IL33115A - Charging system - Google Patents

Description

Improved charging system HUGHES AIRCRAFT COMPANY C; 31392 1 Background of the Invention · · 2 This . invention relates to pulse charging cir- 3 cuits and particularly to an. improved and efficient * 4 transformer charging system.

In high voltage power supply systems such as 6 the type utilized to charge pulse forming networks in 7 laser range finders or utilized to charge any energy 8 storage system, inefficiency and the presence of switch- 9 ing transients has been found to' cause severe problems. O 10 .Conventionally, a transformer is utilized with the primary. 11 winding coupled across a relatively low voltage power ) 12 source through a switch and with the secondary winding 13 coupled through a diode to a storage unit such as a pulse 14 forming network. The switch' is continuously pulsed until the pulse forming netv/ork is charged with a desired amount 16 of charge at a selected high voltage. A typical network 17 in this type of system may be charged to +2000 volts from 18 a +28 volt power, source, for example. The transformer 19 and primary charging current required by the stray capaci- : 20 tance voltage changes has been found to result in an in- 21' efficient operation because of the current dissipation in O 22 the switch and in the windings. Also, this undesired • 23 current increases the switching transients so as to ad- 24 versely affect the power source and the switch control circuits. . · 26 Briefly, one high voltage charging system, in 27 accordance with this invention includes a transformer 28 structure with the primary winding coupled across a power 1 source through a switch such as a transistor. The high 2 · voltage winding is segmented with each segment electri- 3 cally isolated from the others and from the output leads ♦ 4 by diodes or diode type devices arranged with a selected polarity. The voltage change across the stray capacitance 6 is substantially reduced as a result of this segmentation 7 so that dissipation of reflected current in the primary . 8 winding during the switching operations as well as inter- 9 ference with the switching is substantially reduced.

