GB2300079A

GB2300079A - Circuitry of a charging circuit for a welding capacitor

Info

Publication number: GB2300079A
Application number: GB9608132A
Authority: GB
Inventors: Oliver Rarrek
Original assignee: Obo Bettermann GmbH and Co KG
Current assignee: Obo Bettermann GmbH and Co KG
Priority date: 1995-04-20
Filing date: 1996-04-19
Publication date: 1996-10-23
Anticipated expiration: 2016-04-19
Also published as: GB2300079B; DE19514555A1; GB9608132D0

Description

2300079 Circuitgy of a charcring circuit for a weldin-cr caDacitor The

present invention relates to circuitry of a charging circuit for a welding capacitor, in which a rectifier connected in use to a mains voltage source is provided on a primary side and the welding capacitor is charged on a secondary side via a means supplied with the rectified voltage on a primary side.

Previous charging circuits use a normal mains transformer with rectification and charging resistor or switched mode mains power supply (downward converter) and primary switched mode mains power supply (flyback converter, flux converter).

In the latter the mains voltage is rectified and equalised with a filter capacitor, which disadvantageously results in a high pulse-shaped current consumption as well as a change in the shape of the sinusoidal mains current waveform itself. In addition, this circuitry is associated with a high reactive power consumption. The energy transfer to the welding capacitor occurs via a transformer which is connected on the primary side to the rectified mains voltage and on the secondary side to a welding capacitor having a rectifying element.

Proceeding f rom this prior art, the aim of the present invention is to create circuitry which by dispensing with the f ilter capacitor makes possible a current consumption from the mains supply which is adapted as far as possible to the mains voltage waveform so that the reactive power consumption is thus small.

Accordingly, the present invention provides circuitry of a charging circuit for a welding capacitor, in which a rectifier connected in use to a mains voltage source is provided on a primary side and the welding capacitor is charged on a secondary side via a means supplied on a primary side with the rectified voltage, wherein the charging operation is controlled via a control circuit which is fed with the rectified mains voltage value, the mains voltage waveform, the mains current and the capacitor voltage, by means of which control circuit the current adjustment, the current waveform adjustment and the switched mode energy release from the primary to the secondary winding of a transformer and the charging of the welding capacitor is performed at high clock speed.

In one embodiment, the control circuit is adapted to control the charging operation such that when the capacitor is discharged only a small energy transfer occurs and with an increase in capacitor charging an increase in the energy to be transferred, which increases proportionally with the capacitor voltage, occurs with the result that the capacitor voltage rises linearly or almost linearly over time.

Preferably, the circuitry comprises a first voltage divider circuit for dividing the rectified mains voltage, the mean value of the mains voltage being tapped and fed into the control circuit as the mains voltage value.

Preferably, the circuitry comprises a second voltage divider circuit for dividing the rectified mains voltage, the divided voltage being fed into the control circuit for the adjustment of the shape of the mains voltage waveform.

In a preferred embodiment a load is connected to the rectified circuit, from which load a voltage proportional to the mains current is tapped and fed into the control circuit as a controlled magnitude for the current adjustment.

Preferably, the load is an ohmic resistor.

The circuitry of the present invention is based, in the same manner as the prior art, on the principle of the switched mode mains power supply. However, in the present invention the mains voltage is directly rectified and supplied to a switched mode mains power supply. By the corresponding control circuit it is also ensured that the current taken from the mains supply is approximately sinusoidal. In accordance with the invention the mains voltage may vary in voltage from 90 volts to 240 volts since the control circuit increases the current consumption as the input voltage decreases. In addition, the energy to be transferred is controlled by the capacitor voltage. This means that, when for example the capacitor is discharged, only a little energy has to be transferred. As the capacitor voltage increases, the energy to be transferred increases proportionally with the capacitor voltage. An almost linear rise in the capacitor voltage over time is consequently produced.

When the welding capacitor is discharged full power can not immediately be applied as the rectifier diode would then be destroyed. The power transfer occurs in switched mode by the switching transistor being connected and disconnected in a pulsed manner controlled by the control circuit. The mains current is adjusted by the control circuit so as to correspond to the waveform of the mains voltage, whereby the sinusoidal waveform is retained. In the described embodiment of the present invention a cos p of 0.99 is achieved.

