Jump to content
Electronics-Lab.com Community

Dual o/p Voltage regulator


Recommended Posts

Hi Kevin,
I am sorry to say that your simple circuit is not a voltage regulator. Its output voltage will change with load current changes and temperature changes. It doesn't even have a voltage reference, like a biased-from-the-9V zener diode instead of the lower transistor's emitter resistor. That emitter resistor causes the lower transistor to have loss, instead of gain. ::)
Why not use an inexpensive voltage regulator IC like a 7805 instead? Its regulation is superb and it even has current-limiting if the load is shorted or attempts to draw too much current. It also has over-temperature protection, if it gets too hot it simply turns-off until it has cooled. ;D

Link to post
Share on other sites

Hi Npatel,
Why do you need positive and negative supplies?
If it is for an audio amp, simply use a bridged audio amp IC. It uses a single supply like your 9V one and effectively doubles the voltage across the load for up to 4 times more power output. A bridged amp also doesn't need a large output coupling capacitor. ;D

Link to post
Share on other sites

Hi Kevin,
I made simple regulators like that about 40 years ago.
The transistor regulator has my recommended "biased-from-the-9V zener diode instead of the lower transistor's emitter resistor" as a voltage reference. To make a 5V supply it would need a low-voltage voltage-reference IC or zener diode. Low voltage zener diodes don't regulate very well.

post-1706-14279142132537_thumb.gif

Link to post
Share on other sites

Why do you recommend the zener in it's postion. I find the zener unnecessay. The voltage will rise at the base and produce current. The voltage will fall at the base of the pass transistor. The only function of the zener is to maintain a reasonable bias should the voltage of the out put drastically change. In fact the zener is biased from the input should the output voltage fall drastically.

Link to post
Share on other sites

Kevin,
Of course the zener helps regulate the output voltage. It holds the voltage at the emitter constant so the transistor can amplify the difference between it and a divided-down sample of the output at its base.
In your circuit with a resistor instead of a zener, the emitter voltage followed the output voltage so the transistor couldn't amplify. It also didn't have a reference voltage for comparison.

Link to post
Share on other sites

Hi Alun,
When I clicked on your bridged-amp attachment, Adobe asked if I wanted to download their new version 7.0, so I did. Thanks.

Ahh, just a whopping 1W from that little amp?
Here's a nice monster bridged-amp IC with a built-in power supply voltage doubler. Operating in class-H (it doubles the supply voltage only when the signal requires it), it gives 70W to a 4 ohm speaker from a 14.4V car battery! http://www.semiconductors.philips.com/acrobat/datasheets/TDA1562Q_ST_SD_2.pdf

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
  • Create New...