saturates after a certain time and generates the output current. The control circuit 2 converts the saturable reactor Ls through the diode D3 and applies DC excitation to the saturable reactor Ls.
The current flow time is controlled by changing the voltage/time product at, thereby stabilizing the output voltage Eo at the load RL.

FIG. 11 shows the operating waveforms of the circuit shown in FIG. 10, in which the input voltage (■) obtained by subtracting the voltage drop (■2) in the saturable reactor L3 from the voltage VI generated in the secondary winding N2 is shown in FIG. , the rectifier circuit operates to generate an output voltage. Based on the control of the control circuit 2, the voltage of the saturable reactor 2 is as shown by the dotted line in FIG.
The trailing edge changes. On the other hand, the leading edge of the input voltage (3) of the rectifier circuit changes based on this.

[Problem to be solved by the invention] In the secondary side control circuit of a conventional DC/DC converter, the current flow time is controlled by a saturable reactor, but the voltage/time product in the saturable reactor is not controlled. It does not become zero even at maximum excitation. In FIG. 11, ■2' indicates the voltage of the saturable reactor when it is not controlled, and ■ and ° indicate the rectifier circuit input voltage at this time.

FIG. 12 shows the output voltage characteristics of the circuit of FIG. 10, where the output current at the load is . The relationship between the output voltage E0 and the output voltage E0 is shown, where A indicates the controlled state and B indicates the non-controlled state. Further, C is the output voltage E when there is no saturable reactor. This is what is shown.

In this way, in the secondary side control circuit of a conventional DC/DC converter, a voltage drop always occurs even when the saturable reactor is not controlled, which causes power loss and reduces efficiency. The problem was that it was unavoidable.

Furthermore, in the secondary side control circuit of the conventional DC/DC converter, there was a problem in that it was difficult to increase the frequency due to the saturable reactor.

The present invention is an attempt to solve the problems of the prior art, and by using an FET instead of a saturable reactor as a current control element, the output voltage characteristics are good and high frequency can be achieved. The purpose is to provide a secondary side control circuit for a DC converter.

[Means to solve the problem]

The basic structure of the present invention is shown in FIG.

The DC/DC converter that is the object of the present invention has a switching field effect transistor FET provided in series with the primary winding N of the transformer T, when the switching field effect transistor FET is turned on, the secondary winding N2 of the transformer T The generated voltage is rectified by diode D.
1 and a choke coil L, and when the field effect transistor FET1 is off, the energy stored in the choke coil L is used to rectify the DC power via a commutating diode D2 to supply DC power to the load RL. be.

The present invention is directed to such a C/DC converter, whose source and drain are connected between one end of the secondary winding N2 of the transformer T and the rectifier diode DI, and whose gate is biased through a resistor R8. A field effect transistor FET2 to which a voltage is applied, a transistor Tr provided to short-circuit between the gate and source of the field effect transistor FETz when a base current is applied, and a load RL.
By controlling the base current of the transistor Tr in accordance with the output voltage E0 of the switching field effect transistor FET, the current flow time of the switching field effect transistor FET is controlled to increase the output voltage E0.
A control circuit 2 is provided to stabilize the current.

Further, in the present invention, in the C/DC converter as described above, the control circuit 2 controls the trailing edge of the output current of the switching field effect transistor FET+.

Furthermore, in these DC/DC converters, the present invention provides a tertiary winding N in the transformer T1, generates a voltage E proportional to the input power supply voltage E4 by the output voltage of the tertiary winding N3, and performs switching. By supplying it to the drive circuit 1 that controls the on/off of the switching field effect transistor FET, the drive circuit 1 changes the input power supply voltage E to the ON time of the switching field effect transistor FET
, which is controlled in inverse proportion to .

