WO2002097549A1

WO2002097549A1 - Variable multi-channel high voltage power source, with accurate current sense

Info

Publication number: WO2002097549A1
Application number: PCT/US2002/017165
Authority: WO
Inventors: William E. Wevers; Torleif O. Bjornson; George Dumitrescu
Original assignee: Aclara Biosciences, Inc.
Priority date: 2001-05-31
Filing date: 2002-05-31
Publication date: 2002-12-05

Abstract

A circuit generates a plurality of channels of high-voltage output signals (212) from the substantially constant bulk power source output signal of a high-voltage power source (204) that is powered by a low-voltage power source (206). The circuit includes a plurality of high-voltage regulators (208), each high voltage regulator corresponds to a particular one of the channels. Each high-voltage regulator (208) regulates the bulk power source output signal based on an input control voltage signal for that channel e.g., provided from a microprocessor (202) to generate a regulated high-voltage output signal for that channel. The regulated high-voltage output signal has voltage level corresponding to a level of the input control voltage signal for that channel. The high-voltage regulator circuit (208) also generating a high-voltage tracking power signal (211) for that channel having a voltage level within a predetermined range of the regulated high-voltage output signal. Furthermore, each channel has associated with a current sensor (210). The current sensor (210) for a particular channel is powered by the high-voltage tracking power signal (211) for that channel and generates an output high-voltage digital current sensing signal for that channel that corresponds to the current in the regulated high-voltage output signal for that channel. An isolation barrier (216) is provided for each channel. Each isolation barrier (216) translates the voltage level of the output high-voltage digital current sensing signal for that channel to a low-voltage level.

Description

VARIABLE MULTI-CHANNEL HIGH

VOLTAGE POWER SOURCE, WITH ACCURATE CURRENT SENSE

TECHNICAL FIELD [0001] The present invention is in the field of high- voltage power sources and, in particular, relates to high- voltage power sources that can sink or source even relatively small amounts of current while highly accurately maintaining one or more desired output voltages.

BACKGROUND [0002] High- voltage power sources are well-known in the art. For example, Figure 1 illustrates a conventional high voltage power source. The configuration and operation of the Figure 1 conventional high- voltage power source is now briefly discussed. Thereafter, some disadvantages of the Figure 1 conventional high- voltage power source are described. [0003] Turning now to Figure 1, a conventional high- voltage power source circuit 100 is schematically illustrated. As can be seen from Figure 1, a number of the circuits of the power source circuit 100 are powered by a low- voltage power circuit 104. A circuit 101 is provided for each channel of high- voltage output. The variable high- voltage output 110 of each circuit 101 is controlled nominally by an analog input voltage control signal 103 provided to a variable high- voltage power source circuit 106 of that circuit 101. The analog input voltage control signal 103 for each circuit 101 is provided to the variable high- voltage power source for the circuit 101 from a microprocessor 102 via a digital-to-analog converter (DAC) 118. [0004] For each circuit 101, the current in the high- voltage output signal of the variable high- voltage power source circuit 106 is measured by an analog current sense circuit 114 (typically comprised of high-gain current sense amplifier components), as a function of a voltage drop across a current sense resistance 108. The analog sense circuit 114 generates an analog current sense signal nominally indicative of the current of the high- voltage output signal of the variable high- voltage power source circuit 106.

[0005] A "tracking" power supply circuit 112 operates on the output of the variable high- voltage power source circuit 116 to generate a low- voltage power signal, which is used to power the analog current sense circuit 114 and tracks the output of the variable high- voltage power source circuit 106. [0006] The current sense output of the current sense circuit 114 is provided to an analog isolation barrier circuit 116, also powered by the tracking signal from the tracking power supply 112. The analog isolation barrier circuit 116 voltage-translates the analog current sense signal, and the thus-translated analog current sense output is provided to a ground-referenced analog-to-digital converter (ADC) 120. The digital output of the ADC 120 is then provided to microprocessor 102.

