JPS598469Y2 - Current limiter signal generation circuit in switching regulator - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a current limiter signal generation circuit in a switching regulator.

Switching regulators are attracting attention as power supply circuits for amplifiers and the like because they can be made relatively small and have good regulation.

However, this switching regulator must be equipped with a current limiter to protect it from destruction due to large currents.

FIG. 1 shows an example of a switching regulator equipped with a current limiter signal generation circuit.

That is, in FIG. 1, 1 and 1' are DC current input terminals, and the DC current applied to the input terminals is applied to the switching circuit 2, and a switching action is performed based on the control signal from the pulse width modulation circuit 3. It is done.

The switching output is applied to the primary winding 41 of the transformer 4, and the output delivered to the secondary winding 42 is rectified by the rectifier circuit 5 and passed through the coils L and L' respectively to the positive output terminal 6 and the negative output terminal. is provided to the output terminal 6'.

7 is a load circuit connected between the positive output terminal 6 and the negative output terminal 6', and the illustrated example shows a peer complementary SEPP power amplifier circuit.

Resistors RS and RS' are connected between the rectifier circuit 5 and the load 7, and the resistors RS and RS'
The bases and emitters of transistors Q and Q' are connected to both ends of the transistor.

The collectors of transistors Q and Q' are connected to ground via collector load resistors R1 and R1', respectively, and the respective collector outputs are configured to be applied to the pulse width modulation circuit 3.

Therefore, if a current exceeding a certain level flows into the load 7 side, the resistance RS
and RS', transistor Q
and Q' are turned on, and the collector load resistances R0 and Rl
'The current limiter control signal generated in the switching circuit 2 is applied to the pulse width modulation circuit 3.
The switching width is controlled to be small.

Therefore, the current flowing into the load 7 is limited to a certain value or less.

A capacitor is generally inserted between the rectifier circuit 5 and the load 7 to smooth the rectified output.

When a power amplifier circuit is connected as the load 7 as shown in the illustrated example, the load current is alternating current, and under such conditions, if capacitors C and C' are inserted at points A and A' in Figure 1, the resistance will increase. Half-wave alternating current commands as shown in FIG. 2A and 2A flow through RS and RS', respectively.

The peak value of this current is independent of the frequency of the alternating current flowing into the load.

However, if the output current characteristics of the power supply are guaranteed at the peak current, for example, when the output terminal of the power supply is short-circuited, the current will flow up to the peak current value, and if the switching circuit 2 does not have enough margin, the switching circuit 2 etc. will be destroyed. There is.

Also, if capacitors C and C' are inserted at points B and B' in Figure 1, if the capacitances of capacitors C and C' are sufficiently large, the currents flowing through resistors RS and RS' will be averaged despite the AC load. As shown by the dashed lines in FIGS. 2B and 2B, a current of approximately constant value flows.

However, when the frequency of the load current is extremely low, ripples occur in the current waveform, as shown by the broken lines in E and G of the figure.

In other words, when a power supply circuit is designed to guarantee an output of, for example, 100 W, when a current with an extremely low frequency flows, a knockout occurs as described above.
Since this ripple intermittently turns on transistors Q and Q', a current limiter control signal is generated, causing the inconvenience that the pulse width modulation circuit 3 operates the switching circuit 2 to limit the current. , a situation arises in which an output of 100 W cannot be guaranteed for a low frequency load current.

In order to eliminate such defects, capacitors C and C
It is conceivable to make the capacity of ' extremely large, but this would lead to an increase in cost or an increase in the volume occupied by the equipment, and would not produce favorable results.

In view of the above-mentioned problems, the purpose of this invention is to provide a current limiter signal generation circuit that can eliminate the above-mentioned disadvantages without using large-capacity, high-voltage capacitors. Specific examples from Part 3
This will be explained based on FIG.

Note that the example shown in FIG. 3 shows only the positive side of the current detection circuit provided between the rectifier circuit and the output terminal to the load.

In other words, in FIG. 3, the base and emitter of a transistor Q are connected to both ends of a resistor RS via two identical base and emitter resistors in series, and the connection midpoint of each base resistor and each A capacitor Cr is inserted between the connection midpoint of the emitter resistor.

In this example, the base and emitter of the transistor Q are operated to be short-circuited by the capacitor Cr, and the resistor R
r and capacitor Cr operate to convert ripple voltage into direct current.

Therefore, the capacitor Cr has the advantage that it can be used with a smaller capacitance and lower breakdown voltage than the capacitor C inserted at the point B in FIG. 1 to achieve the same effect.

As is clear from the above explanation, the current limiter signal generating circuit of this invention has the inconvenience of performing a current limiter action due to the generation of ripples even when the load current is at an extremely low frequency. Moreover, since this can be achieved without using a capacitor with a large capacity and high voltage resistance, it is highly economical and can also contribute to downsizing of equipment.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram showing an example of a switching regulator equipped with a current limiter signal generation circuit, Figs. 2A and 2B are characteristic diagrams showing the arrangement position of the smoothing capacitor and the current relationship, and Fig. 3 is a diagram showing an example of a switching regulator equipped with a current limiter signal generation circuit. 1 is a wiring diagram showing an embodiment of a current limiter signal generating circuit according to the present invention. 2... Switching circuit, 3... Pulse width modulation circuit, 4... Transformer, 5... Rectifier circuit, 7... Load, RS... Resistor, Q... Transistor, Cr...・
capacitor.

Claims (1)

[Scope of utility model registration request] A switching circuit that switches a DC power supply, a transformer that uses the output of this switching circuit as a primary side input, and a rectifier circuit that is connected to a secondary output side of this transformer.
A current detection circuit connected between the rectifier circuit and the load, and a pulse width modulation circuit that controls the switching width of the switching circuit based on the output of the current detection circuit generated by a current exceeding a predetermined value. In,
The above current detection circuit includes a resistor connected between the rectifier circuit and the load, a transistor whose base and emitter are connected to both ends of this resistor via a base resistor and an emitter resistor, respectively, and the base resistor and emitter resistor. 1. A current limiter signal generation circuit in a switching regulator, comprising a capacitor having both ends connected between respective midpoint positions of the switching regulator.