I came up with this circuit yesterday, it's basically an h-bridge and astable multivibrator in one.
I've not actually built it yet but LTSpice says it works all the way down to 0.9V, making it ideal for single cell operation. The saturation loss for both transistors ranges from 184mV to 224mV as the supply voltage is varied between 0.9V to 1.5V. The output waveform is not perfectly square and the RMS value ranges from 715.4mV to 1.278V as the supply voltage is varied between 0.9V to 1.5V so the power in the speaker will range from 64mW to 204mW. The cirucit won't be very loud but should be fine for simple indicator applications and is certainly louder than a half bridge which would give an estimated 40mW to 120mW over the range of 0.9V to 1.5V.
The current consumption is 103mA to 216mA over the supply voltage range of 0.9V to 1.5V.
The frequency ranges from 1.72kHz to 2.36kHz as the supply voltage is varied between 0.9V and 1.5V and can be altered by changing the values of R3, R4 and C1 and C2 but the resistor values stillneed to be low enough to ensure adequate base drive.
The transistors are BC338 and BC328 for NPN and PNP respectively.
I'll test the circuit but testing at voltages below 1.25V will be difficult for me as I only have an LM317 based PSU.
My local supplier sells 1.5V buzzers but the datasheet gives a minimum operating voltage of 1.3V and the current consumption is only 25mA so they won't be anywhere near as loud as my circuit.
http://www.rapidonline.com/netalogue/specs/35-0085e.pdf
This circuit can be used to drive a piezo sounder but the resistor values will need to be increased and C1 and C2 decreased.
View attachment 41059
I've not actually built it yet but LTSpice says it works all the way down to 0.9V, making it ideal for single cell operation. The saturation loss for both transistors ranges from 184mV to 224mV as the supply voltage is varied between 0.9V to 1.5V. The output waveform is not perfectly square and the RMS value ranges from 715.4mV to 1.278V as the supply voltage is varied between 0.9V to 1.5V so the power in the speaker will range from 64mW to 204mW. The cirucit won't be very loud but should be fine for simple indicator applications and is certainly louder than a half bridge which would give an estimated 40mW to 120mW over the range of 0.9V to 1.5V.
The current consumption is 103mA to 216mA over the supply voltage range of 0.9V to 1.5V.
The frequency ranges from 1.72kHz to 2.36kHz as the supply voltage is varied between 0.9V and 1.5V and can be altered by changing the values of R3, R4 and C1 and C2 but the resistor values stillneed to be low enough to ensure adequate base drive.
The transistors are BC338 and BC328 for NPN and PNP respectively.
I'll test the circuit but testing at voltages below 1.25V will be difficult for me as I only have an LM317 based PSU.
My local supplier sells 1.5V buzzers but the datasheet gives a minimum operating voltage of 1.3V and the current consumption is only 25mA so they won't be anywhere near as loud as my circuit.
http://www.rapidonline.com/netalogue/specs/35-0085e.pdf
This circuit can be used to drive a piezo sounder but the resistor values will need to be increased and C1 and C2 decreased.
View attachment 41059
