Adjustable three-output dc voltage supply with short circuit protection
By combining a parallel regulator and a short-circuit protection component, the problems of easy damage to Zener diodes and expensive voltage regulation in existing three-output DC voltage supplies are solved, achieving flexible voltage regulation and short-circuit protection, reducing costs and improving circuit reliability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MURATA MFG CO LTD
- Filing Date
- 2021-12-17
- Publication Date
- 2026-07-14
AI Technical Summary
In existing three-output DC voltage supplies, Zener diodes are susceptible to short-circuit damage, voltage regulation is expensive, and they cannot effectively limit the current during short circuits.
A parallel regulator and short-circuit protection component are used to achieve voltage regulation and short-circuit protection through a combination of resistors and voltage dividers. Inexpensive transistors are used instead of Zener diodes, and a comparator is used to set the reference voltage.
It achieves flexible voltage adjustment and short-circuit protection, reduces costs, limits the current during short circuits, protects the Zener diode, and improves circuit reliability.
Smart Images
Figure CN116601858B_ABST
Abstract
Description
Technical Field
[0001] This application relates to an adjustable three-output DC voltage supply with short-circuit protection, and more specifically, to an adjustable three-output DC voltage supply for gate driving of transistors. Background Technology
[0002] A three-output DC voltage supply is used for components or circuits that require positive, intermediate, and negative voltage supplies.
[0003] One application of this type of power supply is for driving the gates of transistors such as insulated-gate bipolar transistors (IGBTs), silicon carbide (SiC), gallium nitride (GaN), and other metal-oxide-semiconductor field-effect transistors (MOSFETs). Transistors like these require specific positive and negative gate voltages to turn on or off. In these cases, the power supply will provide positive (+V), neutral (0V), and negative (-V) voltages, which is achieved by connecting the intermediate voltage output to a ground reference.
[0004] A known three-output DC voltage supply provides a precise voltage drop between the intermediate voltage output terminal and either the positive or negative voltage output terminal by inserting a Zener diode between the appropriate voltage outputs. The remaining voltage is absorbed by a resistor connected in series with the Zener diode. In this sense, the resistor and Zener diode provide a voltage divider, with the intermediate voltage output provided at the center of the divider. Figure 1 and Figure 2 An example of this three-output DC voltage supply is provided.
[0005] However, this means that to change the voltage drop across the positive or negative DC output and the intermediate DC output, the Zener diode needs to be changed. Zener diodes are relatively expensive components compared to resistors, so we have realized that it would be beneficial to provide an adjustable three-output DC voltage supply using a voltage regulator that can be adjusted by replacing or modifying relatively inexpensive components such as resistors.
[0006] Furthermore, if a short circuit occurs across the resistors of the voltage divider, the total voltage will be applied across the Zener diode, causing it to break down and resulting in a large current flowing through it. There is no way to limit this current through the Zener diode. This means the Zener diode is exposed to overvoltage and may be damaged. Therefore, we have realized that it would be beneficial to protect the Zener diode or voltage regulator in the event of a short circuit. Summary of the Invention
[0007] The invention is defined in the independent claims, which are now to be referenced. Advantageous features are defined in the dependent claims.
[0008] The adjustable three-output DC voltage supply according to the present invention provides positive, intermediate, and negative voltage supplies, as well as a positive DC voltage bus and a negative DC voltage bus for connection to a DC power supply, and a first voltage divider connected between the positive and negative DC voltage buses. The first voltage divider includes a parallel regulator connected to the positive DC voltage bus and having a reference input, and the output of the first voltage divider provides the intermediate voltage supply. The power supply circuit also includes a second voltage divider connected between one of the positive or negative DC voltage buses and the intermediate voltage supply, and the output of the second voltage divider is connected to the reference input of the parallel regulator. The power supply circuit also includes a short-circuit protection component connected in series to the low-voltage side of the parallel regulator and configured to limit the current through the parallel regulator in the event of a short circuit in the intermediate voltage supply.