[0007] A significant disadvantage of conventional high- voltage power sources, such as are illustrated in Figure 1 , is the high cost of providing a variable high- voltage power source for each channel of high- voltage output. Furthermore, while such circuits are typically timely in responding to commands for increasing output voltage, they are typically not timely in responding to commands for decreasing output voltage. A further disadvantage of the Figure 1 circuit 100 is the error in current sense results associated with the analog voltage translation performed by the analog isolation barrier circuit 116.

SUMMARY [0008] A circuit generates a plurality of channels of high- voltage output signals from the substantially constant bulk power source output signal of a high- voltage power source that is powered by a low-voltage power source. The circuit includes a plurality of high- voltage regulators, each high voltage regulator corresponds to a particular one of the channels. Each high- voltage regulator regulates the bulk power source output signal based on an input control voltage signal for that channel (e.g., provided from a microprocessor) to generate a regulated high-voltage output signal for that channel. [0009] The regulated high-voltage output signal has voltage level corresponding to a level of the input control voltage signal for that channel. The high-voltage regulator circuit also generating a high- voltage tracking power signal for that channel having a voltage level within a predetermined range of the regulated high- voltage output signal. Furthermore, each channel has associated with it a current sensor. The current sensor for a particular channel is powered by the high- oltage tracking power signal for that channel and generates an output high- voltage digital current sensing signal for that channel that corresponds to the current in the regulated high- voltage output signal for that channel.

[0010] An isolation barrier is provided for each channel. Each isolation barrier translates the voltage level of the output high- voltage digital current sensing signal for that channel to a low-voltage level.

BRIEF DESCRIPTION OF FIGURES [0011] Figure 1 schematically illustrates a prior art variable power supply circuit with current sensing.

[0012] Figure 2 schematically illustrates a variable power supply circuit in accordance with an embodiment of the invention.

[0013] Figure 3 schematically illustrates an embodiment of the high voltage regulator and current sense power circuit 208 of the Figure 2 circuit 200.

[0014] Figure 4 schematically illustrates an embodiment of the current sense and isolation barrier circuit 213 of the Figure 2 circuit 200.

[0015] Figure 5 schematically illustrates an alternate embodiment of the

Figure 3 embodiment. [0016] Figure 6 schematically illustrates an alternate embodiment of the

Figure 4 embodiment.

[0017] Figure 7 schematically illustrates an alternate embodiment of an isolation barrier circuit. DETAILED DESCRIPTION [0018] In accordance with one aspect of the invention, an improved high- voltage power supply circuit (with current sensing) is provided. An embodiment of the improved high- voltage power supply circuit is illustrated in Figure 2. [0019] Turning now to Figure 2, the improved high- voltage power supply circuit 200 includes a circuit 201 for each channel of high- oltage output. In particular, for each channel of high- voltage output, the corresponding circuit 201 includes a high voltage regulator circuit 208 that operates on the high-voltage output signal of the single fixed DC high- voltage power source 204 to generate a variable high voltage power signal 209. (Depending on the number of channels of high- voltage output, more than one fixed DC high- voltage power source may ^' be employed.) As with the prior art circuit 100 shown in Figure 1 and discussed in the Background, the analog control voltage (in this case, analog control voltage 203) is provided from a DAC (in this case, DAC 218) based on a command from a microprocessor (in this case, microprocessor 202).

[0020] The current in the high- voltage output signal 209 of the variable high-voltage power regulator circuit 208 is measured by a current sense circuit 214, as a function of a voltage drop across a current sense resistance 210. The analog current sense circuit 214 employs the high voltage output signal 209 as a reference voltage, instead of ground or zero volts. As a result, the accuracy of the current sense circuitry 214 output is substantially unaffected by large changes in the high voltage output signal 209 that would otherwise result from common mode voltage differences between the tracking signal and amplifier components of the analog current sense circuit 214. [0021] Now, a particular circuit embodiment 300 of the high voltage power regulator circuit 208 is described with reference to Figure 3. Then, a particular embodiment of the current sense circuit 214 is described with reference to Figure 4. [0022] Turning now to Figure 3, the circuit 300 operates on a "bulk source" input high-voltage signal BLKSRC 301 from the high-voltage power source 204 and a control voltage VCNT0 303 based on analog control voltage signal 203 from the DAC 218. As output, the circuit 300 provides signal TRKREFO 316, which is the regulated high- voltage output (also used as the "tracking reference", or ground, for the current sensing circuitry). The circuit 300 also provides as output the tracking power source signal TRKPWR0 314 to power the current measurement circuitry ~ approximately five volts above

