Post History
Do the math. At 5 V in and 1.2 V out, a linear regulator is limited to (1.2 V)/(5.0 V) = 24% efficiency. At 3 V in, the limit is 40%. The actual efficiency will be little less due to the current...
Answer
#3: Post edited
by
Olin Lathrop
·
2024-07-06T16:40:49Z (3 months ago)
- Do the math.
At 5 V in and 1.2 V out, a linear regulator is limited to (1.2 V)(5.0 V) = 24% efficiency. At 3 V in, the limit is 40%. The actual efficiency will be little less due to the current that the regulator itself uses to operate, but compared to 150 mA that will be negligible with pretty much any modern regulator.- So, the question becomes can a switcher do better than 40% efficiency in going from 5 V to 1.2 V? Absolutely. I'd expect to find switchers that can do 80% or better with 3 to 5 V in and 1.2 V out at 150 mA.
- At these low voltages, you definitely need synchronous rectification to achieve good efficiency, but that will be built into any competent chip aimed at this kind of operating point. At 150 mA, you should be able to find a chip with the switching element built-in, which also helps with synchronous rectification. You will need to supply the inductor, input and output caps, and possibly a charge pump cap for making a higher voltage to drive the FET switch gate with. The datasheet will give you all the details. Read it carefully, then do what it says.
- Multiple manufacturers should have products that do what you want. Some of the usual suspects are TI, Microchip, and Linear.
- Do the math.
- At 5 V in and 1.2 V out, a linear regulator is limited to (1.2 V)/(5.0 V) = 24% efficiency. At 3 V in, the limit is 40%. The actual efficiency will be little less due to the current that the regulator itself uses to operate, but compared to 150 mA that will be negligible with pretty much any modern regulator.
- So, the question becomes can a switcher do better than 40% efficiency in going from 5 V to 1.2 V? Absolutely. I'd expect to find switchers that can do 80% or better with 3 to 5 V in and 1.2 V out at 150 mA.
- At these low voltages, you definitely need synchronous rectification to achieve good efficiency, but that will be built into any competent chip aimed at this kind of operating point. At 150 mA, you should be able to find a chip with the switching element built-in, which also helps with synchronous rectification. You will need to supply the inductor, input and output caps, and possibly a charge pump cap for making a higher voltage to drive the FET switch gate with. The datasheet will give you all the details. Read it carefully, then do what it says.
- Multiple manufacturers should have products that do what you want. Some of the usual suspects are TI, Microchip, and Linear.
#2: Post edited
by
Olin Lathrop
·
2024-07-06T16:39:23Z (3 months ago)
- Do the math.
At 5 V in and 1.2 V out, a linear regulator is limited to (1.2 V)(5.0 V) = 24% efficiency. At 3 V in, the limit is 60%. The actual efficiency will be little less due to the current that the regulator itself uses to operate, but compared to 150 mA that will be negligible with pretty much any modern regulator.So, the question becomes can a switcher do better than 24% efficiency in going from 5 V to 1.2 V? Absolutely. Can a switcher do better than 60% in going from 3 V to 1.2 V? That really shouldn't be hard to find. I'd expect to find switchers that can do 80% or better with 3 to 5 V in and 1.2 V out at 150 mA.- At these low voltages, you definitely need synchronous rectification to achieve good efficiency, but that will be built into any competent chip aimed at this kind of operating point. At 150 mA, you should be able to find a chip with the switching element built-in, which also helps with synchronous rectification. You will need to supply the inductor, input and output caps, and possibly a charge pump cap for making a higher voltage to drive the FET switch gate with. The datasheet will give you all the details. Read it carefully, then do what it says.
- Multiple manufacturers should have products that do what you want. Some of the usual suspects are TI, Microchip, and Linear.
- Do the math.
- At 5 V in and 1.2 V out, a linear regulator is limited to (1.2 V)(5.0 V) = 24% efficiency. At 3 V in, the limit is 40%. The actual efficiency will be little less due to the current that the regulator itself uses to operate, but compared to 150 mA that will be negligible with pretty much any modern regulator.
- So, the question becomes can a switcher do better than 40% efficiency in going from 5 V to 1.2 V? Absolutely. I'd expect to find switchers that can do 80% or better with 3 to 5 V in and 1.2 V out at 150 mA.
- At these low voltages, you definitely need synchronous rectification to achieve good efficiency, but that will be built into any competent chip aimed at this kind of operating point. At 150 mA, you should be able to find a chip with the switching element built-in, which also helps with synchronous rectification. You will need to supply the inductor, input and output caps, and possibly a charge pump cap for making a higher voltage to drive the FET switch gate with. The datasheet will give you all the details. Read it carefully, then do what it says.
- Multiple manufacturers should have products that do what you want. Some of the usual suspects are TI, Microchip, and Linear.
#1: Initial revision
by
Olin Lathrop
·
2024-07-06T15:22:02Z (3 months ago)
Do the math. At 5 V in and 1.2 V out, a linear regulator is limited to (1.2 V)(5.0 V) = 24% efficiency. At 3 V in, the limit is 60%. The actual efficiency will be little less due to the current that the regulator itself uses to operate, but compared to 150 mA that will be negligible with pretty much any modern regulator. So, the question becomes can a switcher do better than 24% efficiency in going from 5 V to 1.2 V? Absolutely. Can a switcher do better than 60% in going from 3 V to 1.2 V? That really shouldn't be hard to find. I'd expect to find switchers that can do 80% or better with 3 to 5 V in and 1.2 V out at 150 mA. At these low voltages, you definitely need synchronous rectification to achieve good efficiency, but that will be built into any competent chip aimed at this kind of operating point. At 150 mA, you should be able to find a chip with the switching element built-in, which also helps with synchronous rectification. You will need to supply the inductor, input and output caps, and possibly a charge pump cap for making a higher voltage to drive the FET switch gate with. The datasheet will give you all the details. Read it carefully, then do what it says. Multiple manufacturers should have products that do what you want. Some of the usual suspects are TI, Microchip, and Linear.