BETAPIN 1 · Current and frequency outputs
Switched current sourceIOUT
Function
Delivers reference-controlled charge pulses to the integration network.
How to connect
Join THRESH6 at the RL/CL top node.
Electrical note
Not the logic frequency output.
Voltage-to-frequency converter
LM331 Pinout
Explore LM331 pins, signal names, electrical functions and connection guidance for each package.
8Physical pins
LM331N/NOPBPDIP-8
Manufacturer-referencedTexas Instruments
Pin diagram
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LM331PDIP-8Top view
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PIN 2 · Reference current
Reference current settingIREF
Function
Approximately1.89V at the current-setting contact.
How to connect
Connect12kΩ plus5kΩ gain-adjust rheostat in series toGND.
Electrical note
Tie rheostat wiper to its unused end for reliable adjustment.
PIN 3 · Current and frequency outputs
Open-collector pulse outputFOUT
Function
Outputs a pulse train whose frequency follows the input.
How to connect
Pull up through10kΩ to+5V; connect a frequency counter.
Electrical note
Requires a pull-up; do not assume a push-pull HIGH.
PIN 4 · Ground
Supply returnGND
Function
Common analog and logic reference.
How to connect
Connect all ground symbols here.
PIN 5 · Timing network
Timing nodeRC
Function
Charges toward the internal timer threshold and then resets.
How to connect
Connect6.8kΩ to+15V and10nF toGND.
Electrical note
Use stable, low-leakage timing parts.
PIN 6 · Comparator inputs
Comparator thresholdTHRESH
Function
Monitors the integrated feedback voltage.
How to connect
Join IOUT1; RL100kΩ and CL1µF in parallel connect to the47Ω return node.
PIN 7 · Comparator inputs
Comparator signal inputCOMPIN
Function
Receives the filtered voltage to convert.
How to connect
Apply VIN through100kΩ; bypass this pin toGND with100nF.
Electrical note
Keep normal input below VS−2V.
PIN 8 · Supply
Positive supplyVS
Function
Powers the converter.
How to connect
Apply+15V in this example; bypass locally with100nF.
Electrical note
Recommended device supply4–40V; circuit limits also matter.