JPH0537670Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a switching regulator that stabilizes a DC power supply using a feedback circuit using PWM or frequency modulation.

[Prior Art] A conventional device of this type is shown in FIG. In the figure, 1 is pulse width modulation (PWM) that changes the pulse width according to the divided potential of DC output.
, and its PWM signal is passed through the switching element Q.
1 to turn on/off the switching element Q1. The source of the switching element Q1 is connected to ground, the drain thereof is connected to the other end of the transmission transformer T1, and one terminal of the transmission transformer T1 is connected to the power supply source +B, and the switching element Q1 is turned on/off. The induced power is then transmitted to the secondary side of the transformer T1 according to a predetermined winding ratio. Therefore, the secondary output of the transmission transformer T1 is connected to the rectifier diode D1 and the smoothing capacitor C2.
and becomes the DC output Vout. This DC output Vout is divided by dividing resistors R2 and R3, and the pulse generation means of the pulse width modulator 1 is controlled to change the duty ratio of the pulse width to configure negative feedback according to the DC output voltage. change.

Therefore, if the time during which the switching element Q1 is on is t1, the time when the current flows through the diode D1 on the secondary side of the transmission transformer T1 is t2, and the entire period of this switching is T, then the relational expression t1+t2<T is obtained. To establish. In other words, the duty ratio on the primary side of the transmission transformer T1 changes depending on the current required for the load on the secondary side of the transmission transformer T1, and there is a timing when the switching element Q1 is turned off and the diode D1 is also turned off. Also, one of the transmission transformers
There are cases where the switching element Q1 does not turn on until the excitation energy on the next side is exhausted.

[Problems to be solved by the invention] Since the conventional switching regulator is configured as described above, the total period T cannot be t1+t2=T as described above, but T-(t1+t2 ), the stray capacitance of the transmission transformer T1 and its winding (the stray capacitance of the winding is shown by the dotted line in Figure 2)
A resonant current flows between the capacitor C1 and the voltage protection capacitor C1 of the switching element Q1. Due to this resonant current, an excessive current flows when switching element Q1 is turned on, and the current when turning on differs depending on the timing when switching element Q1 turns on, so that a large current is required on the secondary side when switching element Q1 turns off. This caused the inconvenience that a certain amount of current could not be extracted.

[Means for solving the problem] This invention was made in order to eliminate the drawbacks of the conventional ones as described above.
A switching element that turns on/off opposite to the on/off of this switching element is connected in parallel with a power supply and a forward diode in series on both ends of the next side, and a transformer and stray capacitance and voltage protection capacitor are connected. [Embodiment] An embodiment of this invention will be described below with reference to the drawings. In FIG. 1, a switching element Q2 of the opposite conductivity type driven by the pulse width modulator 1 at the same timing as the switching element Q1 is connected in parallel to the primary side of the transformer T1 via a diode D2. Therefore, when switching element Q1 is on, switching element Q2 is off.

Here, during the period when switching element Q1 is off, switching element Q2 is on, but the electromagnetic energy on the primary side of transformer T1 stored during the previous period when switching element Q1 was on is absorbed. Transmitted to the secondary side. In that case, the voltage at the drain (point A) of switching element Q1 is:
The number of turns of the primary and secondary of the transmission transformer T1 is n1, n
2, +B+(n1/n2)·Vout, the diode D2 becomes a reverse potential, and no current flows through the switching element Q2. When the power transfer ends, the potential at point A begins to decrease, and A
From the moment the point drops below the +B potential, the diode D
2 becomes conductive, and current begins to flow through switching element Q2. Therefore, unlike the conventional example, during the period when current flows through this switching element Q2, a resonance phenomenon due to the transmission transformer T1 and the stray capacitance shown by the dotted line in FIG. 2 and the voltage protection capacitor C1 does not occur. No error will occur in the required current supplied to the load when element Q1 is off.

Next, during the period when switching element Q1 is on, switching element Q2 is off, so the operation is the same as in the conventional example.

As another embodiment of this invention, as shown in FIG. 3, if a transformer T2 is connected between the switching element Q2 and the diode D2 of FIG. 1, the same effect as the above example can be obtained, and A second power source can be obtained due to this effect. In this case, as described above, the period during which the diode D2 is on is short in the switching period T, so the power that can be taken out from the rectifier diode D3 is small.

[Effects of the invention] As described above, according to this invention, among the switching period consisting of the period when the switching element of the switching regulator is on, the period when the rectifier diode is on, and other periods, Since a switching element is provided that bypasses the current to the transmission transformer during other periods, the DC output current can be kept constant without error, and the switching element Q
Excessive current to 1 can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a switching regulator according to one embodiment of this invention, Fig. 2 is a circuit diagram showing a conventional switching regulator, and Fig. 3 is a circuit diagram showing another embodiment of this invention. It is a circuit diagram. 1... Pulse width modulator, T1, T2... Transformer, Q1, Q2... Switching element.

Claims (1)

[Scope of utility model registration request] Feedback is made to the primary side of the transmission transformer according to the DC output via the rectifier circuit on the secondary side of the transmission transformer, and this feedback signal drives a switching element connected in series to the primary side of the transmission transformer. The switching regulator is a switching regulator that stabilizes a power supply, in which a forward-connected diode and a switching element of a conductivity type opposite to that of the switching element are connected in series to both ends of the primary winding of the transmission transformer. A switching regulator, characterized in that the switching element and the opposite conductivity type switching element are driven by the feedback signal.