JPS633622A - Electric source circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a power supply circuit used as a power supply for an electric water bottle, and more particularly to a switching power supply circuit equipped with a starting circuit that supplies a power supply voltage to a control circuit when the power is turned on. It is related to.

(Prior art) Switching power supply circuits have traditionally required a control circuit that controls switching elements and an auxiliary power supply circuit that supplies power to this control circuit, and requires that the power supply circuit operate normally when input power is turned on. has been done.

An example of such a conventional switching power supply circuit is shown in FIG.

In FIG. 5, a diode bridge rectifier circuit rectifies an AC input voltage v1, and a capacitor C1 smoothes the rectified voltage. The starting transistor Tr1 is
Its collector is connected to line e1 via resistor R2, and supplies power supply voltage Vcc to control circuit A via diode D1 when AC input voltage 1 is applied. This power supply voltage Vcc is supplied by the emitter follower output of the transistor Tr1.

The switching transistor Tr2 connects lines e1 and e2
The DC voltage applied to the primary coil Np of the transformer T is switched through the secondary coil Ns of the transformer T.
This outputs a pulse voltage. Secondary coil Ns
Diodes D3 and D4 are connected to the secondary coil Ns
The output pulse voltage is rectified, connected to a choke coil, and a capacitor Co smoothes the rectified voltage to obtain a DC output voltage Vo.

The diode D2 and the capacitor C2 rectify the induced voltage from the auxiliary coil Nc of the transformer T in steady state.
Smooth the control circuit A1. : It is given as the power supply voltage VCC. Zener diode DZ and resistor R1 are
This is for determining the base potential of the starting transistor Tr1.

Next, the operation of this conventional power supply circuit will be explained.

The AC input voltage Vi is rectified and smoothed by the rectifier bridge circuit and the capacitor C1 to become a DC voltage, and this DC voltage is applied to the primary coil Np of the transformer T. The control circuit A drives and controls the switching transistor Tr2, and the pulses induced in the secondary coil NS of the transformer T are rectified and smoothed by the diodes D3 and D4, the choke coil L, and the capacitor CO, thereby making this power supply circuit a direct current. An output voltage VO is obtained. The auxiliary power source of the control circuit A during steady operation is to convert the induced voltage of the auxiliary coil Nc of the transformer T into a diode D2 and a capacitor C2.
It is obtained by rectifying and smoothing.

On the other hand, when the power is turned on, the power supply voltage is supplied to the control circuit by the emitter follower output of the starting transistor Tr1 until the main switching circuit including the transformer T and the switching transistor Tr2 starts operating. As a result, the control circuit A starts the switching operation of the switching transistor Tr2, and an induced voltage is generated from the auxiliary coil Nc of the transformer T. Therefore, by making this induced voltage higher than the Zener voltage of the Zener diode Dz, the starting transistor Trt is turned off. That is, when the power supply circuit reaches a steady state, the starting transistor Tr1 is turned off.

However, in a power supply circuit having such a configuration,
Even in the normal state after the starting transistor Tr1 is turned off, the Zener diode DZt is connected through the resistor R1:
Current flows, causing power loss and reducing power supply efficiency. Therefore, if the resistance value of the resistor R1 is increased to reduce this power loss, the current amplification factor hF
A transistor with a large E is required. However, when the current amplification factor hFE of the transistor Trt is large, it becomes difficult to turn off the transistor Tr1, and the transistor Tr1 becomes difficult to turn off.
1 and the loss of resistor R2 becomes a problem.

(Object of the invention) The present invention solves the above-mentioned technical problem, and in a power supply circuit equipped with a control circuit for operating a switching element, completely turns off a starting circuit element that supplies power to the control circuit during normal operation, The purpose is to provide a power supply circuit that improves reliability as well as improving power supply efficiency.

(Structure of the Invention) The present invention includes a transformer having a primary coil, a secondary coil, and an auxiliary coil, and a switching element connected to the primary coil of the transformer to generate a pulse in the primary coil. The auxiliary coil includes a control circuit, a starting transistor that supplies a power supply voltage to the control circuit only when the power is turned on, and a constant voltage element that determines the base voltage of the starting transistor, and the auxiliary coil is connected to the control circuit during steady operation. A power supply circuit that supplies a power supply voltage and obtains a DC voltage from an output from the secondary coil, comprising a detection means for detecting the steady operation, and a detection means connected in series to the constant voltage element to detect the output of the detection means. and switching means for turning off the starting transistor in response to the above.