A preferred embodiment of the present invention will now be described hereinbelow by way of example only with reference to the accompanying Figure.

A rectifier is designated by reference sign V1. The input side of the rectifier V1 is connected in use to an alternating mains voltage and the output side is connected to a rectified mains voltage circuit.

Ohmic resistances are designated by reference signs R1 to R7.

A switching transistor is designated by reference sign V2, a rectifier diode by reference sign V3, a welding capacitor by reference sign Cl and a transformer having a primary winding 1,2 and secondary winding 3,4 by reference sign T1.

A control circuit is designated by reference sign Si.

In the primary circuit of the transformer T1, a first voltage divider circuit Rl, R2 is formed, from which the mean value of the mains voltage is tapped and is made available to the control circuit S1 for current adjustment. The mains voltage is also divided by a second voltage divider circuit R3, R4, from which the mean value of the mains voltage is tapped and made available to the control circuit S1 for the adjustment of the waveform shape. R5 represents a load from which a voltage proportional to the mains cur:ent is tapped and made available to the control circuit S1.

In the secondary circuit a further voltage divider circuit R6, R7, is formed, which circuit divides the capacitor voltage. This divided voltage is made available to the control circuit S1 for current adjustment.

The mains voltage is rectified by the rectifier V1. The current is passed to the switching transistor V2 via the rectifier V1, the primary winding 1, 2 of transformer T1 and the resistor load RS. At the same time energy is stored in the transformer T1, and after the transistor V2 is switched off this energy is transferred via the secondary winding 3, 4 of the transformer Tl and the rectifier diode V3 to the capacitor Cl. The capacitor voltage is increased with each switching cycle. This is repeated at very high frequency until the capacitor voltage has reached its set value.

1 the The mains current consumed is controlled by means o control circuit S1 and the sequential voltage values are fed into the control circuit S1 so that the mains current increases with the capacitor voltage. The mains current is in addition made to conform to the mains voltage waveform (sinuscidal) and in the case of lower mains voltages (mains input) the mains current is increased. The control of the mains current is performed by pulse width and frequency modulation.

By employing the control principle of the control circuit S1 of the present invention, it is no longer necessary to use a very large mains filter capacitor as required by the prior art after the rectification at rectifier V1. Indeed, the transformer Tl may have a very small and simple construction on account of the high switching frequency. Furthermore, the current consumption from the mains input is largely adapted to the mains voltage waveform of the mains input, and thus the reactive power consumption is very small.

It will be understood that the present invention is not restricted to the exemplified embodiment, but may be modified in many different ways within the scope of the invention as defined in the appended claims.

claims 1. Circuitry of a charging circuit for a welding capacitor, in which a rectifier connected in use to a mains voltage source is provided on a primary side and the welding capacitor is charged on a secondary side via a means supplied on a primary side with the rectified voltage, wherein the charging operation is controlled via a control circuit which is fed with the rectified mains voltage value, the mains voltage waveform, the mains current and the capacitor voltage, by means of which control circuit the current adjustment, the current waveform adjustment and the switched mode energy release from the primary to the secondary winding of a transformer and the charging of the welding capacitor is performed at high clock speed.

Claims

2. Circuitry according to Claim 1, wherein the control circuit is adapted

to control the charging operation such that when the capacitor is discharged only a small energy transfer occurs and with an increase in capacitor charging an increase in the energy to be transferred, which increases proportionally with the capacitor voltage, occurs with the result that the capacitor voltage rises linearly or almost linearly over time.

Circuitry according to Claim 1 or 2, comprising a first voltage divider circuit for dividing the rectified mains voltage, the mean value of the mains voltage being tapped and fed into the control circuit as the mains voltage value.

4. Circuitry according to one of Claims 1 to 3, comprising a second voltage divider circuit for dividing the rectified mains voltage, the divided voltage being fed into the control circuit for the adjustment of the shape of the mains voltage waveform.

Circuitry according to one of claims 1 to 4, comprising a load connected to the rectified circuit, from which load a voltage proportional to the mains current is tapped and is fed into the control circuit as a controlled magnitude for the current adjustment.

6. Circuitry according to claim 5, wherein the load is an ohmic resistor.

7. Circuitry of a charging circuit for a welding capacitor substantially as hereinbefore described with reference to the accompanying Figure.