JPS6321190Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching control type power supply circuit, and particularly to an AC voltage range detection circuit for a switching control type power supply circuit that can input a wide range of AC voltages. For example, in the Middle East, the voltage values of commercial AC power supplies vary depending on the region, such as 100V, 110V, 220V, and 240V, and each voltage is extremely unstable. Therefore, power supply circuits for devices used in such regions are required to perform stable constant voltage operation over a very wide input voltage range. A switching control type power supply is an example of a power supply circuit that satisfies such requirements, but even this power supply circuit cannot achieve stable operation when the upper limit of the input voltage is more than twice the lower limit as mentioned above. This is the current situation. For this reason, in the past, the number of turns on the primary side of the converter transformer was changed depending on the magnitude of the input voltage.
Alternatively, the AC input rectifier circuit is switched between a double wave rectification type and a voltage doubler rectification type. However, since all of the above conventional methods switch the input side, they require relatively high-voltage switching relays, etc., and have the disadvantage that the switching circuit cannot be isolated from the AC input line. Ta. Therefore, the present invention proposes a switching control type power supply circuit that eliminates such drawbacks, and the details thereof will be explained below with reference to the drawings. The drawing shows one embodiment of the present invention, and this circuit is roughly divided into a power supply circuit section 1 and an input voltage detection section 2. The power supply circuit section 1 basically constitutes a well-known half bridge type inverter, I ₁ and I ₂ are AC input terminals, SW is a power switch, BG is a bridge type rectifier circuit, and C ₁ and C ₂ are voltage dividing capacitor,
Tr ₁ and Tr ₂ are switching transistors, and CT is a converter transformer. Further, DR is a driver circuit that switches and drives the transistors Tr ₁ and Tr ₂ , and CN indicates the length of the on period of each transistor, that is, the duty ratio, at the output terminal O ₁ ,
This is a control circuit that controls according to the fluctuation of the DC output voltage between _O2 . In the power supply circuit section 1 , what requires special attention is the output winding _N2 of the converter transformer CT.
Switching taps Ta and Tb are provided separately from the center tap _T0 , and each switching tap and both ends of the winding _N2 are connected to rectifying diodes _D1 , _D2 whose cathodes are commonly connected to a smoothing coil LC. The point is that the connection is switched to each anode side. that time,
This switching is performed by relay RY, and
This relay is driven by an input voltage detection section 2 as described later. On the other hand, the detection section 2 basically consists of the input terminal
The AC input voltage between I ₁ and I ₂ is stepped down by a transformer DT,
The output is rectified by a voltage doubler rectifier circuit DC to obtain a DC voltage, and the magnitude of the AC input voltage is detected. ZD is a Zener diode for setting the detection level, Tr ₃ is a detection transistor that is turned on when this diode is conductive, Tr ₄ is a switch transistor that is turned off when this transistor is on, and Tr ₅ is a switch transistor that is turned off when this transistor is turned on. This is a relay driving transistor that turns off when The reason why the step-down transformer DT and the voltage doubler rectifier circuit DC are provided in the input voltage detection section 2 will be explained later, but first of all, let's focus on the fact that the detection level of the AC input voltage is set as follows. You should be careful. That is, for example, if we assume the aforementioned 100V, 110V, 220V, and 240V as AC inputs to the input terminals I ₁ and I ₂ , and further take into account these voltage fluctuations and set the input voltage range to 80 to 280V, The point is that the detection level is approximately 170 to 190V, which is approximately the center of the input voltage range. Therefore, if the primary-to-secondary turns ratio of the step-down transformer DT is 10:1, it is sufficient to use a Zener diode ZD with a Zener voltage of about 17 to 19V. In this way, when an AC input of 100V or 110V is supplied between the input terminals I ₁ and I ₂ , the Zener diode ZD does not conduct and the detection transistor Tr ₃ is turned off, so the switch transistor Tr ₄ is on, and therefore, drive transistor Tr ₅ is also on. For this reason, the relay
RY is driven and the relay switches S ₁ and S ₂ are switched to the state shown in the figure, and the number of turns of the output winding of the converter transformer CT is increased. In addition, the switching taps Ta and Tb of the above output winding _N2
may be provided at approximately 1/2 of the number of turns, but it is not necessary to do so if the constant voltage control range can be relatively wide. Next, when an AC input of 220V or 240V is supplied between the input terminals I ₁ and I ₂ , the Zener diode ZD becomes conductive and, contrary to the above, the driving transistor Tr ₅ is turned off, so the relay switch is turned off. S ₁ , S ₂
is switched to a state opposite to that shown in the figure, and therefore the number of turns of the output winding _N2 is reduced. Therefore, when the AC input voltage is low, the power supply circuit section 1 operates with a large turns ratio between the primary and secondary windings, and conversely, when the AC input voltage is high, it operates with a small turns ratio. Therefore, depending on the magnitude of the above input voltage, the switching transistor
This means that the load conditions of Tr ₁ and Tr ₂ do not change drastically, and a stable constant voltage control operation is always performed, thereby preventing damage to the switching transistors. The detection section 2 is provided with a step-down transformer DT and a voltage doubler rectifier circuit DC in order to obtain DC power from this detection section to, for example, a timer circuit or a remote control circuit of the equipment.
That is, when an AC input of 100V or 110V is supplied, a DC voltage of 20 or 22V appears at point A due to the conduction of the switching transistor Tr ₄ , and an AC input of 220V or 240V is supplied. In this case, since a DC voltage of 22V or 24V appears at point B, the above-mentioned points A and B are used as DC power supply terminals. Furthermore, by configuring as described above, it is possible to insulate the detection section 2 and the circuit on the output winding _N2 side of the converter transformer CT. Since the AC voltage range detection circuit of the switching control type power supply circuit of the present invention is configured as described above, it can be used against various AC inputs with greatly different voltage values and each voltage being extremely unstable. It can always perform stable constant voltage operation, and
There is an advantage that the output side of the power supply circuit and the switching circuit can be completely isolated from the AC input line, and that low voltage withstand voltage can be used for the relay of the switching circuit.