With this configuration, when the N source is turned on, the switching means is turned on to turn on the starting transistor, supplying the power supply voltage to the control circuit, and during normal operation, the switching means is turned off to turn off the starting transistor, and the auxiliary coil of the transformer T is turned off. The power supply voltage is supplied to the control circuit by the output from the control circuit. In this manner, the switching means is turned off during steady operation, and therefore no current flows through the constant voltage element.

(Embodiment) FIG. 1 is an electrical circuit diagram of a power supply circuit according to a first embodiment of the present invention.

In FIG. 1, a diode bridge rectifier circuit rectifies an AC input voltage Vi, and a capacitor C1 smoothes the rectified voltage. The collector of the starting resistor Tr1 is connected to the line e1 via the resistor R2, and supplies the power supply voltage Vcc to the control circuit via the diode D1 when the input voltage Vi is applied. The power supply voltage Vcc is supplied by the emitter follower output of the transistor Tr1.

The switching transistor Tr2 connects lines e1 and e2
The DC voltage applied to the primary coil ND of the transformer T is switched through the secondary coil NS of the transformer T.
This outputs a pulse voltage. Secondary coil NS
Diodes D3 and D4 are connected to the secondary coil NS
The output pulse voltage is rectified, connected to a choke coil, and a capacitor Co smoothes the rectified voltage to obtain a DC output voltage Vo.

The diode D2 and the capacitor C2 rectify and smooth the induced voltage from the auxiliary coil NO of the transformer T in a steady state, and provide it to the control circuit A as the power supply voltage Vcc. The comparator CMP as a detection means is
a reference voltage divided by resistor R3 and resistor R4;
The output of the auxiliary coil NC of the transformer T is compared with the detection voltage applied to the capacitor C3 via the diode D5 to control the transistor Tr3 as a switching means. This transistor Tr3 has its emitter connected to the line e1 via the resistor R1, its collector connected in series to the Zener diode Dz, and receives the output of the comparator CMP via the resistor R5 to turn off the starting transistor Tr1. It is something.

The thyristor SCR controls the inrush current protection resistor Ro provided on the line e2 so that it operates only in the activated state. Resistance Rs.

R7 and capacitor C4 are for creating the gate voltage of thyristor SCR.

Next, the operation of this first embodiment will be explained with reference to the timing chart shown in FIG.

First, the operation at startup will be described. AC input voltage Vi
is input into the diode bridge rectifier circuit, line e1. A DC input voltage (FIG. 2(a)) appears at e2 (both ends of the capacitor C1), but a voltage of a predetermined level is not yet induced in the auxiliary coil NG of the transformer T as shown in FIG. 2(C).

Therefore, the inverting input terminal voltage of comparator CMP (
The non-inverting input terminal voltage (Fig. 2(b)) is the non-inverting input terminal voltage (Fig. 2(b))
d)) becomes higher, thereby comparator CMP
The output (FIG. 2(e)) becomes low level, and the transistor Tr'3 is turned on as shown in FIG. 2m. By turning on this transistor 7r3, the Zener diode Dz operates, and the base potential of the starting transistor Tr+ is given by the Zener voltage of the Zener diode DZ. Therefore, the power supply voltage Vcc is supplied to the control circuit A from the emitter of the transistor Tr1 through the diode D1.

As the control circuit Δ operates, the switching transistor Trz starts a switching operation, and a steady voltage is induced in the auxiliary coil NG of the transformer T as shown in FIG. 2(C). This induced voltage is rectified and smoothed by the diode D5 and the capacitor C3, and the comparator C
It is applied to the non-inverting input terminal of MP. Therefore, the non-inverting input terminal voltage of comparator CMP (Fig. 2(d))
becomes larger than its inverted input terminal voltage (Fig. 2(b)), the output of the comparator CMP is inverted to high level as shown in Fig. 2(e), and the transistor Tr3 is inverted as shown in Fig. 2(f). It goes from on to off. When the transistor Tr3 is turned off, the base potential applied to the starting transistor Tr1 disappears, and the transistor Trt
Also turns off. After the starting transistor Tr1 is turned off, the power supply voltage VCC of the control circuit A is supplied by the induced voltage from the auxiliary coil Nc.