[0009] When a short circuit occurs at the intermediate voltage output terminal, the short-circuit protection component operates to reduce the current and power dissipated in the parallel regulator. Specifically, when a short circuit exists and the intermediate output voltage terminal receives overvoltage or undervoltage, the parallel regulator may be damaged by an uncontrolled current flow. The second voltage divider of the present invention ensures that the parallel regulator provides a fixed voltage drop during normal operation, which is a portion of the supply voltage. The remaining supply voltage drops across the latter half of the first voltage divider. When this latter half is bypassed by a short circuit at the load, the entire supply voltage can be applied across the parallel regulator. Since there is essentially no load in this case, the current through the regulator increases. The short-circuit protection component, in conjunction with the second voltage divider, limits this current. During normal operation of the circuit, the power loss caused by the short-circuit protection component is minimal.
[0010] According to the present invention, the parallel regulator of the adjustable three-output DC voltage supply is connected to the positive DC voltage bus or the negative DC voltage bus via a resistor.
[0011] In these cases, the short-circuit protection component is connected between the output of the parallel regulator and the first voltage divider.
[0012] According to an alternative aspect of the invention, the short-circuit protection component of the adjustable three-output DC voltage supply is connected to the negative DC voltage bus.
[0013] In these cases, the parallel regulator is connected between the short-circuit protection assembly and the output of the first voltage divider.
[0014] The parallel regulator according to the present invention includes a transistor.
[0015] This arrangement of components provides a simple way to use a reference input to turn the transistor on or off the "bypass" of the second voltage divider. The transistor can switch to a closed circuit when the output of the second voltage divider equals the reference voltage of the transistor. The components of the second voltage divider are selected such that the reference voltage is output when the voltage across the second voltage divider is the expected output voltage between the positive supply and the negative supply and the intermediate supply.
[0016] The parallel regulator according to the invention includes a comparator that operates a transistor when the input of the comparator is higher than a reference voltage input defined by the parallel regulator.
[0017] The comparator allows specifying a particular reference voltage, independent of the intrinsic electrode voltage of the transistor. This allows circuit designers to maintain the appropriate value for the second voltage divider.
[0018] The transistor according to the present invention is a bipolar junction transistor (BJT). BJTs are relatively inexpensive components, therefore using BJTs can reduce the cost of circuits.
[0019] The transistor according to an alternative aspect of the invention has an intrinsic body diode. In this case, the transistor may be a field-effect transistor (FET).
[0020] A FET has a diode caused by one of its terminals being connected to the body of the FET itself, known as a body diode. This typically means that the transistor can only block current in one direction when it is off. In this case, the FET provides the diode when needed, without requiring additional components.
[0021] According to any of the above aspects of the invention, the parallel regulator is an adjustable reference diode.
[0022] This provides a single solid-state component to handle the task of regulating the circuit's voltage output, while also allowing the voltage to be regulated either internally within the component or by providing a set reference voltage that can be based on external components at different supply voltages.
[0023] The short-circuit protection component according to the present invention is a short-circuit protection resistor.
[0024] The first voltage divider according to the invention includes a resistor.
[0025] The second voltage divider according to an aspect of the invention includes a first setting resistor and a second setting resistor.
[0026] The power source of this invention is the rectified output of a transformer.
[0027] The adjustable three-output DC voltage supply is designed to be connected to a DC power source; however, this need not be an absolute DC power source, such as one provided by a battery, but can be an approximate DC power source, such as the output of a converter, i.e., the rectified output of a transformer.
[0028] The advantage of this invention is that it solves the above-mentioned problems in a synergistic manner, that is, configuring the supply in an adjustable manner also helps to protect the Zener diode or other regulators.
