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Skywave · 13th Dec 2016, 10:39 pm

An idea: is what follows sound?

For various reasons, it would be convenient to replace the two P-channel FETs with N-channel types. To do this, the following changes will need to be made:

1. Replace both FETs with N-channel types; R12 stays same value
2. The -9v. rail becomes + 9v. But all the 0v. / gnd. connections stay the same.
3. CR5 and CR6 stay in the same position in the circuit, but they are reversed (the cathodes become the anodes, and vice-versa); but R11 stays same value.
4. The four rectifying diodes, CR1 - CR4 similarly will need anode and cathode 'swop'.
5. Q3 and Q4 (NPN) are replaced by PNP types.

And just as an after-thought, would replacing the FET's common source resistor, R12, with a constant-current sink, be worthwhile?

I cannot think of any other changes that may be necessary. And there are no polarized capacitors to consider!

Can anyone spot any flaws in my thinking and proposed changes here?

Thanks,
Al.

13th Dec 2016, 10:39 pm	#20
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: R.F. voltmeter: your thoughts, please An idea: is what follows sound? For various reasons, it would be convenient to replace the two P-channel FETs with N-channel types. To do this, the following changes will need to be made: 1. Replace both FETs with N-channel types; R12 stays same value 2. The -9v. rail becomes + 9v. But all the 0v. / gnd. connections stay the same. 3. CR5 and CR6 stay in the same position in the circuit, but they are reversed (the cathodes become the anodes, and vice-versa); but R11 stays same value. 4. The four rectifying diodes, CR1 - CR4 similarly will need anode and cathode 'swop'. 5. Q3 and Q4 (NPN) are replaced by PNP types. And just as an after-thought, would replacing the FET's common source resistor, R12, with a constant-current sink, be worthwhile? I cannot think of any other changes that may be necessary. And there are no polarized capacitors to consider! Can anyone spot any flaws in my thinking and proposed changes here? Thanks, Al.