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Keantoken's CFP cap multiplier
Keantoken's CFP cap multiplier
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Old 1st December 2017, 03:28 PM   #1121
merlin el mago is offline merlin el mago
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Could I use BC337-40.FSC?
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Old 1st December 2017, 03:44 PM   #1122
keantoken is offline keantoken  United States
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If you mean Fairchild, it will work, just not as well as the ONSemi transistors.
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Old 1st December 2017, 03:47 PM   #1123
merlin el mago is offline merlin el mago
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Yes it's Fairchild, I can't get ONsemi.

All resistors 1/4W?
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Old 1st December 2017, 03:49 PM   #1124
merlin el mago is offline merlin el mago
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For 30mA HV is BD139 or BD140?
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Old 4th January 2018, 08:00 PM   #1125
DNi is offline DNi  Switzerland
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Searching for a replacement for the venerable 2SA1837/2SC4793 pair I ran across the new Toshiba TTA004B & TTC004B transistors which, at least according to the DS, seem to be a good substitute.
In any case I'm ordering them for the two 200mA K-Multipliers that I'm about to build.

Regards,
Braca
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Old 5th January 2018, 06:55 AM   #1126
keantoken is offline keantoken  United States
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Good. Let us know how it turns out.
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Old 5th January 2018, 03:18 PM   #1127
Krisfr is offline Krisfr  United States
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Has there been any layouts for a PCB for this?

Thanks
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Old 5th January 2018, 08:30 PM   #1128
keantoken is offline keantoken  United States
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Yes, you can PM me if you want boards.
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Old 20th January 2018, 11:51 AM   #1129
DNi is offline DNi  Switzerland
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So far it's been a rather disappointing experience with the circuit.
I built first the positive version on the PCB, with TTA004B and BC337-40, but the voltage drop across Q2 was some 2.4 Volts, and the LED does not extinguish after the initial light-up. Suspecting that the BC337-40 was out of spec (it is not OnSemi), I tried a couple of others from the same bag, but without significant improvement. It filters, to be sure, but only about 45dB @ 100Hz.
Replacing BC337-40 with BC54xx only worsened the voltage drop by up to 0.2V.
The capacitors in the positions C1 and C2 are 100uF low-ESR Oscon from Panasonic.
I then put together the negative version on the breadboard, and tested a number of configurations with TTC004B and 2SC5171 (Toshiba, from a German distributor) as Q2, and BC327-40 (10 parts), BC55x & BC560 as Q1. The best result re. voltage drop achieved was 2.2V with the LED never fully extinguishing, and the voltage drop being dependent upon the load (the goal for the latter is 170mA at an input voltage of approx. 20V).

All BC3xx that I have come from the same manufacturer (apparently Continental Device India Ltd.), and are marked with CTBC3xxx, so now I ordered the OnSemi parts from a reputable distributor.
I'll report back after I tested the circuit with the OnSemi parts.

Regards,
Braca
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Old 26th January 2018, 07:43 PM   #1130
DNi is offline DNi  Switzerland
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Well, my OnSemi parts arrived, but there was almost no change in the K-Multiplier performance, i.e. the LED kept faintly glowing. So it seems that my CTBC33xx do not differ much from the OnSemi ones.
The LED in all the tests so far has been the same one - a generic, no-name, 5mm red one. Having replaced it with a Kingbright L-1034IDT (also red) the Q2 voltage drop went down from 2.3V to 2.18V - still higher than the 1.8V desired, but I thought there might be a trend appearing here.
Luckily, there was an IR LED in the junk box, and with it in place, the voltage drop hit the bull's eye at 1.84V.
With my K-Multiplier now being at a correct operating point, I did a small study of the LED parameters that I thought may be of importance in this application. The results are summarized in the table attached.
The first test was to measure the LED voltage & current at the onset of light emission as I visually perceived it, followed by the LED voltage at a current of 100uA.
The second group of numbers refer to the K-Multiplier performance with the three LEDs used. It is seen that the Q2 voltage drop reduces with practically the same increment as the LED voltage @ 100uA as the LEDs are rolled. The last column in the table shows that it is the Q1 bias voltage that determines the Q2 voltage drop, since the Q1 base currents (Iled) do not differ much in the three cases shown.
I obtained similar results with the BC337-40/2SA1930 pair at the same operating point, so it seems that the new Toshiba TTA004B is a good replacement for the non-obtainable 2SA1837 in this application.
As regards the filtering action, my input ripple was to low at 155mV,rms, and the measurement limit was reached too soon.

Now, I know that several Members built this circuit with red LEDs and reported correct results, but I still don't know why it was different in my case.

Regards,
Braca
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