[0029] The intermediate voltage supply for a three-output DC voltage power supply can be a 0V voltage supply. Attached Figure Description
[0030] Embodiments of the invention will now be described by way of illustration only, with reference to the accompanying drawings, in which:
[0031] Figure 1 This is an example circuit diagram of a three-output DC voltage supply based on existing technology.
[0032] Figure 2 This is a second example circuit diagram based on the existing technology of a three-output DC voltage supply.
[0033] Figure 3a and Figure 3b A circuit is illustrated by comparison examples to help understand the benefits of the present invention.
[0034] Figure 4 This is a circuit diagram of a three-output DC voltage supply with short-circuit protection according to an aspect of the present invention.
[0035] Figure 5 Through Figure 4 The power and current dissipation of the parallel regulator and through Figure 4 An example representation of current dissipation in a short-circuit protection component.
[0036] Figure 6 This is a circuit diagram of a three-output DC voltage supply with short-circuit protection according to another aspect of the present invention. Detailed Implementation
[0037] Figure 1 The diagram illustrates a first example of a known three-output DC voltage supply. This figure shows a three-output DC voltage supply 100 without any short-circuit protection and helps in understanding... Figure 4 The circuit is described and shown.
[0038] Figure 1A three-output DC voltage supply circuit 100 with a positive DC voltage bus 101 and a negative DC voltage bus 103 is shown. Buses 101 and 103 have input terminals 105 and 107 at their input terminals, respectively, and output terminals 109 and 113 at their output terminals, respectively.
[0039] The positive voltage input terminal 105 is configured to be connected to the positive terminal of a DC power supply (not shown). The negative input voltage terminal 107 is configured to be connected to the negative terminal of a power supply (not shown). Note that in this specification, the terms "positive voltage" and "negative voltage," etc., are relative, such that the positive terminal of the DC voltage supply is positive relative to the negative terminal of the DC voltage supply, and the negative terminal of the DC voltage supply is negative relative to the positive terminal of the DC voltage supply.
[0040] DC power supplies include power sources, the output of DC-DC or AC-DC converters, batteries, and any power source that provides a basic DC voltage supply.
[0041] A voltage divider consisting of a Zener diode 115 and a resistor 117 is connected between the positive DC voltage bus 101 and the negative DC voltage bus 103. The Zener diode 115 is connected to the positive DC voltage bus 101 through its cathode. The output of the voltage divider is formed between the anode of the Zener diode 115 and the resistor 117.
[0042] For the purposes of this description, the term resistor is used to refer to a component that provides a resistance that can be specified or set by the user. Note that other components besides resistors can also provide this function, such as potentiometers, capacitors, coils, inductors, lamps, heating elements, etc.
[0043] The output of the voltage divider provides an intermediate voltage output terminal 111, which provides an intermediate voltage that is negative relative to the positive output voltage terminal 109 and positive relative to the negative voltage output terminal 113.
[0044] For the purposes of this description, the output of a voltage divider is defined as the voltage divided from the point where the components of the voltage divider meet.
[0045] The Zener diode 115 is sized to provide a set voltage drop between the positive voltage output terminal 109 and the intermediate voltage output terminal 111. A resistor 117 is provided to reduce the residual voltage supplied to the positive voltage input terminal 105 and the negative voltage input terminal 107.
[0046] Capacitors 125 and 127 are provided for cases where the circuit is used to power a power transistor (not shown) to provide the necessary gate drive current. If the circuit is not used to drive the power transistor, capacitors 125 and 127 can be omitted.
[0047] Figure 1 Circuit 100 is suitable for applications where the voltage between the positive voltage output terminal 109 and the intermediate voltage output terminal 111 is a critical voltage and must be maintained at a precisely defined voltage. Zener diode 115 will provide the correct voltage across these terminals 109 and 111, regardless of the input voltage at voltage input terminals 105 and 107, as long as that input voltage at voltage input terminals 105 and 107 is greater than the required voltage.
