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| Solenoid driver design |
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| viperidae:
Weird, wouldn't D1 bypass the tvs and other diode in the high-side configuration? |
| MagicSmoker:
--- Quote from: mbless on December 26, 2019, 03:29:01 am ---As an update, I made three driver versions: low-side, high-side, and combination low- and high-side driver previously shown. Here's a brief schematic of them. ... --- End quote --- D1 and D2 should be removed from the first two circuits if you want current to decay quickly. The same could be applied to the 3rd circuit, or just remove D2 and add another flyback connected from lower drain to +BATT to automatically recycle energy stored in the solenoid inductance back to the supply (this would be the traditional two-switch configuration). |
| langwadt:
--- Quote from: MagicSmoker on December 26, 2019, 03:23:31 pm --- --- Quote from: mbless on December 26, 2019, 03:29:01 am ---As an update, I made three driver versions: low-side, high-side, and combination low- and high-side driver previously shown. Here's a brief schematic of them. ... --- End quote --- D1 and D2 should be removed from the first two circuits if you want current to decay quickly. The same could be applied to the 3rd circuit, or just remove D2 and add another flyback connected from lower drain to +BATT to automatically recycle energy stored in the solenoid inductance back to the supply (this would be the traditional two-switch configuration). --- End quote --- sure? afaikt the first circuit has fast decay via D2/D3, D1 doesn't do anything, second circuit has slow decay via D1, D2/D3 doesn't do anything. Third circuit has fast decay when switching lowside, slow decay when switching highside |
| MagicSmoker:
--- Quote from: langwadt on December 27, 2019, 12:00:20 pm --- --- Quote from: MagicSmoker on December 26, 2019, 03:23:31 pm ---D1 and D2 should be removed from the first two circuits if you want current to decay quickly. The same could be applied to the 3rd circuit, or just remove D2 and add another flyback connected from lower drain to +BATT to automatically recycle energy stored in the solenoid inductance back to the supply (this would be the traditional two-switch configuration). --- End quote --- sure? afaikt the first circuit has fast decay via D2/D3, D1 doesn't do anything, second circuit has slow decay via D1, D2/D3 doesn't do anything. Third circuit has fast decay when switching lowside, slow decay when switching highside --- End quote --- Sure, I'm sure: your explanation on circuits 1 and 2 is correct, but that doesn't make what I wrote incorrect. As you noted, D1 does nothing in the first circuit, but also note that D2 is redundant, so it doesn't do anything, either, as long as the TVS breakdown voltage is higher than the supply voltage (which it should be), and it is, indeed, a bidirectional type as shown. In the second circuit, D1 renders D2 and D3 redundant and once removed the same applies to D2 as above, so it can also be removed. The 3rd circuit is halfway to being a proper two-switch driver but needs the corollary flyback diode to D1 to work properly, and note that both switches must be driven simultaneously for current to flow through the solenoid, so there is no option of just doing high side or low side switching. Finally, D2 is redundant as per usual and should be removed. |
| mbless:
--- Quote from: MagicSmoker on December 27, 2019, 12:25:10 pm ---Sure, I'm sure: your explanation on circuits 1 and 2 is correct, but that doesn't make what I wrote incorrect. As you noted, D1 does nothing in the first circuit, but also note that D2 is redundant, so it doesn't do anything, either, as long as the TVS breakdown voltage is higher than the supply voltage (which it should be), and it is, indeed, a bidirectional type as shown. --- End quote --- Yes, the TVS is bi-directional and rated for 27V, and the supply voltage is 24V. I tested your suggestion see here. Removing D1 and D2 decreased the current turn-off by ~5%. Incidentally, I did a test without any of the diodes installed, and the turn-off time was reduced from 1.75ms to 0.3ms! I'm surprised the solenoid current can decay so fast without any diodes. Any thoughts on why that would happen, and is then better to leave it without diodes or keep them for protection? (I do have a 470uF electrolytic on the supply rail.) |
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