TRKREFO 316. Finally, the circuit 300 provides signal VSNS0 318, which is the high- voltage sensing amplifier output ~ a voltage proportional to the regulated high-voltage output TRKREFO 316. [0023] The operation of the Figure 3 circuit embodiment 300 is now described. There are two current sources 302, 308 operating to regulate the output voltage TRKREFO 316. The top current source 302 is a sourcing circuit comprised of six high- voltage MOSFET transistors, each of which share an equal voltage drop from the high- voltage source signal BULKSRC 301 to the regulated output TRKREFO 316. The number of high- voltage MOSFET transistors may be adjusted based on the desired total voltage drop from the high- voltage source signal BULKSRC 301 to the regulated output TRKREFO 316. More than one such MOSFET transistor is employed to distribute the high-voltage load. In other examples, other devices such as IGBT or BIMOSFET transistors are employed. The current through the top current source 302 is controlled by the current steering circuit 304, which provides for an "idling current" or "quiescent current" to maintain a DC bias in the current source 302, and also to keep the tracking voltage regulator 320 in conductive mode so that the regulated output TRKREFO 316 remains available. Additionally, the current steering circuit 304 controls the gate voltages of MOSFETS of the top current source 302 to increase or decrease the current through the top current source 302.

[0024] The bottom current source 308 is commanded to increase the amount of current through it whenever the regulated output TRKREFO 316 is above the target voltage set by the control voltage VCNT0 303. Conversely, the bottom current source 308 is commanded to decrease the amount of current through it whenever the regulated output TRKREFO 316 is below the target voltage set by the control voltage VCNT0 303. As the current through the bottom current source 308 is reduced, the current steering circuit also increases the current through the top current source 302, causing more current to be sourced to the regulated high- voltage output signal TRKREFO 316. The regulated high- voltage output signal TRKREFO 316 will increase until brought into balance such that the high- voltage sensing amplifier output VSNSO 318 is equal to the control voltage VCNTO 303. Additionally, VSNSO 318 is used by the microprocessor to monitor the high- voltage tracking signal TRKREFO 316. [0025] The control properties of the circuit 300 are determined at least in part by the values of the resistor 320 and capacitor 322 of the integrator circuit 310. In both the top current source 302 and the bottom current source 304, transient suppressor diodes are employed to protect the MOSFET transistors from being subjected to excessive voltages.

[0026] Turning now to Figure 4, the embodiment schematically illustrated therein is now described. As discussed above with respect to Figure 3, TRKREFO 316 is the regulated high- voltage output signal of the voltage regulator circuit 300, and TRKPWRO 314 is a reference voltage output of the voltage regulator circuit 300 that is, in one embodiment, five volts above TRKREFO 316. The current in the TRKREFO 316 signal flows through a resistor 402 operating as the current sense resistor 210 (Figure 2) and, thus, the voltage across the resistor 402 is proportional to the current in the TRKREFO 316 signal. [0027] In some examples, an operational amplifier 404 (e.g., part number

