JPH0353597Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) This invention is a current-driven type equipped with an undervoltage protection circuit.
It relates to DC-DC converters.

(Prior Art) A current-driven DC-DC converter has the following circuit configuration. In Fig. 1, PW1 is the input DC power supply of the converter, and is a commercial frequency current power supply,
It is formed from a full-wave rectifier circuit, an input capacitor C1, etc. Reference numeral 7 denotes a main output transformer, which includes a primary winding 8 and a secondary winding 9. 10 and 11 are diodes, 12 is a choke, and 13 is a capacitor, which together form a rectifying and smoothing circuit. RL is the load.

Next, PW2 is an auxiliary DC power supply for the drive circuit, which is operated by the output of the input DC power supply PW1, and is formed of, for example, a DC-DC converter, an output transformer, a rectifier circuit, an input capacitor C2, and the like. CON is a control circuit whose operation power supply is the auxiliary DC power supply PW2 for the drive circuit, and includes a differential amplifier that compares the detected output of the output voltage of the rectifying and smoothing circuit with a reference voltage for setting the output voltage. It consists of a PWM signal sending circuit that corresponds to the differential voltage. Reference numeral 2 denotes a driving transistor, and 3 a driving current transformer, which includes a primary winding 4, a base winding 5, and a control winding number 6. 1 is a main converting transistor; 14 is a resistor, which connects the primary winding 8 of the output main transformer 7, the primary winding 4 of the driving current transformer 3, and the collector/emitter of the main converting transistor 1; The input DC power source PW1 is connected in series with the output terminals of the input DC power source PW1.
The base winding of the drive current transformer 3 is connected between the base and emitter of the main conversion transistor 1, and the control winding 6 is connected in series with the resistor 14 between the collector and emitter of the drive transistor 2. It is connected to the output end of the circuit auxiliary DC power supply PW2, and the above forms a current-driven DC-DC converter, which operates as follows.

The control circuit CON compares the output voltage Vout with a reference voltage for setting the output voltage, and sends out a PWM signal with a period corresponding to the comparison difference voltage to turn the driving transistor 2 on and off.

As shown in FIG. 2A, which is an explanatory diagram of the operation, the excitation energy accumulated in the driving current transistor 3 during the ON period of the driving transistor 2 is transferred to the driving current transformer 3 when the driving transistor 2 is OFF. An auxiliary DC power supply for the drive circuit is connected to the control winding 6.
When no current flows from PW2, it is discharged to the base winding 5, and a base kick current flows through the main conversion transistor 1. As a result, when the main transistor 1 starts to turn on as shown in Fig. 2b, the current feedback action of the driving current transformer 3 causes the base current to flow rapidly as shown in Fig. 2d, and as shown in Fig. 2b. Turn on the main conversion transistor 1.

In addition, when the drive transistor 2 is on as shown in FIG. Figure 2b shows a reverse bias current flowing through the main transistor 1.
Turn it off like this.

And when the main conversion transistor 1 is on,
As shown in Figure 2e, the secondary winding 9 of the output main transformer 7
The voltage is rectified and smoothed by the diode 10 and the smoothing circuit to supply power to the load RL. When the main conversion transistor 1 is off as shown in FIG. 2b, the energy stored in the inductance 12 is transferred to the diode 11 as shown in FIG. 2g.
to continuously supply power to the load RL.

(Problems with the Prior Art) As described above, the OFF operation of the main conversion transistor 1 in the current-driven DC-DC converter is caused by the reverse bias current flowing through the control winding 6 that is carried out when the drive transistor 2 is ON. This is done by supplying Therefore, in order to reliably turn off the main conversion transistor 1, it is necessary for the drive transistor 2 to maintain the on operation until the main conversion transistor 1 is turned off. CON is designed to not operate when the input voltage drops. Therefore, during the turning off operation of the main conversion transistor 1, the output voltage of the input DC power supply PW1 decreases due to the commercial input being turned off or a power outage, and as a result, the output voltage of the auxiliary DC power supply PW2 for the drive circuit, which operates based on this output voltage, decreases. When the voltage drops below the operating voltage of the control circuit CON,
Since the control circuit CON ceases to operate, the driving transistor 2 is also turned off. Therefore, at the same time, the supply of reverse bias current to the main conversion transistor 1 is cut off, and at the same time, the input capacitor C1
By holding the output voltage of the input DC power source PW1 for a certain period of time, a base current that turns on the main conversion transistor 1 is caused to flow.

