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| RPS with from 0-30V and Current variable up to 3 A design Circuit Please.... |
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| Zero999:
I've never heard of a class S amplifier don't you mean class D? Why do you need a 0 to 30V, 0 to 3A PSU for an audio amplifier? I presume you want a general purpose bench power supply, rather than a dedicated audio amplifier PSU. A decent audio amplifier design shouldn't need a tightly regulated power supply. It should be designed to reject changes in the power supply voltage, without passing them through to the speakers. The problem with a constant voltage and constant current PSU is Ohm's law states that it can't be in both modes simultaneously. When the load resistance is above a certain point which would exceed the output voltage setting, it will be in constant voltage mode, then when the load resistance drops below the point when the current limit would be exceeded, it will switch to constant voltage mode. The problem is switching from constant current to constant voltage modes and back with minimal oscillation and current/voltage over/undershoot. Oscillation can be avoided, but it's actually impossible to prevent over/undershoot. Here's a simple constant VI regulator I lashed up in LTSpice. U1 needs to work with its inputs down to 0V and U2 with its inputs up to +V. V2 and V3 set the voltage and current limits respectively. D1 turns on when the regulator current limits, otherwise it's off. RL1/2/3 test the transient voltage and current response. RL1 applies a step load of 500mA, for 10ms. RL2 takes it into constant current mode and back again. RL3 as good as short circuits the power supply, when it's in the constant current mode. C2, C2, R8, R9 and R10 form phase compensation networks which reduce the oscillation. The transient response isn't great. Adding a capacitor across the output will cut down on the voltage over/undershot, at the expense of current overshoot and adding an inductor will improve the current mode, at the expense of the voltage mode. |
| techguru:
Sorry it is class d amplifier. Thanks a lot. I will try to understand the schematic. |
| rstofer:
--- Quote from: techguru on January 08, 2019, 09:54:01 am ---If any other possibility are there? Like Mr.bravo said I am trying this project for more than a year.now I came to know that linear mode that is class A mode of design is intractable. You all guide in design class s amplifier (smps), where my efficiency is nearly 100 percent. Buck topology.I think I am moving in right direction.help me in this regard. --- End quote --- If there was a circuit out in the wild that would actually deliver 0-30V and 0-3A, it would be all over this forum. It would be a sticky on every forum. Everybody on the Internet would know where to find it. Instead of dozens of replies, the matter would be settled with a simple link and the comment to "build this". Alas, it's just a lot harder than it looks. Any design without 3 or 4 parallel pass transistors is probably not going to deliver 3A at 0.1V without transformer taps. High voltage op amp selection is a challenge. There's a reason that 'real' bench power supplies cost so much money. There's a lot of parts! If the power supply is for a fixed load, like an audio amplifier, the 0-30V 0-3A spec doesn't make sense. If it's for a bench PS then why in the world do you need anywhere near 3A? For that matter, why 30V? A 1A adjustable supply is perfectly reasonable for the bench and, in fact, adjustable voltage isn't a real requirement either. 5V, +-15V and, maybe, +12V fixed 1A supplies will probably cover just about every conceivable situation that is 'general purpose'. Sure, vacuum tube circuits clearly need other voltages but that arena is covered by dedicated fixed supplies. My view on the 0-30V 0-3A: Somebody wrote it down once and now it is the assumed standard in the industry. In fact, there are few DIY projects that succeed. Try audioguru's project and if it works out, it will be one of the few designs that actually delivers. But don't substitute parts! See Reply #6 here: https://www.eevblog.com/forum/beginners/diy-0-30v-0-3a-again/ As a reference point, the Rigol DP832 PS costs about $500. It has 3 outputs that will presumably deliver up to 3A each, 2 at 0-30V and 1 at 0-5V. But it costs $500 and there's a lot of reasons why. There are a lot of cheap power supplies - they are all over the Internet. https://www.amazon.com/Lab-Power-Supplies/b?ie=UTF8&node=318022011 |
| David Hess:
The first example below is a design which almost meets your requirements. I would not implement it as shown because it uses LM395 integrated power transistors but it could be modified to use normal transistors. It could also be modified to work without a negative supply. Notable features are very low output capacitance and fast transitioning between constant current and voltage modes. The second example below from the Tektronix PS501 is closer to what I would do. Notably: 1. The current sensing is on the high side of the output making it more accurate. The current shunt in series with the output can be used to make the regulation loop more stable although that was not done in the PS501. 2. For a high power supply, I would replace the output transistor with an integrated regulator like a 317 driving a set of big power transistors. This allows the integrated regulator to protect the output transistors however it also means that a negative supply is required to allow the output to get down to zero volts. 3. I would add clamping to the error amplifiers to reduce transition time between voltage and current mode. |
| rstofer:
--- Quote from: David Hess on January 08, 2019, 06:09:26 pm ---The first example below is a design which almost meets your requirements. I would not implement it as shown because it uses LM395 integrated power transistors but it could be modified to use normal transistors. It could also be modified to work without a negative supply. Notable features are very low output capacitance and fast transitioning between constant current and voltage modes. --- End quote --- That National LB-28 design seems pretty nice. Minimal components, reasonable specs and the LM395 is still available albeit expensive ($4). Still, a quality supply just can't be built for a buck ninety five. Changing to normal transistors will be a challenge for a newcomer. The LM395s only take 10 uA of base current (3 uA typical) so the op amp can easily drive several. In addition, the LM395 has a lot of built-in protection, well beyond that of a 2N3055. I would be tempted to build the LB-28 as shown. http://www.ti.com/lit/ds/symlink/lm395.pdf It's still going to take a pretty beefy heatsink! ETA: The LM395 also has a 0.1 Ohm ballast resistor to aid in current sharing across multiple devices. |
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