TLC27L7C) operates to translate (reference) the voltage across the resistor 402 to 2.5 volts above the TRKREFO 316 signal. The 2.5 V reference is from a voltage reference source circuit 406 (e.g., part number LT1004). The output voltage range from the resistor 402 is from OVto 2.5V over the range of measured currents, matching the input range of the analog-to-digital converter (ADC) 408 (e.g., part number AD7714). A twenty-four bit result is provided in the ADC 408 result register in two's complement form (where negative numbers represent negative currents). [0028] Now, with further reference to Figure 4, two other input signals are described. As described above with reference to Figure 2, these input signals are provided by the microprocessor 202 via the isolation barrier 216, and are utilized by the current sense circuitry 300 to configure the operation thereof. DATA_IN 410 is an input to the ADC 408 for binary, serial data from the microprocessor 202, for controlling the ADC 408. CON_CLK 414 is employed to clock the serial data into DATA_IN 410. For even more flexibility, other signals may be provided. For example, a select line (not shown) from the microprocessor 202 may be employed to select a particular channel for operation. As another example, a signal (not shown) may be provided to put the current sensing circuit 400 in a sleep mode when, for example, the channel is not in use. [0029] The twenty-four bit result from the (ADC) 408 is transmitted serially through a high voltage capacitor 419 (which is part of isolation barrier 420), thereby translating the logic levels referenced to TRKREFO 316 to a normal ground level associated with the microprocessor 202. The output signal CONV-DAT 421, contains digital data from the ADC 408. [0030] Figure 5 schematically illustrates an alternate circuit embodiment

1300 of the high voltage power regulator circuit 208, and Figure 6 schematically illustrates an alternate circuit embodiment 1400 of the current sense circuit 214. [0031] Turning now to Figure 7, an alternate circuit embodiment 700 of the isolation barrier 420 is schematically illustrated. The read data from the ADC 408 is indicated by reference numeral 702, while the TRKREFO 316 signal is indicated by reference numeral 704. The converted data output signal is indicated by reference numeral 706. The read data 702 is provided through a capacitor 708. The capacitor 708 and resistors 712, 714, 716 and 718 are all associated with node A and are collectively characterized by a time constant TCA that, in one example, is high enough not to significantly alter the read data 702. [0032] The reference signal 704 is provided through a capacitor 710. The capacitor 710 and resistors 720, 722, 724 and 726 are all associated with node B and are collectively characterized by a time constant TCβ. The impedance of the combination of capacitor 708 and resistors 712, 714, 716 and 718 is substantially the same (e.g., within about 5%) as the impedance of the combination of capacitor 710 and resistors 720, 722, 724 and 726. The diodes 728 and 730 protect the comparator 736 should the signals input to the comparator 736 go above a particular voltage (in one example, above +12V). Similarly, the diodes 732 and 734 protect the comparator 736 should the signals input to the comparator 736 go below a particular voltage (in one example, below ground). [0033] In one example, the voltage on the positive input 738 of the comparator 736 is slightly below 6V (i.e., half of 12V) and the voltage on the negative input 740 of the comparator 736 is slightly above 6V. The amount by which the inputs are below and above 6 V depends on the value of the resistor 716 for the positive input 738 and on the value of the resistor 722 for the negative input 740. These voltage offsets create a threshold for the comparator 736, which improves noise rejection. That is, the threshold is a nominal voltage difference between the inputs 738 and 740 of the comparator 736 when the read data 702 and the tracking reference signal 704 are not present. The threshold is further a function of the time constants TC_A and TCβ, in such a way that the signal on the positive input 738 does not drop below the signal on the negative input 740 before the converted data output signal 706 is transmitted.

Claims

WHAT IS CLAIMED IS:

1. A circuit to generate a high- voltage output signal, comprising: a high- voltage power source, powered by a low- voltage power source, that generates a substantially constant bulk power source output signal; a high-voltage regulator that regulates the bulk power source output signal based on an input control voltage signal to generate a regulated high- voltage output signal having a voltage level corresponding to a level of the input control voltage signal, the high- voltage regulator circuit also generating a high-voltage tracking power signal having a voltage level within a predetermined range of the regulated high- voltage output signal; a current sensor powered by the high- voltage tracking power signal and generating an output high- voltage digital current sensing signal that corresponds to the current in the regulated high- voltage output signal; and an isolation barrier that translates the voltage level of the output high-voltage digital current sensing signal to a low- voltage level.