Also, the amplitude of developed switching transient 11 spikes is greatly reduced. In other arrangements in 12 accordance with the invention, the primary winding may 13 also be segmented and diode isolated. Further, the prin- 14 ciples of the invention are applicable to systems utili.zing half wave rectification or full wave rectification. 16 Therefore, it is an object of this invention 17 to provide an improved charging system. 18 It is a further object of this invention to 19 provide a voltage transformer charging system that is highly efficient. 21 It is another object of this invention to pro- O 22 vide a high voltage charging system · responsive to a rela- 23 tively low voltage power source and operable with a minimum 24 of current dissipation. ' ■ · It is still another object of this invention 26 to provide a transformer charging system in which the 27 effect of stray capacitance is substantially reduced. 28 It is still another object of this invention 29 to provide improved transformer structures. 1 Description of the Drav/ings 2 The novel features of this invention, as well 3 as the invention itself, both as to its organization and 4 method of operation, will best be understood from the accompanying description, taken in connection with the 6 accompanying drawings, in which. like reference characters 7 refer to like parts, and in which: ' 8 FIG. 1 is a schematic block and circuit diagram 9 of a high voltage transformer charging system in accordance with the principles of the invention; 11 FIG. 2 is a .schematic circuit diagram of an 12 alternate transformer arrangement that may be utilized 13 in the system of FIG. 1. within the principles of the ■ 14 invention; - 15 FIG.. 3 is an equivalent circuit diagram of the 16 transformer of the system of FIG. 1 in accordance with 17 the ' invention; 18 FIG. 4 is a schematic diagram of waveforms of 19 voltage and current as a function of time for explaining the operation of the system of FIG. 1; 21 FIG. 5 is a schematic diagram of voltage versus 22 two points of time for further explaining1 the relationships 23 of the stray capacity voltages; 24 FIG. 6 is a schematic circuit and block diagram of a full wave charging system in accordance with the in- 26 vention; arid . ' 27 FIG. 7 is a schematic circuit and block diagram 28 of a transformer charging system responsive to a two phase 29 driving source in accordance with the invention. . . . · ψ> Description of the Preferred Embodiment Referring first to FIG. 1, a high voltage charging . system in accordance with the invention in-eludes a transformer 10 having a primary winding 12, a secondary winding 14 and a suitable magnetic coupling material or medium 16. The winding.12 is coupled from a suitable power source such as a +28 volt power source 18 to one terminal of a switch such as to the collector of an npn type transistor 20. The. emitter of the tran-sistor 20 is coupled through a resistor 24 to a suitable source of reference potential such as ground and is also coupled to a differential amplifier or current comparator circuit 26.' The other input terminal of the differential amplifier 26 is coupled between resistors 28 and 30 which in turn are coupled between a +E reference voltage source 32 and ground. A bistable multivibrator or flip flop 36 has one output terminal coupled through a lead 31 to the base of the transistor 20 and has first and second input terminals with the first input terminal coupled to the differential amplifier 26 for terminating the charging transformer pulses.. The second input terminal is respon-sive to a signal from a turn on oscillator (not shown) for starting the charging operation. The high voltage or secondary winding 14 of the transformer 10 is divided into segments or portions 38, 40 and 42 which may be of sub- stantially the same number of turns. The segment 38 has one end coupled to a lead 44 which in turn is coupled to the cathode of a diode 46 and has a second end coupled 1. to the anode of a diode 48. The segment 40 has one end 2 coupled to the cathode of the diode 48 and the other end 3 coupled to the anode of a diode 50. The segment 42 has 4 one end coupled to the cathode of the diode 50 and has the other end coupled through a lead 51 to the anode of 6 a diode 52. The anode of the diode 46 and the cathode 7 of the diode 52 are coupled through respective leads 45 8 and 53 to a pulse forming network 54 which may periodi- 9 cally pass charge energy through a switch' 57 and a lead 56 to a utilization device such as a pump