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| How to use the same RELAY on 12V & 24V vehicles |
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| BrianHG:
Just use one of those TI simple switcher IC regulators which only need 1 inductor and 3 caps and 2 resistors to set the output voltage. You will get a 4.5v to 42v input voltage range with a 350ma or 500ma output, almost no heat as they operate from 82-94% efficiency. Here: Integrated inductor module: (36v max) 500ma https://www.digikey.com/product-detail/en/texas-instruments/LMZM23600SILR/296-51378-1-ND/9745742 Place your own inductor: (42v max) 100ma https://www.digikey.com/product-detail/en/texas-instruments/LM2840XMK-ADJL-NOPB/LM2840XMK-ADJL-NOPBCT-ND/3527199 300ma https://www.digikey.com/product-detail/en/texas-instruments/LM2841YMK-ADJL-NOPB/LM2841YMK-ADJL-NOPBCT-ND/2056741 600ma https://www.digikey.com/product-detail/en/texas-instruments/LM2842XMK-ADJL-NOPB/LM2842XMK-ADJL-NOPBCT-ND/2056742 |
| JDW:
--- Quote from: BrianHG on August 09, 2019, 04:27:53 am ---Just use one of those TI simple switcher IC regulators... --- End quote --- I've actually been pondering the LM5008A which has 6-95V Vin, 350mA output, and can produce a 3.3V output. Alternatively, there is the LM5018, which has 7.5-100V Vin, 300mA output, and can produce a 3.3V output. This would be more expensive than an LDO, but I cannot effectively dissipate 2W, so a switcher seems the only recourse. And that would give me the current output to also drive a 3V relay as well, solving my primary problem. Thanks to all who have contributed to this thread. |
| BrianHG:
--- Quote from: JDW on August 09, 2019, 04:55:41 am --- --- Quote from: BrianHG on August 09, 2019, 04:27:53 am ---Just use one of those TI simple switcher IC regulators... --- End quote --- I've actually been pondering the LM5008A which has 8-95V Vin, 350mA output, and can produce a 3.3V output. Alternatively, there is the LM5018, which has 7.5-100V Vin, 300mA output, and can produce a 3.3V output. This would be more expensive than an LDO, but I cannot effectively dissipate 2W, so a switcher seems the only recourse. And that would give me the current output to also drive a 3V relay as well, solving my primary problem. Thanks to all who have contributed to this thread. --- End quote --- The SOT-23 devices I listed start at 4.5v. The 7.5v devices may cut out during the starting of a 12v car in the winter with a weak battery. |
| JDW:
--- Quote from: BrianHG on August 09, 2019, 05:12:28 am --- --- Quote from: JDW on August 09, 2019, 04:55:41 am --- --- Quote from: BrianHG on August 09, 2019, 04:27:53 am ---Just use one of those TI simple switcher IC regulators... --- End quote --- I've actually been pondering the LM5008A which has 8-95V Vin, 350mA output, and can produce a 3.3V output. Alternatively, there is the LM5018, which has 7.5-100V Vin, 300mA output, and can produce a 3.3V output. This would be more expensive than an LDO, but I cannot effectively dissipate 2W, so a switcher seems the only recourse. And that would give me the current output to also drive a 3V relay as well, solving my primary problem. Thanks to all who have contributed to this thread. --- End quote --- The SOT-23 devices I listed start at 4.5v. The 7.5v devices may cut out during the starting of a 12v car in the winter with a weak battery. --- End quote --- Yes, I am aware. But if I get that picky about low voltage, I need to consider that ridiculously small car batteries in today's cars, especially Japanese cars, can bottom out at 4.0V or slightly lower even in good weather. I've measured this so I know. As such, a SEPIC regulator would be best (buck & boost), but the cost is higher, which is something I need to avoid. Another very important consideration is Iq (Quiescent current). According to the LM2841 datasheet (Vin-min=4.5V), the typical Iq is 1.35mA with the device ON and no load. In contrast, the LM5008A (Vin-min=6V) has a typical Iq = 485mA. |
| soldar:
--- Quote from: JDW on August 09, 2019, 12:49:56 am --- So in your schematic, that 12-24V nominal incoming voltage would be AFTER my TVS, which means it would see a maximum voltage of 50 to 54V, depending on which TVS I use. And I am not sure your design is best suited to that. --- End quote --- That circuit can be designed for any voltage you want. The drawback is that it dissipates heat. The advantage is that it is simple. If you want something more efficient you need to go to switching solutions. Or you could go to a solution with two relays, one for 12 V, one for 24 V, and only activate the right one depending on the voltage. That would be quite easy to do. |
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