[0048] The terms positive, intermediate, and negative are relative. The full meaning of these terms is as follows: Positive voltage output terminal 109 provides a voltage that is positive relative to the voltage provided by both intermediate voltage output terminal 111 and negative voltage output terminal 113. Negative voltage output terminal 113 provides a voltage that is negative relative to the voltage provided by both intermediate voltage output terminal 111 and positive voltage output terminal 109. Intermediate voltage output terminal 111 provides a voltage that is negative relative to the voltage provided by positive voltage output terminal 109 and positive relative to the voltage provided by negative voltage output terminal 113.
[0049] When a 0V intermediate voltage is desired, the intermediate voltage output terminal 111 is grounded.
[0050] Figure 2 The diagram illustrates a second example of a known three-output DC voltage supply. This figure shows a three-output DC voltage supply 200 without any short-circuit protection and helps in understanding... Figure 6 The circuit is described and shown.
[0051] Except that Zener diode 215 is connected to negative DC voltage bus 203 via its anode, and the output of the first voltage divider is formed by the cathode of Zener diode 215 and resistor 217 (which is then connected to positive DC voltage bus 201), circuit 200 operates in the same manner as circuit 100.
[0052] therefore, Figure 2 The three-output DC voltage supply 200 is particularly suitable for applications where the voltage between the intermediate voltage output terminal 211 and the negative voltage output terminal 213 is a critical voltage and must be maintained at a precisely defined voltage.
[0053] Figure 1 and Figure 2 The problem with this circuit is that the Zener diode provides a fixed voltage drop, meaning that if the user expects to use the circuit for a different application, they will have to change the Zener diode, which is a relatively expensive component. Another problem is that a Zener diode that matches the exact required voltage may not be available. Furthermore, Zener diodes do not readily offer accurate voltage tolerances, and these tolerances vary significantly with temperature.
[0054] Figure 1 and Figure 2 Another problem with the circuit is that if either resistor 117 or 217 is bypassed by a short circuit across the relevant DC voltage terminal, the full supply voltage is applied across Zener diode 115 or 215, which could damage Zener diode 115 or 215.
[0055] For descriptive purposes, the term "short circuit" is used to define a load connected to a three-output DC voltage supply that approaches 0Ω.
[0056] pass Figure 3a and Figure 3b The comparative examples illustrate a solution to the problem outlined. In these circuits 300, a parallel regulator 315 and a resistor 323 are provided to limit the current to the parallel regulator 323. The parallel regulator 315 sets the voltage between the intermediate voltage output terminal 311 and one of the positive voltage output terminal 309 or the negative voltage output terminal 313, which is determined by the resistors 319 and 321. See below for reference. Figure 4 This describes the complete operation of circuit 300 under normal use. Essentially, this is beneficial because the voltage set by the parallel regulator 315 can be adjusted by changing the values of setting resistors 319 and 321.
[0057] when( Figure 3a Between the intermediate output voltage terminal 311 and the negative output voltage terminal 313 and (in) Figure 3b When a short circuit occurs between the positive output voltage terminal 309 and the intermediate output voltage terminal 311, the resistor 323 absorbs the overvoltage applied to the system.
[0058] However, we have realized that resistor 323 must be relatively large due to the power dissipated through it. Furthermore, we have realized that parallel regulator 315 can withstand much more power than the power it dissipates due to the limited current caused by resistor 323, which means that resistor 323 will be unnecessarily large to dissipate that extra power.
[0059] Therefore, we realized that improvements were needed. Figure 3a and Figure 3b Circuit 300. Now refer to... Figures 4 to 6 This will be described.
[0060] like Figure 4 and Figure 6As shown, circuits 400 and 600 place resistors 423 and 623 after parallel regulators 415 and 615 (i.e., on the low-voltage side of parallel regulators 415 and 615). This means that resistors 423 and 623 can be smaller because a larger amount of short-circuit power is dissipated by parallel regulators 415 and 615. Furthermore, since current-limiting resistors 423 and 623 work in conjunction with voltage-setting resistors 419, 421, 619, and 621, parallel regulators 415 and 615 are not fully saturated in the event of a fault, as explained in more detail below.
