JPS6260465A - Boosting type chopper circuit - Google Patents

Abstract

PURPOSE:To prevent the variation of output voltage by connecting a transistor in series with a choke coil and at an intermediate step between a switching element and a load side capacitor. CONSTITUTION:With a boosting type chopper circuits, a series body of a choke coil 1 and a diode 2a is connected between input/output terminals 9, 10, a transistor (hereinafter called Tr) 3 for storing energy in the coil 1 is turned ON-OFF by a control circuit 4, and the load side is supplied with DCs through a capacitor 5, etc. A Tr 8' is inserted in series with a diode 2 at that time. Accordingly, the titled circuit is made equivalent to a circuit in which two diodes are connected in series, thus sufficiently compensating output voltage Eout by a feedback from output voltage Eout detected through detecting resistors 6, 8, then preventing output variation due to a load.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a step-up type circuit with stable output.

[Prior art]

A conventionally used boost type choke circuit consists of a choke coil 1 and a diode 2, as shown in the circuit example in Figure 1.
terminal 9 to which the input voltage (E, n) is applied and the output voltage (
When the transistor 3 is turned on and off by the control circuit 4, energy is stored in the choke coil 1, and the diode 2 and capacitor 5 transfer it to the load side. Direct current flows. According to this circuit, the direct current voltage of input voltage Ein is E.u
Ein, Q
E. The voltage of ut can be increased. and.

The control circuit 4 divides the specific output voltage by the detection resistors 6 and 7.
and controls the on/off time of transistor 3. This keeps the output voltage constant. The control circuit 4 includes a high frequency oscillator, a reference voltage power source, a comparator, a drive circuit, etc., and is commercially available in the form of a dedicated integrated circuit.

[Problem that the invention seeks to solve]

According to the above chopper circuit, transistor 30 is on,
When the transistor 3 is turned off,
Even if the switching operation is stopped, the input voltage is output through the choke coil l and diode 2. Therefore, to cut off the output, connect a power line such as transistor 8 in series! If necessary, a dipping method must be used to completely cut off the output. The transistor 8 is connected to the control terminal 1
A method of control is taken by applying a voltage to 1. Note that there is a method of placing the transistor 8 before the choke 1 to connect and disconnect the input voltage Ein, but since it is a step-up switch, the input current is larger than the output current, and the power loss due to the transistor becomes large. Also, as shown in Figure 1, if the transistor 8 is inserted on the output side, the loss is relatively small, but the drawback is that the saturation voltage between the collector and the emitter varies depending on the current, so the output voltage fluctuates depending on the load. Ah, Rin.

[Means for solving problems]

The step-up chopper circuit according to the present invention includes a choke coil whose one end is connected to a DC input terminal, a north transistor connected between the other end of the choke coil and an output terminal, and a return line connected to the output terminal side of the transistor. 9 capacitors connected between the choke coil and the transistor, and 9 switching elements connected between the return line and the connection between the choke coil and the transistor, and the switching elements are connected intermittently according to the value of the output voltage. control to obtain a DC output voltage higher than the input voltage on the output side, and to disconnect the circuit on the output side by controlling the transistor to turn off when the switching element stops operating in an off state. Features.

[Embodiments of the invention]

Next, two embodiments of the present invention will be described with reference to two drawings.

FIG. 2 is a circuit diagram showing a first embodiment of the present invention. This example differs from the conventional example shown in FIG. 1 in that a transistor 8' is inserted in series with the diode 2. This makes it equivalent to two diodes connected in series. Therefore, the output voltage is sufficiently corrected by feedback from the output voltage (Eout) detected via the detection resistors 6 and 7, and is hardly affected by the output load. Also, the loss of transistor 8'.

This circuit is almost equivalent to the circuit shown in FIG. Furthermore, the input voltage E,
and output voltage E. If the voltage difference with ut is small and the reverse potential between the cap and the emitter is small, the diode 2 can be omitted, thereby reducing losses.

Note that in this example, E and n are E. If a fluctuation occurs that exceeds ut', that is, if the input voltage is 3v~
8V, if the required output voltage is 5V, when the input voltage exceeds 5V, transistor 3 turns on.
Even if the power is turned off, a voltage of 5V or more is generated in the output voltage. Therefore, to avoid this, a voltage stabilizing circuit may be required at the next stage of the boost chopper circuit.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention. This example differs from the first embodiment in that a transistor 12 is added between the base of the transistor 8' and the return line, and its base is connected to the input terminal 9 via a Zener diode 13. According to this, when the input voltage is low, the transistor 8' is supplied with a sufficient base current and is in a saturated state. When the input voltage is high (input voltage is high), when current flows through the Zener diode 13, current begins to be supplied to the base of the transistor 12. This supply current is approximately a current compared to the input voltage;
This increases the collector current.

The base current of transistor 8' increases the collector-emitter voltage.

The relationship between the input voltage and the collector-emitter voltage of the transistor 8' can be seen in the graph of FIG. If you look at this trend, it seems.

This is equivalent to a state in which diode 2 is gradually added as the input voltage increases, and as a result, the input voltage ``in'' decreases and becomes similar to 9.Therefore, without using any other stabilizing circuit, .

Ein is E. The output voltage can be sufficiently stabilized against fluctuations exceeding "ut".

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a transistor for controlling connection and disconnection to a load is connected in series with a choke coil and to an intermediate stage such as a switching element and a load-side capacitor. Load-induced output voltage fluctuations caused by the saturation voltage of the output voltage are eliminated.

The benefits obtained are significant in that respect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional step-up chopper circuit, FIG. 2 is a circuit diagram showing a first embodiment according to the present invention, and FIG. 3 is a circuit diagram showing a second embodiment according to the present invention. 4 shows the input voltage and transistor 8 in the embodiment of FIG.
1 is a graph showing the relationship between collector-emitter voltage and collector-emitter voltage. In the figure, 1 is a choke coil, 2 is a diode,
3 is a switching element, and 4 is a control circuit. 5 is a capacitor, 6 and 7 are resistors, 8.8' and 12 are transistors, and 13 is a Zener diode. Figure 1 Figure 2 Figure 3 Taichi - ◆εin (input voltage) M4 diagram...

Claims (1)

[Claims] 1. A choke coil whose one end is connected to a DC input terminal, a transistor connected between the other end of the choke coil and an output terminal, and a return line connected to the output terminal side of the transistor. a capacitor connected between the choke coil and the transistor, and a switching element connected between the return line and a connection between the choke coil and the transistor, and the switching element is controlled intermittently according to the value of the output voltage. A DC output voltage higher than the input voltage is obtained on the output side, and when the switching element stops operating in an off state, the circuit on the output side is disconnected by controlling the transistor to turn off. A step-up chopper circuit. 2. A step-up chopper circuit according to claim 1, characterized in that a diode is connected in series with the transistor. 3. In the step-up chopper circuit according to claim 1 or 2, a second transistor is connected between the base of the transistor and the return line, and the base of the second transistor is connected to a Zener. A step-up chopper circuit, characterized in that it is connected to the DC input terminal via a diode.