Converter with hold-up circuit and inrush-control circuit
A holdup circuit includes a high-voltage generation circuit that outputs a high voltage and a holdup capacitor charging/discharging circuit that includes a holdup capacitor that is charged by the high voltage output by the high-voltage generation circuit. An inrush control circuit includes a constant-current source that includes a first transistor and a second transistor. During start-up, input current flows through the second transistor, and after start-up and during normal operation, the input current flows through the first transistor.
1 . A DC-DC converter comprising:
an input terminal and an output terminal;
a first stage that is connected to the input terminal and that provides a regulated voltage to a voltage bus; and
a second stage including:
a switching circuit connected to the voltage bus; and
a transformer including primary and secondary windings, the primary winding is connected to the switching circuit; and
a holdup circuit including:
a voltage generation circuit that outputs a holdup-charging voltage that is larger than a voltage of the voltage bus and that includes:
an additional transformer including primary and secondary windings;
a driver connected to the primary winding of the additional transformer; and
an oscillator that generates a symmetric square wave that is applied to the driver; and
a holdup capacitor charging/discharging circuit that includes a holdup capacitor that is charged by the holdup-charging voltage output by the voltage generation circuit, wherein
an output voltage of the holdup capacitor charging/discharging circuit is connected to the voltage bus; and
the regulated voltage is maintained within a predetermined voltage range independent of variations in an input voltage applied to the input terminal.
2 . The DC-DC converter of claim 1 , wherein the voltage generation circuit includes a push-pull converter.
3 . The DC-DC converter of claim 1 , wherein the voltage generation circuit includes a DC blocking capacitor between the driver and the additional transformer.
4 . The DC-DC converter of claim 1 , wherein the holdup capacitor charging/discharging circuit includes at least one Zener diode that limits the voltage of the holdup capacitor.
5 . The DC-DC converter of claim 1 , wherein:
the holdup capacitor charging/discharging circuit includes a transistor and a resistor that are each connected to the holdup capacitor; and
a charging current of the holdup capacitor is limited to:
a
base
-
emitter
voltage
of
the
transistor
a
resistance
of
the
resistor
.
6 . The DC-DC converter of claim 1 , wherein the holdup capacitor provides energy to the DC-DC converter when an input voltage to the input terminal of the DC-DC converter is interrupted.
7 . The DC-DC converter of claim 6 , wherein:
the holdup capacitor charging/discharging circuit includes an optocoupler; and
when the optocoupler receives a holdup control signal, the holdup capacitor charges a capacitor connected to the voltage bus of the DC-DC converter.
8 . The DC-DC converter of claim 1 , further comprising an inrush control circuit including:
a first transistor; and
a constant-current source that includes a second transistor; wherein
during start-up, an input current flows through the second transistor; and
after start-up and during normal operation, the input current flows through the first transistor.
9 . A DC-DC converter comprising:
an input terminal and an output terminal;
a first stage that is connected to the input terminal and that provides a regulated voltage to a voltage bus; and
a second stage including:
a switching circuit connected to the voltage bus; and
a transformer including primary and secondary windings, the primary winding is connected to the switching circuit; and
a holdup circuit including:
a voltage generation circuit that outputs a holdup-charging voltage that is larger than a voltage of the voltage bus; and
a holdup capacitor charging/discharging circuit that includes a holdup capacitor that is charged by the holdup-charging voltage output by the voltage generation circuit;
an inrush control circuit including:
a first transistor; and
a constant-current source that includes a second transistor;
a third transistor connected to a gate of the first transistor;
a fourth transistor connected to a gate of the second transistor; and
a first resistor connected to the second transistor such that the input current flows through the first resistor; wherein
an output voltage of the holdup capacitor charging/discharging circuit is connected to the voltage bus;
during startup, an input current flows through the second transistor and is limited to:
a
base
-
emitter
voltage
of
the
fourth
transistor
a
resistance
of
the
first
resistor
;
after startup and during normal operation, the third transistor turns off, causing the input current to flow through the first transistor.
10 . The DC-DC converter of claim 8 , further comprising:
a second resistor connected to a gate of the first transistor; and
a third resistor connected to a gate of the second transistor.
11 . The DC-DC converter of claim 8 , further comprising:
a first Zener diode that is connected to the gate of the first transistor and that limits a gate-source voltage of the first transistor; and
a second Zener diode that is connected to the gate of the second transistor and that limits a gate-source voltage of the second transistor.
12 . The DC-DC converter of claim 8 , wherein the input current charges an input capacitor of the DC-DC converter.
13 . The DC-DC converter of claim 1 , wherein
the second stage further includes a rectification and filter circuit connected to the transformer; and
the output terminal is connected to the transformer through the rectification and filter circuit.
14 . The DC-DC converter of claim 1 , further comprising:
an input filter connected to the input terminal;
a controller that regulates an output voltage and/or an output current of the output terminal; wherein
the input terminal is connected to the switching circuit through the input filter and the first stage.
15 . The DC-DC converter of claim 1 , wherein the symmetric square wave generated by the oscillator has a frequency between about 10 KHZ and about 1 MHz.
16 . The DC-DC converter of claim 1 , wherein the first stage is a boost circuit.
17 . A DC-DC converter comprising:
an input terminal and an output terminal;
a first stage that is connected to the input terminal and that includes a control circuit that controls the first stage to provide a regulated voltage within a predetermined range to a voltage bus; and
a second stage including:
a switching circuit connected to the voltage bus; and
a transformer including primary and secondary windings, the primary winding is connected to the switching circuit; and
a holdup circuit including:
a voltage generation circuit that outputs a holdup-charging voltage that is larger than a voltage of the voltage bus and that includes:
an additional transformer including primary and secondary windings;
a driver connected to the primary winding of the additional transformer; and
an oscillator that generates a symmetric square wave that is applied to the driver; and
a holdup capacitor charging/discharging circuit that includes a holdup capacitor that is charged by the holdup-charging voltage output by the voltage generation circuit, wherein
an output voltage of the holdup capacitor charging/discharging circuit is connected to the voltage bus.