flash tube in 11. a laser system. The network 54 may be capacitive as Q 12 represented by a capacitor 55 coupled. etween the lead. 13 53 and the lead 45 which in turn is coupled to a suitable 14 source of reference potential such as ground. It is to be noted that the charging system of the invention is 16 applicable to charging any of a plurality of energy util- 17 ization and storage devices and is not to be limited to 18 any particular type. 19 Referring now to FIG. 2, which is another transformer arrangement in accordance with the invention, 21 the primary winding. may also be divided in segmented O 22 fashion corresponding to segments of the. secondary v/ind- 23 ing. . A transformer 58 includes a secondary winding 60 24 segmented similar to the winding 14 of FIG. 1 with the segments separated. by diodes 46, 48, 50 and 52 and in- 26 eludes a primary winding 61 having segments 62, 64 and • 27 68 separated by diodes 69, 70 and 72.' The winding 61 28 may be coupled between the source 28 and the switch 20 responsive to a switch drive source 63 similar to the arrangement of FIG. 1. In the illustrated arrangement, the switch 20 operates as one of the isolating diodes for the winding segments.

Referring now back to FIG. 1 as well as to the equivalent circuit diagram of FIG. 3, the transistor 20 is represented by a. switch 76 and the primary, sec-ondary and mutual inductances are represented by respec-, tive inductors L„, and L . A diode 78 represents a P. s. m ^ composite of the diodes in the secondary winding charging the stray capacitance Cs which has a value proportional to the numbe of secondary turns over the number of pri-mary turns. The system of the invention provides pulses of current to' the inductive elements but after the ini-tial charging of the stray capacitance Cg, very little current is required to be supplied to the capacitance Cs because of relatively small voltage changes thereacross Referring now to FIG. 4 as well as to FIG. 1, the oscillator pulse of a waveform 82 triggers the flip flop 36 to a first state which applies a switching pulse of a waveform 84 to the base of the transistor 20 so that current is conducted through the primary winding 12. At a time tQ which may represent the start of a charging operation, current of a waveform 86 flows through the collector of the . transistor 20 while the voltage of a waveform 88 starts to rise on the emitter of the transis- tor 20. The voltage of a waveform 90 on the collector of the transistor 20 oscillates similar to the current of the waveform 86 caused by the change of voltage of the stray capacitance C„. The resonant fluctuation of the waveform 86 is relatively small compared to that of a conventional transformer arrangement indicated by a waveform 92. Dissipation at the transistor 20 and in the transformer windings is indicated as a curve 96. for the system. of the invention, which energy loss is substantially larger for a conventional system. During the first half cycle or the period between times t^ and t^, the diodes 46,. 48, 50 and 52 are back biased so that current does not flow out of the winding 14 and the stray capacitance maintains its; charge. V7heri the emitter cur-rent of the waveform 88 increases to a threshold level 100, the differential amplifier 26 develops a pulse indicated as a' dotted pulse 102 to trigger the flip flop 36 to the opposite state. .The switching pulse of the waveform 84 falls to the lower level at time t^ to bias the transistor 20 to the nonconductive state. As a result, the current of the waveform 86 is terminated, the voltage is rapidly reversed across the secondary winding 14 and the diodes 46, 48, 50 and 52 are biased into conduction so that current of a waveform 106 flows to the pulse forming network 54. Thus, at time t-^, a positive flyback voltage is generated in the winding 14 and on the lead 53 and current flows into the capacitor 55 of the' network 54. The energy in the transformer 10, which is retained as lines of flux between times tQ and t^,' is transferred out of the winding 14 between times V · t^ and t2 when the flux lines collapse in the second half cycle of operation and the diodes 46, 48, 50 and 52 are all forward biased because of the reversal of voltage across the winding segments. During each second half cycle, the flyback voltage increases on the leads 51 and 53 from the previous half cycle as current flows to .the network 54. At time t2, the energy in the trans- former 10 is not completely, discharged as shown by the waveform 106.

