Simple circuit to generate 12VDC from a 9v battery?

[royalmp2001]

Hello everyone,
I need to generate 12vdc from a 9v square battery, cheaply and simply,
supplying about 20mA.
I have looked at DC-DC convertors, but haven't come across anything
suitable.

I found this circuit that does something similar with a 555 timer but
it can only supply about 12mA. Any ideas how to increase the current
capability a little?

http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#5volts.gif

Any other simple circuit ideas welcome
Thanks
Marius

 

[Jonathan Kirwan]

Hello everyone,
I need to generate 12vdc from a 9v square battery, cheaply and simply,
supplying about 20mA.

I have looked at DC-DC convertors, but haven't come across anything
suitable.
<snip>
Any other simple circuit ideas welcome

If you can tolerate a quarter volt of p-p ripple:

L1
---- D1
,---------+-------+-----+---^^^^--+------|>|-----+-----------+---> 12.3V
| | | | 30uH | | | OUT
| | | | | MBR0540 | |
| | | | | | |
| | | | | \ |
| | | ,---------------, / R1 |
| | | | Vin SW | \ 820k |
| | | | | / |
| | | | LT1615-1 | | | C2
--- | C1 | | (sot23) | | ---
- Vin --- | | | | ---
--- 9 --- '--| /SHDN FB |-----------+ | 1uF
- | 4.7uF | | | |
| | | | | |
| | | | \ |
| | | | / R2 |
| | | | \ 91k |
| | | GND | / |
| | '---------------' | |
| | | | |
| | | | |
gnd gnd gnd gnd gnd

I think that one is pretty efficient. You can tweak R1 and R2 to get
closer to 12V, but figure about 500k-1Meg total resistance for the
pair and that you need some 1.23V at the FB pin.

Jon

 

[Anthony Fremont]

Hello everyone,
I need to generate 12vdc from a 9v square battery, cheaply and simply,
supplying about 20mA.
I have looked at DC-DC convertors, but haven't come across anything
suitable.

I found this circuit that does something similar with a 555 timer but
it can only supply about 12mA. Any ideas how to increase the current
capability a little?

http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#5volts.gif

That circuit creates a negative voltage that is smaller than the supply.
You need a boosting converter with a positive output. You need
something arranged more like this:
http://www.reconnsworld.com/power_voltdoubler.html
This should supply enough current, just put a 1K resistor on the output
and a 12V Zener to ground (after the resistor) to clamp the voltage at
12V.

 

[Anthony Fremont]

http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#5volts.gif

That circuit creates a negative voltage that is smaller than the supply.
You need a boosting converter with a positive output. You need
something arranged more like this:
http://www.reconnsworld.com/power_voltdoubler.html
This should supply enough current, just put a 1K resistor on the output
and a 12V Zener to ground (after the resistor) to clamp the voltage at
12V.

Oops, I just re-read your post and you need 20mA out. Lower the 1K
resistor I suggested to about 220 ohms and use a 1W Zener.

 

[Tim Williams]

I need to generate 12vdc from a 9v square battery

^^^^
Ah, well 9V squared is 81V, plenty to use a resistor to drop down to 12V.
;o)

Tim

 

[kell]

Oops, I just re-read your post and you need 20mA out. Lower the 1K
resistor I suggested to about 220 ohms and use a 1W Zener.

And if you still don't get enough current out, reduce the value of R2.
Output current from a doubler circuit like that is proportional to
frequency.

 

[Brian]

Hello everyone,
I need to generate 12vdc from a 9v square battery, cheaply and simply,
supplying about 20mA.
I have looked at DC-DC convertors, but haven't come across anything
suitable.

I found this circuit that does something similar with a 555 timer but
it can only supply about 12mA. Any ideas how to increase the current
capability a little?

http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#5volts.gif

Any other simple circuit ideas welcome
Thanks
Marius

Another approach is to use a switching converter IC, such as the MC34063A.
Take a look at the drawing at http://www.fncwired.com/9to12VoltExample/

Brian

 

[Rune D. Jørgensen]

Det var smuk og solrig dag da royalmp2001 skrev
i
sci.electronics.basics:

Hello everyone,
I need to generate 12vdc from a 9v square battery, cheaply and simply,
supplying about 20mA.
I have looked at DC-DC convertors, but haven't come across anything
suitable.

Any other simple circuit ideas welcome

How about two 1.5V batteries in series with your 9V battery. That is
simple, and you don't throw away a lot of energy in conversions.

 

[John Fields]

Det var smuk og solrig dag da royalmp2001 skrev
i
sci.electronics.basics:


How about two 1.5V batteries in series with your 9V battery. That is
simple, and you don't throw away a lot of energy in conversions.

 

[Deefoo]

Det var smuk og solrig dag da royalmp2001 skrev
i
sci.electronics.basics:


How about two 1.5V batteries in series with your 9V battery. That is
simple, and you don't throw away a lot of energy in conversions.

This thread reminded me of a funny error from a freshly graduated
electronics engineer that we hired some years ago. He needed something like
7.5V from a 5V power supply, so he simply wired a resistor voltage divider
in "reverse", ie he connected 5V to the output... Luckily I spot the error
before he made a pcb for it.

--DF