Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:Here's a modification of the previous inverter circuit where the load is of a low(ish) impedance.
Steve Anderson wrote:Ask any electronic circuit designer worth their salt and they'll say that it's best to avoid electromechanical components, pots, switches, connectors...anything with moving parts. Simply for the unreliable nature of these items compared to rest.
This is in the context of a mass-produced item, when cost, reliability and warrenty claims are paramount. This is in contrast to the auto industry where things, both mechanically and electricaly, seem to be getting more complex.
GL is quite right, if needed I can re-draw the circuit with switch.
Steve A.
Steve Anderson wrote:Here's a modification of the previous inverter circuit where the load is of a low(ish) impedance. The previous circuit is OK with loads greater than 10k, but there will be a bit of attenuation in the 'inverted' position with loads of around 10k. (Around 30%).
Adding the second transistor provides a lower output impedance restoring the circuit to (almost) unity gain but with inversion. This will drive loads as low as 1k but C2 will need to be increased in value to retain the low frequency -3db point at around 2Hz. With a 1k load a value of 100uF will be needed.
As before Vcc can be anything from 12 to 24V, it doesn't need to be regulated, but it should be clean and ripple free, otherwise some of the noise/ripple/spikes will be added to the signal. At the higher volages of above 18V R5 should be a 1W resistor as it is dissipating just over half a Watt at 24V. TR2 will run warm, but it's within its ratings.
The circuit consumes about 36mA at 24V, half that at 12V. The transistors can almost be any general-purpose NPN device, 2N2222, BC107/8/9. I hope this is useful. I removed the switch just to make the circuit simpler.
Steve A.
Tonight I put this circuit together and gave it a trial run. No luck, but after a bit of checking pinouts on the transistor alternate, I realised I had the transistors in backwards -- fixed that, and voila!! Yes, this circuit works as advertised -- teriffic! I used BC549C as the transistors.
Users browsing this forum: No registered users and 65 guests