JPS5972980A - Stabilized dc power source - Google Patents

Abstract

PURPOSE:To efficiently and stably operate a stabilized DC power source by forming a quasi-load circuit operated only at no load or a light load time, detecting a current flowed to the load by a transformer and controlling the load current flowed to the load circuit. CONSTITUTION:A load current flowed to the primary winding of a smoothing coil 6' is detected by a secondary winding and a rectifying the smoothing circuit composed of a diode 13, a condenser 14 and a resistor 15. A quasi-load current is controlled through a Schmitt trigger circuit composed of transistors 16, 17 and resistors 18-20 by the voltage. This current is flowed through a quasi-load resistor 21 by ON or OFF control of the output transistor 17 of the Schmitt trigger circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching type DC power supply device that controls switching of DC input to supply stable DC current to an output load. The present invention relates to a DC power supply device designed to prevent rise in power.

FIG. 1 is a circuit configuration diagram of a conventional stabilized DC power supply device using this type of pulse width control method, in which 1 is an input terminal into which a DC current is input, 2 is a switching transistor, and 3
is an output transformer for voltage conversion, 4 and 5 are rectifier diodes, 6 is a smoothing coil, 7 is a smoothing capacitor, 8 is a diode for discharging the excitation energy of the output transformer 5,
Reference numeral 9 denotes a pulse width control circuit, which obtains a DC output from the output transformer 6 and controls the switching of the transistor 2. 10 is a resistor for a pseudo load to maintain the output voltage at a constant voltage even when there is no load, and 11 is an output terminal.

According to the circuit shown in FIG. 1, the output voltage of the pulse width control circuit 9 turns on the transistor 2, which causes the input terminal 1
The direct current applied to the output transformer 3 is converted into voltage, rectified, and smoothed in a pulsed manner through the output transformer 3, and outputs a direct current voltage. Then, the control circuit 9 controls the transistor 2 to turn on and off so as to maintain the output at a constant voltage by controlling the pulse width.

FIG. 2 shows the output characteristics of the circuit shown in FIG. 1, and the output voltage shows a constant voltage characteristic with respect to the load current Iot/C. This output characteristic is such that when the load current decreases due to the accumulation time during switching of the transistor 2, etc., the output voltage V is as shown by the broken line VC-c. may rise. Therefore, the resistance value of the resistor 10 is lowered, and the iE flow I
By increasing D, the output maintains constant voltage characteristics even under no load or light load.

However, this current ID always flows at a constant amount regardless of increases or decreases in the load current, and in some cases it may be necessary to increase it to 10 to 20% of the rated load current. Therefore, the power loss of the resistor 10 increases, the power efficiency of the DC power supply device is significantly reduced, and the mounting space for heat dissipation is increased.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a DC power supply device with low power loss and a stable pseudo load circuit.

In order to achieve the above object, the present invention forms a pseudo load circuit that operates only during no load or light load, detects the current flowing to the load with a transformer that also serves as a smoothing coil,
The load current flowing to the artificial load circuit is controlled on and off via a Schmitt trigger circuit.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 6 and 4. In the circuit of Fig. 5, those with the same reference numerals as those in Fig. 1 have the same functions, but in Fig. 3, a pseudo load circuit 12 is provided in place of the resistor 100 in Fig. 1. , and the provision of a transformer 6' which also serves as a smoothing coil. This pseudo load circuit 1♀ includes a diode 13, a capacitor 14, a resistor 15, which constitutes a rectifying and smoothing circuit, and transistors 16, 1, which switch in response to the output voltage and constitute a Schmitt trigger circuit.
7 and resistors 18, 19, and 20, and are connected and configured as shown in the figure. The transformer 6', which also serves as a smoothing coil, has its primary winding inserted in series with the output transformer 3.
The secondary winding is connected to the rectifying, smoothing and Schmitt trigger circuit.

The operation of the pseudo load circuit 12 shown in FIG. 3 is as follows: First, the load current is transferred from the primary winding of the smoothing coil 6' to the secondary winding and the diode 13. It is detected by a rectifier and smoothing circuit composed of a capacitor 14 and a resistor 15, and this voltage causes the transistor 1 to
The pseudo load current I0 is controlled through a Schmitt trigger circuit composed of 6, 17 and resistors 18-20. This current is the output transistor 1 of the trigger circuit.
7, the current flows through the pseudo load resistor 21.

FIG. 4 shows the current flowing through the primary winding of the smooth chain 1-6' in FIG. 3, that is, the load current 1. FIG. 4 is an operating characteristic diagram of a detection voltage V and a pseudo load current ID for TiC. The detection voltage Vs also fluctuates as the load current increases or decreases, but the system
'Mituto trigger circuit high.

Due to the low opening values Vihr, VthL, the pseudo load current changes with hysteresis characteristics. Due to this characteristic, load instability and switching noise caused by main switch transistor 2, rectifier diode 4, etc.
Even if the dummy load current is added to 2, it is unlikely that the pseudo load current will cause oscillatory fluctuations. Also.

Detecting the load current using the smooth chime 6' eliminates the power loss caused by additionally inserting a detection resistor in series at the output section of the device, and it is possible to reduce power consumption.

As is clear from the above explanation, according to the present invention, a pseudo load circuit is provided that allows current to flow only during no load or light load, and the no load or light load state is detected by a transformer that also serves as a smoothing coil. - Since it is configured to control the load current flowing to the pseudo load circuit via the trigger circuit, it is possible to obtain a DC power supply device with low power loss, high efficiency, and a stable pseudo load circuit.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional stabilized DC power supply;
1 is a circuit characteristic diagram of FIG. 1, FIG. 6 is a circuit configuration diagram of a stabilized DC power supply device showing an embodiment of the present invention, and FIG. 4 is a circuit characteristic diagram of FIG. 6. 6'...Transformer that also serves as a smoothing coil7.14...
Capacitor 9...Pulse width control circuit 12...Pseudo load circuit 13...Diode 15, 18-21...Resistor L6, 17...Transistor Almost 1 figure, 2 figures, 6 AT style Engineering 〇No. 3 Figure 4 - Charge current I. Continued from page 1 ■Applicant: Nippon Telegraph and Telephone Public Corporation ■Applicant: NEC Corporation 5-33-1-0 Shiba, Minato-ku, Tokyo Applicant: Fujitsu Ltd. 1015 Kamiodanaka, Nakahara-ku, Kawasaki City■ Applicant Shindengen Kogyo Co., Ltd. 2-2-1 Otemachi, Chiyoda-ku, Tokyo

Claims (1)

[Claims] A stabilized DC power supply device that converts DC input into voltage via a transformer, rectifies and smoothes it, and outputs a load current, and prevents an increase in output voltage when the load is no load or light load, a load current detection transformer in which a primary winding is inserted in series with the transformer and also serves as a smoothing coil;
Consists of a Schmitt Φ trigger circuit that detects the voltage generated in the primary winding of the detection transformer via a rectifying and smoothing circuit, and a pseudo load driven by the output of the Schmitt trigger circuit, so that the output is unloaded. Alternatively, a stabilized DC power supply device comprising a dummy load circuit that allows a dummy load current to flow during light loads and blocks it during actual loads.