GB2137442A

GB2137442A - Rectifier circuit

Info

Publication number: GB2137442A
Application number: GB08407168A
Authority: GB
Inventors: William L Rorden
Original assignee: Grass Valley Group Inc
Current assignee: Grass Valley Group Inc
Priority date: 1983-03-28
Filing date: 1984-03-20
Publication date: 1984-10-03
Also published as: DE3410379A1; GB8407168D0; JPS59181970A

Abstract

The circuit includes a full wave rectifier 11 whose DC output is applied via a current limiter 31 to a storage circuit 27, 29. As shown, the current limiter consists of two coils 21, 23 wound on a common magnetic core with the one ends of the coils connected across the DC output of the rectifier and the other ends of the coils connected across the storage circuit. The circuit may be arranged to provide the same DC voltage output magnitude regardless of whether 120V or 240V AC is applied. If 240V AC is applied a switch 25 is opened whereas if 120V AC is applied the switch is closed and the circuit acts as a voltage doubler. <IMAGE>

Description

SPECIFICATION Voltage doubler circuit Background & Summary of the Invention Most electronic devices, including digital computers, operate on D.C. voltages, making it necessary that an A.C. line voltage be converted to a D.C.

voltage before it can be used to power the device.

The first step in the conversion process is to rectify the A.C. line voltage and to produce a D.C. output having a unregulated D.C. voltage. Since the A.C.

line voltage is often either 120 or 240 volts R.M.S., it is desirable that a nominally constant D.C. voltage of the same value be produced regardless of which A.C. voltage is available.

One well known conversion circuit is the full wave bridge rectifier, shown in Figure 1, which produces a D.C. voltage having a value which is equal to the average value of the A.C. line voltage. In Figure 2, there is shown a prior art conversion circuit which produces a no-load D.C. voltage having a vlaue which is equal to the peak-to-peak value of the A.C.

line voltage. In Figure 3, there is shown another prior art circuit which is capable of producing a no-load D.C. voltage having a value which is equal to either the peak value of the A.C. line voltage or to the peak-to-peakvalue, depending on the position in which the switch is set. Unfortunately, because of the low impedance A.C. current path in the circuit of Figure 3, a high peak current is experienced before the filter capacitors are fully charged. It is highly desirable that the peak current be kept as low as possible and that the crest factor, which is defined as the ratio of the values of the peak current to the average current, be minimized.One reason for this is that regulations in a number of European countries now specify the maximum harmonic power that a customer is permitted to reflect back to a public utility A.C. line and this inherently limits the maximum crest factor of the customer's equipment.

Another reason is that a high peak current can often actuate the protection circuitry of an uninterruptible power supply connected to the device being powered.

In accordance with the illustrated preferred embodiment of the present invention, a low crest factor voltage doubler circuit is introduced. This circuit produces a D.C. output voltage having a value which is equal to the average value of the input A.C.

voltage (Figure 6, switch 25 open) or to twice the average value of the input A.C. voltage (Figure 5 and Figure 6, switch 25 closed). The voltage doubler circuit comprises a diode bridge which is connected to a pair of filter capacitors through a dual winding limiting inductor. With the switch open (Figure 6), an A.C. current limited D.C. output voltage is produced having a value which is equal to the average value of the input A.C. voltage. With the switch closed (Figure 6 or Figure 5 without a switch), the two capacitors are effectively series connected since one is charged by the positive half cycle of the input A.C. signal and the other by the negative half cycle of the input A.C.

signal. Thus, the A.C. current is still inductor limited, but the value of the D.C. output voltage is equal to twice the average value of the input A.C. voltage. In either case, the circuit exhibits the regulation characteristic of a choke input filter.

Brief Description ofthe Drawings Figure 1 shows a prior art bridge rectifier circuit.

Figure 2 shows a prior art voltage doubling circuit.

Figure 3 shows a prior art switchable voltage doubling circuit.

Figure 4 is a block diagram of an A.C. to D.C.

voltage conversion system.

Figure 5 depicts a voltage doubler circuit which is constructed in accordance with the preferred embodiment of the present invention and which is used in the system shown in Figure 4.

Figure 6 depicts a voltage doubler circuit which is constructed in accordance with another preferred embodiment of the present invention.

Description of the Preferred Embodiment In Figure 4, there is show a block diagram of a system which is capable of converting an A.C. line voltage signal to a regulated D.C. voltage signal for use by an electronic device such as a digital computer. A source 1, which may comprise a direct or inductive coupling to a public utility A.C. line, provides an A.C. voltage signal. A voltage doubler 3 rectifies the A.C. voltage signal and produces a D.C.

voltage signal which has a value equal to either the average value or to twice the average value of the A.C. voltage signal supplied by source 1, as desired.

Typically, twice the average value of the A.C. voltage signal will be selected when source 1 supplies voltage at 120 volts R.M.S., and the average value of the A.C. voltage signal will be selected when source 1 supplies a voltage at 240 volts R.M.S.

Regulator 5 is used to hold the value of the output D.C. voltage of voltage doubler3 at the exact voltage which is required by device 7. Regulator 5 may comprise any of a number of well known circuits.

Device 7 may comprise any device, such as a digital computer, which requires a D.C. power source Voltage doubler 3 and regulator 5 may be either internal, or external, to device 7.

Figure 5 shows a voltage doubler 3 which produces an output D.C. voltage signal having a value that is twice the average value of the A.C. voltage signal supplied by source 1. An A.C. voltage signal is supplied by source 1 to series diodes 13 and 17.

