JPS60204258A - Switching power source - Google Patents

Abstract

PURPOSE:To reduce the loss of a switching power transistor by forcibly applying the base current of the power transistor to the secondary side of a pulse transformer in response to the ON/OFF of a control transistor. CONSTITUTION:When an input voltage Vin is applied, a transistor Q1 is turned ON, a voltage V1 proportional to the voltage Vin is applied by a control winding Nc of a transformer T1 to both terminals of an integrator having a resistor R3 and a capacitor C3 in a sawtooth wave generator SWG. The charging voltage V2 of the capacitor C3 is applied to the non-inverting input terminal of a comparator COMP, and an output voltage V3 from an inverting amplifier IAMP is applied to the inverting input terminal of the comparator COMP. When the comparator COMP detects the fact that the voltage V2 exceeds the voltage V3, it turns ON a transistor Q4 to forcibly the base current of the transistor Q1 through a rectifier CR5 to the secondary winding N22 of a pulse transformer T2, thereby abruptly turning OFF the transistor Q1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a ringing choke converter type switching power supply device, and more particularly to a control circuit that performs off control of a switching power transistor.

[Technical background of the invention and its problems] In general, a ringing choke converter type switching power supply device generates a sawtooth wave-like current at the output by self-sustaining oscillation by repeatedly turning on and off the switching power transistor, and DC power is supplied continuously to the load. Conventionally, this type of power supply device is generally provided with an output control circuit in order to stabilize the output voltage. FIG. 1 shows a conventional switching power supply device having such an output control circuit. In FIG. 1, CNT is an output control circuit that monitors the output voltage vout. This output control circuit CNT applies a voltage corresponding to the output voltage Vout to a parallel circuit of a resistor R and a capacitor C. This parallel circuit is inserted between the emitter of the switching power transistor Q1 and the base of the control transistor Q2 for turning off the transistor Q1. The collector of transistor Q2 is connected to the base of transistor Q1. However, due to the output control circuit CNT,
A voltage corresponding to the output voltage vout is applied to the resistor R and capacitor C.
When the base voltage of the transistor Q2 becomes sufficiently high, the transistor Q2 turns on. As a result, the base current of transistor Q1 is drawn to transistor Q2, turning off transistor Q1. The off timing of the transistor Q1 is determined by the applied voltage from the output control circuit CNT, that is, the output voltage VO
It varies depending on the ut. By controlling the on/off time of the transistor Q1 according to the output voltage Vout in this manner, the output voltage vout can be stabilized.

However, in such conventional switching power supplies,
As described below, the switching power transistor Q
There was a problem that 1 could not be turned off efficiently. That is, in the power supply device of FIG. 1, when the control transistor Q2 is turned on, the base current of the transistor Q1 is drawn, and the transistor Q
1 approaches the off state, the emitter current of the transistor Q1 decreases. As a result, the base potential of transistor Q2 decreases, and transistor Q2, which was in the on state,
approaches the off state. When transistor Q2 approaches the off state, the base current of transistor Q1 is no longer drawn sufficiently, and therefore it becomes difficult to forcefully turn off transistor Q1.

Therefore, the conventional switching power supply device has the following two drawbacks.

■The collector loss of the switching power transistor is large.

■When the input voltage is high, the base current of the switching power transistor also increases, which increases the maximum transmitted power of the output. Conversely, when the input voltage is low, the maximum transmitted power decreases, making overload protection difficult.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to provide a switching power supply device in which the loss of switching power transistors can be reduced and the output maximum transmitted power can be kept constant regardless of the input voltage. It's about doing.

[Summary of the Invention] According to the present invention, a ringing choke converter type switching power supply device including a switching power transistor is provided.

This power source 1 is provided with a sawtooth wave generation circuit that has a resistor and a capacitor and generates a sawtooth wave voltage based on a voltage proportional to the input voltage. The sawtooth wave voltage generated by the sawtooth wave generation circuit is compared with the output voltage by a comparator, and the control m+- transistor is turned on/off according to the comparison result of the comparator. This system t [
The states of the transistors are transmitted to the switching power transistors by the pulse transformers. Thereby, the base current of the switching power transistor is forcibly drawn to the secondary side of the pulse transformer in accordance with the on/off state of the control transistor.

[Embodiments of the invention] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

Note that the same parts as in FIG. 1 are given the same reference numerals.

