JP2569493Y2 - DC-DC converter - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a DC-DC converter having an auxiliary output.
The present invention relates to an auxiliary output stable supply circuit of a DC converter.

[0002]

2. Description of the Related Art A conventional circuit example is shown in FIGS. FIG.
If the circuit is used in a signal transmission circuit or a protection circuit for transmitting an auxiliary output in parallel with a main load which is an output of a power supply, the signal transmission circuit or the protection circuit will not operate when the main load is short-circuited. In addition, in the case of FIG. 2, the voltages of the output 1 and the output 2 are almost the same, and when the main load is short-circuited, the output voltage becomes zero and the added protection circuit or the like does not operate. The circuit in FIG. 3 shows a case where the overcurrent protection circuit performs ON width control. In this circuit, since the choke is on the main power 1 side, during normal operation, the output 2 connected to the signal transmission circuit and the protection circuit has a higher voltage than the output 1 connected to the main load.
In the case of this circuit, when the output 1 is short-circuited, a voltage is output to the output 2 to some extent. The required voltage cannot be maintained. or,
When an output voltage is required to some extent, the ON width cannot be reduced, and good results cannot be obtained as overcurrent characteristics.

[0003]

2. Description of the Related Art In response to demands for downsizing a power supply, a power supply system has been made by combining a DC-DC converter. Therefore, when a protection circuit and a signal transmission circuit are supplied from a power supply system, it is desired that those power supplies can also be supplied from Modicol. In such a case, it is necessary that the output of the protection circuit and the signal transmission circuit be stable even if the main load is short-circuited.

[0004]

FIG. 4 shows an embodiment of the present invention. T1 is a transformer, Q1 is a main switch element, D2 and D3 are smoothing diodes for output 1, L1 is a choke, C2 is a capacitor, and D1 is a capacitor. Is a diode for output 2, and C3 is a capacitor. R1 is a current detecting resistor, and may be a current transformer. M1 is a control circuit for the power supply, and a built-in overcurrent protection circuit is a circuit for intermittently controlling the oscillation as shown in FIG. C1 is a capacitor that determines the duration of the switching pulse during overcurrent protection based on the charging / discharging time constant of the capacitor. M2 is a circuit for controlling the voltage of the output 2 by changing the interruption time during overcurrent protection, and R2 and Q2 are a resistor and a transistor for controlling the interruption time constant.

In the overcurrent protection operation of the intermittent control, when the overcurrent protection operation is started, the fact that the protection operation is started is detected by using an output voltage or the like, and the oscillation is continued for a certain time (ON). Oscillation is stopped (OFF), and after a certain time, oscillation is restarted. If an overload is present, an overcurrent protection operation is started, and the operation is detected, and the above operation is repeated. The time for intermittently oscillating in the overcurrent protection operation utilizes the charge and discharge time of the capacitor, and the intermittent time is determined by the capacity of the capacitor and the charge and discharge current.

Referring to FIG. 6, (a) Q1 current indicates the current of the main switch element. As a judgment as to whether or not the overcurrent protection operation has been started, the output voltage of the output 1 of (b) is detected, and when the output voltage falls below a certain voltage, (c)
When the charging of C1 is started and the voltage of C1 reaches a certain voltage, the oscillation is stopped. At the same time, the discharging of C1 starts at a certain voltage, and the oscillation is restarted.
Repeat the above.

This circuit operates normally, for example, when the output 1 is 5 V
In the case of output, output 2 is 15 V to 30 V depending on the input voltage.
Is output. When the output 1 is short-circuited with the load and the overcurrent protection film circuit operates and the oscillation circuit is intermittently controlled, the output 2
C3 is charged while it is ON, and an output voltage can be supplied. Therefore, the voltage of the output 2 can be controlled by changing the intermittent time during overcurrent protection. With such a circuit configuration, even if the output 1 is short-circuited, a voltage can be supplied from the output 2 by controlling the intermittent time ratio during overcurrent protection.

[0008]

The power supply system is constructed by combining several DC-DC converter modules. In this case, the power supply of the protection circuit and the signal transmission circuit added in the power supply system must be able to supply power even if the main load or the like is short-circuited, and there is a demand for a converter module having such an auxiliary output. It is effective for such a power supply.

[Brief description of the drawings]

FIG. 1 shows a conventional circuit example 1

FIG. 2 shows a conventional circuit example 2

FIG. 3 shows a conventional circuit example 3

FIG. 4 is a circuit diagram of the present invention.

FIG. 5 is a current waveform of Q1 when the overcurrent protection circuit operates.

FIG. 6 shows operation waveforms of various parts of the present invention.

[Explanation of symbols]

T1 Transformer Q1 Main switch element D2, D3 Rectifying diode for output 1 L1 Smoothing choke for output 1 C2 Smoothing capacitor for output 1 D1 Rectifying diode for output 2 C3 Smoothing capacitor for output 2 R1 Current detecting resistor M1 Control circuit C1 Discharge time constant of overcurrent protection circuit Capacitor M2 Circuit for controlling voltage of output 2 by changing disconnection time during overcurrent protection R2 Controlling time constant of C1 Transistor controlling time constant of C2 C1

Claims (1)

(57) [Scope of request for utility model registration] 1. A series circuit of a main DC power supply and a primary coil of a transformer is turned on and off by a main switching element, an output voltage of a secondary coil of the transformer is smoothed and rectified, and one or more output voltages are respectively passed through forward diodes. A multi-output type DC-DC converter that supplies DC power to two or more outputs having a main output and one or more auxiliary outputs, and includes an overcurrent protection circuit that operates when at least one of the main outputs is overcurrent. In the DC converter, the oscillation of the control circuit of the main switching element is interrupted only when the at least one main output is overcurrent, and the inductance provided on the plus side of the main output has an output voltage at the time of short circuit. , Auxiliary output keeps stable voltage,
When the oscillation is stopped, the stable voltage is continuously held by a capacitor provided at the output terminal of the auxiliary output, and power is stably supplied to the load from the auxiliary output. converter.