23.04.2015

Dc dc boost converter high voltage

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Whether it is used for biasing avalanche photodiodes (APDs) found in optical receivers, driving photoflash tubes in flash cameras, or charging high-voltage capacitors, the need for high-voltage sources continues to grow.
This article examines such solutions and discusses the topologies and techniques used by each to boost output voltages by ratios of 10:1 or better in order to generate high-DC voltages from very-low DC inputs. Per ADI’s application note, with high boost ratios, simple boost imposes both high-voltage and high-current stress on MOSFET Q1, which results in high switching and conduction losses.
With tapped-inductor boost topology, the voltage stress on the output rectifier is high, and it suffers from the effects of transformer leakage inductance, according to ADI.
ADI’s application note AN-1126 proposes a new converter topology that overcomes the drawbacks of conventional topologies to deliver significant power at large boost ratios with minimum voltage and current stress imposed on the switches.
Again according to ADI’s application note, the single-ended primary inductance converter (SEPIC) multiplied boost converter (Figure 2) achieves all of the above goals by reducing voltage and current stresses on the main switch and rectifiers, as well as reducing peak-to-peak voltage swing on the switch node to significantly curb switching losses, EMI, and noise. Using the fixed-frequency, current-mode step-up controller ADP1621 in SEPIC multiplied boost configuration, ADI engineers have built and tested a 12 VDC input to 200 VDC output boost converter at 250 mA output current (Figure 3).
For photoflash and strobe devices that operate by discharging a high-voltage capacitor into a bulb, Micrel has developed a boost flyback charger circuit using switching regulator MIC3172.
The circuit uses a minimum number of components to reduce board space and increase reliability.
For more information on the parts discussed in this article, use the links provided to access product information pages on the Digi-Key website. Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. To be able to charge a high voltage battery (~400V) from solar panels I need a dc-dc converter that can boost up the voltage from the low voltage system (~12V) to the higher voltage. I have read that it is not practical to boost more that a factor of 6, and this is a factor of about 30-35.
Would two boost (step-up) converters connected is series work or is there a better solution? Because a transformer is necessary to economically achieve the power output, the turns ratio is going to be an easily achievable 40:1.
More than likely (given the power), you'll need a H-bridge driver which will apply nearly 24Vp-p to your primary winding and the turns ratio will be 40:1 to produce +400VDC. Given the power supply's sophistication I'd be very hesitant to believe that two boosters would be at all more effective than one booster on the grounds of efficiency, performance, physical size or cost. My main point was that there is a fighting chance of finding the appropriate inductors off-the shelf, but the appropriate transformer would almost certainly have to be a custom job. LT3751 is a High Voltage Capacitor Charger (and I suppose that it can be used for batteries with the help of some protection ICs). Not the answer you're looking for?Browse other questions tagged high-voltage dc-dc-converter or ask your own question.


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These include simple boost, charge-pump multiplied boost, and tapped-inductor boost, as shown in Figure 1.
This leakage inductance causes voltage spikes and ringing, which, in turn, causes EMI and increases voltage stress on both the MOSFET and the output rectifier. This allows moderately rated MOSFETs and Schottky rectifiers to be used while operating at moderate duty cycles for easier continuous-conduction-mode (CCM) and PWM control. Besides increasing the number of series-connected rectifiers, which increases the total rectifier forward-voltage drop resulting in higher losses, it also increases circuit complexity and the number of parts. In this design, 60 V-rated MOSFET and Schottky rectifiers are used, and the comparator ADCMP354 (U2) serves as an input undervoltage lockout (UVLO).
As depicted in Figure 4, the circuit is simple and reliably produces 300 VDC from a low input voltage of 3 to 10 VDC to charge a high-voltage capacitor. Micrel indicates that the voltage across the capacitor is increased with each switching cycle until it reaches the preset voltage; once this voltage is reached the MIC3172 stops switching. It features a high-side fixed-voltage-drop APD current monitor with better than 10 percent relative accuracy over the entire temperature range. There is no problem going up from 12V to 400V providing you are not looking to source more than a few milliamps. I say this because, given the powers you require, a transformer is the most efficient way to do the step-up from 12V to 400V. At these sorts of power levels you'd be hard-pushed to find a booster that doesn't use one. The step-up transformer was a large ferrite operating at 50kHz and, with about 1200 turns on the secondary you were starting to hit self-resonance. It will need a reasonably sophisticated control system that involves pulse width modulating the drive to the primary and decent monitoring of the output to ensure you stay regulated. I have skimmed the datasheet and it seems that it can handle several tens of amps as input, and can go to 400V output. Two stage boost is one option, it is definitely the easy option as you can use off the shelf controllers and you don't need to design a transformer. The LT1308A features automatic shifting to power saving Burst Mode operation at light loads and consumes just 140µA at no load. The shutdown pin enables the device when it is tied to a 1V or higher source and does need to be tied to VIN as on the LT1308.
For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor. To address these requirements, suppliers such as Analog Devices, Linear Technology, Maxim Integrated, and Micrel Inc., among others, have produced boost converters with output voltages at 70 V and above. While there are many advantages delivered by each topology, these techniques also have noteworthy drawbacks for delivering significant power at large boost ratios. Similarly, with charge-pump multiplied boost topology each charge-pump multiplier stage requires two added series diodes, which contribute to loss from forward-voltage drop.


Although such effects can be controlled with snubbers, it wastes power and results in additional components and board space. Additionally, it avoids voltage spikes and ringing associated with transformer leakage inductance.
As a result of all of this, it allows easy component selection trade-offs in terms of cost and performance. What’s more, the SEPIC multiplied boost technique is not recommended when the input and output voltages are both high. Since energy leakage in the output components causes the capacitor to discharge over time, the MIC3172 provides occasional pulses of energy to keep the capacitor fully charged, Micrel says. The integrated power switch, Schottky diode, and APD current monitor enable a small-footprint solution at low cost. Consequently, the designer must carefully read the product’s data sheet to ensure that it will generate the desired solution for a given end application. It was a resonant transformer circuit so that was no problem but more than 1200 turns and you were on the downward slope of decreasing efficiency. I would also say that a secondary shut-down circuit would be needed should a single-fault arise. One stage boost is probably also an option but it will require more know-how and state of the art semiconductors and magnetics (to get ok efficiency). The LT1308B features continuous switching at light loads and operates at a quiescent current of 2.5mA. An internal VCC clamp results in improved transient response and the switch voltage rating has been increased to 36V, enabling higher output voltage applications. In addition, the pump capacitors must be large in value to avoid causing high peak currents and significant cyclic droop. It combines a traditional voltage loop and a unique current loop to operate as a constant-current or -voltage source.
If you choose to use an isolated topology you can probably go with forward or push-pull converter. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application. High peak currents also are likely to increase rms switch current, which tends to corrupt current-mode control waveforms. The output fed a multi-stage cockcroft-walton voltage multiplier to take the output up from about 2000Vrms to 50kV. For similar applications that need around 2 percent accuracy for APD current monitor, Linear offers its LT3905 with narrower-input voltage range.



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