[Effect]

When the switching field effect transistor connected in series with the primary winding of the transformer is turned on, the voltage generated in the secondary winding of the transformer is rectified through the rectifier diode and the choke coil, and when the field effect transistor is turned off, the voltage generated in the secondary winding of the transformer is rectified by the choke coil. For a Ford type DC/DC converter configured to supply DC power to a load by rectifying the energy stored in the DC via a commutating diode,
A field effect transistor is provided, the source and drain of which are connected between one end of the secondary winding of the transformer and the rectifier diode, and whose gate is supplied with a bias voltage through a resistor.
By controlling the base current of the transistor according to the output voltage of the load, the current of the switching field effect transistor is Since the output voltage is stabilized by controlling the flow time, the current control element FE
The voltage drop when T is not controlled can be reduced to almost zero, and the output voltage characteristics can therefore be improved. Furthermore, the operating frequency of the DC/DC converter circuit can be increased, and the device can be made smaller.

In this case, the control circuit may control the trailing edge of the output current of the switching field exchange transistor, which facilitates control.

In addition, by generating a voltage proportional to the input power supply voltage using the output voltage of the tertiary winding of the transformer and applying it to the drive circuit, the drive circuit controls the on-time of the switching field effect transistor in inverse proportion to the input power supply voltage. By doing so, it is possible to keep the voltage-time product on the secondary side constant and prevent excessive power from being fed into the secondary side output circuit of the transformer, thus reducing losses in the switching field effect transistor. can be reduced.

〔Example〕

FIG. 2 shows a first embodiment of the present invention,
The same parts as in FIG. 10 are indicated by the same symbols.

FET is a P-channel field effect transistor for secondary side control, and Tr is a FET.

Transistor R+ for controlling on/off.

R7 is a resistor, C2 is a capacitor, D4. Ds is a backflow prevention diode.

In the circuit shown in FIG. 2, the control circuit 2 receives the secondary voltage of the transformer TI as a synchronizing signal, so that the FE
A control signal synchronized with the on/off of the transistor Tr+ is generated to control the on/off of the transistor Tr+.

When the transistor Tr is off, the FET,
is in an on state by being applied with a gate voltage via the resistor R3, and therefore the voltage V of the secondary winding of the transformer T1 is applied as is to the rectifier circuit via the FET.

When the transistor Tr is turned on, the FET.

loses the source-gate bias voltage and turns off, cutting off the input voltage to the rectifier circuit.

When the FET is turned on, the voltage V generated in the secondary winding N2
l, rectifier diode D+, choke coil L
1, power is supplied to the load Rt, and F E T
When L is off, the energy stored in the choke coil L1 passes through the commutating diode D2 to the load R.
Power is supplied to t.

Capacitor CI smoothes the supply voltage of load RL to output voltage E0. Output current■. occurs.

Note that the series circuit of capacitor C8 and resistor R2, which is connected in parallel to resistor R1, is an FET.

This circuit forms a speed-up circuit for the switching operation of the FET 2, and functions to speed up the operation by eliminating the delay in the change in bias voltage in the FET 2.

FIG. 3 shows the operating waveforms of the circuit in FIG. The circuit operates and generates an output voltage. FET, voltage v2
Under the control of the control circuit 2, the leading edge changes as shown by the dotted line in FIG. On the other hand, the trailing edge of the input voltage V3 of the rectifier circuit changes based on this.

Therefore, in the control circuit 2, the transistor Tr.

By controlling the on-time of FET, the output voltage E at load RL is controlled by controlling the current flow time in FET.
0 can be stabilized.

In this case, when the transistor Tr is not controlled (off), the voltage drop V tl of the FET is almost zero, and the input voltage v,° of the rectifier circuit is approximately equal to 1.

Note that the current flow time in the FET can be controlled not only at the trailing edge of the output current but also at the leading edge, but from the standpoint of operational stability, control at the trailing edge is superior. .

FIG. 4 shows the output voltage characteristics of the circuit of FIG. 2, and shows the output current I0 and output voltage E at the load RL. , A indicates the time of control, and B indicates the time of no control. Further, C indicates the output voltage E0 when no FET is included. As shown in FIG. 4, the voltage E0 generated in the uncontrolled load according to the present invention is approximately equal to the output voltage when no FET is provided, and therefore, the power loss is approximately zero, and the 10th Efficiency can be improved over the conventional case shown in the figure.

