From 318902d7d9d2b49c2e55681d2dceb9690302bc9c Mon Sep 17 00:00:00 2001 From: Liam Hays Date: Sun, 5 Sep 2021 16:34:07 -0600 Subject: [PATCH] Revision v1.1: Added information on 12 V input and low voltage thresholds. --- game-gear-power-docs.tex | 102 +++++++++++++++++++++++++++++++-------- 1 file changed, 81 insertions(+), 21 deletions(-) diff --git a/game-gear-power-docs.tex b/game-gear-power-docs.tex index 3e94f98..8355ee0 100644 --- a/game-gear-power-docs.tex +++ b/game-gear-power-docs.tex @@ -13,7 +13,9 @@ \newcommand{\chippin}{\texttt} \newcommand{\model}{\textsf} -% TODO: What is the LED blinking voltage? +% TODO: what's the output voltage of the Car Adapter? +% It's 800 mA at 9V + \begin{document} \section{About This Document} @@ -101,6 +103,7 @@ \section{Power Input Section} $C_{10}$ and $C_{11}$. \subsection{Batteries and Chemistry} +\label{sec:batteries_chemistry} For this section, reference the graphs at \url{https://www.powerstream.com/AA-tests.htm}. The various battery facts and statistics I state here are from the graphs on this @@ -135,6 +138,7 @@ \subsection{Batteries and Chemistry} % briefly power on if a cartridge wasn't inserted well? That sounds % like SCP to me. \subsection{DC Jack Switching} +\label{sec:jack_switching} Note: this subsection describes the DC jack in an American Game Gear. For a European model (see Section \ref{sec:plug_dimensions}), switch the polarities of the jack. @@ -166,6 +170,20 @@ \subsection{DC Jack Switching} 2. This means that $D_6$ is completely extraneous, likely a remnant from some old design. +\subsection{Switching While Powered On} +The Game Gear can change power sources from the DC jack to the +batteries (or vice versa) on the fly, while powered on. However, this +causes the power to flicker for long enough that the console resets, +on both plugging in and unplugging the DC plug. + +There probably isn't a good way to solve this aside from a very +fast-switching diode (a Schottky diode or similar). What it does +indicate, though, is that the recovery time for $D_1$ is longer than +the frequency of the switcher on at least the \qty{5}{\volt} output, +and probably the \qty{34}{\volt} output (I'm not sure of this, but the +screen doesn't seem to flicker in the same way as it does when the +console is power-cycled). + \subsection{Plug Dimensions and Switch} \label{sec:plug_dimensions} An American unit will use the uppermost power input block (labeled @@ -198,33 +216,74 @@ \subsection{Plug Dimensions and Switch} \subsection{Input Voltage} This is an area that is actually very confusing, especially if you're trying to build your own power cord, like I did. The Game Gear case -labels the power jack as \texttt{DC 9V}. However, the official Sega -power supply (model \model{MK-2103}) for the Game Gear is -\qty{10}{\volt}. Clearly, the voltages don't match---why doesn't this -cause a problem? +labels the power jack as \texttt{DC 9V}. The official Game Gear Car +Adapter outputs \qty{9}{\volt}. However, the official Sega wall wart +(model \model{MK-2103}) for the Game Gear is \qty{10}{\volt}. The +voltages don't match---why doesn't this cause a problem? The exact input voltage doesn't matter too much, within reason, because: \begin{enumerate} \item An alkaline AA will only be at \qty{1.5}{\volt} for the first - few minutes of its life, at the discharge rate used by the Game - Gear. From there, it will slowly drop to about \qty{1}{\volt}, where - the voltage will drop sharply. This means that the voltage will be - at about $\qty{1.3}{\volt} \times{} 6 = \qty{7.8}{\volt}$, give or - take. This is clearly far beneath the optimal \qty{9}{\volt} (or - even \qty{10}{\volt}) that Sega suggests one should be using. + few minutes of its life (see Section \ref{sec:batteries_chemistry}), + at the discharge rate used by the Game Gear. From there, it slowly + drops. This means that the average input voltage will be about + $\qty{1.3}{\volt} \times{} 6 = \qty{7.8}{\volt}$. Clearly, this is + far beneath the optimal \qty{9}{\volt} (or even \qty{10}{\volt}) + that Sega suggests one should be using, but the console is tolerant + and works fine. \item The \model{MB3775} can operate from \qty{3.6}{\volt} to - \qty{18}{\volt}. -\item The error amplifier means that the precise value of \Vcc{} - doesn't matter (within reasonable limit), as the chip's output will - adjust to compensate. + \qty{18}{\volt}. It is designed to significantly adjust the + switching regulators in response to \Vcc{}, among other factors. +%\item The error amplifier means that the precise value of \Vcc{} +% doesn't matter (within reasonable limit), as the chip's output will +% adjust to compensate. \end{enumerate} -All this is to say that the power circuit is designed to work fine -with a significant (at least $\pm{}\qty{2}{\volt}$, and probably even -greater) deviation in \Vcc{} voltage. +All this is to say that the power circuit is designed to work with a +significant (at least $\pm{}\qty{2}{\volt}$, and probably even +greater) deviation in \Vcc{} voltage. For example, I powered my unit +with \qty{12}{\volt} and it worked perfectly. + +\subsection{Low Voltage Threshold} +When the ASIC (or the non-video ASIC in a \model{VA0}) detects low +input voltage, it blinks the red power LED to notify the user. If the +voltage drops even further, the entire console shuts off. I have +determined the voltages where these behaviors occur. For this +experiment, I built a small adjustable regulator with a \model{LM317}, +and connected the regulated output to both the DC jack on my Game Gear +and a voltmeter. The initial input voltage was \qty{10.07}{\volt}, and +I turned down the voltage until the console's behavior changed. + +This is what I observed: + +\begin{description} +\item[input voltage above \qty{6.8}{\volt}] The LED is fully on. +\item[\qty{6.8}{\volt}--\qty{6.4}{\volt}] The LED blinks, but when it + is in the ``off'' state, it is not fully off---instead, it is dim + and flickering. +\item[\qty{6.4}{\volt}--\qty{6}{\volt}] The LED blinks and it is fully + off in the ``off'' state. +\item[\qty{6}{\volt} and below] The console shuts off completely. +\end{description} +I believe the shutdown below \qty{6}{\volt} is triggered by the +under-voltage lockout. However, as far as I can tell, the +under-voltage lockout is only triggered when \Vcc{} falls beneath +about \qty{2.6}{\volt}, which is obviously much lower than the +\qty{6}{\volt} threshold I observed. I do not know the precise +cause of the shutoff. + +% These values were almost surely configured on the basis of an alkaline +% AA's discharge profile (Section \ref{sec:batteries_chemistry}). For +% example, a total input voltage of \qty{6}{\volt} corresponds to +% \qty{1}{\volt} per battery. At a \qty{500}{\milli{}A} discharge rate, +% \qty{1}{\volt} output is just before the battery voltage drops +% rapidly (see the AA discharge graphs). This is probably a safety +% measure, to make sure that the console + +% Note above: at least, I think so. It may be just a result of the uvlo. \subsection{Compatible Plugs} I do not have a European Game Gear, but I assume that an Arduino or similar power supply would work fine, as Arduinos use the same size @@ -344,6 +403,7 @@ \subsection{Short Circuit Protection} I don't know why $C_1$ is tantalum. Possibly to save space on the board. +% \subsection{Capacitor ESR} The \model{MB3775} datasheet warns that electrolytic smoothing capacitors with low equivalent series resistance (ESR) can create @@ -884,12 +944,12 @@ \section{Remaining Questions} \item How are $C_7$ and $R_9$ controlling the oscillator? \item Why is $t_{PE}$ so long? Just to accommodate a large load? \item Why is $C_1$ tantalum? -\item At what \Vcc{} voltage does the main board start blinking the - power LED? \end{itemize} \section{Revision History} \begin{description} -\item[v1.0] First release. +\item[v1.0, July 2021] First release. +\item[v1.1, September 2021] Added information on running a Game Gear + at \qty{12}{\volt}, and added the section on the low voltage thresholds. \end{description} \end{document}