In the switching power supply device shown in FIG. 2, T1 is a flyback transformer, and Ql is a switching power transistor. The collector of transistor Q1 is transformer T
It is connected to one end of the primary winding N11 of No. 1. A series circuit including a resistor R1 and a resistor R2 is inserted between the other end (first input end) of the primary winding N11 and the base of the transistor Q1. Resistor R1 is connected to transistor Q at startup.
The ignition resistor R2 for turning on transistor 1 is a base current limiting resistor for transistors 1 to Q1. Resistance R1
One end of a parallel circuit consisting of a rectifier CRI and a capacitor C1 is connected to a common connection point between and a resistor R2, and one end of a base winding NB of a transformer T1 is connected to the other end of this parallel circuit. Capacitor C1 is used to turn on transistor Q1 in the next cycle. Base winding N
The other end (second input end) of a is connected to the emitter of transistor Q1.

One end of the secondary winding N12 of the transformer T1 is connected to the anode of the output rectifier OR2. The cathode (first output end) of the rectifier OR2 and the other end (second output end) of the secondary winding N12
An output smoothing capacitor C2 is inserted between the output # and the output #). One end of the control sound taNc, which is one of the secondary windings of the transformer (1), is connected to the anode of the rectifier CR3.

An integrating circuit consisting of a resistor R3 and a capacitor C3 is inserted between the cathode of the rectifier CR3 and the other end of the control winding Nc. One end of capacitor C3 (the common connection point between capacitor C3 and resistor R3) is connected to the collector of transistor Q3, and the other end of capacitor C3 is connected to transistor Q.
It is connected to the emitter of 3. This transistor Q3
is used to discharge the charging voltage of capacitor C3.

Transistor Q3, resistor R3 and capacitor C3 are
It constitutes a sawtooth wave generation circuit SWG.

The base of the transistor Q3 is connected to the cathode of a rectifier CR4 via a resistor R4, and the anode of the rectifier CR2 is connected to the anode of the rectifier CR4. The cathode (first output terminal) of the rectifier OR2 is the inverting amplifier IAMP.
The output terminal of the inverting amplifier IAMP is connected to the inverting input terminal of the comparator COMP. The collector of the transistor Q3 is connected to the non-inverting input terminal of the comparator GOMP. The output terminal of the comparator GOMP is
It is connected to the base of a transistor (control transistor) Q4 for turning off the transistor Q1. The emitter of transistor Q4 is connected to the emitter of transistor Q3, and the collector of transistor Q4 is connected to one end of primary winding N21 of pulse transformer T2. Power supply +V is supplied to the other end of this primary winding N21. Secondary of pulse transformer T2'! 41 N 22 one end is connected to the emitter of transistor Q1, 2
The other end of N22 is connected to the transistor Q via the rectifier CR5.
It is connected to the base of 1.

Next, the operation of the configuration shown in FIG. 2 will be explained with reference to the signal waveform diagram shown in FIG. When an unstable DC power supply, that is, an input voltage Vin is applied to the switching power supply shown in FIG. 2, the switching power transistor Q1 is turned on by the resistor R1. When transistor Q1 turns on, transformer T1
A voltage approximately equal to the input voltage ■in is applied across the primary winding Nil of the transformer T1, and therefore the base 'Mf of the transformer T1
A voltage proportional to the input voltage Vin is induced in aNs. Then, due to this induced voltage, the rectifier CR1 and the resistor R2
The base current IB flows through the transistor Q1 through the transistor Q1, and the transistor Q1 becomes in a stable on state.

On the other hand, the control winding Nc of the transformer T1 applies a voltage V! proportional to the input voltage ■in across both ends of the integrating circuit of the resistor R3 and capacitor C3 in the sawtooth wave generating circuit SWG, as shown in FIG. is added. As a result, this voltage
1 charges capacitor C3 through resistor R3. The charging voltage (voltage across both ends) V2 of the capacitor C3 is applied to the non-inverting input terminal of the comparator GOMP. This comparator C
The output voltage 3 from the inverting amplifier IAMP is applied to the inverting input terminal of OMP. This voltage (3) is the result of inversion amplification by the inverting amplifier IAMP with respect to the voltage across the output capacitor C2 (ie, the output voltage Vout of the switching power supply). Comparator GOMP compares these two voltages V2 and V3 and outputs voltage V2 as shown in FIG.
When it is detected that (the charging voltage of C3) exceeds the voltage (3), the 1-transistor Q4 is turned on.

