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--- modular_synthesizers:negative_buck [2024/06/16 21:06] – [Power consumption for a single op-amp and for 10 quad op-amps] utedass
+++ modular_synthesizers:negative_buck [2024/06/22 10:08] (current) – [Implementing a negative buck regulator] utedass
@@ Line 20: / Line 20: @@
 The few regulators that I checked the efficiencies for are: MAX17530, MAX17550, TPS629203 and TPS6212x.
-I will count with 65% efficiency for 100µA to 1mA, 70% for 1mA - 5mA and 80% for 5mA - 10mA.
+I will count with 65% efficiency for 100µA to 1mA, 70% for 1mA - 5mA, 80% for 5mA - 10mA and 85% for >10mA.
 For convenience I will decide on the lower choice of supply voltage to be +-3 V.
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 And then for the power consumption at different voltages and number of op amps. The input power to the switch regulator will be ''P = (current @ 3V times 3V) / (regulator efficiency in %)''
-^ OP-amp ^ Power @24V ^ Input power with buck @6V ^ Saved ^
+^ OP-amp ^ Power @+-12V ^ Input power with +-3V buck ^ Power saved ^
 | TL071 | 24 mW | 8.6 mW | 64.3 % |
 | OPA186 | 3.12 mW | 1.2 mW | 61.5 % |
@@ Line 40: / Line 40: @@
 | 40 pcs OPA186 | 124.8 mW | 39 mW | 68.8 % |
+And if we do some algebraic juggling we can see that the expression for power saved is ''Saved % = 1 - Vout / (Vin * efficiency)''. That is, we save more if the secondary voltage is lower than the input voltage, and we save more if the buck regulator can work more efficiently.
+Based on that, and the knowledge that all variables are always positive, we can solve the inequality ''1 - Vout / (Vin * efficiency) > 0'' to see when we actually benefit from this. I would argue that the most intuitive way of expressing this is ''efficiency > Vout / Vin''. That is, the buck regulator must be more efficient than the ratio of the voltages. For +-12V vs +-3V this is 25% efficiency, which is reaaally low for a buck converter.
+===== What do commercial modules consume and how are they built? =====
+This, of course, differs. I have assembled this table of modules of which I was able to find the schematics for. However, I do not know the conditions for the stated current consumption.
+^ Model ^ Brand ^ +12V mA ^ -12V mA ^ +5V mA ^ Technique ^ Comments ^ Links ^
+| Castor and Pollux II | Winterbloom | 100 | 35 | - | LDO 3.3V | Could benefit alot with buck | [[https://winterbloom.com/shop/castor-and-pollux|Info and shop]] [[https://github.com/wntrblm/Castor_and_Pollux/blob/main/hardware/mainboard/mainboard.pdf|Schematics]] |
+| Blinds | Mutable Instruments | 70 | 70 | - | 24V fed ICs | Could benefit alot with buck | [[https://pichenettes.github.io/mutable-instruments-documentation/modules/blinds/|Info]] [[https://pichenettes.github.io/mutable-instruments-documentation/modules/blinds/downloads/blinds_v60.pdf|Schematics]] |
+| DIY Modulator | Erica Synths | 27 | 22 | - | 24V fed ICs |  | [[https://github.com/erica-synths/diy-eurorack/blob/master/Modulator%20DIY.zip|Schematics]] |
+| VCF-4 | Skulls & Circuits | 163 | 91 | - | Mostly 24 fed ICs, some 12V and some LDO 5V fed | Could probably benefit alot from switch mode regulators | [[https://www.skullandcircuits.com/vcf-4/|info]] [[https://www.skullandcircuits.com/wp-content/uploads/2023/04/VCF-4-v5.2.pdf|Schematics]] |
+| BURST | Befaco | 56 | 10 | - | LDO 5V and probably some 24V fed ICs |  | [[https://www.befaco.org/burst-2/|Info]] [[https://befaco.org/docs/Burst/Burst_V3_Schematic.pdf|Schematics]] |
+|  |  |  |  |  |  |  |  |
+|  |  |  |  |  |  |  |  |
+===== Other work on the topic =====
+[[https://www.analog.com/en/resources/technical-articles/positive-buck-regulator-makes-negative-boost-dcdc-converter.html|Positive Buck Regulator Makes Negative Boost DC/DC Converter]]
+[[https://www.ti.com/lit/an/slyt516/slyt516.pdf?ts=1717195408219&ref_url=https%253A%252F%252Fwww.google.com%252F|Designing a negative boost converter from a standard positive buck converter]]
+====== Implementing a negative buck regulator ======
+{{:modular_synthesizers:normal_buck.png?300}}
+{{:modular_synthesizers:negative_buck.png?300}}
+===== The Parallel Universe of Negative Input Voltagess =====
+[[https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/The-Parallel-Universe-of-Negative-Input-Voltages.pdf|The Parallel Universe of Negative Input Voltages]]
+By John Betten and Brian King suggests using a UCC3813 with an external switch mosfet and also provides a circuit to adjust the feedback voltage to make the reference work properly.
+{{:modular_synthesizers:parallel_negative_fig3.png?500}}
+It is (according to me) a bit easier if we rewrite the circuit and remove some compensation capacitors like this:
+{{:modular_synthesizers:parallel_negative_fig3_better.png?500}}
 ===== Risks and other considerations =====
 There are also some risks that needs some investigation before this can be deemed a good way forth.
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   * Higher impact by offset-voltages
   * Higher price
+  * Better to pick a positive-in-dual-rail-out available solution?