[0061] Figure 4 An adjustable three-output DC voltage supply 400 with short-circuit protection according to an aspect of the invention is shown. This circuit is suitable for applications where the voltage between the positive voltage output terminal 409 and the intermediate voltage output terminal 411 is a critical voltage and must be maintained at a precisely defined voltage.
[0062] Figure 4 The circuit has a positive DC voltage bus 401 and a negative DC voltage bus 403. Each DC voltage bus has a connected positive voltage input terminal 405 and a negative voltage input terminal 407, as well as a positive voltage output terminal 409 and a negative voltage output terminal 413. An intermediate voltage output terminal 411 is configured to be connected to the output of the first voltage divider. The intermediate voltage output terminal 411 is also shown as grounded because the specific application requires the intermediate voltage output terminal to be 0V.
[0063] The first voltage divider consists of a parallel regulator 415 and a resistor 417, with the parallel regulator 415 replacing... Figure 1 The Zener diode 115 of circuit 100. The output of the first voltage divider becomes the intermediate voltage output terminal 411.
[0064] A second voltage divider, including resistors 419 and 421, is connected between the output of the first voltage divider and the positive DC voltage bus 401. The output of this voltage divider is connected to the reference input of the parallel regulator 415.
[0065] The short-circuit protection resistor 423 is located between the parallel regulator 415 and the resistor 417.
[0066] The second voltage divider is selected to provide a set reference voltage for the output value of the voltage divider. This set reference voltage is required to operate the parallel regulator once the voltage across the entire voltage divider reaches the desired voltage drop across the positive output voltage terminal 409 and the intermediate voltage terminal 411. Components including the second voltage divider (resistors 419 and 421) can be considered as setting resistors because their values set the voltage drop across the terminals.
[0067] Once the voltage across the second voltage divider reaches this voltage, the output of the voltage divider provides the set reference voltage. This reference voltage is specified by the parallel regulator 415, which switches from providing an open-circuit voltage to providing a short-circuit voltage.
[0068] Describe example operation using example values of a supply voltage of 9V, a required positive voltage of 6V, a required negative voltage of -3V, and a reference voltage of 2.5V for the parallel regulator 415.
[0069] When the voltage drop across the entire second voltage divider is 6V, the resistor values of 319 = 34KΩ and 321 = 26KΩ provide an output voltage of 2.6V. Resistor 423 provides a voltage drop of approximately 0.1V, which is determined by the values of resistors 417 and 423. In this example, the value of resistor 423 can be as low as 100Ω or in the range of tens to hundreds of ohms.
[0070] This means that, due to a drop of 0.1V in the 2.6V across resistor 423, the parallel regulator reference voltage provided by the output of the second voltage divider is 2.5V when observed by the parallel regulator 415.
[0071] This means that the parallel regulator 415 provides a 6V voltage drop between the positive output voltage terminals 409 and 411. If the voltage across the second voltage divider rises above this value, the parallel regulator will be fully turned on, and the voltage drop across the second voltage divider will decrease, causing the parallel regulator 415 to turn off.
[0072] To maintain a stable position, the shunt regulator 415 operates in the linear region between fully on and fully off to keep the voltage drop at a reference voltage of 2.5V, a value specified by the particular shunt regulator component. In this example, the voltage drop is 6V.
[0073] If the specified reference voltage of the parallel regulator 415 is a value other than 2.5V, the resistor value will be changed, but basically, the resistor value is selected such that the reference voltage of the parallel regulator 415 is output when the desired output voltage appears across the resistor.
[0074] The resistor value can be changed to provide a parallel regulator reference voltage with different total voltage drops across the second voltage divider. Therefore, if a different voltage is required at the output terminals, this can be achieved by changing the value of the second voltage divider resistor (specifically, the value of resistor 419).