At time t2 in response to the oscillator pulse of the waveform 82, the transistor 20 is biased into conduction and current flows through the winding 12 as indicated by the waveform 86. The diodes 46, 48, 50 and 52 are all reverse biased and the stray capacitance of the segments · is not discharged. The threshold voltage 100 at the' emitter of the transistor 20 is reached at time t^ in a relatively short period because energy re- mains in the transformer from the previous cycle. Also during the period between times t2 and ^3, current is not required for charging the stray capacitance in the transformer. Because of the relatively small fluctua- tions of voltage on the stray capacitance between times t2 and t^, dissipation in the transistor 20 and in the transfomer is relatively small to provide an efficient operation. Also, a minimum of voltage transients are applied to the power source 18.

After a few initial cycles have occurred, the charging operation continues in a similar manner with ' 1 the energy all passing out of the winding 14 into the 2 network 54 and as the energy discharge increases, the 3 charge up time increases . such as between times t^ and 4 t^. The stray capacitance remains substantially charged and the charge in the storage network is gradually in- 6 creased to a larger value during each second half cycle 7 as the flyback voltage increases on the lead 51. When 8 the network 54 is charged to a sufficient level, a . 9 sensing circuit (not shown) may. close the switch 57 and ( 10 transfer a high voltage pulse on the lead 56 to a util- 11 ization circuit (not shown) . For example, a voltage of Q 12 2000 volts may b.e developed in the network 54 as a result .13 of the continual transfer, of energy from the +28 volt 14 power source 18. The segmented primary winding of FIG. 2 operates in a similar · manner with the diodes conducting 16 such as between times tQ and t-^ but back biased such as 17 during times t^ and t2 to prevent the discharge of the 18 stray capacitance in each segment. It is to be noted 19 that the voltage swings in the primary and secondary windings may determine the desirability of segmenting 21 the first or second windings .or both windings in accor- .22 dance with the principles of the invention. 23 To further explain the segmented operation, 24 the graph of FIG. 5 shows the change of the stray capa- 25 citance voltage E-^, ∑2 and across each segment 38, 26 40 and 42 relative to 0 volts on the lead 45. After 27 the first charging cycle or period, lines 110, 112 and 28 114 show the voltage across the stray capacitance of 1 respective . segments 38 , 40 and 42 during a first half 2 cycle (t^ to t2) when the diodes are all forward biased. 3 During the following half cycle (t2 to t^) , when the ■ switch 20 is again conducting, the stray capacitance voltage of each segment reverses as shovm by lines 116 , 6 118 and 120 . In the graph of FIG. 1 the voltage changes 7 of lines 110 , 112 and 114 occur simultaneously. during 8 the period between times t-j_ and t2 and the voltage changes • 9 of lines 116 , 118 and 120 occur simultaneously between , 10 times t2 and t^. Thus in the system of the invention,- 11 the voltage reverses in each segment rather than around 12 the reference or 0 voltage level. This. small voltage 13 change across the stray capacitance results in a rela- 14 tively small reflected current flow in the primary wind- 15 ing 12 and a minimum of -energy dissipation. If the 16 voltage on the lead 53 is EQ at any charge up time, the 17 conventional change across the stray capacitance is 2EQ 18 during each switching operation which would cause a C„ x 2EN 19 current flow I m the primary of I .= —≤ - where AT <6T is the switching time of the .switch 20 . However in the 21 illustrated system of the invention, the voltage change e segments is E0 22 . with thre 2 X -g— since each winding re- 23 . verses about the average "on" voltage or average voltage 24 of that segment at any particular time of charge up of ■ a load or network, instead of around ground potential. 26 The stray . capacitance, current is thus reduced by a factor 27 of 6 in the illustrated system of FIG. 1 . The overall 28 efficiency of the arrangement of FIG. 1 , with the network 1 54 being charged to 2000 volts, has been estimated to 2 be improved by 20 percent over the conventional arrange- 3 ment. 4 Referring now to FIG. 6, a full wave drive source 130 applies, a signal such as a sine wave to a 6 primary winding 134 of a transformer 132. A secondary 7 winding 136 of the transformer 132 is divided into 8 winding segments 138, 140, 142, 144, 146- and 148. The ' 9 winding 136 has a center tap -141 coupled to a lead 149 with diodes 154 and 156 respectively coupled between 11 the center tap and the windings 142 and 144. Diodes 12 152, 150 and 147 are respectively coupled between wind- 13 ings 142 and 140, windings 140 and 138 and winding 138 14 and a lead.153. Diodes 158, 160 and 162 are respectively . coupled between v/indings 144 and 146, windings 146 and 16 148 and winding 148 and a lead 163. A load 166, which 17 may include a resistance RL, is coupled between the leads 18 163 and 149 and the lead 153 is coupled to the lead 163. 19 During a first half cycle, the diodes 156, 158, 160 and 162 are biased into conduction and DC (direct current) 21 current flows into the load in the direction of an 22 arrow 168. During this first half cycle, the diodes 23 154, 152, 150 and 147 are back biased so that a rela- 24 tively small change of voltage occurs across the stray capacitance of each segment resulting in a very small 26 stray capacitance current flowing through the primary 27 winding 134. During the second half cycle, the diodes 28 154, 152, 150 and 147 are biased into conduction and DC current flows into the load 166 along the path of the arrow 168. At the same time, the diodes 156, 158, 160 and 162 are back biased and a relatively small change ♦ occurs across the stray .capacitance of each segment resulting in a very small stray capacitance current flowing through the primary winding 134. Thus current dissipation due to charging stray capacity in the windings and in the drive source 130 are substantially eliminated as well as undesirable switching transients by the segmenting arrangement in accordance with the invention.

Referring now to the DC (direct current) to DC converter of FIG. 7, a two phase square wave drive source 170 applies pulses such as the square wave pulses of waveforms 172 and 174 which are 180 degrees out of phase from each other, to the bases of respective switching transistors 176 and 178, which may be npn type devices The emitters of the transistors 176 and 178 are coupled to a suitable reference potential such as ground and the collectors are coupled to opposite ends of a primary ■ winding 180 of a transformer 182. A source of reference potential 183 is coupled to a center point 184 of the winding 180 and may also be coupled to a center point 186 of a secondary winding 188. The winding 180 includes a suitable number, of segments such as 190, 192, 194 and 196 with "the cathode to anode paths of the diodes 198 and 200 respectively coupled between the point 184 and the winding 192 and between the windings 192 and 190.

Also, in a second portion of the primary winding, diodes 204 and 205 have anode to cathode paths respectively coupled between the point 184 and the winding 194 and between the windings 194 and 196. It is to be noted that the transistors 176 and 178 perform the diode or unidir-ectional function for the respective segments 196 and 190 The secondary winding 188 includes a selected.number of segments which may be 212, 214, 216, 218, 220 and 222. Diodes 224, 226, .228 and 230 have anode to cathode paths respectively coupled between the point 186 and the seg-ment 216, between the segments 216 and 214, between the ' segments 214 and 212 and between the segment 212 and an output lead 232. Diodes.'234, 236, 238 and 240 have anode to cathode paths respectively coupled between the point. 186 and the winding 218, between the windings- 218 and 220, between the windings 220 and 222 and between the winding 222 and the output lead 232.