In addition, the induced voltage from the auxiliary coil NC is applied to the diode D5.
and capacitor C3 for rectification and smoothing;
), and this gate voltage is applied to the gate of thyristor SCR to turn on thyristor SCR. That is, thyristor SCR
A trigger is not applied to the gate of the auxiliary coil NC until a voltage is induced in the auxiliary coil NC, the thyristor SCR is off, and a resistor RO is connected in series with the capacitor C1 to limit the inrush current. When the capacitor C1 is charged and the switching transistor Tr2 starts switching operation in a steady state, a voltage is induced in the auxiliary coil NG, and the power supply voltage of the control circuit A is supplied from the auxiliary coil NC. D5, resistor Re, capacitor C4
from the induced voltage of the auxiliary coil NG through the thyristor SC.
A trigger is applied to the gate of R, turning on the thyristor SCR.

When the steady state is reached, a pulse voltage is output to the secondary coil Ns of the transformer T by the switching operation of the switching transistor Tr2, and this pulse voltage is rectified and smoothed by the diode 03, D4, choke coil, and capacitor CO. DC output voltage Vo
becomes.

According to this first embodiment, after the power supply circuit starts steady operation, the transistor Tr3 is turned off, so that the operating current of the Zener diode [2] can be cut off.
Power supply efficiency is improved compared to the conventional example. That is, in the conventional example, current continues to flow through the Zener diode DZ even when steady operation starts, but in this first embodiment, the operating current of the Zener diode Dz does not flow, and therefore the power supply efficiency is improved compared to the conventional example. It turns out.

Furthermore, since the base bias voltage of the starting transistor Trt disappears after steady operation, the transistor Tr1 can be completely turned off, reducing power loss in the resistor R2 and the transistor Tr+, and improving power supply efficiency. Furthermore, due to the current amplification effect of the transistor Tra, the starting transistor Tr1 does not require a very large current amplification factor hFE, so the starting transistor Trt does not become difficult to turn off, and the loss of the transistor Tr1 and the resistor R2 is reduced. Not a problem.

Further, since the auxiliary coil Nc that supplies the power supply voltage to the control circuit A can be shared with the gate trigger circuit of the thyristor SCR for inrush current protection, the coil of the transformer T can be saved, which is advantageous in reducing the size of the transformer T.

FIG. 3 is an electrical circuit diagram of a power supply circuit according to a second embodiment of the present invention.

In FIG. 3, components corresponding to those shown in FIG. 1 are given the same reference numerals. The feature of this second embodiment is that an amplifier i5AMP is provided as an output detection means for detecting the output voltage Vo, and the output of this amplifier AMP is
This signal is applied as an inverted operation signal to the comparator CMP via the photocoupler PC. amplifier AM
Zener diode D connected to the inverting input terminal of P
zO is for setting the reference voltage, and the amplifier AMP
The resistor R8 connected to the output terminal of the photocoupler P
This limits the current flowing through the light emitting diode D6 of C. The voltage of line e1 is applied to the collector of phototransistor Tr4 of photocoupler PC via resistor R6, the emitter of phototransistor Tr"4 is connected to a parallel circuit of resistor R9 and capacitor C5, and resistor R9 is connected to comparator CMP. This creates a non-inverting input terminal voltage.

Next, the operation of this second embodiment will be explained with reference to the timing chart shown in FIG.

First, the operation at startup will be described. AC input voltage ■i
is input into the diode bridge rectifier circuit, line e1. e2 (one end of capacitor C1) is shown in Figure 4 (
Although the DC input voltage is flattened as shown in a), the output voltage V
As shown in FIG. 4(C), o has not yet reached the steady value (in this case, the reference voltage ef). Since the output voltage Vo does not reach the steady-state value, the amplifier AMP continues to output a low level signal, and therefore the photocoupler PC does not operate. This causes the non-inverting input terminal voltage of the comparator CMP (Fig. 4(d)
) becomes lower than its inverted input terminal voltage (Fig. 4(b)), and the output terminal voltage of comparator CMP becomes lower than its inverting input terminal voltage (Fig. 4(e)).
) becomes low level as shown. This comparator C
The low level signal from MP turns on the transistor Tr3 as shown in FIG. 4(f), which turns on the transistor Tr1, and the signal is sent to the control circuit A as shown in FIG. (h)
A power supply voltage as shown in is supplied.