[0075] This therefore means that the voltage supplied between the positive output voltage terminal 409 and the intermediate output voltage terminal 411 can be adjusted by replacing a relatively inexpensive resistor, rather than replacing the relatively expensive parallel regulator 415 or... Figure 1 The Zener diode 115. This also means that any voltage can be easily selected.
[0076] Resistor 423 is provided to protect the parallel regulator in the event of a short circuit between the intermediate voltage output terminal 411 and the negative voltage output terminal 413.
[0077] When the load across the intermediate voltage output terminal 411 and the negative voltage output terminal 413 approaches 0Ω, the effective resistance between the intermediate voltage output terminal 411 and the negative voltage bus 403 tends to 0Ω. Although resistor 417 is present, the way the resistor operates in parallel connection (as with the load) means that the resistance of the load becomes the dominant resistance and resistor 417 is effectively bypassed.
[0078] This means that the entire supply voltage is applied across the parallel regulator 315 connected in series with resistor 423 and across the second voltage divider.
[0079] However, due to the presence of resistor 423, as the voltage across resistor 423 increases, negative feedback is applied to the reference pin of the parallel regulator 415. This counteracts the effect of the rising voltage across the second voltage divider. As described above, increasing the voltage across the second voltage divider causes the parallel regulator 415 to turn on. However, simultaneously, the rising voltage across resistor 423 causes the parallel regulator 415 to turn off, and balance is reached when 9V is fully applied across the parallel regulator 415. At this point, a safe low current is allowed to flow through the parallel regulator 415, and the power dissipated in the parallel regulator, although higher than the reference voltage, is still within acceptable limits. Figure 3a and Figure 3b The power is as described, but still within the limitations of the device.
[0080] The voltage not dissipated across the parallel regulator 415 is dissipated across the resistor 423. Furthermore, since the second voltage divider is used to set the reference voltage for the parallel regulator 415, the total current flowing through the resistor 423 and thus through the parallel regulator 415 is limited.
[0081] Essentially, when there is no short circuit, the DC voltage supply 400 now operates as described above. When the supply voltage is 9V, the output of the second voltage divider increases to, for example, 3.9V. This switches the parallel regulator 415 from cutoff to conduction, thereby allowing unrestricted current to flow through the parallel regulator 415 and the resistor 423.
[0082] However, once 1.4V (the output voltage of the second voltage divider minus the reference voltage) appears across resistor 423, the parallel regulator 415 sees 2.5V at its reference input, which keeps the circuit stable in the same way as in normal operation described above.
[0083] Since resistor 423 in this example has a value of 100Ω, the total current through resistor 423 and parallel regulator 415 is 14mA. Due to the action of the second voltage divider, 14mA becomes the maximum current through resistor 423 and parallel regulator 415.
[0084] Note that resistor 423 can be provided with Figure 1 Circuit 100, however, will have a reducing effect because there is no stabilizing circuit provided by the second voltage divider. The entire supply voltage will be allowed to pass through Zener diode 115, and the resistor will need to dissipate this voltage, resulting in a total fault current of almost 100mA. The resistor value will therefore need to be higher to reduce the fault current, so the power loss during normal use will be higher than expected. Figure 1 Power loss in a circuit.
[0085] The parallel regulator mentioned in this specification refers to any component or arrangement of components that can switch between on and off when a reference voltage is applied. For example, circuitry involving comparing an input voltage with a reference voltage and activating a transistor, in some embodiments, a comparator bypassing a diode, is suitable. Furthermore, if a suitable reference voltage is required for the gate or base voltage of the transistor, the comparator can be omitted. As another example, a field-effect transistor with a body diode and an applicable gate voltage is suitable. As yet another example, a Zener diode with a reference voltage is suitable.
[0086] Figure 5 The graph in Figure 3 illustrates the effect of the DC voltage supply of 400.
