JP2665936B2 - One-stone converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a single converter for use in a DC power supply circuit of a video device, an audio device, and the like.

[Prior Art] As shown in FIG. 4, a series circuit of a primary winding Np of a transformer T1 and a switching transistor Q1 is connected to a DC power supply P, and a diode D5 and a capacitor C6 are connected to a secondary winding Ns of the transformer T1. And a transformer T1 is provided with a base winding Nb for driving the base.
Nb is connected to the base of transistor Q1 via resistor R5,
Further, a switching regulator that connects a control circuit B to the base of the transistor Q1 and obtains a constant voltage at the output terminal U is known. Note that AC is a commercial AC power supply, and is connected to a DC power supply P including a rectifier circuit. R1 is a starting resistor, which is connected between the DC power supply P and the base of the transistor Q1. The control circuit B is a switching transistor
A control transistor Q2 connected between the base and emitter of Q1 to bypass the base current, and a diode D, a capacitor, and a Zener diode DZ for controlling the transistor Q2
The capacitor C is charged with the voltage of the base winding Nb (equivalent to the output voltage) when the transistor Q1 is off, and the transistor Q2 is controlled based on a comparison between this voltage and the reference voltage of the Zener diode DZ. Is configured.

In the above-described switching regulator, when the supply of the DC power is started, a starting current flows through the starting resistor R1, and transmission starts. When the transistor Q1 is on, 1
A voltage is applied to the power supply P to the next winding Np, and a corresponding voltage is generated to the base winding Nb.
The base current IB is supplied to Q1. Thereafter, when the collector current of the transistor Q1 is saturated, the transistor Q1 is turned off. During this off period, the diode D5 is turned on, and the energy of the transformer T1 is released to the output side. The output voltage is controlled by making a part of the current I1 of the base winding Nb bypass the transistor Q2. By the way, the power supply P
Increases, the voltage of the primary winding Np and the voltage and current of the base winding Nb also increase. Since FIG. 4 has the control circuit B, the entire current I1 of the base film line Nb is not supplied to the transistor Q1, but is bypassed to the control transistor Q2. Since the bypass current I2 is irrelevant to the driving of the transistor Q1, it results in power loss. The problem is that the AC power supply voltage connecting the equipment is 100V to 220V, for example.
And the control transistor increases the bypass current I2, and consequently requires a large-capacity transistor. Also, in this circuit, the droop current increases at the time of overcurrent, and the above input voltage range cannot be compensated.

[Problems to be Solved by the Invention] The present invention makes the base current of the main transistor substantially constant, reduces the bypass current to improve the efficiency, reduces the capacity of the control transistor, and reduces the overcurrent. To prevent overdrive.

Means for Solving the Problems In order to achieve the above object, the present invention will be described with reference to the drawings (FIG. 1) showing an embodiment. A primary winding Np, a secondary winding Ns, and a base winding A collector is connected to the output transformer T1 having the line Nb and the primary winding N1, and a switching main transistor Q1 having a base and an emitter connected between the base windings, and a rectifier connected to the secondary winding side. diode
In the single converter having D5 and a control circuit B connected to the base of the main transistor Q1, the control circuit B is connected between the connection point of the first and second base windings Nb and Nb2 and the base of the main transistor Q1. A resistor R5 connected to
The control transistor Q2 connected between the base and the emitter of the seed transistor Q1, the cathode is connected in common, and the anode is connected to one end of the first base winding Nb1 and the second
Diodes D3 and D4 connected to the other end of the base winding Nb2
A rectifying / smoothing circuit including a choke coil L1 and a capacitor C5 connected between a common connection point (cathode) of the diodes and the other end of the second base winding Nb2; A transistor Q3 connected between a connection point and the base of the main transistor Q1 via a resistor R3, and a resistor connected between the base of the transistor Q3 and one end of the first base winding Nb1 ( R4).

[Operation] First, in the control circuit B, the operation of the base winding Nb1, the rectifier diodes D3 and D4, the smoothing choke coil L1 and the capacitor C5, and the transistor Q3 will be ignored.

The basic operation of this circuit is to output the energy stored in the transformer T1 when the main transistor Q1 is on through the rectifier diode D5 when off. Note that the OFF operation of the main transistor Q1 is performed when the point potential (a) exceeds the voltage (VBE) of the control transistor Q2 in the time constant circuit of the photocoupler light receiving portion PT, the Zener diode DZ1, and the current capacitor C4 flowing through the resistor R6. Q2 turns on, thereby bypassing the base current of main transistor Q1 and turning it off. Incidentally, if the loss of each part of the converter is neglected, the relationship between the output voltage E0 and the ON time TON of Q1 can be approximated by the expression (1).

