Maker Pro
Maker Pro

quick n dirty boost

K

kell

Jan 1, 1970
0
I'd like to boost 12 volts to 24 volts at a few milliamps using minimal
circuit board space. Regulation is not important, so I thought of
using this
12v
|
+------,
| |
| )||
| )||
| )||
,------,--,------+ )||
| | | | |
1K R R 1K +->|-+---,
| | | | __| | |
| | | | | | |
+--||--+ +--||--+--||nmos --- |
| \/ | |__ --- |
\c /\ c/ | | |
|----' '----| | | load
/e e\ | | |
| | | | |
'----------------+------'----'---'
|
gnd

with equivalent values for the timing caps and resistors giving 50%
duty cycle for a nominal 24 volts out.
Any other ideas or suggestions...?
 
J

John Popelish

Jan 1, 1970
0
kell said:
I'd like to boost 12 volts to 24 volts at a few milliamps using minimal
circuit board space. Regulation is not important, so I thought of
using this
12v
|
+------,
| |
| )||
| )||
| )||
,------,--,------+ )||
| | | | |
1K R R 1K +->|-+---,
| | | | __| | |
| | | | | | |
+--||--+ +--||--+--||nmos --- |
| \/ | |__ --- |
\c /\ c/ | | |
|----' '----| | | load
/e e\ | | |
| | | | |
'----------------+------'----'---'
|
gnd

with equivalent values for the timing caps and resistors giving 50%
duty cycle for a nominal 24 volts out.
Any other ideas or suggestions...?

That circuit does not produce a regulated output voltage.

At a few milliamperes output, a charge pump might be a simpler open
loop supply:
http://ww1.microchip.com/downloads/en/DeviceDoc/21468b.pdf
See figure 4-6.
 
T

Tim Williams

Jan 1, 1970
0
kell said:
Do you have a link or something I can see?

Bottom of:
http://webpages.charter.net/dawill/Images/Induction_Heater_Draft1.gif
Part of "Floating Supply Inverter".

Q14, C27 (L2 optional), C28, R77, C28, erm, huh, I put two C28's on that
schematic, and T4.

Q14 was a ZTX651 but for your current requirement, a 2N3904, 2222, 4401 or
anything else rated for the voltage will work.

On the transformer, instead of a secondary winding, you can use a highspeed
diode from the transistor collector to get the doubled voltage. In this
schematic, I needed an isolated supply, so I needed a secondary.

The primary winding (labelled 20uH) should come to around 20-40 turns of
fine wire on a ferrite transformer core. The capacitor across it should be
smaller, more like 0.01uF. The feedback winding (going to the transistor
base) should be 1-5 turns, depending on supply voltage and primary turns.

It's pretty fool-proof.

Tim
 
B

Bob Monsen

Jan 1, 1970
0
I'd like to boost 12 volts to 24 volts at a few milliamps using minimal
circuit board space. Regulation is not important, so I thought of
using this
12v
|
+------,
| |
| )||
| )||
| )||
,------,--,------+ )||
| | | | |
1K R R 1K +->|-+---,
| | | | __| | |
| | | | | | |
+--||--+ +--||--+--||nmos --- |
| \/ | |__ --- |
\c /\ c/ | | |
|----' '----| | | load
/e e\ | | |
| | | | |
'----------------+------'----'---'
|
gnd

with equivalent values for the timing caps and resistors giving 50%
duty cycle for a nominal 24 volts out.
Any other ideas or suggestions...?

You can add regulation by using a TL431 as a feedback element. it should
shunt the gate of the nmos when the output reaches the appropriate
voltage... use a voltage divider to feed the R input. You could also use a
zener and an NPN transistor to do this.

JP mentioned the TC7662, which is also a nice solution, will probably
require fewer parts, and will be less likely to stall or fail. For a small
current requirement, it works well (although it won't give you 2x voltage,
due to the diode drops required.)

--
Regards,
Bob Monsen

The unleashed power of the atom has changed everything save our modes
of thinking and we thus drift toward unparalleled catastrophe.
Albert Einstein, Telegram, 24 May 1946
 
K

kell

Jan 1, 1970
0
Tim said:
Bottom of:
http://webpages.charter.net/dawill/Images/Induction_Heater_Draft1.gif
Part of "Floating Supply Inverter".