[0087] Graph 501 shows the power dissipation through parallel regulator 415 via line 5011, and also shows the power dissipation through resistor 423 via line 5013.
[0088] As can be seen, as the load resistance approaches 0Ω, the power dissipated through the parallel regulator 415 increases until the second voltage divider and resistor 423 prevent any further power dissipation.
[0089] The same situation is shown for resistor 423, whereby as the load approaches 0Ω, the power dissipated through resistor 423 rises to a point and then levels off due to the action of the second voltage divider. With the values mentioned above, where resistor 423 has a value of 100Ω and the current through it is 14mA, the power dissipated can be shown as just less than 20mW.
[0090] The power follows the line through the parallel regulator 415, and with approximately 7.6 volts applied across the parallel regulator 315, the power dissipated is approximately 100 mW.
[0091] The point at which the power on the two lines 5011 and 5013 stops increasing and begins to level off is the point in the transition period of the parallel regulator 315. Therefore, the “leveling off” of the lines occurs when the parallel regulator 415 sees 2.5V at its reference input, as described above.
[0092] Graph 503 illustrates this as it shows the current at the “cathode” of the parallel regulator 415 and that it tends to plateau at 14 mA, as described above.
[0093] The values used to illustrate these two graphs are merely illustrative and are related to the specific resistor and voltage values used to describe the circuit described above. Any set of input voltage, output voltage, reference voltage, resistors, etc., can be chosen depending on the application. The above description illustrates the principles for selecting these values.
[0094] Figure 6 A DC voltage supply 600 according to an embodiment of the present invention is shown, wherein the critical voltage is the voltage between the negative voltage output terminal 613 and the intermediate voltage output terminal 611 and must be maintained at a precisely defined voltage.
[0095] Except that the parallel regulator 615 provides the set voltage between the intermediate voltage output terminal 611 and the negative voltage output terminal 613, the operation of the DC voltage supply 600 is the same as described above. Figure 4 The example DC voltage supply is the same as 400. The resistors are sized to provide the reference voltage required by the parallel regulator 615 when the voltage applied across the second voltage divider of resistors 619 and 621 reaches the required output voltage between the intermediate output voltage terminal 611 and the negative output voltage terminal 613. The current-limiting resistor 623 provides a further voltage drop, such that the sizes of resistors 619 and 621 are designed to be the output reference voltage plus the voltage drop.
[0096] When the load applied between the positive voltage output terminal 609 and the intermediate voltage output terminal 611 approaches 0Ω (as if short-circuited), the entire supply voltage is applied across resistor 623 and parallel regulator 615, and resistor 617 is bypassed. This provides the second voltage divider with an output much higher than the reference input voltage required by parallel regulator 615, so parallel regulator 615 switches to provide a short circuit, allowing voltage to be applied to resistor 623. Once the voltage equal to the output of the second voltage divider minus the reference input voltage required by parallel regulator 615 is dissipated through resistor 623, parallel regulator 615 begins to switch back to an open circuit, bringing circuit 600 to a stable position.
[0097] If all values selected for DC voltage supply 600 are the same as those for circuit 400, then circuit 600 will present the same voltage difference between intermediate voltage output terminal 611 and negative voltage output terminal 613 as circuit 400 presents between positive voltage output terminal 409 and intermediate voltage output terminal 611. The values of resistors 619 and 621 can be varied to provide the necessary parallel regulator reference voltage for different voltage drops across intermediate voltage output terminal 611 and negative voltage output terminal 613. This therefore means that the voltage can be adjusted by replacing the relatively inexpensive resistors, rather than replacing the relatively expensive parallel regulator 615 or... Figure 2 Zener diode 215.
