Table of Contents
CHAPTER 1 — GENERAL INFORMATION
1-1. SCOPE
This manual covers construction of a multi-voltage reference using temperature-compensated zener diodes and precision resistor dividers. The circuit provides multiple calibrated DC reference voltages from a single stable source. Less precise than band-gap references but adequate for ±0.5% calibration work.
CHAPTER 2 — THEORY OF OPERATION
2-1. TEMPERATURE-COMPENSATED ZENER
Zener diodes exhibit a negative temperature coefficient (TC) below approximately 5.6 V and a positive TC above 5.6 V. At ~5.6 V zener voltage, TC ≈ 0. The 1N829 and LM336 are designed to operate at this compensation point.
A forward-biased diode (TC ≈ −2 mV/°C) in series with a 6.2 V zener (TC ≈ +2 mV/°C) achieves near-zero overall TC. The LM336 IC integrates this compensation internally.
| Device | Voltage | TC | Accuracy | Notes |
|---|---|---|---|---|
| LM336-2.5 | 2.5 V | <20 ppm/°C | ±1% | Adjustable with ext R |
| LM385-2.5 | 2.5 V | <50 ppm/°C | ±1% | Micropower |
| 1N829 | 6.2 V | <10 ppm/°C | ±0.5% | Hermetic zener |
| 1N5234 | 6.2 V | <100 ppm/°C | ±5% | General purpose |
2-2. RESISTOR DIVIDER
A precision resistor divider derives lower voltages from the master reference. Use 0.1% tolerance resistors for <0.2% division error.
CHAPTER 3 — MATERIALS AND CONSTRUCTION
3-1. BILL OF MATERIALS
| Qty | Item | Specification |
|---|---|---|
| 1 | LM336Z-2.5 | 2.5 V adjustable reference |
| 1 | 50kΩ trim pot | Multiturn, Bourns 3296W |
| 2 | 10kΩ resistor | 0.1%, metal film, for trim network |
| 4 | Precision resistor | 0.1% for divider outputs |
| 2 | 100 nF capacitor | C0G, output bypass |
| 4 | Banana jack | Color coded per voltage |
| 1 | 9 V battery | With snap connector |
CHAPTER 4 — ASSEMBLY PROCEDURES
- Connect LM336Z-2.5 with 1kΩ bias resistor from supply positive to anode (+). Connect cathode (K) to positive output terminal. Ground is common.
- Connect 50kΩ trimmer between ADJ pin and a midpoint in the 10kΩ divider for fine adjustment.
- Build precision divider: for 1.000 V from 2.500 V use R1=1.5kΩ and R2=1.0kΩ (1.000/2.500 = 0.400 ratio; choose R2/(R1+R2) = 0.400).
- Add 100 nF C0G capacitor at each output to suppress HF noise.
- Verify all connections before applying power.
- Apply 9 V. Measure reference output. Adjust trimmer to exactly 2.500 V using reference DMM.
CHAPTER 5 — CALIBRATION PROCEDURE
- Allow 15-minute warm-up.
- Measure master reference output. Trim to 2.500 V ±1 mV.
- Measure all divider outputs. Record vs. calculated values.
- Example: if 1.000 V nominal divider output reads 1.002 V, divider error = +0.2%, acceptable for ±0.5% calibration.
- If divider error exceeds ±0.5%, verify resistor values and divider wiring.
CHAPTER 6 — TUNING AND ADJUSTMENT
Use the trimmer pot to set master reference to exactly 2.500 V at room temperature. Readjust if ambient temperature changes more than 10°C.
CHAPTER 7 — VERIFICATION
- Verify master reference against precision voltage reference (TM-CAL-006).
- Verify all divider outputs match calculations within ±0.5%.
- Log date, temperature, and all voltages.
APPENDIX A — CALCULATIONS AND FORMULAS
APPENDIX B — EXAMPLE RESULTS
| Output | Nominal (V) | Measured (V) | Error (mV) |
|---|---|---|---|
| Master ref | 2.500 | 2.500 | 0 |
| Divider 1 | 1.000 | 1.001 | +1 |
| Divider 2 | 1.250 | 1.251 | +1 |
| Divider 3 | 2.000 | 2.001 | +1 |