Diodes 13 and 17 are connected through inductor 31 to series connected capacitors 27 and 29. The junction of capacitors 27 and 29 is in turn connected to source 1. This circuit operates in the same manner as does the circuit of Figure 6 with switch 25 closed.

A discussion of that operation is given below.

In Figure 6, there is shown a voltage doubler circuit 3 which is constructed in accordance with the preferred embodiment of the present invention. An A.C. voltage signal is supplied by source 1, at either 120 volts or 240 volts R.M.S., to a bridge 11 which comprisesfourdiodes 13,15,17, and 19. Four a typical 500 watt application, the four diodes 13-19 may comprise a Motorola MDA 2504 bridge rectifier assembly. Bridge 11 is connected, through inductor 31, to series connected capacitors 27 and 29 which may comprise, for example, 100 microfarad, 250 volt D.C., electrolytic capacitors. Inductor 31 may comprise, for example, an Arnold Engineering Co. AH188 core with two windings (21 and 23) of 420 turns each, and an air gap to produce an inductance of 288 mHY with the two windings 21 and 23 connected in series.A single-throw-single-pole switch 25 connects bridge 11 and source 1 to the junction of capacitors 27 and 29.

When source 1 supplies an A.C. voltage signal at 240 volts R.M.S., switch 25 is opened and the loaded D.C. output voltage signal value from voltage doubler 3 is equal to the average value of A.C. voltage, approximately 216 volts. During the positive half cycle of the A.C. voltage signal, the current path from source 1 is through diode 13, inductor winding 21, capacitors 27 and 29, inductor winding 23, diode 19, and back to source 1. During the negative half cycle, the current path from source 1 is through diode 15, inductor winding 21, capacitors 27 and 29, inductor winding 23, diode 17, and back to source 1. Thus, the peak current required from source 1 is limited by the series connection of inductor windings 21 and 23.

The D.C. output voltage is filtered and stored by the series connection of capacitors 27 and 29.

When source 1 supplies an A.C. voltage signal of 120 volts R.M.S., switch 25 is closed and a loaded D.C. output voltage signal value equal to approximately 216 volts is again produced. During the positive half cycle of the A.C. signal, the current path from source 1 is through diode 13, inductor winding 21, capacitor 27, switch 25, and back to source 1.

During the negative half cycle, the current path from source 1 is though switch 25, capacitor 29, inductor winding 23, diode 17, and back to source 1. Thus, it can be seen that current limiting is provided by inductor 31 regardless of the polarity of the A.C.

signal. The loaded D.C. output voltage signal value is equal to twice the average value of the inputAC.

voltage since capacitors 27 and 29 are effectively connected in series and each capacitor is charged independently to the average value of the input A.C.

voltage.

The circuit of Figure 6 was operated with a constant load and was found to be capable of generating a constant power of 540 watts. The output D.C. voltage range was found to be 180 to 240 volts for an inputAC. voltage of either 100 to 130 volts R.M.S. or 200 to 260 volts R.M.S. The D.C. load current was 3 amperes at 180 volts or 2.25 amperes at 240 volts. The D.C. output voltage rose to the no-load maximum below approximately 20% of the maximum output current. The crest factor remained below 2 under the above-described operating constraints in Europe.

Claims

1. An A.C. to D.C. voltage converter comprising: means for receiving an A.C. signal from a selected source, said A.C. signal having both an A.C. voltage and an A.C. current; rectifier means for routing the positive and negative going half cycles of the A.C. signal; current limiting means, coupled to the rectifier means, for limiting the A.C. current during each of its half cycles; storage means, coupled to the current limiting means, for storing a D.C. voltage therein, said D.C.

voltage being the output D.C. voltage of the converter.

2. An A.C. to D.C. voltage converter as in claim 1 wherein said current limiting means comprises: a magnetic core; and a pair of substantially equivalent coils wound on said core; one of the ends of each coil being coupled across the rectifier means and the other ends of each coil being coupled across the storage means.

3. An A.C. to D.C. voltage converter as in claim 2 wherein said storage means is capacitive.

4. An A.C. to D.C. voltage converter as in claim 2 wherein: said rectifier means includes a pair of serially connected diodes with the anode of one connected to the cathode of the other, the junction of said diodes being disposed to be coupled to one terminal of the A.C. source; and said storage means includes a pair of serially connected capacitors each of substantially the same value as the other, the junction of said capacitors being disposed to being coupled to the other terminal of the A.C. source to present a D.C. voltage across the pair of capacitors of a value equivalent to twice the average value of the A.C. voltage from the A.C. source when the converter is loaded.

5. An A.C. to D.C. voltage converter as in claim 2 further comprising switch means for selecting the value of the D.C. voltage stored by the storage means from a first and a second value.

6. An A.C. to D.C. voltage converter as in claim 5 wherein: the first D.C. voltage value being substantially equal to the average value of the A.C. voltage from the A.C. source when the converter is loaded; and the second D.C. voltage value being substantially equal to twice the average value of the A.C. voltage from the A.C. source when the converter is loaded.

7. An A.C. to D.C. voltage converter as in claim 6 wherein: said rectifier means includes a diode bridge being disposed to be coupled to one terminal of the A.C.

source; said storage means includes a pair of serially connected capacitors each of substantially the same value as the other; and switch means, being disposed to interconnect the other terminal of the A.C. source to the junction between said pair of capacitors, for selecting between said first and second D.C. voltage values.

8. An a.c. to d.c. voltage converter substantially as hereinbefore described with reference to Figures 4 and 5 or Figures 4 and 6 of the accompanying drawings.