Here, E1 is an input voltage, I0 is an output current, and K1K2 is a constant. By controlling the TON by detecting the output voltage and varying the current of the photocoupler, the output voltage E0 can be kept constant by equation (1). When the output voltage is controlled to be constant as described above, the on-time (TON) of the main transistor Q1 increases due to an increase in the load current or a decrease in the input voltage (E1). Decrease. Therefore, when the input voltage (E1) is the lowest and the load current is the maximum, the on-time becomes the maximum. Now, if the current of the photocoupler light receiving section PT via the voltage detecting section A is set to be zero, the charging time constant of the capacitor C4 becomes maximum for an output current larger than this. FIG. 2 shows the output voltage-current characteristic of this circuit, and the ON time (TON) of the main transistor Q1.
Increases in proportion to the load current, but does not increase beyond the maximum load current, so that a so-called F-shaped droop characteristic is obtained.

However, this characteristic is particularly effective when the change width of the input voltage E1 is small. However, when the input voltage is 100 V or 200 V, the input voltage range is sufficiently increased by increasing the current dotted line (c) sharing the same. Can not compensate for. The reason for this is that the collector current of the control transistor Q2 is a pulsating current, so when the input voltage changes significantly (for example, when 100V input changes to 200V input), the base current of the main transistor Q1 cannot be controlled, and as a result This is considered to be due to the fact that the base current is not constant.

Next, the operation of the base winding Nb1 and the like will be described. Therefore, the present invention provides two base windings (Nb
1, Nb2) to provide a base current supply through both base windings Nb1 and Nb2, and one base winding Nb
The base current IB1 from 1 is set to flow more than the base current IB2 from the other winding Nb1. (Eg I
B2 ≒ 0.1IB1), and the voltage of one base winding Nb1 charges the capacitor C5 through the diodes D3 and D and the smoothing choke coil L1, so that the voltage of the capacitor C5 has a substantially constant value even if the input voltage changes. maintain. Therefore, the base current IB1 is supplied to the transistor Q3 by using the capacitor C5 as a power supply.
A substantially constant base current IB1 to the main transistor Q1 through
Supply. On the other hand, in the base winding Nb2, a resistor R5 having a large resistance value is inserted in the base circuit in order to limit the base current compared to the above IB1, so that the voltage of the base winding Nb2 changes due to a change in the input voltage. Also, the current location (IB2) can be regarded as substantially constant.

(Note that the windings of the base windings Nb1 and Nb2 are the same.) Therefore, the base current (IB1 + IB2) of the main transistor Q1 can be made substantially constant irrespective of the change in the input voltage.
In addition, since the bypass current of the control transistor Q2 hardly changes, the capacity of the control transistor Q2 can be reduced. In FIG. 2, the characteristic curve (a) shows that the input voltage is 20
At the time of 0V system, (b) shows the drooping characteristic at the time of 100V system,
This shows that the droop point currents are almost the same. In the above embodiment, an example was described in which the output voltage of the base windings Nb1 and Nb2 was half-wave rectified to charge the capacitor C5. However, as shown in FIG. 3, the base windings Nb1 and Nb2 were set to a center tap method. The same can be achieved by performing full-wave rectification and setting the voltage of the capacitor C5 to the average voltage.

As is clear from the above description, according to the present invention, it is possible to provide an output voltage function to the RCC circuit by simplifying the configuration and to provide an all-input converter having a droop current function that compensates for the input voltage range. The effect is great.

[Brief description of the drawings]

1 and 2 are circuit diagrams of an embodiment of the present invention and explanatory diagrams of characteristics thereof, FIG. 3 is a circuit diagram of another embodiment of the present invention, and FIG. 4 is a conventional circuit diagram. In the figure, T is an output transformer, Np,
Ns, Nb are the primary, secondary and base windings, Q1 is a main switching transistor, A is an output voltage detector, B is a control circuit, Q2 and Q3 are control transistors, and R1 to R9 are resistors C1.
~ C6 is a capacitor, DZ1 is a Zener diode, PD, PT
Denotes a photocoupler light emitting unit and a light receiving unit.

Claims (3)

(57) [Claims] An output transformer having a primary winding, a secondary winding, and a base winding, and a collector connected to the primary winding;
In a single converter having a base, a switching main transistor connected between the base windings, a rectifying diode connected to the secondary winding side, and a control circuit connected to the base of the main transistor, The control circuit includes a resistor (first) connected between a connection point of first and second base windings and a base of the main transistor, and a control transistor connected between a base and an emitter of the main transistor. And a cathode connected in common and an anode connected to one end of the first base winding and a second
A diode connected to the other end of the base winding, a rectifying / smoothing circuit including a choke coil and a capacitor connected between a common connection point (cathode) of the diode and the other end of the second base winding; A transistor connected via a resistor (second) between a connection point of the choke coil and the capacitor and the base of the main transistor; a transistor connected between the base of the transistor and one end of the first base winding; And a resistor (third). 2. A resistor and a constant voltage diode connected between a connection point of the first and second base windings and a base of a control transistor, and connected between a base and an emitter of the control transistor. A time constant circuit comprising a capacitor (second) is provided.
Item one-stone converter. 3. An adjusting circuit for adjusting a time constant of a time constant circuit according to an output voltage between one end of a smoothing capacitor and a base of a control transistor. One-stone converter as described.