### Author Topic: Att.: Angad - 10V Out From 7805 Voltage Regulator  (Read 942 times)

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#### Soeren

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##### Att.: Angad - 10V Out From 7805 Voltage Regulator
« on: November 06, 2012, 07:36:14 PM »
Hi,

First of all, please start a new topic, rather than confusing the flow of another thread, when your question is about something else!

how can i use 7805 to generate 10 V power supply for my robot.
Is the output of 7805 equals to 5V +voltage applied to 2nd pin of 7805
Regards
As I already told you, this is not what I recommend, but yes (sortof) you can put a zener diode between the ground terminal (middle pin and metal tab) and ground proper. You can't find a 5.0V zener, nearest is 5.1V (or 4.7V if 10.1V out is too high.

However, when doing this, the ground terminal will see a much higher impedance than when gounded directly and the regulation will suffer, plus the zener will add a little noise.

An LM317 can be set by two resistors to any voltage between ~1.25V and ~37V, while still maintaining the proper ground connection, so I haven't bought any 78nn regulators for decades, as stocking all of the available voltages (5, 6, 8, 9, 12, 15, 18 and 24V) is more expensive, some will be used rarely and they just take up space - LM317 replaces all of them (and LM337 for the negative voltages) and you can get any voltage, not just what the manufacturer decided to make available.

If you decide to go with the 7805 anyway, remember that the input voltage should be minimum 2.5V to 3.5V (depending on the manufacturer of the 7805) higher than the output at all times.
This means that if you want to run it from a rectified and buffered mains transformer, the troughs (low points) of the ripple must be that much higher than the output voltage to stay in regulation. If it goes out of regulation, there's a good chance that it will oscillate and may output much higher peaks than the input voltage would point to.

If run from eg. a NiMH battery, you'll need at least 13 cells to get the full capacity of the battery and that means ~17.5V when fully charged, which will result in a power loss of around 43% with a freshly charged battery, falling to ~23% when almost flat.

The zener should have its cathode towards pin 2 of the 7805 and its anode to ground
The input (220nF) and output (22µF) caps should go to ground (not to pin 2).

What do you need 10V for and at what current?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?