Increasing Capacitance on power supply

[bluetubes]

I am going to build the GGG regulated power supply --> http://www.generalguitargadgets.com/pdf/ggg_reg_power_supply.pdf  Unfortunately, I don't have the right value caps to build it exact.  Would there be any negative side affects to increasing the values (i.e. 470 to replace the 220).

thanks,
BT

[Sir H C]

Not too much, the thing is that a shorter portion of the incoming AC wave will be used to charge the capacitor, and so if you make it too big you can overstress the diodes in the bridge.  But you are just doing a 2:1 so that shouldn't be too bad.

[markphaser]

To much capacitance in the power supply does cause a bigger load on the circuit and power supply also takes out the hum tho

[Paul Perry (Frostwave)]

No problem at all. Hell, put 1,000 uF in if you want, I do!

[R.G.]

Paul is correct, and Sir H C is mostly correct.

In a capacitor-input filter, the rectifier diodes conduct only in short pulses near the peak of the AC waveform. Since they are only on for a short time, then all of the current provided to the load from the AC being rectified comes in during those short pulses. Since the duty cycle of the pulses is quite short, the peak current must be something like 1/(duty cycle) times the average DC currrent. The bigger the cap, the shorter the conduction time and therefore the higher the peaks of current.

This was a big deal when all rectifiers were vacuum tubes. A vacuum tube has a maximum peak current limited by the cathode emission. Go above that and you start damaging the tube. However, semiconductor diodes have comparatively huge peak current ratings. The ever-ready 1N400x series of 1A diodes has a peak surge current rating of 30 amps, for instance. This is one reason that vacuum rectifiers died off so quickly in the electronics world. Their only good characteristics, even in guitar amps, is that they come on slowly so they take the voltage stress off the other tubes at turn on, and that they sag. The sag can be done as well by resistors.

Semiconductor diodes are quite difficult to overstress by using large capacitance in the first filter position. I have used up to 10,000uF after a 1N400x diode with no ill effect. This is the only thing Sir H C got modestly incorrect. It is possible to overstress semiconductor diodes with too-big caps, but it takes a truly gigantic cap, and you usually have to specially construct an array of caps so that the effective capacitance is both large and fast - the cap array has to have low ESR and low ESL to make the current pulses be as quick and as un-limited as possible.

So double, triple, four-ple or five-ple it. No worries.

[bluetubes]

Thanks guys.  Thanks for explanation and increasing my comprehension of this stuff R.G.!!!

[Sir H C]

It is more of a lifetime thing.  I have had to fix several video game supplies that have used 15,000 uF on the rail then followed by a regulator.  The big diodes were smoked.  There is a regulator after that first cap, it takes care of a lot of the issues, 120 Hz is practically DC for most regulators.