In operation, during each half cycle of the ■ waveforms 172 and.174, one transistor 176, 178 or the other conducts and cvirrent is passed through one portion or the other of the primary winding 180, that is, betv/een the potential -source 183 and the conducting transistor. when the lower portion of the primary winding 180 is conducting, for example, the diodes 224, 226, 228 and 230 are back biased as the- energy is transferred to the upper portion of the winding 188. During the same half cycle, the transistor 176 is biased out of conduction and the upper portion of the secondary winding 188 is conducting current through the forward biased diodes 234, 236, 238 and 240 to the lead 232 as indicated by an arrow 233. The diodes 204 and 206 are reverse biased so that a stray capacitance current does not flow in section 194 and 196 of the primary winding. During the next half cycle, of the waveforms 172 and 174, the tran-sistor 176 is conducting, the transistor 178 is biased out of conduction, the diodes 234, 236, 238 and 240 are biased out of conduction and the diodes 224, 226, 228 and 230 are forward biased as current flows to the lead 232 as shown by the arrow 233. Also, the diodes 198 and 200 are reverse biased so that stray capacitance current does i not flow between 192 and 190 in the primary winding. Be-cause during the half cycle charging period of each half of the secondary winding 188 the diodes are back biased, a relatively small stray capacitance current flows, in the primary v/inding 180 as discussed relative to FIGS. 1, 2 and 6. Thus a highly efficient DC generator is provided in response to waveforms 172 and 174 which may be gener-ated by a bistable multivibrator responding to DC voltages, for example..

Thus there has been described an improved high voltage charging system operating with a high efficiency in which the transformer v/inding or v/indings are segmented and isolated with unidirectional elements so that when energy is transferred in the transformer through the pri-- mary winding, 'substantially no stray capacitive current flows in the 'secondary winding. Thus, substantial current is not induced in the primary winding from change of stray capacitance voltage and switching transients are minimized in the transformer. Upon removal of the source of energy, the flyback voltage in the secondary v/inding transfers current through all segments of the secondary winding to a load. The principles of the invention are applicable to either half wave or full wave operation.

What is claimed is:

Claims (6)

1. A pulse charging system Including a transformer having a primary winding terminated by a pair of input terminals adapted to be connected to a source of periodic pulses, and a secondary winding inductively coupled to the primary winding and terminated by a pair of output terminals across which a load is adapted to be connected, at least the secondary winding between the pair. of output terminals comprising separate segments, each with a given sense, serially interconnected by unidirectional current conductive devices, e.g., diodes, each having a polarity that agrees with the sense of the segments interconnected thereby.

2. A pulse charging system according to Claim 1 wherein the primary winding between the pair of .input terminals, comprises separate segments^ each with a given sense, serially interconnected by unidirectional current conductive devices, e.g., diodes, each having a polarity that agrees with the sense of the segments interconnected thereby.

3. A pulse charging system according to either of Claims 1 or 2 wherein a unidirectional current conduotive device, e.g., a diode, is connected to each one of the pair of output terminals, of the secondary winding and has a polarity that agrees with the sense of the segmen of the secondary winding connected to the same terminal as the device.

4. A pulse charging system according to either of Claims 1 or 2 wherein the secondary winding has a center-tap that divides the winding into two portions each of which comprises separate segments, each with a given sense, serially interconnected by a unidirectional current devicei e.g., a diode, the polarity of the devices agreeing with the sense of the segments interconnected thereby.

5. · A pulse charging system according to any of the preceeding claims wherein a direct current source is coupled to one of the input terminals and a transistor type switch is coupled to the other of the input terminals, and a current comparator circuit and a bistable multivibrator being connected to the transistor type switch for causing periodic pulses to be applied to the primary winding of the transformer.

6. A pulse charging system substantially as described above by way of example and with reference to the accompanying drawings . For the Applicants DR.RE HOLD (JOHN AMD PARTNERS