[0098] exist Figure 4 DC voltage supply 400 and Figure 6 When both DC voltages are supplied at 600Ω, and as mentioned above, a short circuit occurs when the load across the corresponding terminals approaches 0Ω. When this happens, because the load resistance cannot dissipate the remaining voltage, more supply voltage than originally required is dissipated through the parallel regulator 415 or 615. When the load approaches 0Ω, what is presented to the parallel regulator 415 or 615 or the second voltage divider may not be the entire supply voltage; therefore, resistor 423 or 623 may not dissipate its entire expected voltage, but rather a portion of it. That is, the voltage dissipated across all components is proportional to the degree of the short circuit.
[0099] Throughout the accompanying drawings, the intermediate voltage output terminal is shown as grounded. The intermediate voltage output terminal is grounded when a 0V intermediate voltage output is required, but as stated above, this is not always the case. When a 0V intermediate voltage output is not required, this terminal will not be grounded, and therefore the grounding connection shown in the figures will be omitted.
[0100] The above description and accompanying drawings are intended to be purely illustrative and are not intended to limit the scope of the invention as defined by the appended claims.
Claims
1. An adjustable three-output DC voltage supply for providing a positive voltage supply, an intermediate voltage supply, and a negative voltage supply, comprising: Positive DC voltage bus and negative DC voltage bus are used to connect to a DC power supply; A first voltage divider is connected between the positive DC voltage bus and the negative DC voltage bus, wherein the first voltage divider includes a parallel regulator connected to one of the voltage buses, the parallel regulator having a reference input, and wherein the output of the first voltage divider provides the intermediate voltage supply; A second voltage divider is connected between a voltage bus to which the parallel regulator in the positive DC voltage bus or the negative DC voltage bus is connected and the intermediate voltage supply, wherein the output of the second voltage divider is connected to the reference input of the parallel regulator; and A short-circuit protection component is connected in series to the low-voltage side of the parallel regulator to limit the current through the parallel regulator in the event of a short circuit in the intermediate voltage supply.
2. The adjustable three-output DC voltage supply according to claim 1, wherein, The first voltage divider includes a resistor.
3. The adjustable three-output DC voltage supply according to claim 2, wherein, The parallel regulator is connected to the positive DC voltage bus via the resistor.
4. The adjustable three-output DC voltage supply according to claim 2, wherein, The parallel regulator is connected to the negative DC voltage bus via the resistor.
5. The adjustable three-output DC voltage supply according to claim 1, wherein, The short-circuit protection component is connected between the output of the parallel regulator and the first voltage divider.
6. The adjustable three-output DC voltage supply according to any one of claims 1 to 4, wherein, The short-circuit protection component is connected to the negative DC voltage bus.
7. The adjustable three-output DC voltage supply according to claim 6, wherein, The parallel regulator is connected between the short-circuit protection component and the output of the first voltage divider.
8. The adjustable three-output DC voltage supply according to claim 1, wherein, The parallel regulator includes transistors.
9. The adjustable three-output DC voltage supply according to claim 8, wherein, The parallel regulator also includes a comparator that operates the transistor when the input voltage of the comparator is higher than a reference voltage input defined by the parallel regulator.
10. The adjustable three-output DC voltage supply according to claim 8 or 9, wherein, The transistor is a BJT.
11. The adjustable three-output DC voltage supply according to claim 8 or 9, wherein, The transistor includes an intrinsic diode.
12. The adjustable three-output DC voltage supply according to claim 11, wherein, The transistor is a FET.
13. The adjustable three-output DC voltage supply according to claim 1, wherein, The parallel regulator is an adjustable reference diode.
14. The adjustable three-output DC voltage supply according to claim 1, wherein, The short-circuit protection component is a short-circuit protection resistor.
15. The adjustable three-output DC voltage supply according to claim 1, wherein, The second voltage divider includes a first setting resistor and a second setting resistor.
16. The adjustable three-output DC voltage supply according to claim 1, wherein, The power source is the rectified output of the transformer.
17. The adjustable three-output DC voltage supply according to claim 1, wherein, The intermediate voltage supply is a 0V voltage supply.