I lately revealed a Design Thought (DI) exhibiting some quite simple circuits for PWM programming of ordinary regulator chips, each linear and switching, “Revisited: Three discretes suffice to interface PWM to switching regulators.”
Determine 1 reveals one of many topologies “Revisited” visited, the place:
R1 = beneficial worth from U1 datasheet
DF = PWM responsibility issue = 0 to 1
R2 = R1/(Vomax/Vsense – 1)
Vout = Vsense(R1/(R2/DF) + 1) = DF(Vout_max – Vsense) + Vsense
DF = (Vout/Vsense – 1)(R2/R1) = (Vout – Vsense)/(Vout_max – Vsense)
DF = (Vout – 0.8)/9.2 for elements proven
Determine 1 5 discrete elements comprise a circuit for linear regulator programming with PWM.
Wow the engineering world along with your distinctive design: Design Concepts Submission Information
An inherent limitation of the Determine 1 circuit is its incapacity to program Vout < Vsense. Its minimal
Vout = Vsense @ DF = 0. For many purposes this doesn’t quantity to a lot, if any, of an issue. However typically it might be helpful, or a minimum of handy, for Vout to be zero (or thereabout) when DF = zero. Determine 2 reveals a simple modification that may make that occur, the place:
R1 and R2 chosen as in Determine 1
(R4 + R5/2) = (5v – Vsense)/(Vsense/R1) – R2
R5 ~ R4/5
Vout = R1 DF(Vsense(1/R2 + 1/R1)) = DF Vout_max
DF = Vo/(R1(Vsense(1/R2 + 1/R1)) = Vout/Vout_max
DF = Vout/10 for half values proven
Determine 2 In an effort to make Vout programmable right down to zero volts, add R4 and (optionally) R5 trimmer.
A cool characteristic of the Determine 1 topology is that, in contrast to another schemes for digital energy provide management, solely the precision of R1, R2, and the regulator’s personal inside voltage reference determines regulation accuracy. Precision is wholly impartial of exterior voltage references. It stays equal to the precision of R1, R2, and Vsense (e.g., ±1%) for all output voltages.
Sadly, as the traditional maxim says, one thing’s (normally) misplaced when one thing’s gained. In gaining Vout < Vsense functionality, the Determine 2 circuit loses that characteristic, and for outputs lower than full scale, Vout precision turns into considerably depending on the +5v rail. That is the place the R5 trimmer turns out to be useful.
The design equation (R4 + R5/2) = (5v – Vsense)/(Vsense/R1) – R2, makes the values chosen for the R4, R5 pair depending on the accuracy of the 5v rail. They will solely be as right as it’s. This makes output voltages considerably suspect, particularly after they strategy zero. Together with R5 and adjusting it for Vout = 0 @ DF = 0 makes low Vout settings precisely programmable. If that isn’t a important issue, then R5 could be omitted, simply make R4 = (5v – Vsense)/(Vsense/R1) – R2.
The simplicity of the arithmetic for computing DF from the specified Vout can also be a fascinating characteristic of Determine 2.
In closing: This DI revises an earlier submission: “Three discretes suffice to interface PWM to switching regulators.” My thanks go to remark makers oldrev, Ashutosh Sapre, and Val Filimonov for his or her useful recommendation and constructive criticism. And particular thanks go to editor Shaukat for her creation of an surroundings pleasant for the DI teamwork that made it potential.
Stephen Woodward’s relationship with EDN’s DI column goes again fairly a good distance. Over 100 submissions have been accepted since his first contribution again in 1974.
Associated Content material
- Revisited: Three discretes suffice to interface PWM to switching regulators
- Three discretes suffice to interface PWM to switching regulators
- Cancel PWM DAC ripple with analog subtraction
- Add one resistor to permit DAC management of switching regulator output
The publish Easy PWM interface can program regulators for Vout < Vsense appeared first on EDN.