FIG. 5 shows a second embodiment of the present invention and shows the case of multiple outputs, in which an output circuit similar to that shown in FIG. This example shows a case where two sets of second output circuits having a similar configuration are provided in parallel, and each component is shown with a "°". In addition,
The number of output circuits may be any number.

In the circuit of FIG. 5, the tertiary winding N3 in the transformer T
The voltage generated by the tertiary winding N3 is rectified by a circuit consisting of a diode Db and a capacitor C3.
Circuit 1 that drives voltage E3 proportional to human power supply voltage E
, the on-time of the switching field effect transistor FET is controlled in inverse proportion to the human power supply voltage E.

In this case, by applying a drive signal inversely proportional to the input power supply voltage E to the switching field effect transistor FET, the voltage-time product on the secondary side is kept constant and excess power is removed from the transformer T.

The loss of the switching field effect transistor FET is reduced because it is prevented from being sent to each secondary output circuit.

FIG. 6 shows a third embodiment of the present invention, and shows the case of two outputs, and FIG. An output circuit similar to that shown in Figure 1 and a load RL from the quaternary winding N4.
A rectifier diode D1.I supplies power to I. Commutation diode D8, choke coil Lz, smoothing capacitor C4
A case is shown in which an output circuit consisting of the following is provided.

In the circuit of FIG. 6, the second control circuit 3 controls the switching field effect transistor FET according to the output voltage Eo2 of the second output circuit, and changes the on-time of the switching field effect transistor FET. , the output voltage E for a change in the power supply voltage E. 2, and also stabilizes the output voltage EOI by the control circuit 2.
In the case of output, the circuit configuration is simplified.

In the embodiments shown in FIGS. 2, 5, and 6, a P-channel FET is used for secondary side control, but an N-channel FET may also be used. FIGS. 7 to 9 show this case.

FIG. 7 shows a fourth embodiment of the present invention,
The same parts as in FIG. 2 are indicated by the same numbers, and N5 is the tertiary winding of the transformer T and FET.

is an N-channel field effect transistor for secondary side control, R3 is a resistor, D is a rectifier diode, and Dl. , D.I.
+ is a backflow prevention diode.

In the circuit shown in FIG. 7, the control circuit 2 receives the secondary voltage of the transformer T1 as a synchronizing signal, so that the FE
A control signal synchronized with the on/off of the transistor T is generated to control the on/off of the transistor Trz.

When transistor Trz is off, FET3
is the tertiary winding N, and the diode D1. It is in the on state by applying a gate voltage through the resistor R,
Therefore, the voltage V of the secondary winding of the transformer TI is applied as is to the rectifier circuit via the FET, thereby generating an output current.

When the transistor Tr is on, the FET,
loses its gate voltage and turns off, cutting off the output current. Other operations are the same as in the embodiment shown in FIG.

FIG. 8 shows a fifth embodiment of the present invention, and shows a case of multiple outputs, in which an output circuit similar to that shown in FIG. 7 is used for the transformer T. A case is illustrated in which two sets of second output circuits having a similar configuration are provided in parallel with each corresponding component indicated by "". Note that the number of output circuits may be both sets.

In the circuit of Fig. 8, the tertiary winding N3 is connected to the transformer T1.
, and the voltage generated in the tertiary winding N3 is connected to the diode D6.
By supplying the drive circuit 1 with a voltage E3 proportional to the input power supply voltage E, which is generated by rectification by a circuit consisting of a capacitor C3, the on-time of the switching field effect transistor FET can be changed as in the circuit shown in FIG. is controlled in inverse proportion to the input power supply voltage E1 to keep the voltage-time product on the secondary side constant and prevent excessive power from being sent to each secondary output circuit of the transformer T. Therefore, the switching field effect transistor FET,
losses are reduced.

