Another transistor equivalent question - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 28, 2014, 10:17:49 pm
content: I am building the final amp section of the circuit attached. I ordered an MPS6652 but then found MPS6650 was unobtainable. I looked at the data sheet, also hopefully attached, and wonder if there is an error in the schematic? It looks like I can use an MPS6601 as the other one. Am I OK with that? Thanks.

author: dannyf
author_rank: Super Contributor
timestamp: December 28, 2014, 11:30:19 pm
content: If it is driven by some opamp, particularly TL0xx, any (small) signal transistor would be more than sufficient.

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 28, 2014, 11:39:55 pm
content: Thanks Danny, as a beginner these are difficult calls, I probably already have a pair of something suitable amongst my bits and bobs, but without a lot more experience I try and play safe and just order what the schematic shows. I assume whatever PNP / NPN pair is used they have to be from the same family in this push pull setup? As in say XXV10 and XXV11 or however they differentiate between PNP /NPN fo the particular devices? Thanks again!

author: dannyf
author_rank: Super Contributor
timestamp: December 28, 2014, 11:43:53 pm
content: Generally no, but typically preferred.It is a Class B amp so I would watch out for break down voltage, maximum current and Ft, if you want to play safe.If you already have the pcb made, make sure that the pin layout is compatible too.

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 28, 2014, 11:49:05 pm
content: PCB? Oooh dear no, strip board I'm afraid for this, it's going in a little box just to boost the 0dBm from the drive out socket of my Kenwood TS-590 on 136khz, up to the level needed to run a frequency doubler, (schematic attached). Cheers Danny.

author: dannyf
author_rank: Super Contributor
timestamp: December 28, 2014, 11:56:14 pm
content: Since you already have a 4046 there, why don't you just feed the 136Khz to the 4046 and let it double it for you? Or there are some other special considerations here?

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 29, 2014, 12:23:03 am
content: That's what I am doing. Amplifying the 0dBm output of the transceiver to a level that will feed the doubler, using the tail end of the circuit I posted originally. I am not needing or building the rest of that circuit, just the amp bit. I am then using the doubler circuit to get to 272kHz, and then this feeds a Class D amp, with the push pull driver dividing it back down to the desired 136khz.This is the blurb from the designer of the two circuits site:Here's a circuit that allows one to drive a Class D push-pull amplifier with the output from a linear transmitter or transverter. It should be noted that this is only usable for frequency modulated modes such as RTTY, Pactor, Amtor, MFSK, Olivia, Domino, Throb, WSJT, WSPR etc. It can not be used with amplitude modulated signals such as PSK, BPSK, QPSK, WOLF etc.The circuit is a frequency doubler that provides the required Class D drive at two times the final output frequency. For example, supply a 505 kHz carrier at the input and get a 1010 kHz carrier at the output. The modulation (or frequency shift) is also doubled ... which is exactly what is required. The input to the Class D push-pull amplifier utilizes a flip flop (divide by 2) that provides the two phases to drive the push pull arrangement. This divide by two restores the proper frequency shift.X2LinearClassDinterface2.pdfThe frequency doubler is a full wave rectifier that uses a bifilar wound transformer and two diodes. The five-element, low-pass filter that follows provides a clean sinewave to the 74HCT4046 that squares up the X2 frequency signal. A clean sinewave helps ensure an accurate 50% duty cycle signal at X2 frequency.The input to the multiplier should be in the +7 to +20 dBm range. If the drive level is in excess of +20 dBm consider adding an attenuator between the output of the transceiver / transverter and the input to the doubler.

author: dannyf
author_rank: Super Contributor
timestamp: December 29, 2014, 01:07:51 am
content: I am not sure if I understand you.The transformer + rectifiers are there to double the incoming frequency. What does the 4046 do in your circuit?If all you want is to double the frequency (of a 0dbm signal), you probably don't need something this fancy / convoluted.

author: Chris Wilson
author_rank: Super Contributor
timestamp: January 03, 2015, 04:33:53 pm
content: I think it's needed to get a perfectly 50 / 50 ratio balanced output at double the input frequency, to correctly run the MOSFET driver in the Class D transmitter. I posted the explanation from the originator, does it not show why the 4046 is used? I see it as the means to get a true square wave out. It will feed a TC4426 driver chip in the amp.