When transistor Q4 turns on, the primary winding 1 of pulse transformer T2! A current flows through N21. As a result, a current Is flows through the secondary winding N22 of the pulse I lance T2 as shown in FIG. That is, the base current In of the transistor Q1 is forcibly drawn to the secondary winding N22 of the pulse transformer T2 through the rectifier CR5. As a result, 1-transistor Q1 turns off rapidly and its collector 1R8! becomes approximately zero. In this way, in this example, the base current of the transistor Q1 is forcibly drawn by the pulse transformer T2, so that the loss of the transistor Q1 can be significantly reduced compared to the conventional switching power supply device.

When transistor Q1 turns off, the energy stored in primary winding N11 of transformer T1 is transferred to secondary winding N12 and released. As a result, the second volume 1! The voltage V4 across N12 changes to a positive voltage as shown in FIG. As a result, current flows through the rectifier CR2 and is smoothed by the capacitor C2, thereby obtaining the output voltage VOut. Moreover, when the voltage 4 becomes a positive voltage, the rectifier CR4,
A base current is supplied to the transistor Q3 through the resistor R4, and the transistor Q3 is turned on. As a result, as shown in FIG. 3, the charging voltage V2 of the capacitor C3 is instantaneously discharged. Eventually, the primary winding 1i1N11 of transformer T1
When the release of the energy stored in is completed, the l-transistor Q1 is turned on again, and the above-described operation is repeated. Then, as the above operation is repeated, capacitor C3
Due to repeated charging and discharging, the voltage (2) becomes sawtooth wave-like.

Capacitor C3 that determines the on-state of transistor Q1
The charging time depends on the time constants of R3 and C3, 1 and V3. If Vl is constant, the maximum charging time of C3, that is, the maximum on-time of transistor Q1 (
01 ON maximum pulse width) is determined by the above-mentioned time constant, Vr, and V3max (inverted amplified output of the maximum value of the output voltage vout), and remains constant. In this case, the input voltage Vi
A problem arises in that the output transmitted power changes depending on the fluctuation of n. However, in this embodiment, as is clear from the above description of the operation, the voltage Vl, that is, the voltage supplied to the integrating circuit consisting of R3 and C3 is proportional to the input voltage Vin and is not constant. Therefore, if the input voltage Vin
When V2 becomes higher, voltage v1 becomes higher, and the charging time until V2 (charging voltage of capacitor C3) reaches V3 max becomes shorter. That is, the maximum pulse width of Q1 ON becomes smaller. As a result, the output maximum transmitted power becomes equal to the input voltage v
i1) is maintained constant regardless of fluctuations in i1).

[Effects of the Invention] As described in detail above, according to the present invention, the loss of the switching power transistor can be reduced, and the output maximum transmitted power can be made constant regardless of the input voltage. Also,
In this invention, unlike the conventional method in which a voltage proportional to the output voltage is transmitted to the primary side for control, the control is performed on the secondary side and the power transistor is turned off via a pulse transformer. It is possible to improve response characteristics due to output fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional switching power supply device, FIG. 2 is a circuit diagram of a switching power supply device according to an embodiment of the present invention, and FIG. 3 is a signal waveform diagram for explaining the operation. Ql, Q3. Q4...Transistor, T1...Flyback transformer, T2...Pulse transformer, R1-
R4...Resistor, 01-C3...Capacitor, SWG
...Saw, wave generation circuit, GOMP...Comparator. Applicant's agent Patent attorney Takehiko Suzue Figure 1 n 〇-

Claims (1)

[Claims] A ringing choke converter type switching power supply device equipped with a switching power transistor includes a main circuit for generating a sawtooth waveform, which has a resistor and a capacitor and generates a sawtooth waveform voltage based on a voltage proportional to the input voltage, and a main circuit that generates a sawtooth waveform voltage based on a voltage proportional to the input voltage. A comparator that compares the voltage with the output voltage, and turns on/off depending on the comparison result of this comparator.
A control 1-transistor that is turned off, and a pulse transformer that transmits the state of the control transistor to the base of the switching power transistor, and the base current of the switching power transistor is controlled depending on whether the control transistor is turned on or off. The switching device is configured such that the pulse transformer is forcibly drawn to the secondary side of the pulse transformer.