FIG. 9 shows a sixth embodiment of the present invention, and shows a two-output case, and FIG. 7 supplies power from the secondary winding N2 to the load RLI for the transformer T1. An output circuit similar to that shown in Figure 1 and a load RL from the quaternary winding N4.
2, the rectifier diode D? , commutation diode D8, choke coil Lz, smoothing capacitor C
A case is shown in which an output circuit consisting of four output circuits is provided.

In the circuit of FIG. 9, the output voltage E of the second output circuit is controlled by the second control circuit 3. By controlling the switching field effect transistor FET according to the control circuit 2, the output voltage Eoz is stabilized against changes in the power supply voltage, and the output voltage E is controlled by the control circuit 2. This stabilizes I, and in the case of two outputs, the circuit configuration is simplified.

[Effects of the Invention] As explained above, in the secondary side control circuit of the DC/DC converter of the present invention, a field effect transistor that can reduce the voltage drop to almost zero during no control is used as a current control element. Therefore, the output voltage characteristics can be improved. In addition, field effect transistors have superior high frequency switching characteristics compared to conventional saturable reactors using amorphous cores, so
The operating frequency of the converter circuit can be increased, and the device can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of the present invention, FIG. 2 is a diagram showing a first embodiment of the present invention, FIG. 3 is a diagram showing operating waveforms of the circuit in FIG. 2, and FIG. is a diagram showing the output voltage characteristics of the circuit of FIG. 2, FIGS. 5 to 9 are diagrams showing the second to sixth embodiments of the present invention, respectively, and FIG. 10 is a diagram showing the conventional DC/DC converter. A diagram showing the secondary side control circuit of
Figure 11 is a diagram showing the operating waveforms of the circuit in Figure 10;
The figure is a diagram showing the output voltage characteristics of the circuit of FIG. 10. 1 is a drive circuit, 2 is a control circuit, T is a transformer, N
1 is the primary winding, N2 is the secondary winding, N3 is the tertiary winding, N4
is a quaternary winding, Ns is a tertiary winding, FET, ~FET, is a field effect transistor, D. is a rectifier diode, D2 is a commutation diode, and L. are choke coils, R1, RZ, R:l is a resistance, RL is a load, E is an input voltage, and Eo is an output voltage.

Claims (3)

[Claims] (1) A switching field effect transistor (FE) installed in series with the primary winding (N_1) of the transformer (T_1)
When T_1) is on, the secondary winding (
The voltage generated in the choke coil (L_1) is rectified through the rectifier diode (D_1) and the choke coil (L_1), and when the field effect transistor (FET_1) is off, the energy stored in the choke coil (L_1) causes the voltage generated in the commutator diode (L_1) to be rectified. In a DC/DC converter that rectifies and supplies DC power to a load (R_L) through a rectifier (D_2), a source and A field effect transistor (FET_2) whose drain is connected and a bias voltage is applied to its gate through a resistor (R_1), and when a base current is applied, the field effect transistor (FET_2)
A transistor (Tr) provided to short-circuit between the gate and source of FET_2), and a transistor (Tr) provided to short-circuit between the gate and source of the FET_2), and a
A control circuit (2) that controls the current flow time of the field effect transistor (FET_2) and stabilizes the output voltage (E_O) by controlling the base current of the DC/DC. Converter secondary side control circuit. (2) The secondary side control circuit of the DC/DC converter according to claim 1, wherein the control circuit (2) controls the trailing edge of the output current of the field effect transistor (FET_2). (3) A tertiary winding (N_3) is provided in the transformer (T_1), and a voltage (E_3) proportional to the input power supply voltage (E_i) is generated by the output voltage of the tertiary winding (N_3) for the switching purpose. Field effect transistor (FET_
1), so that the drive circuit (1) controls the on-time of the switching field effect transistor (FET_1) in inverse proportion to the input power supply voltage (E_i). D according to claim 1 or 2, characterized in that
Secondary side control circuit of C/DC converter.