2. The circuit of claim 1 , wherein the current sensor includes: current sensor analog circuitry that generates a high- voltage current sense analog signal having a voltage level that corresponds to the current in the regulated high- voltage output signal; and current sensor analog-to-digital converter (ADC) circuitry that translates the current sense analog signal into the output high- voltage digital current sensing signal.

3. The circuit of claim 2, wherein the ADC circuitry includes output circuitry to transmit the output high- voltage digital current sensing signal in a serial manner.

4. The circuit of claim 1, wherein the high- voltage regulator includes: a first current source ; a second current source that sinks an amount of sink current based on the voltage level of the regulated high- voltage output signal, wherein the first current source sources an amount of source current based on the current being sunk by the second current source; a current controller that controls the second current source based on a degree of correspondence between the regulated high- voltage output signal and the input control voltage signal, thereby controlling the voltage level of the regulated high-voltage output signal for that channel.

5. The circuit of claim 4, wherein: each of the first current source and the second current source includes a plurality of high-voltage regulating devices.

6. The circuit of claim 5, wherein: the number of high- voltage regulating devices is in accordance with a desired maximum voltage level of the regulated high- voltage output signal.

7. The circuit of claim 1 , wherein the current controller, wherein: the high- voltage regulator includes a sense amplifier that generates a sense amplifier output signal having a voltage proportional to the high- voltage tracking power signal; and the second current source determines the degree of correspondence between the regulated high- voltage output signal and the input control voltage signal based on a voltage difference between the input control voltage signal and the sense amplifier output signal.

8. The circuit of claim 2, wherein the current sensor analog circuitry includes: a current sense resistance across which the regulated high-voltage signal flows; a comparator that compares a resultant voltage across the current sense resistance with a reference voltage; and a difference generator operates based on the compare operation by the comparator to generate the current sense analog signal.

9. The circuit of claim 2, wherein the current sensor circuit includes: circuitry to receive a switching signal and, in response, switch the current sensor between an operating mode and a standby mode.

10. The circuit of claim 1, wherein the isolation barrier includes: first capacitor circuitry having an input to which the output high- voltage digital current sensing signal is provided, the first capacitor circuitry further having an output; second capacitor circuitry having an input to which the regulated high- voltage output signal is provided, the second capacitor circuitry further having an output; a comparator having a first input coupled to the output of the first capacitor circuitry and a second input coupled to the output of the second capacitor circuitry, the comparator further having an output, wherein the output high- oltage digital current sensing signal, translated to the low- oltage level, is provided at the output of the comparator.

11. The circuit of claim 10, wherein the isolation barrier further includes: threshold circuitry coupled to the first and second input of the comparator to create a nominal threshold voltage difference between the first and second input of the comparator.

12. The circuit of claim 11, wherein the threshold circuitry includes: a first resistor element coupling the output of the first capacitor circuitry to a ground across a first diode; and a second resistor element coupling the output of the second capacitor circuitry to a power supply across a second diode.

13. The circuit of claim 10, wherein: the isolation barrier is characterized by a first impedance at the input to the first capacitor circuitry and a second impedance at the input to the second capacitor circuitry; and the first impedance is substantially equal to the second impedance.

14. The circuit of claim 13, wherein: the first impedance is substantially equal to the second impedance such that the first impedance is equal to the second impedance within a 5% tolerance.

15. A circuit to generate a plurality of channels of high- voltage output signals, comprising: a high- voltage power source, powered by a low- voltage power source, that generates a substantially constant bulk power source output signal; a plurality of high- voltage regulators, each high voltage regulator corresponding to a particular one of the channels, each high- voltage regulator regulates the bulk power source output signal based on an input control voltage signal for that channel to generate a regulated high- voltage output signal for that channel having a voltage level corresponding to a level of the input control voltage signal for that channel, the high- voltage regulator circuit also generating a high- voltage tracking power signal for that channel having a voltage level within a predetermined range of the regulated high- voltage output signal; a plurality of current sensors, each current sensor corresponding to a particular one of the channels, powered by the high- voltage tracking power signal for that channel and generating an output high- oltage digital current sensing signal for that channel that corresponds to the current in the regulated high- voltage output signal for that channel; and a plurality of isolation barriers, each isolation barrier corresponding to a particular one of the channels, and translating the voltage level of the output high- voltage digital current sensing signal for that channel to a low- voltage level.