Q14, C27 (L2 optional), C28, R77, C28, erm, huh, I put two C28's on that
schematic, and T4.

Q14 was a ZTX651 but for your current requirement, a 2N3904, 2222, 4401 or
anything else rated for the voltage will work.

On the transformer, instead of a secondary winding, you can use a highspeed
diode from the transistor collector to get the doubled voltage. In this
schematic, I needed an isolated supply, so I needed a secondary.

The primary winding (labelled 20uH) should come to around 20-40 turns of
fine wire on a ferrite transformer core. The capacitor across it should be
smaller, more like 0.01uF. The feedback winding (going to the transistor
base) should be 1-5 turns, depending on supply voltage and primary turns.

It's pretty fool-proof.

Tim
Okay, I think I will try it. Instead of winding my own inductor, I'll
just take one of those little chokes that looks like a two-watt
resistor and wrap a few turns of fine wire around it; if it doesn't
work I'll wrap it in the other direction.
 
D

Don Foreman

Jan 1, 1970
0
I'd like to boost 12 volts to 24 volts at a few milliamps using minimal
circuit board space. Regulation is not important, so I thought of
using this
12v
|
+------,
| |
| )||
| )||
| )||
,------,--,------+ )||
| | | | |
1K R R 1K +->|-+---,
| | | | __| | |
| | | | | | |
+--||--+ +--||--+--||nmos --- |
| \/ | |__ --- |
\c /\ c/ | | |
|----' '----| | | load
/e e\ | | |
| | | | |
'----------------+------'----'---'
|
gnd

with equivalent values for the timing caps and resistors giving 50%
duty cycle for a nominal 24 volts out.
Any other ideas or suggestions...?

Depending on load and inductor value, the output voltage of that
circuit could climb until something (MOSFET, diode or capacitor)
breaks down.
 
B

Bob Monsen

Jan 1, 1970
0
Depending on load and inductor value, the output voltage of that
circuit could climb until something (MOSFET, diode or capacitor)
breaks down.

I suggested using a feedback element to regulate it. He can do it like this:


12v
|
+-------,
| |
| )||
| )||
| )||
,------,--,------+ )||
| | | | |
1K R R 1K +->|-+---+----OUT
| | | | __| | |
| | | | | | |
+--||--+ +--||--+-o-||nmos --- |
| \/ | | |__ --- |
\c /\ c/ | | | |
|----' '----| B | | load
/e e\ | | |
| | | | |
'----------------+-------'----'---'
|
gnd


B OUT
| |
| [150k]
--- |
/x\------- +
--- |
| [17.4k]
| |
GND-+---------'

x is a TL431A

He can also do this:

B
| /
c |\|
b---| |--[100]---OUT
e |/|
| /
| 23V Zener
GND-'

However, just using the TC7662 is the easiest, and it probably won't fail
to start in 2 years due to a decreased beta in Q1 and smoke...

--
Regards,
Bob Monsen

Science is a wonderful thing if one does not have to earn one's living
at it.
Albert Einstein (1879 - 1955)
 
D

Don Foreman

Jan 1, 1970
0
Depending on load and inductor value, the output voltage of that
circuit could climb until something (MOSFET, diode or capacitor)
breaks down.

I suggested using a feedback element to regulate it. He can do it like this:


12v
|
+-------,
| |
| )||
| )||
| )||
,------,--,------+ )||
| | | | |
1K R R 1K +->|-+---+----OUT
| | | | __| | |
| | | | | | |
+--||--+ +--||--+-o-||nmos --- |
| \/ | | |__ --- |
\c /\ c/ | | | |
|----' '----| B | | load
/e e\ | | |
| | | | |
'----------------+-------'----'---'
|
gnd


B OUT
| |
| [150k]
--- |
/x\------- +
--- |
| [17.4k]
| |
GND-+---------'

x is a TL431A

He can also do this:

B
| /
c |\|
b---| |--[100]---OUT
e |/|
| /
| 23V Zener
GND-'

However, just using the TC7662 is the easiest, and it probably won't fail
to start in 2 years due to a decreased beta in Q1 and smoke...

Right. Probably less board space as well.
 
Top