#607 CD4049 Voltage Doubler
Testing a voltage doubler circuit based on a CD4049 inverter-driven bucket brigade.
Notes
The CD4049 is a hex inverter buffer/driver with the ability to operate over a wide voltage range of 3V to 15V. Unlike standard inverters, it can provide higher output drive capability, making it suitable for interfacing between different logic families and driving capacitive or resistive loads. It features symmetrical output rise and fall times, low power consumption, and high noise immunity. The CD4049 is often used in logic level shifting, waveform generation, and simple amplification applications, especially where standard logic gates do not provide sufficient drive strength.
Circuit Design
An relaxation oscillator uses two inverters with an RC network to drive the circuit.
The frequency is determined by the RC time constant,
and in the Inverter/NAND Gate Waveform configuration can be estimated as f = 1 / (2.2 * R1 * C). R2 should be approximately 10 times R1.
With R1=6.8kΩ and C=100nF, the expected frequency is 668.4 Hz.
The oscillator output drives 4 inverters in parallel (to 4x the output current capacity). These drive a two-stage charge pump that delivers the doubling of the voltage.
Test Results
The scope trace below captures the system in operation:
- CH1 (Yellow): oscillator output at OSC.
- Measured: 684 Hz at 46.4%
- Calculated: 668.4 Hz
- CH2 (Blue): voltage at VOUT
- Measured: 23.6V