For this reason, current continues to flow through the primary winding 8 of the output main transformer 7, saturating the iron core, and the resulting large current poses a problem in that the main conversion transistor 1 may be damaged.

(Purpose of the invention) The present invention has been made for the purpose of providing a current-driven DC-DC converter with an undervoltage protection circuit that can solve the above-mentioned problems.

(Means of the present invention for solving problems) The features of the present invention are as follows. That is, an undervoltage detection circuit for detecting a drop in the output voltage of the input DC power supply and a semiconductor switching element for supplying reverse bias current that is turned on by the detection output thereof are provided. On the other hand, the drive current transformer is provided with a second control winding other than the conventional control winding, which is connected between the output terminals of the input DC power source via the reverse bias current supply semiconductor switching element. Then, in place of the drive transistor, which is turned off due to the inoperation of the control circuit when the output voltage of the auxiliary DC power supply for the drive circuit drops, it detects the drop in input voltage and supplies a reverse bias current to the main conversion transistor. In this way, damage to the main conversion transistor is prevented. Next, embodiments of the present invention will be described.

(Embodiment) (Structure) FIG. 2 is a circuit diagram of an embodiment of the present invention (portions with the same symbols as in FIG. 1 indicate equivalent parts). In the figure, PW1 is the input DC power supply, which is the commercial frequency current power supply.
AC and full wave rectifier circuit RF1, input capacitor C1
Consists of etc. PW2 is an auxiliary DC power supply for the drive circuit, and includes a DC-DC converter CONV, a transformer T, diodes D2 and D3, and the like. 7 is a main transformer for output; 10, 11, 12 and 13 are diodes forming a rectifying and smoothing circuit;
Capacitor, RL is load, CON is control circuit, 14
2 is a resistor, 2 is a driving transistor, and the above structure is the same as the conventional circuit explained in FIG.

Next, 3 is a driving current transformer, in addition to the conventional primary winding 4, base winding 5, and control winding 6,
A second control winding 6' is provided for the present invention.

PC is an undervoltage protection circuit, and consists of an undervoltage detection circuit DV and a reverse bias current supply semiconductor switching circuit R1, which are formed from the following parts.

In the undervoltage detection circuit DV, R1 and R4 are resistors, and DZ1 is a constant voltage diode, which form a series circuit and are connected between the output terminals of the input DC power source PW1. Q1 is a transistor for undervoltage detection, R3 is a resistor, and transistor Q1
The base of is the voltage regulator diode DZ1 and the resistor R.
The collector and emitter are connected to the output terminals of the input DC power source PW2 via a resistor R3.

Next, in the reverse bias current supply circuit R1, Q
2 is a reverse bias current supply transistor, D1 is a diode, R2 is a resistor, the base of transistor Q2 is connected to the connection point of R3 and transistor Q1, and between the collector and emitter is resistor R6 and the current drive current transformer. 3 to form a series circuit with the second control winding 6' of input DC power supply PW1.
connected between the output terminals of the Further, the collector is connected to the connection point between the resistor R1 and the constant voltage diode DZ1 via the diode D1 and the resistor R2.