16. The circuit of claim 15, wherein each current sensor for a particular channel includes: current sensor analog circuitry that generates a high- voltage current sense analog signal for that channel having a voltage level that corresponds to the current in the regulated high-voltage output signal for that channel; and current sensor analog-to-digital converter (ADC) circuitry that translates the current sense analog signal for that channel into the output high- voltage digital current sensing signal for that channel.

17. The circuit of claim 16, wherein the ADC circuitry of the current sensor for a particular channel includes output circuitry to transmit the output high- voltage digital current sensing signal for that channel in a serial manner.

18. The circuit of claim 15, wherein the high- voltage regulator for a particular channel includes: a first current source; a second current source that sinks an amount of sink current based on the voltage level of the regulated high- voltage output signal for that channel, wherein the first current source sources an amount of source current based on the current being sunk by the second current source; and a current controller that controls the second current source based on a degree of correspondence between the regulated high- voltage output signal for that channel and the input control voltage signal for that channel, thereby controlling the voltage level of the regulated high- voltage output signal for that channel.

19. The circuit of claim 18, wherein for each particular channel: each of the first current source and the second current source includes a plurality of high- voltage regulating devices.

20. The circuit of claim 19, wherein: the number of high- voltage regulating devices is in accordance with a desired maximum voltage level of the regulated high- voltage output signal.

21. The circuit of claim 15, wherein: the high- voltage regulator of a current controller for the particular channel includes a sense amplifier that generates a sense amplifier output signal having a voltage proportional to the high- voltage tracking power signal; and the second current source for the particular channel determines the degree of correspondence between the regulated high- voltage output signal for the particular channel and the input control voltage signal for the particular channel based on a voltage difference between the input control voltage signal for the particular channel and the sense amplifier output signal for the particular channel.

22. The circuit of claim 16, wherein the current sensor analog circuitry of the current sensor for a particular channel includes: a current sense resistance across which the regulated high- voltage signal for that channel flows; a comparator that compares a resultant voltage across the current sense resistance of the current sensor for that channel with a reference voltage for the current sensor for that channel; and a difference generator that operates based on the compare operation by the comparator of the current sensor for that channel to generate the current sense analog signal for that channel.

23. The circuit of claim 15, wherein each isolation barrier for a particular channel includes: first capacitor circuitry having an input to which the output high- voltage digital current sensing signal is provided, the first capacitor circuitry further having an output; second capacitor circuitry having an input to which the regulated high- voltage output signal is provided, the second capacitor circuitry further having an output; a comparator having a first input coupled to the output of the first capacitor circuitry and a second input coupled to the output of the second capacitor circuitry, the comparator further having an output, wherein the output high-voltage digital current sensing signal, translated to the low-voltage level, is provided at the output of the comparator.

24. The circuit of claim 23, wherein the isolation barrier for the particular channel further includes: threshold circuitry coupled to the first and second input of the comparator to create a nominal threshold voltage difference between the first and second input of the comparator.

25. The circuit of claim 24, wherein the threshold circuitry for the isolation barrier for the particular channel includes: a first resistor element coupling the output of the first capacitor circuitry to a ground across a first diode; and a second resistor element coupling the output of the second capacitor circuitry to a power supply across a second diode.

26. The circuit of claim 23, wherein: the isolation barrier for the particular channel is characterized by a first impedance at the input to the first capacitor circuitry and a second impedance at the input to the second capacitor circuitry; and the first impedance is substantially equal to the second impedance.

27. The circuit of claim 26, wherein: the first impedance is substantially equal to the second impedance such that the first impedance is equal to the second impedance within a 5% tolerance.