[Brief explanation of the drawing]

The drawing is a circuit diagram showing one embodiment of the power supply circuit of the present invention. 1 ...Power supply circuit section, 2 ...Input voltage detection section,
CT...Converter transformer, RY...Relay.

Claims (1)

[Claims for Utility Model Registration] An input-side rectifier circuit that inputs high-voltage or low-voltage AC voltage via a power switch, a conversion circuit that converts the output of the input-side rectifier circuit into an AC output, and a primary converter for the AC output. A converter transformer that inputs the full voltage to the side coil and derives the total voltage from both ends of the secondary coil and derives the intermediate voltage from the switching tap, and selectively derives the intermediate voltage when the high-voltage AC voltage is input and the total voltage when the low-voltage AC voltage is input. A relay for selectively deriving the output, an output-side rectifier circuit for inputting the selected and derived output, and a control circuit for detecting the output level of the rectifier circuit and changing the duty ratio of the output of the conversion circuit. In the switching control type power supply circuit, a step-down transformer DT that inputs the alternating current voltage from a stage before the power switch, a voltage doubler rectifier circuit DC that inputs the output of the step-down transformer, and one output line of the voltage doubler rectifier circuit. A switch transistor Tr4 whose collector is connected to the switch transistor Tr4, which turns off due to a drop in base potential, and whose collector-emitter is connected between the base of the switch transistor and the other output line of the voltage doubler rectifier circuit, which turns off due to a rise in base voltage. a detection transistor Tr3 that is turned on and lowers the base potential of the switch transistor;
and a Zener diode ZD connected between the base of the detection transistor and an intermediate connection point of the voltage doubler rectifier circuit, which becomes conductive only when the high-voltage AC voltage is input, and increases the base potential of the detection transistor; A relay driving transistor that uses the emitter output of the transistor as a base input and connects the coil of the relay to the collector.
Tr5, respectively, and a power supply terminal is provided at the intermediate connection point and the base of the relay driving transistor.