Therefore, by putting the control circuit A+ into an operating state, the switching transistor Tr2 starts a switching operation, an induced pulse is output to the secondary coil NS of the transformer T, and the output voltage Vo becomes a steady value. This results in
The non-inverting input terminal voltage of the amplifier AMP becomes higher than its inverting input terminal (reference voltage ■), the photocoupler PC operates, and as a result, the non-inverting input voltage of the comparator CMP becomes higher than its inverting input terminal voltage. . Therefore, the output of the comparator CMP becomes high level, the transistor Tr3 is turned off, and the transistor Tr1 is turned off. This results in
The power supply voltage Vcc of the control circuit A applied through the resistor R2, the transistor Tr1, and the diode D1 is cut off, but the power supply voltage VCC due to the induced voltage from the auxiliary coil Nc of the transformer T is applied to the control circuit A. .

As shown in FIG. 4(g), the gate voltage of the thyristor SCR increases as the DC input voltage increases, and drives the thyristor SCR in a steady state.

This second embodiment also has the same effects as the first embodiment.

(Effects of the Invention) As described above, according to the present invention, the control circuit for controlling the switching element connected to the primary coil of the transformer T to generate a pulse in the primary coil, and the control circuit for controlling the switching element connected to the primary coil of the transformer T, and In the power supply circuit, the power supply circuit includes a starting transistor that supplies a power supply voltage to the control circuit, a constant voltage element that determines a base voltage of the transistor, and an auxiliary coil that supplies the power supply voltage to the control circuit during steady operation. The power supply circuit starts steady operation by providing a detection means for detecting steady operation, and a switching means for receiving an output of the detection means connected in series with the constant voltage element and turning off the starting transistor. After that, the switching means is turned off, and therefore the operating current of the constant voltage element can be cut off, so that if source efficiency can be improved and reliability can also be improved.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of a power supply circuit according to a first embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of the first embodiment, and FIG. 3 is a diagram of a power supply circuit according to a second embodiment of the present invention. FIG. 4 is a timing chart for explaining the operation of the second embodiment, and FIG. 5 is an electrical circuit diagram of a conventional power supply circuit. A...Control circuit, CMP...Comparator (detection means), D5...Diode (detection means), Dz...
Zener diode (constant voltage element), T...transformer,
NO...Primary coil, NS...Secondary coil, NC・
...Auxiliary coil, Trl...Starting transistor, l
"r2...Switching transistor (switching element), Tr3...Transistor (switching means), AMP...Amplifier (output detection means), PC...
Photo coupler. Patent applicant Matsushita Electric Works Co., Ltd. Representative Patent attorney Etsushi Kotani
Patent Attorney Chief 1) Masayuki Patent Attorney Yasuo Itaya Figure 2

Claims (1)

[Claims] 1. A transformer having a primary coil, a secondary coil, and an auxiliary coil, and control for generating pulses in the primary coil by controlling a switching element connected to the primary coil of the transformer. a starting transistor that supplies a power supply voltage to the control circuit only when the power is turned on, and a constant voltage element that determines a base voltage of the starting transistor,
The auxiliary coil supplies a power supply voltage to the control circuit during steady operation, and the power supply circuit obtains a DC voltage from an output from the secondary coil, the power supply circuit comprising a detection means for detecting the steady operation, and the constant voltage element. and switching means connected in series to the circuit for turning off the starting transistor upon receiving the output of the detecting means. 2. The detection means is composed of a diode provided in parallel with the auxiliary coil and a comparator that performs an inverting operation upon receiving the output of the diode, and the output of the comparator is applied to the base of a switching transistor serving as the switching means. A power supply circuit according to claim 1, characterized in that the power supply circuit is configured as follows. 3. Claims characterized in that output detection means for detecting the output voltage of the secondary coil is provided, and the output of the output detection means is applied as an inverted operation signal to the comparator via a photocoupler. The power supply circuit described in item 2.