Fundamental design equations for 3 precision present sources

A often encountered class of analog system part is the precision present supply. Many good designs can be found, however concise and easy arithmetic for selecting the part values essential to tailor them to particular functions isn’t all the time supplied. I suppose some designers really feel such tedious particulars are simply too trivially apparent to benefit mentioning. However I typically don’t really feel that. 

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Listed here are some examples I feel some people would possibly discover helpful. I hope they received’t really feel too terribly apparent, trivial, or tedious.

The circuit in Determine 1 is flexible and able to excessive efficiency.

Determine 1 A easy high-accuracy present supply that may supply present with higher than 1% accuracy.

With appropriate part selections, this circuit can: supply present with higher than 1% accuracy and have Q1 drain currents starting from < 1mA to > 10 A, whereas working with energy provide voltages (Vps) from < 5V to > 100 V.

Listed here are some useful hints for resistor values, resistor wattages, and security zener D1. First notice

• Vps = energy provide voltage
• R1(W), Q1(W), and R2(W) = respective part energy dissipation
• Id = Q1 drain present in amps

Enough warmth sinking for Q1(W). One other factor assumed is:

Vps > Q1 (Vgs ON voltage) + 1.24 + R1*100µA

The design equations are as follows:

1. R1 = (Vps – 1.24)/1mA
2. R1(W) = R1/1E6
3. Q1(W) = (Vps – Vload – 1.24)*Id
4. R2 = 1.24/Id
5. R2(W) = 1.24 Id
6. R2 precision 1% or higher on the temperature produced by #5 warmth dissipation
7. D1 is required provided that Vps > 15V

Determine 2 substitutes an N-channel MOSFET for Determine 1’s Q1 and an anode-referenced 431 regulator chip rather than the cathode-referenced 4041 to supply a really related present sink. Its design equations are similar.

Determine 2 A easy, high-accuracy present sink makes use of similar design math.

Okay, okay, I can nearly hear the (very affordable) objection that, for these easy circuits, the design math actually was just about tedious, trivial, and apparent. 

So I’ll end with a really much less apparent and extra inventive instance from frequent contributor Christopher Paul’s DI “Precision, voltage-compliant present supply.”

Taking components parameters from Christopher Paul’s Determine 3, we are able to outline:

1. Vs = chosen voltage throughout the R3R4 divider
2. V5 = voltage throughout R5
3. Id = chosen application-specific M1 drain present

Then:

1. Vs = 5V
2. V5 = 5V – 0.65V = 4.35V
3. R5 = 4.35V/150µA = 30kΩ
4. I4 = Id – 290µA
5. R3 = 1.24/I4
6. R4 = (Vs – 1.24)/I4 = 3.76/I4
7. R3(W) = 1.24 I4
8. R4(W) = 3.76 I4
9. M1(W) = Id(Vs – Vd)

For instance, if Id = 50 mA and Vps = 15 V, then:

•  I4 = 49.7 mA
• R5 = 30 kΩ
• R4 = 75.7 Ω
• R3 = 25.2 Ω
• R3(W) = 1.24 I4 = 100 mW
• R4(W) = 3.76 I4 = 200 mW
• M1(W) = 500 mW

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.

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