(Function) Since the present invention has the above configuration, the output voltage of the input DC power supply PW1 decreases due to an accident, and the output voltage of the drive circuit auxiliary DC power supply PW2 decreases, causing the control circuit CON to operate. gone,
Even if the driving transistor transformer 2 is turned off, the replacement main transistor 1 will not be damaged unlike the conventional circuit. In other words, input DC power supply PW
When the output voltage of Q1 becomes equal to or less than the Zener voltage of the constant voltage diode DZ1 for setting a low voltage, the undervoltage detection transistor Q1 immediately turns off, detects a decrease in the output voltage, and as a result, the base current flows. Then, the reverse bias current supply transistor Q2 of the reverse bias current supply circuit R1 is turned on as shown in FIG. 4a'. For this reason, [input DC power supply PW1
→Resistor R6→Second control winding 6'→Transistor Q
2 emitter/collector → input DC power supply PW1]
A circuit is formed, and a reverse bias current is passed through the second control winding 6'. Therefore, the main converting transistor 1 is turned off at the same time as the drive transistor input is turned off, so it is possible to prevent the main converting transistor 1 from being damaged due to the flow of a large current.

Furthermore, when the reverse bias current supply transistor Q2 is turned on, the cathode voltage of the constant voltage diode DZ1 is lowered, so that the undervoltage detection transistor Q1 is reliably turned off. Therefore, chattering etc. can be prevented and the protection operation can be stabilized.

In addition, in this circuit of the present invention, the input DC power supply PW1
The protection operation is performed only when the output voltage of the drive circuit auxiliary DC power supply PW2 decreases, and when the output voltage decreases only in the drive circuit auxiliary DC power supply PW2, the undervoltage protection circuit of the present invention does not operate and no protection is performed.

(Effect of the invention) As described above, according to the invention, current-driven DC
- Since the output voltage of the input DC power supply in the DC converter is reduced, it is possible to reliably prevent damage to the main conversion transistor.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional circuit, FIG. 2 is a waveform diagram for explaining its operation, FIG. 3 is a circuit diagram of an embodiment of the present invention, and FIG. 4 is a waveform diagram for explaining its operation. PW1...Input DC power supply, AC...Commercial frequency AC power supply, FR1...Full wave rectifier circuit, C1...Input capacitor, PW2...Auxiliary DC power supply for drive circuit, CONV...DC-DC converter, C2... …
Input capacitor, 7... Output main transformer, 8...
...Primary winding, 9...Secondary winding, 10, 11...Diode, 12...Chiyoke, 13...Capacitor, RL...Load, 3...Drive current transformer,
4...Primary winding, 5...Base winding, 6...Control winding, CON...Control circuit, 2...Drive transistor, PC...Undervoltage protection circuit, DV...Undervoltage detection circuit , R1, R3, R4...Resistance, DZ
1...Main voltage diode, Q1...Transistor for undervoltage detection, SSS...Drive transistor short circuit, Q2...Short circuit transistor, R2...
Resistor, D1...diode.

Claims (1)

[Claims for Utility Model Registration] Control that is operated by a predetermined output of an auxiliary DC power supply for a drive circuit operated by an input DC power supply, and sends an on/off signal corresponding to a comparative difference output between an output voltage and a reference voltage for setting the output voltage. a driving semiconductor switching element that is controlled on and off by circuit output;
A series circuit is provided between a primary winding of an output main transformer connected to the input DC power supply, a primary winding of a drive current transformer, and a collector-emitter of a conversion main transistor, and the drive semiconductor switching When the element is turned on, current is caused to flow through a control winding provided in the drive current transformer, and a reverse bias current is applied to the conversion main transistor through the base winding of the drive current transformer to turn the element off; The excitation energy accumulated in the drive current transformer during the ON period of the drive semiconductor switching element causes a base current to be applied to the base winding of the drive current transformer by transformer action when the drive semiconductor switching element is OFF. DC-DC supplies power to a load by rectifying and smoothing the secondary winding voltage of the output main transformer sent by the on-off operation of the main conversion transistor. In the converter, the drive current transformer is provided with a second control winding, and further includes an undervoltage detection circuit that detects a drop in the output voltage of the input DC power supply, and an undervoltage detection circuit that is turned on by the output of the undervoltage detection circuit, and the drive current transformer is turned on by the output of the undervoltage detection circuit. A DC device comprising a reverse bias current supply circuit including a reverse bias current supply semiconductor switching element connected in series with the second control winding of the current transformer and between the output terminals of the input DC power source. -DC converter.