task of Q3

[Unregistered (Nertomarus)]

Hello,

After a longer period I'm back on this forum. My previous name was Norbert.

I have started to assembling the bandido. I am looking for improvements in circuit.

What is the task of Q3 in negative rail? Should it stabilize the voltage?
For optimization I'll try to use an 79L05; suppling the bridge and 4024 with U-BAT instead, and using schottky diodes.

[driscoll]

Hi unregistered,

Regulator = Wrong choice here because the voltage doubler deliver a negative voltage < 4 Vcc !

Please read all articles on the Bandido (specially from Max) before to try to modify anything.

Regards

[Max]

Hello,

After a longer period I'm back on this forum. My previous name was Norbert.

I have started to assembling the bandido. I am looking for improvements in circuit.

What is the task of Q3 in negative rail? Should it stabilize the voltage?
For optimization I'll try to use an 79L05; suppling the bridge and 4024 with U-BAT instead, and using schottky diodes.

Hi,
as driscoll told you... it's not so smart choice.

Suppose you supply the converter transistors with battery rail so... +9V there... do you think it will be enough to use the 79L05 there ???

The drop-out is declared around 1.7V but... do you trust datasheet ??? you'll stay better being conservative considering 2V or more... so you need say at least -7V at unregulated output of converter to successfully apply the regulator there...

Are you sure you'll get -7V with required power there ? Cause I'm not.

Consider that this thing runs at 5Khz so will provide not such smart power conversion... bandidoII is well known for weakness of the converter stuff... and main reason is that low frequency that's not good.

I think you could have more success using 12V battery than 9V there, you'll sure get the -5V this way using a 79L05.

An nice alternative could be an LDO like LM2990-5.0-X, you'll typically waste just 1mA on that stuff... with very narrow dropout of 0.3V !
So...even with -5.3V at converter it will work happy!

I don't suggest you try the 7660 version... cause is out of sync with tx oscillator... so better stay as is using regulator if you like that way.

The Q3 is unimportant if you plan to use a true regulator there... also you must pull it out cause otherwise will cut about 1V due to the Vce there... and you need even the tiny voltage bits to get it work!

Kind regards,
Max