Fried the PPU?

Post by **tepples** » Wed May 04, 2011 1:07 pm

I'm not an electrical engineer, but here's how I understand it:

The voltage on Vcc isn't as constant as one might initially think. It can vary over short periods of time as the load (amount of power drawn by other chips) varies, and occasionally, adjacent signals can "bleed" onto Vcc.

Think of a capacitor as like a balloon that fills up with static charge Q when there's a voltage across it. As the voltage v across the cap changes over time t, it releases some of its charge as current i to even out the voltage change: i = C*dv/dt, where C is the capacitance. A cap between ground and Vcc keeps Vcc from changing rapidly in response to load and noise elsewhere in the circuit.

On Wikipedia, see Reservoir capacitor and Decoupling capacitor.

qbradq · Post by **qbradq** » Wed May 04, 2011 1:19 pm

What he said

Thanks Tepples, good reading for the electrically deficient!

Drag · Post by **Drag** » Wed May 04, 2011 2:55 pm

I guess what I'm confused about is why the capacitor needs to be tied to ground, versus something like Vcc -> + Cap - -> IC.

Post by **tepples** » Wed May 04, 2011 2:58 pm

Because Vcc is direct current (DC), and caps don't pass DC. They work off a difference between the voltages on the terminals.

Drag · Post by **Drag** » Wed May 04, 2011 5:16 pm

Nevermind, I went back to electronics school. I was getting confused because I thought the current always went in one end and came out the other.

82atari5200 · Post by **82atari5200** » Thu May 05, 2011 5:36 am

That's why the Atari 5200 was able to use the same cord for power and video without frying your t.v. I'm just slightly amazed at the frailty of some of these I.C.'s I've never had things just blow out this easily. I just want to get rid of the jailbars from my famicom